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From: Belling Thomas <thomas.belling@siemens.com>
To: "'Colin Perkins'" <csp@csperkins.org>,
        Magnus Westerlund
	 <magnus.westerlund@ericsson.com>
Cc: Belling Thomas <thomas.belling@siemens.com>, mmusic@ietf.org
Subject: Re: [MMUSIC] RTP bandwidth for multiple media streams
Date: Fri, 27 Jun 2003 16:18:21 +0200
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Dear Colin

I would like to suggest the following additions to the SDP new draft
(denoted by ">>> <<<")

Alternatively, removing the <number of ports> and the corresponding =
explanations from page 19f is acceptable to me, if nobody has concerns =
with respect to the backward compatibility.

Thanks, Thomas



On page 13f:

   Bandwidth

      b=3D<modifier>:<bandwidth-value>

...

      Two modifiers are initially defined:

        CT  Conference Total
            If the bandwidth of a session or media in a session is
            different from the bandwidth implicit from the scope, a
            "b=3DCT:..." line should be supplied for the session giving
            the proposed upper limit to the bandwidth used.  The =
primary
            purpose of this is to give an approximate idea as to =
whether
            two or more sessions can co-exist simultaneously.
>>>         For RTP, if several RTP sessions are part of the =
conference,
            the conference total refers to total bandwidth of all RTP =
sessions. <<<
           =20

        AS  Application-Specific Maximum
            The bandwidth is interpreted to be application-specific (it
            will be the application's concept of maximum bandwidth).
            Normally this will coincide with what is set on the
            application's "maximum bandwidth" control if applicable.
            For RTP based applications, AS gives the RTP "session
            bandwidth" as defined in section 6.2 of [RFC1889].

      Note that CT gives a total bandwidth figure for all the media at
      all sites.  AS gives a bandwidth figure for a single media at a
      single site, although there may be many sites sending
      simultaneously.







On page 19f:

   Media Announcements

      m=3D<media> <port> <transport> <fmt list>

      ...

      The second sub-field is the transport port to which the media
      stream is sent. The meaning of the transport port depends on the
      network being used as specified in the relevant "c=3D" field, and =
on
      the transport protocol defined in the third sub-field.  Other
      ports used by the media application (such as the RTCP port
      [RFC1889]) MAY be derived algorithmically from the base media =
port
      or MAY be specified in a separate attribute (e.g. "a=3Drtcp:" as
      defined in [RTCPSDP]).

      For applications where hierarchically encoded streams are being
      sent to a unicast address, it may be necessary to specify =
multiple
      transport ports.  This is done using a similar notation to that
      used for IP multicast addresses in the "c=3D" field:


         m=3D<media> <port>/<number of ports> <transport> <fmt list>

      In such a case, the ports used depend on the transport protocol.
      For RTP, the default is that only the even numbered ports are =
used
      for data and the corresponding one-higher odd port is used for
>>>   RTCP >>> belonging to this RTP session, and the <number of ports> =
denotes the number of RTP sessions<<<.  For example:

         m=3Dvideo 49170/2 RTP/AVP 31

      would specify that ports 49170 and 49171 form one RTP/RTCP pair
      and 49172 and 49173 form the second RTP/RTCP pair. RTP/AVP is the
      transport protocol and 31 is the format (see below). If non-
      contiguous ports are required, they must be signalled using a
      separate attribute (e.g. "a=3Drtcp:" as defined in [RTCPSDP])
      ...


-----Urspr=FCngliche Nachricht-----
Von: Colin Perkins [mailto:csp@csperkins.org]
Gesendet: Mittwoch, 25. Juni 2003 19:03
An: Magnus Westerlund
Cc: thomas.belling@siemens.com; mmusic@ietf.org
Betreff: Re: AW: [MMUSIC] RTP bandwidth for multiple media streams


Can you suggest explicit wording changes to clarify the draft? There is
probably still time to incorporate minor edits for clarification.

Colin



--> Magnus
Westerlund<magnus.westerlund@ericsson.com> writes:
> Hi Thomas,
>=20
> Even more inline:
>=20
> Belling Thomas wrote:
> > Hi Magnus,
> >=20
> > My answers are inline
> >=20
> >=20
> > -----Urspr=FCngliche Nachricht-----
> > Von: Magnus Westerlund [mailto:magnus.westerlund@ericsson.com]
> > Gesendet: Montag, 23. Juni 2003 09:27
> > An: Belling Thomas
> > Cc: 'mmusic@ietf.org'
> > Betreff: Re: [MMUSIC] RTP bandwidth for multiple media streams
> >=20
> >=20
> > Hi,
> >=20
> > I would agree with the interpretation, at least when it comes to =
b=3DAS
> > as it clearly specifies that this is the RTP session bandwidth. =
When
> > one uses a m=3D line with port/2 it becomes two RTP sessions. =
However I
> > am not certain over how one should in this case interpret any of =
the
> > other bandwidth attributes.
> >=20
> > [Thomas] Fine, but is that 100 Percent clear from the wording of =
the
> > RFCs and draft-ietf-mmusic-sdp-new-12? It would prefere a =
clarification
> > there
>=20
> Yes, this should probably be clarified. I don't think it is obvious.
>=20
> >=20
> > The available bandwidth modifiers are:
> > CT
> > RR
> > RS
> >=20
> > Lets look at them:
> >=20
> > CT is defined in draft-ietf-mmusic-sdp-new-12 as:
> >          CT  Conference Total
> >              If the bandwidth of a session or media in a session is
> >              different from the bandwidth implicit from the scope, =
a
> >              "b=3DCT:..." line should be supplied for the session =
giving
> >              the proposed upper limit to the bandwidth used.  The
> >              primary purpose of this is to give an approximate idea =
as
> >              to whether two or more sessions can co-exist
> >              simultaneously.
> >=20
> > Based on this I would interpret that a given CT value should be for =
the
> > complete media, i.e. counting the total of both RTP sessions.
> >=20
> > [Thomas] I agree that this is an interpretation in line with my
> > understanding of the intentions of the CT bandwidth modifier. =
However,
> > the wording is not so clear. What is a "session"? If you understand
> > "RTP session", this would contradict your interpretation. As an =
aside:
> > 3GPP ignores this parameter, so from that perspective a =
clarification
> > is less urgent than for the AS modifier.
>=20
> Yes, the session in the quote is a bit unclear. I think it is a =
larger=20
> session concept, like the complete streaming session, or probably =
when=20
> it was written the conferencing session with all the media included. =
On=20
> media level the text indicates the complete media, which in this case =
is=20
> transported over several RTP sessions. So based on these two=20
> interpretations I arrive at my conclusion.
>=20
> > When it concerns TIAS I will do the same interpretation that the=20
> > bandwidth value apply per RTP session.
> >=20
> > [Thomas] Makes sense if you take TIAS as a kind of refinement of =
the AS
> > modifier. I did not yet read the draft with that question in mind, =
and
> > the draft is still in a stage where this can be clarified.
>=20
> Yes, it can still be modified. I have made an update and I did not=20
> address the issue. The reason being is that I think the SDP draft =
should=20
>   first address this. Based on this clarification I would add to the=20
> TIAS draft if necessary.
>=20
> >=20
> > My concern is that this simplistic model is probably not what you =
would
> > like if you would actually use this functionality. If one uses =
multiple
> > RTP sessions for a single media you are probably doing some form of =

> > scalability, etc., and would like to specify the values =
independently=20
> > per RTP session. Fortunately there exist today alternatives to =
achieve=20
> > this behaviour today. With the help of grouping of media lines it =
is=20
> > possible to specify that several m=3D lines are part of the same =
media.=20
> > Using FID there is only a pitfall with the following sentence:
> > "A media agent handling a media flow that comprises several "m"
> >     lines MUST send a copy of the media to every "m" line part of =
the
> >     flow as long as the codecs and the direction attribute present =
in a
> >     particular "m" line allow it."
> >=20
> > If that is a problem it might be easier to define a new grouping=20
> > attribute for that situation.
> > Finally I have a question to the group, has anyone seen that "m=3D =
port/2
> > ..." ever been used. And in that case how.
> >=20
> > [Thomas] Take the simple example of stereo sound. Why not use the =
"m=3D
> > port/2 " notification for that? Something in that direction might =
have
> > been the original motification. From a 3GPP perspective, where this
> > relates to thev bandwidth on the air and possibly the rate charged =
for
> > a service, we should have a clear understanding as this possibility
> > exists and might also be misused otherwise.
>=20
> I don't think stereo is a good example. First reason is that you=20
> normally don't split left and right channel into different packets,=20
> unless they are really big, reasons are like synchronization. =
Therefore=20
> most audio codecs are possible to transport over RTP using a single=20
> source. The sample based codec normally only specify that every other =

> sample is left  and the other are right. Frame based codec normally =
have=20
> more advanced schemes where they encode left and right together to =
take=20
> advantage of the similarities between channels.
>=20
> My thinking is actually along the lines, if no one uses it, why not=20
> remove it, we will still have to if no implementations are identified =

> when going to draft standard.
>=20
>=20
> Best Regards
>=20
> Magnus Westerlund
>=20
> Multimedia Technologies, Ericsson Research EAB/TVA/A
> =
----------------------------------------------------------------------
> Ericsson AB                | Phone +46 8 4048287
> Torshamsgatan 23           | Fax   +46 8 7575550
> S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com
>=20
>=20
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic
>=20


--=20
Colin Perkins
csp@csperkins.org

_______________________________________________
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Message-ID: <3F026A96.5000907@dynamicsoft.com>
Date: Wed, 02 Jul 2003 01:16:06 -0400
From: Jonathan Rosenberg <jdrosen@dynamicsoft.com>
Organization: dynamicsoft
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Folks,

I'd like to draw your attention to the following I-D that I submitted 
recently:

http://www.ietf.org/internet-drafts/draft-rosenberg-mmusic-rtp-denialofservice-00.txt

This draft describes a denial-of-service attack using RTP. This attack 
can be launched using any protocol that uses an offer/answer-like SDP 
exchange, including SIP and RTSP. The draft also discusses ICE as a 
solution to the problem.

Comments welcome.

Thanks,
Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com



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--NextPart

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Multiparty Multimedia Session Control Working Group of the IETF.

	Title		: Session Description Protocol Offer Answer Examples
	Author(s)	: A. Johnston, R. Sparks
	Filename	: draft-ietf-mmusic-offer-answer-examples-01.txt
	Pages		: 26
	Date		: 2003-7-1
	
This document gives examples of Session Description Protocol (SDP)
offer answer exchanges.  Examples include codec negotiation and
selection, hold and resume, and addition and deletion of media
streams.  The examples show multiple media types, bidirectional,
unidirectional, inactive streams and dynamic payload types. Common
Third Party Call Control (3pcc) examples are also given.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-ietf-mmusic-offer-answer-examples-01.txt

To remove yourself from the IETF Announcement list, send a message to 
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Subject: RE: [MMUSIC] RTP denial of service
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From: "Hearty, John" <John.Hearty@Level3.com>
To: "Jonathan Rosenberg" <jdrosen@dynamicsoft.com>, <mmusic@ietf.org>
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My security knowledge is weak, and I would like some help understanding
why the following from the draft is true:

There
   is no requirement that the calls come from unauthenticated sources.
   The attack can be launched even if the device requires
   authentication. Of course, authentication might provide some amount
   of traceability.

Wouldn't it be more difficult to launch the attack if authentication was
required?  I would think RTP would not start sending if the original
request could not be authenticated.

John

> -----Original Message-----
> From: Jonathan Rosenberg [mailto:jdrosen@dynamicsoft.com]
> Sent: Tuesday, July 01, 2003 11:16 PM
> To: mmusic@ietf.org
> Subject: [MMUSIC] RTP denial of service
>=20
> Folks,
>=20
> I'd like to draw your attention to the following I-D that I submitted
> recently:
>=20
> http://www.ietf.org/internet-drafts/draft-rosenberg-mmusic-rtp-
> denialofservice-00.txt
>=20
> This draft describes a denial-of-service attack using RTP. This attack
> can be launched using any protocol that uses an offer/answer-like SDP
> exchange, including SIP and RTSP. The draft also discusses ICE as a
> solution to the problem.
>=20
> Comments welcome.
>=20
> Thanks,
> Jonathan R.
>=20
> --
> Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
> Chief Technology Officer                    Parsippany, NJ 07054-2711
> dynamicsoft
> jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
> http://www.jdrosen.net                      PHONE: (973) 952-5000
> http://www.dynamicsoft.com
>=20
>=20
>=20
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic

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Subject: RE: [MMUSIC] RTP denial of service
To: "Hearty, John" <John.Hearty@Level3.com>
Cc: "Jonathan Rosenberg" <jdrosen@dynamicsoft.com>, mmusic@ietf.org
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Let me check If I understood correctly what jonathan wanted to mean:

the point is that the attacker COULD be authenticated
e.g. the attacker *buys* a movie (say with a stolen credit card)
from www.holywood-movies.com etc ....
BUT tweaks the streaming request in a way that the
movie will be sent toward whitehouse.gov instead !

Traceability would be if the stolen credit card can be traced,
or if the attacker IP address can be traced etc ...


BTW jonathan, for this exact reason (to my knowledge most) RTSP server implementations
today would refuse to stream except toward the originating RTSP IP address
(or at least this feature can be turned on)
...
which is actually a problem for NAT traversal in case the NAT attributes
a different IP address for the RTSP and RTP traffic !


regards,

Philippe Gentric
philippe.gentric@philips.com
http://www.platform4.philips.com


                                                                                                                                       
                                                                                                                                       
                                                   To:   "Jonathan Rosenberg" <jdrosen@dynamicsoft.com>                                
                                                    <mmusic@ietf.org>                                                                  
                                                   cc:   (bcc: Philippe Gentric/MP4-SUR/CE/PHILIPS)                                    
                                                   Subject:    RE: [MMUSIC] RTP denial of service                                      
               "Hearty, John"                                                                                                          
               <John.Hearty@Level3.com>            Classification:                                                                     
                                                                                                                                       
               Sent by:                                                                                                                
               mmusic-admin@ietf.org                                                                                                   
                                                                                                                                       
               02/07/2003 18:49                                                                                                        
                                                                                                                                       
                                                                                                                                       





My security knowledge is weak, and I would like some help understanding
why the following from the draft is true:

There
   is no requirement that the calls come from unauthenticated sources.
   The attack can be launched even if the device requires
   authentication. Of course, authentication might provide some amount
   of traceability.

Wouldn't it be more difficult to launch the attack if authentication was
required?  I would think RTP would not start sending if the original
request could not be authenticated.

John

> -----Original Message-----
> From: Jonathan Rosenberg [mailto:jdrosen@dynamicsoft.com]
> Sent: Tuesday, July 01, 2003 11:16 PM
> To: mmusic@ietf.org
> Subject: [MMUSIC] RTP denial of service
>
> Folks,
>
> I'd like to draw your attention to the following I-D that I submitted
> recently:
>
> http://www.ietf.org/internet-drafts/draft-rosenberg-mmusic-rtp-
> denialofservice-00.txt
>
> This draft describes a denial-of-service attack using RTP. This attack
> can be launched using any protocol that uses an offer/answer-like SDP
> exchange, including SIP and RTSP. The draft also discusses ICE as a
> solution to the problem.
>
> Comments welcome.
>
> Thanks,
> Jonathan R.
>
> --
> Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
> Chief Technology Officer                    Parsippany, NJ 07054-2711
> dynamicsoft
> jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
> http://www.jdrosen.net                      PHONE: (973) 952-5000
> http://www.dynamicsoft.com
>
>
>
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic

_______________________________________________
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--NextPart

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Multiparty Multimedia Session Control Working Group of the IETF.

	Title		: Real Time Streaming Protocol (RTSP)
	Author(s)	: H. Schulzrinne
	Filename	: draft-ietf-mmusic-rfc2326bis-04.txt,.ps,.pdf
	Pages		: 5
	Date		: 2003-7-2
	
This memorandum is a revision of RFC 2326, which is currently a Pro-
posed Standard.
The Real Time Streaming Protocol, or RTSP, is an application-level
protocol for control over the delivery of data with real-time
properties. RTSP provides an extensible framework to enable con-
trolled, on-demand delivery of real-time data, such as audio and
video. Sources of data can include both live data feeds and stored
clips. This protocol is intended to control multiple data delivery
sessions, provide a means for choosing delivery channels such as UDP,
multicast UDP and TCP, and provide a means for choosing delivery
mechanisms based upon RTP (RFC 1889).

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A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Multiparty Multimedia Session Control Working Group of the IETF.

	Title		: SDP Security Descriptions for Media Streams
	Author(s)	: F. Andreasen, M. Baugher, D. Wing
	Filename	: draft-ietf-mmusic-sdescriptions-01.txt
	Pages		: 22
	Date		: 2003-7-2
	
This document defines a Session Description Protocol (SDP) 
cryptographic attribute for media streams.  The attribute describes 
a cryptographic key and other parameters, which serve to configure 
security for a media stream.  This document defines the Secure Real-
time Transport Protocol (SRTP) parameters for the attribute.  The 
SDP crypto attribute requires the services of a data security 
protocol to secure the SDP message.

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From: Jonathan Rosenberg <jdrosen@dynamicsoft.com>
Organization: dynamicsoft
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Subject: Re: [MMUSIC] RTP denial of service
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philippe.gentric@philips.com wrote:

> Let me check If I understood correctly what jonathan wanted to mean:
> 
> the point is that the attacker COULD be authenticated
> e.g. the attacker *buys* a movie (say with a stolen credit card)
> from www.holywood-movies.com etc ....
> BUT tweaks the streaming request in a way that the
> movie will be sent toward whitehouse.gov instead !
> 
> Traceability would be if the stolen credit card can be traced,
> or if the attacker IP address can be traced etc ...

Yes. But its easier than that. Many media services don't even require 
the user to pay. For example, if you connect to the free world dialup 
voicemail server without needing to pay anyone anything. Just go to 
their website and sign up.

> 
> 
> BTW jonathan, for this exact reason (to my knowledge most) RTSP server implementations
> today would refuse to stream except toward the originating RTSP IP address
> (or at least this feature can be turned on)

Sure, and the draft discusses this. All this means is that the client 
needs to spoof the source address.

> ...
> which is actually a problem for NAT traversal in case the NAT attributes
> a different IP address for the RTSP and RTP traffic !

Yup, exactly.


-Jonathan R.
-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com


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From exim@www1.ietf.org  Thu Jul  3 04:42:34 2003
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Jonathan,

Thanks for bringing up this problem. I agree that the attack
exists, and I also agree that nothing in the RTP packets (such
as SRTP) can help prevent such attacks. I not expert enough
to say anything about suitability of RTCP or STUN.

Attacks of a similar nature have been discussed in the context
of other protocols, for instance Mobile IPv6. The general
nature of such attacks is that a signaling protocol conveys
an address, and the lack of verification for this address
results in a vulnerability; attackers choose the address of
an innocent third party and start "bombing" this address
with packets. What makes these attacks bad is that the
attacker can initiate the attack with just few packets,
a legitimate entity in the network does all the hard work,
and the victim's link becomes congested.

The attack has always serious consequences due to its
amplification factor. In SIP, this factor is due to
the bandwidth difference in signaling vs. payload. In
Mobile IPv6, this factor was due to the ability to "open"
a connection, speed it up, and then move it towards the
victim.

What also makes the attack hard is that the packets to
the victim never come from the attacker, they come from
another, legitimate entity in the network. This makes the
tracing of the attack hard: the attacker may be traceable
from that entity, but can we be sure that the administrator
of the entity can be reached for assistance? This may be
easy if the entity is owned by an operator, but what if
its my home server or someone's windows PC? However,
assuming you do get the help of the administrator, there
seems to be a few different levels of hardness
for tracing the attacker then:

- No verification: The attack was initiated by a
   packet sent to the entity, no assurance of the
   authentication of the attacker or the validity
   of the source address in the packet.

   SIP INVITE without TLS and authentication appears
   to allow this, no?

   What makes this level tricky is that there are
   designs where DoS attackers can be traced even
   if they lie about their addresses, e.g. itrace.
   However, these mechanisms only work for bulk
   attacks, and here we only send a few signaling
   packets.

- Source address verification: The attack can only
   be launched after some exchange of packets, where
   the source address of the packet has been verified
   to be valid.

   In SIP, anon Digest would allow you to do source
   address verification. Similarly, even server-side
   only authenticated TLS would suffice for this
   check.

   Note: in Mobile IPv6, the address of the attacker
   was conveyed also in the packets to the victim,
   but this does not appear to be the case in SIP/RTP,
   because the RTP packets don't contain the address
   of the node that initiated the signaling.

- Authentication: the attacker's identity is
   authenticated in some manner, you can probably
   trace the attacker down to his postal address/passport/
   credit card.

I believe we should strive for making the tracing
of the attack at least so hard that the attacker has
to give his IP address information, i.e., make the first
case not allowed. Still, tracing is a post-attack
activity, expensive and unreliable. So I believe you
are right in trying to prevent such attacks.

A few words about prevention. Typically, a "return
routability test" approach is used, as I think you
are doing also for STUN. I'm not expert enough in
STUN to know if it provides sufficient binding
between requests and responses so that off-path
attackers can't easily spoof responses? But I would
guess you have taken this into account.

Another issue is whether there needs to be a binding
between the signaling exchange and the STUN exchange,
e.g. a session identifier or something like that? Or
is it sufficient to rely on the right timing? What about
busy servers, wouldn't the timing of the attack be
more likely to succeed with them?

Finally, the prevention mechanisms themselves may
be susceptible to an attack. An example: initiate
N sessions with different servers, all pointing to the
same victim node, who gets a lot of STUN queries.
This attack does not have amplification, but it
is hard to trace, harder than a direct dos packet
storm from a single source, and harder than than
a reflection attack. In some other cases, such
attacks have been made easier to trace by using
solely the source address of a packet in initiating
responses and protocol actions. But I understand
that this may not be an option here. Demanding
TlS/anon digest from all SIP signaling exchanges
does force the attacker to give up a lot of
information and some CPU cycles, so that may
be sufficient.

--Jari


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Date: Thu, 03 Jul 2003 15:17:38 +0200
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From: Magnus Westerlund <magnus.westerlund@ericsson.com>
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To: Tom Marshall <tmarshall@real.com>
CC: Aaron Colwell <acolwell@real.com>, mmusic@ietf.org,
        Aravind Narasimhan
 <aravind.narasimhan@sun.com>
Subject: Re: [MMUSIC] Aggregate Control URI
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Hi,

A few words in relation to this. When I filed the bug I was thinking of 
such a case that you try to aggregate two different media that the 
server did not offer as an aggregated session. However during 
discussions I have come to the conclusion that it will be difficult to 
use. However the aggregated control URI resolution may have more usage 
when it comes to session that are supposed to be used where the 
aggregated control URL is missing. I do think it is good to have stated 
a direction on how this is resolved in cased when information is missing 
but the server allows it.

Note that a server can always refuse to perform aggregation of a media 
with another, by responding to a SETUP request trying to aggregate with 
a "459 Aggregate operation not allowed" error code. In that case the 
client will have to perform synchronization, etc. locally using two 
non-aggregated sessions.

"If an Aggregate control URI is not specified in the session 
description, a client MUST create an URI for aggregate control of the 
session."

I don't think this formulation is good. The reason a session description 
does not give a aggregated control URI is that it does not desire the 
media to be aggregated. I would reformulate the sentence into:

If an Aggregate control URI is not specified in the session description, 
it is probably a indication that non-aggregated control SHOULD be used. 
However a client MAY try to SETUP the session in aggregated control. If 
the server refuse to aggregate the specified media, the server SHALL use 
the 459 error code. If the server allows the aggregation, then the 
client MUST create an URI for aggregate control of the session. This URI 
MUST contain the servers host address ...

As a conclusion, I don't see a problem with this resolution, although it 
is not what we had discussed. So I can understand any comments to this. 
What do you think of the updated text?

Best Regards


Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com


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Hi,

Do I understand you correctly that you would like to have some 
indication on why the client performed the TEARDOWN? If not can you 
please be more clear about what you desire.

I would also like to to point out certain things in your mail.

Saurabh Srivastava wrote:
> Hi Folks,
>       This is a requirement that would enable the streaming server to 
> know that why a session is being closed from client and in turn, allow 
> it to give guaranteed delivery service in pay-per-view scenarios.
>  
> TEARDOWN, which indiactes the end of the session can be sent from a 
> client due to:-
> 1. The RTP channel indicating that the clip is over.

There is no explicit indication on that a clip is over. In streaming 
this is normally resolved at the client when it notices that the 
full-range has been played out. The client may also detect that delivery 
has stopped of RTP packets. To verify that this is not due to transport 
errors the client should look at the RTCP SR. However this method does 
not guarantee that a clip is really over, and not simply a part where no 
packets are delivered. For Live content this is basically very difficult 
unless other means indicate that the session has expired.

On possibility in RTSP to notify clients that the session is really over 
is to redirect the client to such a message. Introducing the message in 
the session for live content is also useful, at least for the user.

Normally the client will issue a TEARDOWN in this case when the user 
does not rewind the session or otherwise inactive for some period of 
time. In other words, the end of the clip does not automatically lead to 
a TEARDOWN request.

> 2. The user initiating the request to end the session.

Which is the case you receive a TEARDOWN.

> 3. Network problem due to which the client gets time-out.

In this case there will be no TEARDOWN request. The server side simply 
times out the session.


Best Regards


Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com


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--NextPart

A New Internet-Draft is available from the on-line Internet-Drafts directories.


	Title		: Internet Media Guide Metadata Baseline
	Author(s)	: J. Luoma
	Filename	: draft-luoma-mmusic-img-metadata-01.txt
	Pages		: 29
	Date		: 2003-7-3
	
This document defines the base metadata format for Internet Media
Guides (IMGs), applicable to a wide variety of Internet hosts and
communication links. IMG metadata describes files, resources and
multimedia programs available for streaming or downloading via
multicast or unicast. An IMG metadata model, semantics of the IMG
media metadata entities, and an XML-based framing structure for IMG
media metadata are defined. The aim is to reuse existing metadata
standards for the IMG metadata format where possible.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-luoma-mmusic-img-metadata-01.txt

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--NextPart

A New Internet-Draft is available from the on-line Internet-Drafts directories.


	Title		: MUPPET: Internet Media Guide Unidirectional 
                          Point-to-Multipoint Transport
	Author(s)	: J. Luoma
	Filename	: draft-luoma-mmusic-img-muppet-02.txt
	Pages		: 34
	Date		: 2003-7-3
	
This document defines MUPPET, a unidirectional point-to-multipoint
transport protocol for the delivery of Internet Media Guide metadata.
The MUPPET protocol is based on Asynchronous Layered Coding, a
massively scalable protocol for reliable multicast transport. MUPPET
is intended to be used with the Internet Media Guide framework, and
in addition may be useful with other applications.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-luoma-mmusic-img-muppet-02.txt

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--NextPart

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Multiparty Multimedia Session Control Working Group of the IETF.

	Title		: How to Enable Real-Time Streaming Protocol (RTSP) 
                          traverse Network Address Translators (NAT) and 
                          interact with Firewalls
	Author(s)	: M. Westerlund, T. Zeng
	Filename	: draft-ietf-mmusic-rtsp-nat-01.txt
	Pages		: 37
	Date		: 2003-7-3
	
This document describes six different types of NAT traversal
techniques that can be used by RTSP. For each technique a description
on how it shall be used, what security implications it has and other
deployment considerations are given. Further a description on how
RTSP relates to firewalls is given.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-ietf-mmusic-rtsp-nat-01.txt

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From exim@www1.ietf.org  Thu Jul  3 12:14:57 2003
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A New Internet-Draft is available from the on-line Internet-Drafts directories.


	Title		: A Framework for the Usage of Internet Media Guides
	Author(s)	: Y. Nomura et al.
	Filename	: draft-nomura-mmusic-img-framework-01.txt
	Pages		: 25
	Date		: 2003-7-3
	
This document defines a framework for the delivery of Internet Media
Guides (IMGs). A media guide is a set of information (metadata)
describing the features of multimedia content in order to subscribe
to, manage and exchange multimedia content.
Several protocols and methods exist that are able to deliver metadata
over the Internet, giving information on Internet services, media and
content. This existing knowledge is used to provide a general
framework for Internet Media Guides and outlines existing scalability
and flexibility issues, along with the desirable features that can
solve these problems.

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From: philippe.gentric@philips.com
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Subject: Re: [MMUSIC] reason for teardown
To: Magnus Westerlund <magnus.westerlund@ericsson.com>
Cc: mmusic@ietf.org, Saurabh Srivastava <saurabh@julysystems.com>
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Date: Thu, 3 Jul 2003 18:10:45 +0200
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Magnus you wrote:

> There is no explicit indication on that a clip is over.


there is RTCP "BYE" ;-)

regards,


Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com


                                                                                                                                           
                                                                                                                                           
                                                       To:   Saurabh Srivastava <saurabh@julysystems.com>                                  
                                                       cc:   mmusic@ietf.org                                                               
                                                        (bcc: Philippe Gentric/MP4-SUR/CE/PHILIPS)                                         
                                                       Subject:    Re: [MMUSIC] reason for teardown                                        
               Magnus Westerlund                                                                                                           
               <magnus.westerlund@ericsson.            Classification:                                                                     
               com>                                                                                                                        
                                                                                                                                           
               Sent by:                                                                                                                    
               mmusic-admin@ietf.org                                                                                                       
                                                                                                                                           
               03/07/2003 17:14                                                                                                            
                                                                                                                                           
                                                                                                                                           




Hi,

Do I understand you correctly that you would like to have some
indication on why the client performed the TEARDOWN? If not can you
please be more clear about what you desire.

I would also like to to point out certain things in your mail.

Saurabh Srivastava wrote:
> Hi Folks,
>       This is a requirement that would enable the streaming server to
> know that why a session is being closed from client and in turn, allow
> it to give guaranteed delivery service in pay-per-view scenarios.
>
> TEARDOWN, which indiactes the end of the session can be sent from a
> client due to:-
> 1. The RTP channel indicating that the clip is over.

There is no explicit indication on that a clip is over. In streaming
this is normally resolved at the client when it notices that the
full-range has been played out. The client may also detect that delivery
has stopped of RTP packets. To verify that this is not due to transport
errors the client should look at the RTCP SR. However this method does
not guarantee that a clip is really over, and not simply a part where no
packets are delivered. For Live content this is basically very difficult
unless other means indicate that the session has expired.

On possibility in RTSP to notify clients that the session is really over
is to redirect the client to such a message. Introducing the message in
the session for live content is also useful, at least for the user.

Normally the client will issue a TEARDOWN in this case when the user
does not rewind the session or otherwise inactive for some period of
time. In other words, the end of the clip does not automatically lead to
a TEARDOWN request.

> 2. The user initiating the request to end the session.

Which is the case you receive a TEARDOWN.

> 3. Network problem due to which the client gets time-out.

In this case there will be no TEARDOWN request. The server side simply
times out the session.


Best Regards


Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com


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The RTSP spec states that the client_port and server_port fields indicate
what ports the client and server are expected to receive data on. Is it
also safe to assume that the client and server will send data from these
ports as well? I didn't see anything in the spec that explicitly states
that this is the case. Could someone please clarify.

Thanks,
Aaron

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Hi,

Comments inline

Saurabh Srivastava wrote:
> Hi,
>     This is correct. My question is that I would like to have "some 
> indication on why the client performed the TEARDOWN". It is more from 
> the server perspective so that it can understand the nature of the 
> request and then take appropriate action.
>  
> As far as the solutions are concerned for the problem, I have tried 
> various things, but could not find a fool proof solution that would work 
> in all conditions.
>  
> RTCP BYE as pointed out by Philippe is an indication from the server 
> indicating that the session is over. 

The RTCP BYE is sent when the RTP session is closed, this is normally 
done as a result of a RTSP TEARDOWN. RTCP BYE shall not be used to 
indicate the end of a media stream.

And RR's keep indicating the
> reception quality from the client in the ideal scenario. But due to a 
> possible delay in networks (specially wireless networks) there could be 
> a scenario that the RR's do not reach the server in time and meanwhile 
> the client times out (according to time-out settings on UA). In that 
> case TEARDOWN arrives from client, and the server is unaware of the 
> reason why it came.

In a streaming server -> client scenario the server will mostly be 
sending Sender reports, when not active sending media it will switch to 
RRs after a few reporting interval, normally 2. If any RTCP bandwidth is 
  assigned to the session, the limiting factor in a point to point case 
is the 5 second minimal rule. This means that RTCP packet will at most 
be sent from each end every 7.5 seconds. The default RTSP session 
time-out is 60 seconds, that means that it will be time for at least 8 
RTCP packet. This means that the probability to all be lost is very 
small. Therefore a server should not time out a client unnecessary. And 
when a server times out a client no TEARDOWN request is sent from the 
client or server. The server simply removes the session.

When it comes to client side time outs they must be reasonably set. They 
must allow for some transport problems. And a client would not time out 
a session while it receives media. And I don't see a reason for timing 
out the session very quickly even if no media is received. One must also 
give the user time to react to the end of the clip. Therefore I would 
not recommend such a timer to be shorter than 30 seconds.


>  
> RTCP BYE can be sent by the client to indicate that it is exiting from 
> the session but there too the reason field is not mandatory (So left 
> blank in most of the implementations :-)    ).

Yes, reasons field is seldom used. Also the RTCP bye is normally only 
sent once, therefore has high probability to become lost.

>  
> I believe, if the TEARDOWN contains this information also, then the 
> server will perhaps be able to provide the support systems more 
> information so that appropriate actions could be taken. More so because 
> in most of the implementations RTSP would be implemented on TCP and RTP 
> on UDP. And since this information becomes quite ciritical if end user's 
> money is involved, RTSP would be a better channel to convey this 
> information on account of a more reliable transport.
>  

When it comes to sending charging related information in protocols from 
the client I have a view that this is difficult. The most normal problem 
is how to avoid fraud. If a client can implement in the teardown a 
reason which will mean that the user doesn't have to pay, it will be 
exploited.

Could you please further elaborate on what the different cases you want 
to distinguish are? I have some trouble seeing how different TEARDOWN 
reasons will have impact.

Best Regards


Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com


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Hi Aaron,

It is strongly encouraged that you do this. As you point out it is not 
written in the RFC 2326. We should clarify this recommendation with 
motivation in the updated specification. However I don't think we can 
mandate it. What would people say about a SHOULD?

Reasons for sending media from the respective ports that you also 
receive are: NAT traversal and Firewalls. Also source filtering needs 
this. I could understand that server manufactures desire clients to send 
RTCP from their designated port, otherwise server running many sessions 
on the same port has problems.

I don't know if all implementations do this, probably not. Any one 
knowing this?

Cheers

Magnus

Aaron Colwell wrote:
> The RTSP spec states that the client_port and server_port fields indicate
> what ports the client and server are expected to receive data on. Is it
> also safe to assume that the client and server will send data from these
> ports as well? I didn't see anything in the spec that explicitly states
> that this is the case. Could someone please clarify.
> 
> Thanks,
> Aaron
> 
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic
> 


-- 

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com


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Date: Mon, 07 Jul 2003 16:49:18 +0900
From: "NAKAMURA, Hidefumi" <nakamura.hidefumi@lab.ntt.co.jp>
To: sip@ietf.org, mmusic@ietf.org
Cc: hidefumi.nakamura@staff.east.ntt.co.jp
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Subject: [MMUSIC] Appropriate usage of SIP and RTSP
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Hi, all.

I have a question about the relationship between SIP and RTSP. 

In RFC3261, there is a description that says 
   "SIP is not a vertically integrated communications system.  SIP is
   rather a component that can be used with other IETF protocols to
   build a complete multimedia architecture.  Typically, these
   architectures will include protocols such as the Real-time Transport
   Protocol (RTP) (RFC 1889 [28]) for transporting real-time data and
   providing QoS feedback, the Real-Time streaming protocol (RTSP) (RFC
   2326 [29]) for controlling delivery of streaming media, ..."
   (RFC3261 Section 2)

However, my understanding is that both SIP and RTSP have the capability
for "discovery of UAs or media streams."
If I use SIP to establish a stream session and use RTSP to control
the stream, there will be redundant sequences, i.e. INVITE-OK-ACK and
SETUP-OK.

Was there any discussion on how to use these two protocols appropriately?

With SIP application server, network providers can provide various
services on contents delivery while we will not be able to do so only
with RTSP, I think.  On the other hand, RTSP has enough capability for
discovery of media streams and for negotiation of SDPs.
So, I think, for the simple delivery of contents, RTSP is appropriate to
use, and for various session control services regarding contents
delivery, SIP with RTSP is appropriate to use.

Any opinions?

I wonder why no contents delivery server seems to prepare SIP stack now. 
Is it because, up to now, there exists only a simple contents delivery
service?

best regards,

-- 
NAKAMURA, Hidefumi 
NTT ServiceIntegration /NetworkServiceSystems Labs.
tel: +81(422)59 3904; fax:+81(422)60 4012
---



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CC: sip@ietf.org, mmusic@ietf.org, hidefumi.nakamura@staff.east.ntt.co.jp
Subject: Re: [MMUSIC] Appropriate usage of SIP and RTSP
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Hi,

See comments inline:

NAKAMURA, Hidefumi wrote:
> Hi, all.
> 
> I have a question about the relationship between SIP and RTSP. 
> 
> In RFC3261, there is a description that says 
>    "SIP is not a vertically integrated communications system.  SIP is
>    rather a component that can be used with other IETF protocols to
>    build a complete multimedia architecture.  Typically, these
>    architectures will include protocols such as the Real-time Transport
>    Protocol (RTP) (RFC 1889 [28]) for transporting real-time data and
>    providing QoS feedback, the Real-Time streaming protocol (RTSP) (RFC
>    2326 [29]) for controlling delivery of streaming media, ..."
>    (RFC3261 Section 2)
> 
> However, my understanding is that both SIP and RTSP have the capability
> for "discovery of UAs or media streams."
> If I use SIP to establish a stream session and use RTSP to control
> the stream, there will be redundant sequences, i.e. INVITE-OK-ACK and
> SETUP-OK.
> 
> Was there any discussion on how to use these two protocols appropriately?

Not to my knowledge. The SIP and RTSP combination has not been explored, 
however it seem to contain a number of use cases. For example inviting a 
media server into a SIP session or a conference session.

There are significant overlap in SIP and RTSP, mostly in regards to 
session establishment that are done i different ways.

> 
> With SIP application server, network providers can provide various
> services on contents delivery while we will not be able to do so only
> with RTSP, I think.  On the other hand, RTSP has enough capability for
> discovery of media streams and for negotiation of SDPs.
> So, I think, for the simple delivery of contents, RTSP is appropriate to
> use, and for various session control services regarding contents
> delivery, SIP with RTSP is appropriate to use.

What do you mean with "session control services regarding contents 
delivery"?

> 
> Any opinions?
> 
> I wonder why no contents delivery server seems to prepare SIP stack now. 
> Is it because, up to now, there exists only a simple contents delivery
> service?

I believe that no one has looked into this and have had a need.

Best Regards


Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com


_______________________________________________
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Date: Mon, 07 Jul 2003 18:28:19 +0900
From: "NAKAMURA, Hidefumi" <nakamura.hidefumi@lab.ntt.co.jp>
To: Magnus Westerlund <magnus.westerlund@ericsson.com>
Subject: Re: [MMUSIC] Appropriate usage of SIP and RTSP
Cc: sip@ietf.org, mmusic@ietf.org
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Dear Magnus,

Thank you for your quick response.
I wrote down my opinion after your comments.

> Hi,
> 
> See comments inline:
> 
> NAKAMURA, Hidefumi wrote:
> > Hi, all.
> > 
> > I have a question about the relationship between SIP and RTSP. 
> > 
> > In RFC3261, there is a description that says 
> >    "SIP is not a vertically integrated communications system.  SIP is
> >    rather a component that can be used with other IETF protocols to
> >    build a complete multimedia architecture.  Typically, these
> >    architectures will include protocols such as the Real-time Transport
> >    Protocol (RTP) (RFC 1889 [28]) for transporting real-time data and
> >    providing QoS feedback, the Real-Time streaming protocol (RTSP) (RFC
> >    2326 [29]) for controlling delivery of streaming media, ..."
> >    (RFC3261 Section 2)
> > 
> > However, my understanding is that both SIP and RTSP have the capability
> > for "discovery of UAs or media streams."
> > If I use SIP to establish a stream session and use RTSP to control
> > the stream, there will be redundant sequences, i.e. INVITE-OK-ACK and
> > SETUP-OK.
> > 
> > Was there any discussion on how to use these two protocols appropriately?
> 
> Not to my knowledge. The SIP and RTSP combination has not been explored, 
> however it seem to contain a number of use cases. For example inviting a 
> media server into a SIP session or a conference session.
> 
> There are significant overlap in SIP and RTSP, mostly in regards to 
> session establishment that are done i different ways.
> > 
> > With SIP application server, network providers can provide various
> > services on contents delivery while we will not be able to do so only
> > with RTSP, I think.  On the other hand, RTSP has enough capability for
> > discovery of media streams and for negotiation of SDPs.
> > So, I think, for the simple delivery of contents, RTSP is appropriate to
> > use, and for various session control services regarding contents
> > delivery, SIP with RTSP is appropriate to use.
> 
> What do you mean with "session control services regarding contents 
> delivery"?

For example, if we establish a stream session via SIP application server
owned by the network provider, the application server can redirect the
session to the appropriate contents delivery server from the standpoint
of location, bandwidth prepared between terminals and the server, or
condition of contents server (i.e. in congestion, failure, and so on.)
Say, we get a media stream URI from a portal server.  The terminal(or
set top box) requests a session initiation to the media stream URI to
the SIP application server.  The SIP application server routes the
request to the contents delivery server that stores the media.  However,
if the server is in congestion and returns 503, the SIP application
server can select and redirect the session to another contents delivery
server instead.
I do not think this is possible with only RTSP.
(though the interaction among the portal server, contents delivery
servers and the terminals might enable this type of service in some
extent.)

> > Any opinions?
> > 
> > I wonder why no contents delivery server seems to prepare SIP stack now. 
> > Is it because, up to now, there exists only a simple contents delivery
> > service?
> 
> I believe that no one has looked into this and have had a need.

I understand.  Thank you very much for your comments.
Maybe it is interesting to investigate the use case, anyway.

> Best Regards
> 
> 
> Magnus Westerlund
> 
> Multimedia Technologies, Ericsson Research EAB/TVA/A
> ----------------------------------------------------------------------
> Ericsson AB                | Phone +46 8 4048287
> Torshamsgatan 23           | Fax   +46 8 7575550
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Hi Jonathan,

I have now had time to read your draft. It summaries the problem of the 
attack fairly well. However I think one can elaborate a bit more on some 
use cases and in relation to NAT traversal.

First, the problem of destination addresses in combination with NATs 
that use multiple addresses. If a NAT would assign different NAT 
mappings to different external addresses there is a problem with the 
limiting text that RTSP has. This also is present for a single RTP 
session where RTP and RTCP will be separate flows. This leads to that 
simple limitations can't be used while still NAT traversal or TURN 
servers are in use.

Secondly the RTCP prevention that you mention in chapter 3 has more 
flaws then you describe, but not one of them you describe I would say. I 
don't see a reason to force the sending side to have this stop and go 
behaviour you describe. I would more work in the terms of how TFRC 
behave, I think. If no RTCP reports are received the sending bit-rate is 
throttled back, to almost non existing levels. This will limit the 
severity of the attack. However with using many sessions it might still 
be possible to achieve enough force amplification.

The flaw you missed in your description of using RTCP as limiting factor 
is first that if the attacker directs a RTCP stream to itself and only 
the RTP stream to the target, it can simple generate false RTCP reports. 
  The senders RTCP reports contains the number of packets sent, which 
makes it easy to increase the RTCP receiver reports extended counter. 
The initial RTP sequence number are usually transmitted in RTSP's 
RTP-Info header. Therefore all necessary information for faking a 
perfect reception pattern exist, keeping any congestion control based on 
RTCP reports happy.

Third, the solution space. As you mention an alternative to using STUN 
in this requesting mechanism would be to develop a RTP payload format 
and RTCP packet type to contain necessary information of granting a 
media stream. What may be missing in STUN is the possibility to provide 
information about the media stream that the receiver accepts.

However I don't know if such a solution would be any better. Maybe on 
the paper it would have a clearer demultiplexing than between STUN and 
RTP. However STUN can be used with any media protocol that can be 
differentiated on the first byte, while a RTP/RTCP solution would be 
limited to that protocol.

Fourth, have you looked at what solutions DCCP would provide to this 
problem? I think that the session establishment could ensure that the 
client accepts the media stream.

Fifth, what is the current status of ICE? Can we expect any progress for 
ICE within the IETF.

Sixth, doesn't one need to use STUN with authentication to prevent other 
security attacks that based on falsifying STUN responses, even when the 
session establisher is not an attacker?


Best Regards

Magnus Westerlund


Jonathan Rosenberg wrote:
> Folks,
> 
> I'd like to draw your attention to the following I-D that I submitted 
> recently:
> 
> http://www.ietf.org/internet-drafts/draft-rosenberg-mmusic-rtp-denialofservice-00.txt 
> 
> 
> This draft describes a denial-of-service attack using RTP. This attack 
> can be launched using any protocol that uses an offer/answer-like SDP 
> exchange, including SIP and RTSP. The draft also discusses ICE as a 
> solution to the problem.
> 
> Comments welcome.
> 
> Thanks,
> Jonathan R.
> 


-- 

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com


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From: Aaron Colwell <acolwell@real.com>
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I think adding a SHOULD about this is fine. We should also list the
reasons you stated below so that people think of it being closer to a MUST
if they want a more robust and interoperable implementation.

Aaron

On Fri, 4 Jul 2003, Magnus Westerlund wrote:

> Hi Aaron,
>
> It is strongly encouraged that you do this. As you point out it is not
> written in the RFC 2326. We should clarify this recommendation with
> motivation in the updated specification. However I don't think we can
> mandate it. What would people say about a SHOULD?
>
> Reasons for sending media from the respective ports that you also
> receive are: NAT traversal and Firewalls. Also source filtering needs
> this. I could understand that server manufactures desire clients to send
> RTCP from their designated port, otherwise server running many sessions
> on the same port has problems.
>
> I don't know if all implementations do this, probably not. Any one
> knowing this?
>
> Cheers
>
> Magnus
>
> Aaron Colwell wrote:
> > The RTSP spec states that the client_port and server_port fields indicate
> > what ports the client and server are expected to receive data on. Is it
> > also safe to assume that the client and server will send data from these
> > ports as well? I didn't see anything in the spec that explicitly states
> > that this is the case. Could someone please clarify.
> >
> > Thanks,
> > Aaron
> >
> > _______________________________________________
> > mmusic mailing list
> > mmusic@ietf.org
> > https://www1.ietf.org/mailman/listinfo/mmusic
> >
>
>
> --
>
> Magnus Westerlund
>
> Multimedia Technologies, Ericsson Research EAB/TVA/A
> ----------------------------------------------------------------------
> Ericsson AB                | Phone +46 8 4048287
> Torshamsgatan 23           | Fax   +46 8 7575550
> S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com
>
>

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Attached you will find draft-basso-avt-videoconreq-00.txt

Abstract:

A variety of communication services such as video
conferencing and video messaging rely on the capability of video
encoders and decoders to exchange control commands. This document
outlines this set of commands as well as the requirements for
their transport.

Comments are more than welcome.





Andrea Basso
NMS Communications
(732) 936-2118
(See attached file: draft-basso-avt-videoconreq-00.zip)

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Folks,

attached is the draft MMUSIC agenda.  Please let us know
if there is anything we missed.

Thanks,
Joerg

57th IETF: Draft MMUSIC Agenda
==============================

Thursday, 17 July 2003, 0900 - 1130, Hall IK
--------------------------------------------

0900    Agenda Bashing and Status Update               (chairs, 15)

         Recent RFCs
	- draft-ietf-mmusic-reservation-flows-01.txt	-> RFC 3524

         Status Updates
         - draft-ietf-mmusic-sdp-new-13.txt
         - draft-ietf-mmusic-sdp4nat-05.txt
         - draft-ietf-mmusic-sdpng-trans-03.txt

	- draft-rajeshkumar-mmusic-gpmd-03.txt

	- draft-ietf-mmusic-sdp-bwparam-01.txt
	- draft-ietf-mmusic-srcfilter-03.txt

         - draft-ietf-mmusic-sdp-comedia-05.txt
	- draft-camarillo-mmusic-alt-01.txt

0915 
SDP Security Descriptions for Media Streams	(Wing, 10)
	- draft-ietf-mmusic-sdescriptions-01.txt

0925 
SDP Offer Answer Examples			(Johnston, 10)
	- draft-ietf-mmusic-offer-answer-examples-01.txt

0935 
SDPng Update					(Kutscher, 20)
	- draft-ietf-mmusic-sdpng-06.txt

0955 
RTP DoS Attack					(Rosenberg, 10)
	- draft-rosenberg-mmusic-rtp-denialofservice-00.txt

1010 
RTSP Update					(Westerlund, 15)
	- draft-ietf-mmusic-rfc2326bis-04.txt
	- draft-ietf-mmusic-rtsp-nat-01.txt

1030 
Internet Media Guides				(Manyfolks, 60)
	- draft-luoma-mmusic-img-metadata-01.txt
	- draft-luoma-mmusic-img-muppet-02.txt
	- draft-nomura-mmusic-img-framework-01.txt
	- draft-nomura-mmusic-img-requirements-00.txt
	- draft-nomura-mmusic-pguide-framework-00.txt
	- draft-stallard-mmusic-dvb-thoughts-on-sds-00.txt

1130 
Close



Second (formal) meeting still to be scheduled for RTSP
------------------------------------------------------
Tentatively Wednesday night over dinner

	RTSP spec editing and bug fixing	 (Westerlund/Lanphier, 120)



-----------------------------------------------------------------------------

				NOTE WELL

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The MMUSIC Agenda for the 57th IETF is now available at

	http://www.dmn.tzi.org/ietf/mmusic/57/agenda.txt
	http://www.dmn.tzi.org/ietf/mmusic/57/agenda.html

There have been few changes and version number updates compared
to what we sent to the list yesterday.

Joerg


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From: Jonathan Rosenberg <jdrosen@dynamicsoft.com>
Organization: dynamicsoft
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To: "NAKAMURA, Hidefumi" <nakamura.hidefumi@lab.ntt.co.jp>
CC: Magnus Westerlund <magnus.westerlund@ericsson.com>, sip@ietf.org,
        mmusic@ietf.org
Subject: Re: [MMUSIC] Appropriate usage of SIP and RTSP
References: <20030707134023.181C.NAKAMURA.HIDEFUMI@lab.ntt.co.jp> <3F0930B4.8090202@ericsson.com> <20030707174715.1826.NAKAMURA.HIDEFUMI@lab.ntt.co.jp>
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I agree that there is significant overlap between RTSP and SIP, and 
this is something that has been bothering more and more over time. I 
have had in mind to write a draft on the ways in which they could be 
better merged, but have not had the time.

The primary place where they overlap is session establishment. In this 
area, I think SIP is much richer, in terms of features. SIP would 
allow connections to media servers running on PCs and other end-user 
devices. Its rich routing facilities could allow nice policy-based 
connection to content. It has had a lot of work on firewall/nat 
traversal which is now only getting repeated for RTSP. Plus, in many 
cases, you might initiate a session, but not know, in advance, that 
the session is to be connected to a content server. As an example, I'd 
like to be able to make a sip call to a user, and instead get 
connected to a voicemail greeting that I can control with RTSP.

IMHO, the most obvious way to make this work is to use SIP to initiate 
a session. If the session is to a media server, then, using SDP 
negotiations, one can add an additional "media channel", which is 
actually RTSP, doing just media controls (play, fast-forward, etc.). 
Thus, SIP would set up an RTSP session to control the media that the 
SIP call connected to.

I havent really fleshed this out much, but it seemed like a start.

-Jonathan R.

NAKAMURA, Hidefumi wrote:

> Dear Magnus,
> 
> Thank you for your quick response.
> I wrote down my opinion after your comments.
> 
> 
>>Hi,
>>
>>See comments inline:
>>
>>NAKAMURA, Hidefumi wrote:
>>
>>>Hi, all.
>>>
>>>I have a question about the relationship between SIP and RTSP. 
>>>
>>>In RFC3261, there is a description that says 
>>>   "SIP is not a vertically integrated communications system.  SIP is
>>>   rather a component that can be used with other IETF protocols to
>>>   build a complete multimedia architecture.  Typically, these
>>>   architectures will include protocols such as the Real-time Transport
>>>   Protocol (RTP) (RFC 1889 [28]) for transporting real-time data and
>>>   providing QoS feedback, the Real-Time streaming protocol (RTSP) (RFC
>>>   2326 [29]) for controlling delivery of streaming media, ..."
>>>   (RFC3261 Section 2)
>>>
>>>However, my understanding is that both SIP and RTSP have the capability
>>>for "discovery of UAs or media streams."
>>>If I use SIP to establish a stream session and use RTSP to control
>>>the stream, there will be redundant sequences, i.e. INVITE-OK-ACK and
>>>SETUP-OK.
>>>
>>>Was there any discussion on how to use these two protocols appropriately?
>>
>>Not to my knowledge. The SIP and RTSP combination has not been explored, 
>>however it seem to contain a number of use cases. For example inviting a 
>>media server into a SIP session or a conference session.
>>
>>There are significant overlap in SIP and RTSP, mostly in regards to 
>>session establishment that are done i different ways.
>>
>>>With SIP application server, network providers can provide various
>>>services on contents delivery while we will not be able to do so only
>>>with RTSP, I think.  On the other hand, RTSP has enough capability for
>>>discovery of media streams and for negotiation of SDPs.
>>>So, I think, for the simple delivery of contents, RTSP is appropriate to
>>>use, and for various session control services regarding contents
>>>delivery, SIP with RTSP is appropriate to use.
>>
>>What do you mean with "session control services regarding contents 
>>delivery"?
> 
> 
> For example, if we establish a stream session via SIP application server
> owned by the network provider, the application server can redirect the
> session to the appropriate contents delivery server from the standpoint
> of location, bandwidth prepared between terminals and the server, or
> condition of contents server (i.e. in congestion, failure, and so on.)
> Say, we get a media stream URI from a portal server.  The terminal(or
> set top box) requests a session initiation to the media stream URI to
> the SIP application server.  The SIP application server routes the
> request to the contents delivery server that stores the media.  However,
> if the server is in congestion and returns 503, the SIP application
> server can select and redirect the session to another contents delivery
> server instead.
> I do not think this is possible with only RTSP.
> (though the interaction among the portal server, contents delivery
> servers and the terminals might enable this type of service in some
> extent.)
> 
> 
>>>Any opinions?
>>>
>>>I wonder why no contents delivery server seems to prepare SIP stack now. 
>>>Is it because, up to now, there exists only a simple contents delivery
>>>service?
>>
>>I believe that no one has looked into this and have had a need.
> 
> 
> I understand.  Thank you very much for your comments.
> Maybe it is interesting to investigate the use case, anyway.
> 
> 
>>Best Regards
>>
>>
>>Magnus Westerlund
>>
>>Multimedia Technologies, Ericsson Research EAB/TVA/A
>>----------------------------------------------------------------------
>>Ericsson AB                | Phone +46 8 4048287
>>Torshamsgatan 23           | Fax   +46 8 7575550
>>S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com
>>
>>
>>_______________________________________________
>>mmusic mailing list
>>mmusic@ietf.org
>>https://www1.ietf.org/mailman/listinfo/mmusic
> 
> 

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com


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We revised sdescriptions
<http://www.ietf.org/internet-drafts/draft-ietf-mmusic-sdescriptions-01.txt>
.

If you're unfamiliar with this I-D, the abstract is:
   This document defines a Session Description Protocol (SDP)
   cryptographic attribute for media streams.  The attribute describes
   a cryptographic key and other parameters, which serve to configure
   security for a media stream.  This document defines the Secure Real-
   time Transport Protocol (SRTP) parameters for the attribute.  The
   SDP crypto attribute requires the services of a data security
   protocol to secure the SDP message.

Significant changes from -00 to -01 are:

  * New syntax for a=crypto attribute parameter.  This includes
      - removing the "grouping" which occured before (now everything
        for one crypto suite is on one line);
      - a new key "use" attribute (encrypt, decrypt, both);
      - created SRC tuple for SSRC, SEQ, and ROC in the SRTP session
        parameter (which also allows specifying multiples of each),
        the syntax is "SRC=(ssrc,seq,roc)";
      - removed application=srtp|srtcp;
      - other smaller ABNF changes and bugfixes.

  * Please see the Open Issues section (8.0).

  * Revisions to Offer / Answer (specifically section 5.2 [answerer
    processing, 5.4 [non-RTP/SAVP answerers, and 5.8 [keymgt]).
    Offer / Answer still needs further refinement.

I will be presenting these changes during the MMUSIC meeting in Vienna.

-d


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From: Euchner Martin <martin.euchner@siemens.com>
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RFC 3548 should be considered as a proper reference to Base 64 encoding procedure.


With kind regards

Martin Euchner.
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| Martin Euchner                 Phone: +49 89 722 55790
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 -----Original Message-----
From: 	rfc-editor@rfc-editor.org [mailto:rfc-editor@rfc-editor.org] 
Sent:	Wednesday, July 09, 2003 1:36 AM
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Subject:	RFC 3548 on The Base16, Base32, and Base64 Data Encodings

 <<Unbenannte Anlage>> 
A new Request for Comments is now available in online RFC libraries.


        RFC 3548

        Title:      The Base16, Base32, and Base64 Data Encodings
        Author(s):  S. Josefsson, Ed.
        Status:     Informational
        Date:       July 2003
        Mailbox:    simon@josefsson.org
        Pages:      13
        Characters: 26363
        Updates/Obsoletes/SeeAlso:  None

        I-D Tag:    draft-josefsson-base-encoding-04.txt

        URL:        ftp://ftp.rfc-editor.org/in-notes/rfc3548.txt


This document describes the commonly used base 64, base 32, and base
16 encoding schemes.  It also discusses the use of line-feeds in
encoded data, use of padding in encoded data, use of non-alphabet
characters in encoded data, and use of different encoding alphabets.

This memo provides information for the Internet community.  It does
not specify an Internet standard of any kind.  Distribution of this
memo is unlimited.

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Joyce K. Reynolds and Sandy Ginoza
USC/Information Sciences Institute

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From: Jonathan Rosenberg <jdrosen@dynamicsoft.com>
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Thanks for your comments. Responses inline.

Jari Arkko wrote:

> 
> Jonathan,
> 
> Thanks for bringing up this problem. I agree that the attack
> exists, and I also agree that nothing in the RTP packets (such
> as SRTP) can help prevent such attacks. I not expert enough
> to say anything about suitability of RTCP or STUN.
> 
> Attacks of a similar nature have been discussed in the context
> of other protocols, for instance Mobile IPv6. The general
> nature of such attacks is that a signaling protocol conveys
> an address, and the lack of verification for this address
> results in a vulnerability; attackers choose the address of
> an innocent third party and start "bombing" this address
> with packets. What makes these attacks bad is that the
> attacker can initiate the attack with just few packets,
> a legitimate entity in the network does all the hard work,
> and the victim's link becomes congested.

Right. I agree its the same attack as can be done in Mobile IP.

> 
> The attack has always serious consequences due to its
> amplification factor. In SIP, this factor is due to
> the bandwidth difference in signaling vs. payload. In
> Mobile IPv6, this factor was due to the ability to "open"
> a connection, speed it up, and then move it towards the
> victim.
> 
> What also makes the attack hard is that the packets to
> the victim never come from the attacker, they come from
> another, legitimate entity in the network. This makes the
> tracing of the attack hard: the attacker may be traceable
> from that entity, but can we be sure that the administrator
> of the entity can be reached for assistance? This may be
> easy if the entity is owned by an operator, but what if
> its my home server or someone's windows PC? However,
> assuming you do get the help of the administrator, there
> seems to be a few different levels of hardness
> for tracing the attacker then:
> 
> - No verification: The attack was initiated by a
>   packet sent to the entity, no assurance of the
>   authentication of the attacker or the validity
>   of the source address in the packet.
> 
>   SIP INVITE without TLS and authentication appears
>   to allow this, no?

Yes. We do have a way for a server to prevent this level, though. SIP 
provides an anonymous digest authentication. Really, the only purpose 
of this is for the server to verify that the client can be reached at 
their advertised IP address. I should probably mention in the I-D that 
servers ought to do this. Generally its a good idea not to process 
packets that are completely unauthenticated...


> 
>   What makes this level tricky is that there are
>   designs where DoS attackers can be traced even
>   if they lie about their addresses, e.g. itrace.
>   However, these mechanisms only work for bulk
>   attacks, and here we only send a few signaling
>   packets.

Right. Worse yet, the signaling can be relayed through proxies, which 
would mask the identity of the attacker from the entity, if no 
authentication is used.

> 
> - Source address verification: The attack can only
>   be launched after some exchange of packets, where
>   the source address of the packet has been verified
>   to be valid.
> 
>   In SIP, anon Digest would allow you to do source
>   address verification. Similarly, even server-side
>   only authenticated TLS would suffice for this
>   check.

Right, I see we are on the same page about anonymous digest here.

> 
>   Note: in Mobile IPv6, the address of the attacker
>   was conveyed also in the packets to the victim,
>   but this does not appear to be the case in SIP/RTP,
>   because the RTP packets don't contain the address
>   of the node that initiated the signaling.

Right.

> 
> - Authentication: the attacker's identity is
>   authenticated in some manner, you can probably
>   trace the attacker down to his postal address/passport/
>   credit card.
> 
> I believe we should strive for making the tracing
> of the attack at least so hard that the attacker has
> to give his IP address information, i.e., make the first
> case not allowed.

Agreed.

> Still, tracing is a post-attack
> activity, expensive and unreliable. So I believe you
> are right in trying to prevent such attacks.
> 
> A few words about prevention. Typically, a "return
> routability test" approach is used, as I think you
> are doing also for STUN.

Right. Thats exactly why STUN works.

  I'm not expert enough in
> STUN to know if it provides sufficient binding
> between requests and responses so that off-path
> attackers can't easily spoof responses? But I would
> guess you have taken this into account.

Yes. STUN has a transaction ID present in the request, which has to be 
mirrored in the resposne. An off-path attacker would need to be able 
to eavesdrop the stun request in order to generate a response. STUN 
itself has extensive security considerations, and we protected it as 
best as possible.

> 
> Another issue is whether there needs to be a binding
> between the signaling exchange and the STUN exchange,
> e.g. a session identifier or something like that? Or
> is it sufficient to rely on the right timing? What about
> busy servers, wouldn't the timing of the attack be
> more likely to succeed with them?

Not sure I follow this. In ICE, the STUN exchange is correlated with 
the signaling exchange through the STUN username and password, which 
are conveyed in the SDP. Thus, when a UA receives a STUN request, it 
knows from the username and password the exact sip dialog and media 
stream its associated with.

I'm not sure what this has to do with busy servers, though.

> 
> Finally, the prevention mechanisms themselves may
> be susceptible to an attack. An example: initiate
> N sessions with different servers, all pointing to the
> same victim node, who gets a lot of STUN queries.
> This attack does not have amplification, but it
> is hard to trace, harder than a direct dos packet
> storm from a single source, and harder than than
> a reflection attack. In some other cases, such
> attacks have been made easier to trace by using
> solely the source address of a packet in initiating
> responses and protocol actions. But I understand
> that this may not be an option here. Demanding
> TlS/anon digest from all SIP signaling exchanges
> does force the attacker to give up a lot of
> information and some CPU cycles, so that may
> be sufficient.

I think so. There are many other ways to launch the no-amplification 
version you describe. For example, sip itself! Send a response with a 
Via header pointing to the target. Or a request with a Route header 
pointing to the target.

-Jonathan R.


-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com


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Date: Wed, 09 Jul 2003 05:16:10 -0400
From: Jonathan Rosenberg <jdrosen@dynamicsoft.com>
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Paolo Asprino wrote:

> Hi all
> 
> I'm thinking a solution to join SIP and RTSP in the 3G IMS domain.
> In particular in the IMS, I think that to provide multilmedia
> service (i.e video on demand), one can estabilish a subscription to the service by SIP and then activate the service with RTSP by DIGEST autentication with the 
> parameters exchanged early during the subscription (username and password) 
> 
> What do you think about that?

I'm not sure I follow; it seems like you want SIP to be an enrollment 
protocol.

I believe the right path forward is for SIP to setup the session. If 
you want to execute controls, it would be possible to open a control 
session (using an offer/answer exchange), where the control protocol 
is RTSP. In that usage you would only use the PLAY, PAUSE, RECORD, 
GET-PARAMTER and SET-PARAMETER methods. I think the others would not 
be needed.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com


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Subject: [MMUSIC] Re: [Sip] Appropriate usage of SIP and RTSP
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Hi,

When it comes to IMS and 3G terminals, most will already before having=20
an IMS functionality have support for PSS. PSS is Packet-based Streaming =

Service which is an umbrella kind of standard for streaming service=20
defined in 3GPP targeted at low bit-rates and mobile networks.=20
Specification available from Rel 4 in TS 26.233 and TS 26.234. Already=20
today there exist GSM/GPRS phones that has a PSS client.

So I think that dual stack implementations will not be that impossible=20
to foresee.

However I think the main issue in this discussion is to look at what=20
applications that has need for SIP-RTSP interactions. Based on this we=20
can see if there is solutions easily available or not.

I can agree with Rosenberg that if we where going to design a RTSP=20
functionality protocol today, looking at SIP for session establishment=20
would be interesting. However that opportunity has passed as RTSP has=20
started to be deployed in increasing numbers. I think even the latest=20
Windows media player does support RTSP.


Best Regards

Magnus Westerlund


Pianigiani, Jacopo (Jacopo) wrote:
> Hello all,
> In my undertanding RTSP is suitable for broadcast, unicast or multicast=
 streams distribution. The RTSP protocol was ideated for typical content =
delivery, and in effect for this application could be more than suitable.=
 But referring to an IMS domain, in my point of view adopting RSTP as med=
ia streams control, would imply adopting at least a double protocol stack=
 in the terminal equipment. The IMS concept was mainly driven by the conc=
ept - in my understanding - of simplifying the terminal (making it simple=
r from a protocol stack implementation means lowering costs and increasin=
g penetration on the market) by adopting a single protocol stack in the t=
erminal, and having the RAN and the core evolving toward a unified transp=
ort mechanism for which an almost unified level of control on the network=
 resources allocated to a session (whatever session we refer to, voice , =
multimedia p-t-t call, web browsing, multimedia session with voice call a=
nd dynamic web pages).
> So in this sense, my understanding is that the RTSP could be suitable f=
or media content, but it would imply again new complexity on the IMS UMTS=
/CDMA terminal itself, which is against the idea of IMS of enhancing the =
services the user can access by having an homogeneous protocol stack on t=
he terminal itself for all types of services.
>=20
> After all, the RTSP , apart from content delivery (of streams), could n=
ot definitely handle appropriately sessions like Voice calls + Interactiv=
e Web Pages.=20
> Regards
>=20
> Jacopo Pianigiani
> Lucent Technologies - Italy
> =E839 335 7350536
>=20
> -----Original Message-----
> From: Paolo Asprino [mailto:asprino@coritel.it]
> Sent: Wednesday, July 09, 2003 9:40 AM
> To: NAKAMURA, Hidefumi; sip@ietf.org; mmusic@ietf.org
> Subject: Re: [Sip] Appropriate usage of SIP and RTSP
>=20
>=20
> Hi all
>=20
> I'm thinking a solution to join SIP and RTSP in the 3G IMS domain.
> In particular in the IMS, I think that to provide multilmedia
> service (i.e video on demand), one can estabilish a subscription to the=
 service by SIP and then activate the service with RTSP by DIGEST autenti=
cation with the=20
> parameters exchanged early during the subscription (username and passwo=
rd)=20
>=20
> What do you think about that?
>=20
> Best Regards=20
>=20
> ----- Original Message -----=20
> From: "NAKAMURA, Hidefumi" <nakamura.hidefumi@lab.ntt.co.jp>
> To: <sip@ietf.org>; <mmusic@ietf.org>
> Cc: <hidefumi.nakamura@staff.east.ntt.co.jp>
> Sent: Monday, July 07, 2003 9:49 AM
> Subject: [Sip] Appropriate usage of SIP and RTSP
>=20
>=20
>=20
>>Hi, all.
>>
>>I have a question about the relationship between SIP and RTSP.=20
>>
>>In RFC3261, there is a description that says=20
>>   "SIP is not a vertically integrated communications system.  SIP is
>>   rather a component that can be used with other IETF protocols to
>>   build a complete multimedia architecture.  Typically, these
>>   architectures will include protocols such as the Real-time Transport=

>>   Protocol (RTP) (RFC 1889 [28]) for transporting real-time data and
>>   providing QoS feedback, the Real-Time streaming protocol (RTSP) (RFC=

>>   2326 [29]) for controlling delivery of streaming media, ..."
>>   (RFC3261 Section 2)
>>
>>However, my understanding is that both SIP and RTSP have the capability=

>>for "discovery of UAs or media streams."
>>If I use SIP to establish a stream session and use RTSP to control
>>the stream, there will be redundant sequences, i.e. INVITE-OK-ACK and
>>SETUP-OK.
>>
>>Was there any discussion on how to use these two protocols appropriatel=
y?
>>
>>With SIP application server, network providers can provide various
>>services on contents delivery while we will not be able to do so only
>>with RTSP, I think.  On the other hand, RTSP has enough capability for
>>discovery of media streams and for negotiation of SDPs.
>>So, I think, for the simple delivery of contents, RTSP is appropriate t=
o
>>use, and for various session control services regarding contents
>>delivery, SIP with RTSP is appropriate to use.
>>
>>Any opinions?
>>
>>I wonder why no contents delivery server seems to prepare SIP stack now=
=2E=20
>>Is it because, up to now, there exists only a simple contents delivery
>>service?
>>
>>best regards,
>>
>>--=20
>>NAKAMURA, Hidefumi=20
>>NTT ServiceIntegration /NetworkServiceSystems Labs.
>>tel: +81(422)59 3904; fax:+81(422)60 4012
>>---
>>
>>
>>
>>_______________________________________________
>>Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
>>This list is for NEW development of the core SIP Protocol
>>Use sip-implementors@cs.columbia.edu for questions on current sip
>>Use sipping@ietf.org for new developments on the application of sip
>>
>=20
>=20
>=20
> ---
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)bq=ABb=A2z=1F
>=20
> _______________________________________________
> Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> This list is for NEW development of the core SIP Protocol
> Use sip-implementors@cs.columbia.edu for questions on current sip
> Use sipping@ietf.org for new developments on the application of sip
>=20


--=20

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com


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Subject: RE: [MMUSIC] Re: [Sip] Appropriate usage of SIP and RTSP
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The applications that have need for SIP and RTSP features I
can imagine are:

- Voice&video mail (similar to 'sipum' but VM server is in the SIP =
phone)
- Personal broadcast station from my PC at home.
- Watching video recorded with VCR at home or office from remote...

What I am not sure is if RTSP has any solution or a framework for a
RTSP server behind a NAT. If not, the solution is likely to be a repeat
of what SIP provides. I thought TURN could be used in order for =
signaling
message to reach RTSP server behind a NAT, but I noticed that it is not=20
applicable (purposefully) for a server running behind a NAT because of
a security consideration. Lots of issues for RTSP in this area alone?

I believe a lot of people are interested in this discussion.

Best regards,
Yutaka


> -----Original Message-----
> From: Magnus Westerlund [mailto:magnus.westerlund@ericsson.com]
> Sent: Wednesday, July 09, 2003 5:53 AM
> To: Pianigiani, Jacopo (Jacopo)
> Cc: sip@ietf.org; mmusic@ietf.org
> Subject: [MMUSIC] Re: [Sip] Appropriate usage of SIP and RTSP
>=20
>=20
> Hi,
>=20
> When it comes to IMS and 3G terminals, most will already=20
> before having=20
> an IMS functionality have support for PSS. PSS is=20
> Packet-based Streaming=20
> Service which is an umbrella kind of standard for streaming service=20
> defined in 3GPP targeted at low bit-rates and mobile networks.=20
> Specification available from Rel 4 in TS 26.233 and TS=20
> 26.234. Already=20
> today there exist GSM/GPRS phones that has a PSS client.
>=20
> So I think that dual stack implementations will not be that=20
> impossible=20
> to foresee.
>=20
> However I think the main issue in this discussion is to look at what=20
> applications that has need for SIP-RTSP interactions. Based=20
> on this we=20
> can see if there is solutions easily available or not.
>=20
> I can agree with Rosenberg that if we where going to design a RTSP=20
> functionality protocol today, looking at SIP for session=20
> establishment=20
> would be interesting. However that opportunity has passed as RTSP has=20
> started to be deployed in increasing numbers. I think even the latest=20
> Windows media player does support RTSP.
>=20
>=20
> Best Regards
>=20
> Magnus Westerlund
>=20
>=20
> Pianigiani, Jacopo (Jacopo) wrote:
> > Hello all,
> > In my undertanding RTSP is suitable for broadcast, unicast=20
> or multicast streams distribution. The RTSP protocol was=20
> ideated for typical content delivery, and in effect for this=20
> application could be more than suitable. But referring to an=20
> IMS domain, in my point of view adopting RSTP as media=20
> streams control, would imply adopting at least a double=20
> protocol stack in the terminal equipment. The IMS concept was=20
> mainly driven by the concept - in my understanding - of=20
> simplifying the terminal (making it simpler from a protocol=20
> stack implementation means lowering costs and increasing=20
> penetration on the market) by adopting a single protocol=20
> stack in the terminal, and having the RAN and the core=20
> evolving toward a unified transport mechanism for which an=20
> almost unified level of control on the network resources=20
> allocated to a session (whatever session we refer to, voice ,=20
> multimedia p-t-t call, web browsing, multimedia session with=20
> voice call and dynamic web pages).
> > So in this sense, my understanding is that the RTSP could=20
> be suitable for media content, but it would imply again new=20
> complexity on the IMS UMTS/CDMA terminal itself, which is=20
> against the idea of IMS of enhancing the services the user=20
> can access by having an homogeneous protocol stack on the=20
> terminal itself for all types of services.
> >=20
> > After all, the RTSP , apart from content delivery (of=20
> streams), could not definitely handle appropriately sessions=20
> like Voice calls + Interactive Web Pages.=20
> > Regards
> >=20
> > Jacopo Pianigiani
> > Lucent Technologies - Italy
> > =E839 335 7350536
> >=20
> > -----Original Message-----
> > From: Paolo Asprino [mailto:asprino@coritel.it]
> > Sent: Wednesday, July 09, 2003 9:40 AM
> > To: NAKAMURA, Hidefumi; sip@ietf.org; mmusic@ietf.org
> > Subject: Re: [Sip] Appropriate usage of SIP and RTSP
> >=20
> >=20
> > Hi all
> >=20
> > I'm thinking a solution to join SIP and RTSP in the 3G IMS domain.
> > In particular in the IMS, I think that to provide multilmedia
> > service (i.e video on demand), one can estabilish a=20
> subscription to the service by SIP and then activate the=20
> service with RTSP by DIGEST autentication with the=20
> > parameters exchanged early during the subscription=20
> (username and password)=20
> >=20
> > What do you think about that?
> >=20
> > Best Regards=20
> >=20
> > ----- Original Message -----=20
> > From: "NAKAMURA, Hidefumi" <nakamura.hidefumi@lab.ntt.co.jp>
> > To: <sip@ietf.org>; <mmusic@ietf.org>
> > Cc: <hidefumi.nakamura@staff.east.ntt.co.jp>
> > Sent: Monday, July 07, 2003 9:49 AM
> > Subject: [Sip] Appropriate usage of SIP and RTSP
> >=20
> >=20
> >=20
> >>Hi, all.
> >>
> >>I have a question about the relationship between SIP and RTSP.=20
> >>
> >>In RFC3261, there is a description that says=20
> >>   "SIP is not a vertically integrated communications=20
> system.  SIP is
> >>   rather a component that can be used with other IETF protocols to
> >>   build a complete multimedia architecture.  Typically, these
> >>   architectures will include protocols such as the=20
> Real-time Transport
> >>   Protocol (RTP) (RFC 1889 [28]) for transporting=20
> real-time data and
> >>   providing QoS feedback, the Real-Time streaming protocol=20
> (RTSP) (RFC
> >>   2326 [29]) for controlling delivery of streaming media, ..."
> >>   (RFC3261 Section 2)
> >>
> >>However, my understanding is that both SIP and RTSP have=20
> the capability
> >>for "discovery of UAs or media streams."
> >>If I use SIP to establish a stream session and use RTSP to control
> >>the stream, there will be redundant sequences, i.e.=20
> INVITE-OK-ACK and
> >>SETUP-OK.
> >>
> >>Was there any discussion on how to use these two protocols=20
> appropriately?
> >>
> >>With SIP application server, network providers can provide various
> >>services on contents delivery while we will not be able to=20
> do so only
> >>with RTSP, I think.  On the other hand, RTSP has enough=20
> capability for
> >>discovery of media streams and for negotiation of SDPs.
> >>So, I think, for the simple delivery of contents, RTSP is=20
> appropriate to
> >>use, and for various session control services regarding contents
> >>delivery, SIP with RTSP is appropriate to use.
> >>
> >>Any opinions?
> >>
> >>I wonder why no contents delivery server seems to prepare=20
> SIP stack now.=20
> >>Is it because, up to now, there exists only a simple=20
> contents delivery
> >>service?
> >>
> >>best regards,
> >>
> >>--=20
> >>NAKAMURA, Hidefumi=20
> >>NTT ServiceIntegration /NetworkServiceSystems Labs.
> >>tel: +81(422)59 3904; fax:+81(422)60 4012
> >>---
> >>
> >>
> >>
> >>_______________________________________________
> >>Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> >>This list is for NEW development of the core SIP Protocol
> >>Use sip-implementors@cs.columbia.edu for questions on current sip
> >>Use sipping@ietf.org for new developments on the application of sip
> >>
> >=20
> >=20
> >=20
> > ---
> > Outgoing mail is certified Virus Free.
> > Checked by AVG anti-virus system (http://www.grisoft.com).
> > Version: 6.0.495 / Virus Database: 294 - Release Date:=20
> 30/06/2003J*fj)bz	b=B2=D8m=B6>?=FF=0C> =
0=D6'=AD~S=E0=FEf=A2-f=A7=FEX=AC=B6)=DF=A3=FB"=A58b=B2X=AC=B6+=1F=A2=B3DY=
=D7=AF
> =
zZ)(tm)=E9=ED=A1=FBay=CA+y"=0F>=BA-=A1=CA%R=C7=ACS~=A6=A6W=A6z{h=AE=C7,r?=
n(tm)=B8sy=DBY=A2=BA=AEz=CBb=A2{(=9D=CB=AB
> =
=AD=E9=ED=B2*T=B1=EB"=A6~=A7''=AD~S=E0~S=E7{=07^=BD=E9h=A6g=A7=B6=CA'=B6=17=
s=A6(tm)bq=ABb=A2z=1F
> >=20
> > _______________________________________________
> > Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> > This list is for NEW development of the core SIP Protocol
> > Use sip-implementors@cs.columbia.edu for questions on current sip
> > Use sipping@ietf.org for new developments on the application of sip
> >=20
>=20
>=20
> --=20
>=20
> Magnus Westerlund
>=20
> Multimedia Technologies, Ericsson Research EAB/TVA/A
> ----------------------------------------------------------------------
> Ericsson AB                | Phone +46 8 4048287
> Torshamsgatan 23           | Fax   +46 8 7575550
> S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com
>=20
>=20
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic
>=20

_______________________________________________
mmusic mailing list
mmusic@ietf.org
https://www1.ietf.org/mailman/listinfo/mmusic



From exim@www1.ietf.org  Wed Jul  9 14:42:38 2003
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From: "Rosen, Brian" <Brian.Rosen@marconi.com>
To: "'Yutaka Takeda'" <takeday@kmerl.com>, sip@ietf.org, mmusic@ietf.org
Subject: RE: [MMUSIC] Re: [Sip] Appropriate usage of SIP and RTSP
Date: Wed, 9 Jul 2003 14:40:50 -0400 
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I've been thinking for a long time about what an appropriate
mechanism to provide a voice/videomail client on a sipphone
would be.  It's really clear that you record and play messages
with VCR like functionality.  For that, you need start/stop/pause/
rewind/fast forward, and so I was thinking RTSP.  On the other
hand, you surely establish the session to the voicemail server
with a sip call.

Thus, I like the way Jonathan is thinking, but you also need
message selection/creation/deletion functions, and for those
I was thinking KPML, and then you wonder if you just use that
as the signalling mechanism for the record/play, and I get
confused.

Brian

> -----Original Message-----
> From: Yutaka Takeda [mailto:takeday@kmerl.com]
> Sent: Wednesday, July 09, 2003 2:11 PM
> To: sip@ietf.org; mmusic@ietf.org
> Subject: RE: [MMUSIC] Re: [Sip] Appropriate usage of SIP and RTSP
>=20
>=20
> The applications that have need for SIP and RTSP features I
> can imagine are:
>=20
> - Voice&video mail (similar to 'sipum' but VM server is in=20
> the SIP phone)
> - Personal broadcast station from my PC at home.
> - Watching video recorded with VCR at home or office from remote...
>=20
> What I am not sure is if RTSP has any solution or a framework for a
> RTSP server behind a NAT. If not, the solution is likely to=20
> be a repeat
> of what SIP provides. I thought TURN could be used in order=20
> for signaling
> message to reach RTSP server behind a NAT, but I noticed that=20
> it is not=20
> applicable (purposefully) for a server running behind a NAT because of
> a security consideration. Lots of issues for RTSP in this area alone?
>=20
> I believe a lot of people are interested in this discussion.
>=20
> Best regards,
> Yutaka
>=20
>=20
> > -----Original Message-----
> > From: Magnus Westerlund [mailto:magnus.westerlund@ericsson.com]
> > Sent: Wednesday, July 09, 2003 5:53 AM
> > To: Pianigiani, Jacopo (Jacopo)
> > Cc: sip@ietf.org; mmusic@ietf.org
> > Subject: [MMUSIC] Re: [Sip] Appropriate usage of SIP and RTSP
> >=20
> >=20
> > Hi,
> >=20
> > When it comes to IMS and 3G terminals, most will already=20
> > before having=20
> > an IMS functionality have support for PSS. PSS is=20
> > Packet-based Streaming=20
> > Service which is an umbrella kind of standard for streaming service=20
> > defined in 3GPP targeted at low bit-rates and mobile networks.=20
> > Specification available from Rel 4 in TS 26.233 and TS=20
> > 26.234. Already=20
> > today there exist GSM/GPRS phones that has a PSS client.
> >=20
> > So I think that dual stack implementations will not be that=20
> > impossible=20
> > to foresee.
> >=20
> > However I think the main issue in this discussion is to=20
> look at what=20
> > applications that has need for SIP-RTSP interactions. Based=20
> > on this we=20
> > can see if there is solutions easily available or not.
> >=20
> > I can agree with Rosenberg that if we where going to design a RTSP=20
> > functionality protocol today, looking at SIP for session=20
> > establishment=20
> > would be interesting. However that opportunity has passed=20
> as RTSP has=20
> > started to be deployed in increasing numbers. I think even=20
> the latest=20
> > Windows media player does support RTSP.
> >=20
> >=20
> > Best Regards
> >=20
> > Magnus Westerlund
> >=20
> >=20
> > Pianigiani, Jacopo (Jacopo) wrote:
> > > Hello all,
> > > In my undertanding RTSP is suitable for broadcast, unicast=20
> > or multicast streams distribution. The RTSP protocol was=20
> > ideated for typical content delivery, and in effect for this=20
> > application could be more than suitable. But referring to an=20
> > IMS domain, in my point of view adopting RSTP as media=20
> > streams control, would imply adopting at least a double=20
> > protocol stack in the terminal equipment. The IMS concept was=20
> > mainly driven by the concept - in my understanding - of=20
> > simplifying the terminal (making it simpler from a protocol=20
> > stack implementation means lowering costs and increasing=20
> > penetration on the market) by adopting a single protocol=20
> > stack in the terminal, and having the RAN and the core=20
> > evolving toward a unified transport mechanism for which an=20
> > almost unified level of control on the network resources=20
> > allocated to a session (whatever session we refer to, voice ,=20
> > multimedia p-t-t call, web browsing, multimedia session with=20
> > voice call and dynamic web pages).
> > > So in this sense, my understanding is that the RTSP could=20
> > be suitable for media content, but it would imply again new=20
> > complexity on the IMS UMTS/CDMA terminal itself, which is=20
> > against the idea of IMS of enhancing the services the user=20
> > can access by having an homogeneous protocol stack on the=20
> > terminal itself for all types of services.
> > >=20
> > > After all, the RTSP , apart from content delivery (of=20
> > streams), could not definitely handle appropriately sessions=20
> > like Voice calls + Interactive Web Pages.=20
> > > Regards
> > >=20
> > > Jacopo Pianigiani
> > > Lucent Technologies - Italy
> > > =E839 335 7350536
> > >=20
> > > -----Original Message-----
> > > From: Paolo Asprino [mailto:asprino@coritel.it]
> > > Sent: Wednesday, July 09, 2003 9:40 AM
> > > To: NAKAMURA, Hidefumi; sip@ietf.org; mmusic@ietf.org
> > > Subject: Re: [Sip] Appropriate usage of SIP and RTSP
> > >=20
> > >=20
> > > Hi all
> > >=20
> > > I'm thinking a solution to join SIP and RTSP in the 3G IMS domain.
> > > In particular in the IMS, I think that to provide multilmedia
> > > service (i.e video on demand), one can estabilish a=20
> > subscription to the service by SIP and then activate the=20
> > service with RTSP by DIGEST autentication with the=20
> > > parameters exchanged early during the subscription=20
> > (username and password)=20
> > >=20
> > > What do you think about that?
> > >=20
> > > Best Regards=20
> > >=20
> > > ----- Original Message -----=20
> > > From: "NAKAMURA, Hidefumi" <nakamura.hidefumi@lab.ntt.co.jp>
> > > To: <sip@ietf.org>; <mmusic@ietf.org>
> > > Cc: <hidefumi.nakamura@staff.east.ntt.co.jp>
> > > Sent: Monday, July 07, 2003 9:49 AM
> > > Subject: [Sip] Appropriate usage of SIP and RTSP
> > >=20
> > >=20
> > >=20
> > >>Hi, all.
> > >>
> > >>I have a question about the relationship between SIP and RTSP.=20
> > >>
> > >>In RFC3261, there is a description that says=20
> > >>   "SIP is not a vertically integrated communications=20
> > system.  SIP is
> > >>   rather a component that can be used with other IETF=20
> protocols to
> > >>   build a complete multimedia architecture.  Typically, these
> > >>   architectures will include protocols such as the=20
> > Real-time Transport
> > >>   Protocol (RTP) (RFC 1889 [28]) for transporting=20
> > real-time data and
> > >>   providing QoS feedback, the Real-Time streaming protocol=20
> > (RTSP) (RFC
> > >>   2326 [29]) for controlling delivery of streaming media, ..."
> > >>   (RFC3261 Section 2)
> > >>
> > >>However, my understanding is that both SIP and RTSP have=20
> > the capability
> > >>for "discovery of UAs or media streams."
> > >>If I use SIP to establish a stream session and use RTSP to control
> > >>the stream, there will be redundant sequences, i.e.=20
> > INVITE-OK-ACK and
> > >>SETUP-OK.
> > >>
> > >>Was there any discussion on how to use these two protocols=20
> > appropriately?
> > >>
> > >>With SIP application server, network providers can provide various
> > >>services on contents delivery while we will not be able to=20
> > do so only
> > >>with RTSP, I think.  On the other hand, RTSP has enough=20
> > capability for
> > >>discovery of media streams and for negotiation of SDPs.
> > >>So, I think, for the simple delivery of contents, RTSP is=20
> > appropriate to
> > >>use, and for various session control services regarding contents
> > >>delivery, SIP with RTSP is appropriate to use.
> > >>
> > >>Any opinions?
> > >>
> > >>I wonder why no contents delivery server seems to prepare=20
> > SIP stack now.=20
> > >>Is it because, up to now, there exists only a simple=20
> > contents delivery
> > >>service?
> > >>
> > >>best regards,
> > >>
> > >>--=20
> > >>NAKAMURA, Hidefumi=20
> > >>NTT ServiceIntegration /NetworkServiceSystems Labs.
> > >>tel: +81(422)59 3904; fax:+81(422)60 4012
> > >>---
> > >>
> > >>
> > >>
> > >>_______________________________________________
> > >>Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> > >>This list is for NEW development of the core SIP Protocol
> > >>Use sip-implementors@cs.columbia.edu for questions on current sip
> > >>Use sipping@ietf.org for new developments on the=20
> application of sip
> > >>
> > >=20
> > >=20
> > >=20
> > > ---
> > > Outgoing mail is certified Virus Free.
> > > Checked by AVG anti-virus system (http://www.grisoft.com).
> > > Version: 6.0.495 / Virus Database: 294 - Release Date:=20
> > 30/06/2003J*fj)bz	b=B2=D8m=B6>?=FF=0C> > 0=D6'=AD~S=E0=FEf=A2-f=A7=FE=
X=AC=B6)=DF=A3=FB"=A58b=B2X=AC=B6+=1F=A2=B3DY=D7=AF
> > zZ)(tm)=E9=ED=A1=FBay=CA+y"=0F>=BA-=A1=CA%R=C7=ACS~=A6=A6W=A6z{h=AE=C7=
,r?n(tm)=B8sy=DBY=A2=BA=AEz=CBb=A2{(=9D=CB=AB
> > =AD=E9=ED=B2*T=B1=EB"=A6~=A7''=AD~S=E0~S=E7{=07^=BD=E9h=A6g=A7=B6=CA'=
=B6=17s=A6(tm)bq=ABb=A2z=1F
> > >=20
> > > _______________________________________________
> > > Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> > > This list is for NEW development of the core SIP Protocol
> > > Use sip-implementors@cs.columbia.edu for questions on current sip
> > > Use sipping@ietf.org for new developments on the=20
> application of sip
> > >=20
> >=20
> >=20
> > --=20
> >=20
> > Magnus Westerlund
> >=20
> > Multimedia Technologies, Ericsson Research EAB/TVA/A
> >=20
> ----------------------------------------------------------------------
> > Ericsson AB                | Phone +46 8 4048287
> > Torshamsgatan 23           | Fax   +46 8 7575550
> > S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com
> >=20
> >=20
> > _______________________________________________
> > mmusic mailing list
> > mmusic@ietf.org
> > https://www1.ietf.org/mailman/listinfo/mmusic
> >=20
>=20
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic
>=20

_______________________________________________
mmusic mailing list
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From: Magnus Westerlund <magnus.westerlund@ericsson.com>
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Subject: [MMUSIC] Re: [AVT] Requirements draft on video control
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Hi,

I have some remarks around the posting of these messages. First is the 
receipients list, its way to long. I would recommed that we drop it to 
only the mailing lists. I assume that all persons being directly 
addressed are in fact part at least one of the lists. The list is in 
fact so long that it get caugth in the mailing list software and needs 
approval for every mail.

The second thing is the crosspostings. We should move to a single list, 
I propose AVT as it has the most subscribers while I know there is need 
to include both communities. Due to the crosspostings, if a person is 
not memeber of both list it will get caught in that lists filter and 
need manual approval by the chairs. If you need to inform some other 
list about a subject, the recommended way is to post to each list 
individually and state that any discussion will take place on one of 
these list.

Third, don't post to avt-admin@ietf.org unless it has something to do 
with administrative matters regarding the mailing list. We chairs are 
members of the list and don't need to get a second copy through the 
avt-admin@ietf.org address. In fact before trimming this receipient list 
I should have received 4 copies of each mail.

So please follow this recommendations any you will make us chairs life 
easier.


Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com


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From: "Pianigiani, Jacopo (Jacopo)" <jpianigiani@lucent.com>
To: "'Paolo Asprino'" <asprino@coritel.it>,
        "NAKAMURA, Hidefumi"
	 <nakamura.hidefumi@lab.ntt.co.jp>, sip@ietf.org,
        mmusic@ietf.org
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Subject: [MMUSIC] RE: [Sip] Appropriate usage of SIP and RTSP
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Hello all,
In my undertanding RTSP is suitable for broadcast, unicast or multicast =
streams distribution. The RTSP protocol was ideated for typical content =
delivery, and in effect for this application could be more than =
suitable. But referring to an IMS domain, in my point of view adopting =
RSTP as media streams control, would imply adopting at least a double =
protocol stack in the terminal equipment. The IMS concept was mainly =
driven by the concept - in my understanding - of simplifying the =
terminal (making it simpler from a protocol stack implementation means =
lowering costs and increasing penetration on the market) by adopting a =
single protocol stack in the terminal, and having the RAN and the core =
evolving toward a unified transport mechanism for which an almost =
unified level of control on the network resources allocated to a =
session (whatever session we refer to, voice , multimedia p-t-t call, =
web browsing, multimedia session with voice call and dynamic web =
pages).
So in this sense, my understanding is that the RTSP could be suitable =
for media content, but it would imply again new complexity on the IMS =
UMTS/CDMA terminal itself, which is against the idea of IMS of =
enhancing the services the user can access by having an homogeneous =
protocol stack on the terminal itself for all types of services.

After all, the RTSP , apart from content delivery (of streams), could =
not definitely handle appropriately sessions like Voice calls + =
Interactive Web Pages.=20
Regards

Jacopo Pianigiani
Lucent Technologies - Italy
=E839 335 7350536

-----Original Message-----
From: Paolo Asprino [mailto:asprino@coritel.it]
Sent: Wednesday, July 09, 2003 9:40 AM
To: NAKAMURA, Hidefumi; sip@ietf.org; mmusic@ietf.org
Subject: Re: [Sip] Appropriate usage of SIP and RTSP


Hi all

I'm thinking a solution to join SIP and RTSP in the 3G IMS domain.
In particular in the IMS, I think that to provide multilmedia
service (i.e video on demand), one can estabilish a subscription to the =
service by SIP and then activate the service with RTSP by DIGEST =
autentication with the=20
parameters exchanged early during the subscription (username and =
password)=20

What do you think about that?

Best Regards=20

----- Original Message -----=20
From: "NAKAMURA, Hidefumi" <nakamura.hidefumi@lab.ntt.co.jp>
To: <sip@ietf.org>; <mmusic@ietf.org>
Cc: <hidefumi.nakamura@staff.east.ntt.co.jp>
Sent: Monday, July 07, 2003 9:49 AM
Subject: [Sip] Appropriate usage of SIP and RTSP


> Hi, all.
>=20
> I have a question about the relationship between SIP and RTSP.=20
>=20
> In RFC3261, there is a description that says=20
>    "SIP is not a vertically integrated communications system.  SIP is
>    rather a component that can be used with other IETF protocols to
>    build a complete multimedia architecture.  Typically, these
>    architectures will include protocols such as the Real-time =
Transport
>    Protocol (RTP) (RFC 1889 [28]) for transporting real-time data and
>    providing QoS feedback, the Real-Time streaming protocol (RTSP) =
(RFC
>    2326 [29]) for controlling delivery of streaming media, ..."
>    (RFC3261 Section 2)
>=20
> However, my understanding is that both SIP and RTSP have the =
capability
> for "discovery of UAs or media streams."
> If I use SIP to establish a stream session and use RTSP to control
> the stream, there will be redundant sequences, i.e. INVITE-OK-ACK and
> SETUP-OK.
>=20
> Was there any discussion on how to use these two protocols =
appropriately?
>=20
> With SIP application server, network providers can provide various
> services on contents delivery while we will not be able to do so only
> with RTSP, I think.  On the other hand, RTSP has enough capability =
for
> discovery of media streams and for negotiation of SDPs.
> So, I think, for the simple delivery of contents, RTSP is appropriate =
to
> use, and for various session control services regarding contents
> delivery, SIP with RTSP is appropriate to use.
>=20
> Any opinions?
>=20
> I wonder why no contents delivery server seems to prepare SIP stack =
now.=20
> Is it because, up to now, there exists only a simple contents =
delivery
> service?
>=20
> best regards,
>=20
> --=20
> NAKAMURA, Hidefumi=20
> NTT ServiceIntegration /NetworkServiceSystems Labs.
> tel: +81(422)59 3904; fax:+81(422)60 4012
> ---
>=20
>=20
>=20
> _______________________________________________
> Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
> This list is for NEW development of the core SIP Protocol
> Use sip-implementors@cs.columbia.edu for questions on current sip
> Use sipping@ietf.org for new developments on the application of sip
>=20


---
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From exim@www1.ietf.org  Thu Jul 10 17:23:39 2003
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From: "Even, Roni" <roni.even@polycom.co.il>
To: "'Gary Sullivan'" <garysull@windows.microsoft.com>,
        Andrea Basso
	 <Andrea_Basso@nmss.com>, avt@ietf.org,
        avt-admin@ietf.org, mmusic@ietf.org
Cc: casner@acm.org, jo@tzi.uni-bremen.de, magnus.westerlund@ericsson.com,
        csp@csperkins.org, Orit Levin <orit@radvision.com>,
        "Even, Roni"
	 <roni.even@polycom.co.il>, nismail@cisco.com
Date: Wed, 9 Jul 2003 08:46:19 +0300 
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Subject: [MMUSIC] RE: [AVT] Requirements draft on video control
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Hi Gary

About
"It is also possible to obtain random access recovery without a fast
update.  This is sometimes called "gradual decoder refresh".  See for
example the recovery point SEI message in H.264/AVC."

In case of a video switch in a multipoint conference there is a need to get
a new recovery point since the decoder will receive a stream without a
previous recovery point. The procedure in H.241 allows for either a full
picture at once or gradual recovery based on an SEI recovery point message.
Both method are fine as an encoder response to a fast update request.

Regards
Roni Even

-----Original Message-----
From: Gary Sullivan [mailto:garysull@windows.microsoft.com]
Sent: Wednesday, July 09, 2003 3:03 AM
To: Andrea Basso; avt@ietf.org; avt-admin@ietf.org; mmusic@ietf.org
Cc: casner@acm.org; jo@tzi.uni-bremen.de; magnus.westerlund@ericsson.com;
csp@csperkins.org; Orit Levin; Roni Even; nismail@cisco.com
Subject: RE: [AVT] Requirements draft on video control



Much of the content of this ID will look familiar to those with
experience with ITU-T systems control specifications (such as H.245).

Some of it seems like it could use a bit of updating in that regard
(e.g., videofastupdateGOB).
Draft Recommendation H.241 is one good place to look for such
information.

Section 3 is a bit confused in its terminology.  For example it seems to
say that intra frames are also known as inter frames, which is
definitely not the case.  It mixes the terms "predictive" and
"prediction" and seems to consider a "reference" frame to be synonymous
with an intra frame.  The terms "picture" and "frame" are also kind of
mixed up.

A more consistent terminology would be as follows:

An intra picture is a picture that can be decoded without first decoding
any other picture.

A predicted (or non-intra) picture is a picture that may require data
from one or more previously-decoded pictures in order to be properly
decoded.

A reference picture is a picture that is stored in the decoder for use
as a reference in the decoding process of some subsequent picture in the
bitstream.

A non-reference picture is a picture that is not used as a reference for
the decoding process of any other picture in the bitstream.

The concepts of intra versus non-Intra and reference versus
non-reference are independent.  A particular picture can (in general) be
any one of the four types (intra reference, non-intra reference, intra
non-reference, non-intra non-reference).

A "fast update", also known as an "instantaneous decoder refresh",
involves sending an intra picture and thereafter refraining from using
any picture sent prior to that intra picture as a reference for the
decoding process of any subsequent picture sent in the stream.

In particular it is worth noting that some concepts that applied to some
older codecs are not really valid in general and should be avoided
(e.g., that a non-reference picture is called a B picture or that an
intra picture is the same thing as a fast update or that an intra
picture is always a reference picture).

The characterization of a "slice" or "GOB" as being a "stripe" is not
really quite right.  For example, a single slice in MPEG-1, H.263 Annex
O, or MPEG-4 can consist of a few macroblocks at the right edge of one
row and a few macroblocks at the left edge of the next row (i.e., two
distinct rectangular regions quite far apart from each other in the
picture can be in a single slice).  A GOB in H.261 CIF consists of THREE
partial rows of macroblocks extending only halfway across a picture.
And in H.264/AVC, a slice can be ANY collection of macroblocks scattered
around absolutely anywhere in the picture (by use of a feature known as
a "slice group map").

In regard to section 5.1 VideoFreezePicture, I believe H.262 (also known
as MPEG-2 Video) also supports a freeze picture release within the ITU-T
extension.

It is also possible to obtain random access recovery without a fast
update.  This is sometimes called "gradual decoder refresh".  See for
example the recovery point SEI message in H.264/AVC.

Best Regards,

Gary Sullivan


+> -----Original Message-----
+> From: avt-admin@ietf.org [mailto:avt-admin@ietf.org] On 
+> Behalf Of Andrea Basso
+> Sent: Monday, July 07, 2003 2:34 PM
+> To: avt@ietf.org; avt-admin@ietf.org; mmusic@ietf.org
+> Cc: casner@acm.org; jo@tzi.uni-bremen.de; 
+> magnus.westerlund@ericsson.com; csp@csperkins.org; Orit 
+> Levin; Roni Even; nismail@cisco.com
+> Subject: [AVT] Requirements draft on video control
+> 
+> 
+> Attached you will find draft-basso-avt-videoconreq-00.txt
+> 
+> Abstract:
+> 
+> A variety of communication services such as video
+> conferencing and video messaging rely on the capability of video
+> encoders and decoders to exchange control commands. This document
+> outlines this set of commands as well as the requirements for
+> their transport.
+> 
+> Comments are more than welcome.
+> 
+> 
+> 
+> 
+> 
+> Andrea Basso
+> NMS Communications
+> (732) 936-2118
+> (See attached file: draft-basso-avt-videoconreq-00.zip)
+> 

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Thread-Topic: [AVT] Requirements draft on video control
Thread-Index: AcNGTsrjAD4hxGGpTxa5o1h1z7W8RAABxXyg
From: "Gary Sullivan" <garysull@windows.microsoft.com>
To: "Andrea Basso" <Andrea_Basso@nmss.com>
Cc: <avt@ietf.org>, <casner@acm.org>, <csp@csperkins.org>,
        <jo@tzi.uni-bremen.de>, <magnus.westerlund@ericsson.com>,
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        "Orit Levin" <orit@radvision.com>,
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Andrea et al,

Perhaps I was having some trouble understanding the purpose of this ID.
I thought it was some sort of draft of a formal specification, rather
than just an expression of needs to be taken as input by the group.  So
I criticized the language more heavily than necessary.

In regard to the "intra frames" =3D "inter frames" mix-up:

+> >intra frames are also known as inter frames, which is
+> >definitely not the case
+>=20
+>  I do not think the text says this.  Here is the sentence:
+>=20
+>      Current coding schemes such as H.261 [2], H.263 [3], MPEG-1, 2,4
+>       [5], H.264 [6] can encode video pictures as reference=20
+> frames, also
+>       known as intra frames or predicted frames, also known as inter
+>       frames.

It seems like what we have is a scoping problem.  To what set of words
does the first "also known as" phrase apply?  To me, when you said "A,
also known as B or C, also known as D", I interpreted this as saying
that A, B, C, and D are all synonyms (with the first "also known as"
applying to the "B or C").  Apparently that's not what you meant.

Also, the way the term "reference frame" is used in this document may
have contributed to my confusion.  As I noted in my original message,
that term is used differently here than it is in some other video coding
discussions.

Best Regards,

Gary Sullivan


+> -----Original Message-----
+> From: Andrea Basso [mailto:Andrea_Basso@nmss.com]=20
+> Sent: Wednesday, July 09, 2003 12:17 PM
+> To: Gary Sullivan
+> Cc: Andrea Basso; avt@ietf.org; casner@acm.org;=20
+> csp@csperkins.org; jo@tzi.uni-bremen.de;=20
+> magnus.westerlund@ericsson.com; mmusic@ietf.org;=20
+> nismail@cisco.com; Orit Levin; Roni Even
+> Subject: RE: [AVT] Requirements draft on video control
+>=20
+>=20
+>=20
+> Gary,
+> here are some comments.
+>=20
+>=20
+> > Some of it seems like it could use a bit of updating in that regard
+> > (e.g., videofastupdateGOB).
+> > Draft Recommendation H.241 is one good place to look for such
+> > information.
+>=20
+> H.241 is very focused on H.264 and in very early stages in addressing
+> Commands and Indications applicable to all codecs.
+>  If you look at the H.241 draft section 6 says:
+>=20
+>=20
+>=20
+> 6      Commands and Indications
+>=20
+>=20
+>=20
+> 6.1    C&I applicable to all video codecs
+>=20
+> For further study.
+>=20
+>=20
+> We plan to monitor the evolution the H.241 and to update the=20
+> ID accordingly
+> if needed.
+>=20
+>=20
+> >intra frames are also known as inter frames, which is
+> >definitely not the case
+>=20
+>  I do not think the text says this.  Here is the sentence:
+>=20
+>      Current coding schemes such as H.261 [2], H.263 [3], MPEG-1, 2,4
+>       [5], H.264 [6] can encode video pictures as reference=20
+> frames, also
+>       known as intra frames or predicted frames, also known as inter
+>       frames.
+>=20
+>=20
+> >The terms "picture" and "frame" are also kind of
+> >mixed up.
+>=20
+> For progressive video, a picture is identical to a frame.=20
+> The difference
+> appears for  interlaced video only.
+> The new text will use the term  'picture' only.
+>=20
+>=20
+> >The characterization of a "slice" or "GOB" as being a=20
+> "stripe" is not
+> >really quite right.
+>=20
+> The text does not say "image stripe" says "stripe" and in=20
+> particular it
+> does not imply that such stripe goes border-to-border in the=20
+> image (i.e.
+> can cover a partial macroblock row) nor that is should only include a
+> single  macroblock row (i.e., can cover multiple partial=20
+> rows as in H.261).
+> Clarifications will be addressed in the new version of the draft.
+>=20
+>=20
+> -A
+>=20
+> Andrea Basso
+> NMS Communications
+> (732) 936-2118
+>=20
+>=20
+>=20
+>                                                             =20
+>                                                                  =20
+>                       "Gary Sullivan"                       =20
+>                                                                  =20
+>                       <garysull@windows.mic        To:      =20
+> "Andrea Basso" <Andrea_Basso@nmss.com>, <avt@ietf.org>,          =20
+>                       rosoft.com>                  =20
+> <avt-admin@ietf.org>, <mmusic@ietf.org>                     =20
+>              =20
+>                                                    cc:      =20
+> <casner@acm.org>, <jo@tzi.uni-bremen.de>,                        =20
+>                       07/08/2003 08:03 PM          =20
+> <magnus.westerlund@ericsson.com>, <csp@csperkins.org>, "Orit=20
+> Levin"       =20
+>                                                    =20
+> <orit@radvision.com>, "Roni Even" <roni.even@polycom.co.il>,=20
+>              =20
+>                                                    =20
+> <nismail@cisco.com>                                         =20
+>              =20
+>                                                    Subject: =20
+> RE: [AVT] Requirements draft on video control                    =20
+>                                                             =20
+>                                                                  =20
+>=20
+>=20
+>=20
+>=20
+>=20
+> Much of the content of this ID will look familiar to those with
+> experience with ITU-T systems control specifications (such as H.245).
+>=20
+> Some of it seems like it could use a bit of updating in that regard
+> (e.g., videofastupdateGOB).
+> Draft Recommendation H.241 is one good place to look for such
+> information.
+>=20
+> Section 3 is a bit confused in its terminology.  For example=20
+> it seems to
+> say that intra frames are also known as inter frames, which is
+> definitely not the case.  It mixes the terms "predictive" and
+> "prediction" and seems to consider a "reference" frame to be=20
+> synonymous
+> with an intra frame.  The terms "picture" and "frame" are=20
+> also kind of
+> mixed up.
+>=20
+> A more consistent terminology would be as follows:
+>=20
+> An intra picture is a picture that can be decoded without=20
+> first decoding
+> any other picture.
+>=20
+> A predicted (or non-intra) picture is a picture that may require data
+> from one or more previously-decoded pictures in order to be properly
+> decoded.
+>=20
+> A reference picture is a picture that is stored in the=20
+> decoder for use
+> as a reference in the decoding process of some subsequent=20
+> picture in the
+> bitstream.
+>=20
+> A non-reference picture is a picture that is not used as a=20
+> reference for
+> the decoding process of any other picture in the bitstream.
+>=20
+> The concepts of intra versus non-Intra and reference versus
+> non-reference are independent.  A particular picture can (in=20
+> general) be
+> any one of the four types (intra reference, non-intra=20
+> reference, intra
+> non-reference, non-intra non-reference).
+>=20
+> A "fast update", also known as an "instantaneous decoder refresh",
+> involves sending an intra picture and thereafter refraining=20
+> from using
+> any picture sent prior to that intra picture as a reference for the
+> decoding process of any subsequent picture sent in the stream.
+>=20
+> In particular it is worth noting that some concepts that=20
+> applied to some
+> older codecs are not really valid in general and should be avoided
+> (e.g., that a non-reference picture is called a B picture or that an
+> intra picture is the same thing as a fast update or that an intra
+> picture is always a reference picture).
+>=20
+> The characterization of a "slice" or "GOB" as being a "stripe" is not
+> really quite right.  For example, a single slice in MPEG-1,=20
+> H.263 Annex
+> O, or MPEG-4 can consist of a few macroblocks at the right=20
+> edge of one
+> row and a few macroblocks at the left edge of the next row (i.e., two
+> distinct rectangular regions quite far apart from each other in the
+> picture can be in a single slice).  A GOB in H.261 CIF=20
+> consists of THREE
+> partial rows of macroblocks extending only halfway across a picture.
+> And in H.264/AVC, a slice can be ANY collection of=20
+> macroblocks scattered
+> around absolutely anywhere in the picture (by use of a=20
+> feature known as
+> a "slice group map").
+>=20
+> In regard to section 5.1 VideoFreezePicture, I believe H.262=20
+> (also known
+> as MPEG-2 Video) also supports a freeze picture release=20
+> within the ITU-T
+> extension.
+>=20
+> It is also possible to obtain random access recovery without a fast
+> update.  This is sometimes called "gradual decoder refresh".  See for
+> example the recovery point SEI message in H.264/AVC.
+>=20
+> Best Regards,
+>=20
+> Gary Sullivan
+>=20
+>=20
+> +> -----Original Message-----
+> +> From: avt-admin@ietf.org [mailto:avt-admin@ietf.org] On
+> +> Behalf Of Andrea Basso
+> +> Sent: Monday, July 07, 2003 2:34 PM
+> +> To: avt@ietf.org; avt-admin@ietf.org; mmusic@ietf.org
+> +> Cc: casner@acm.org; jo@tzi.uni-bremen.de;
+> +> magnus.westerlund@ericsson.com; csp@csperkins.org; Orit
+> +> Levin; Roni Even; nismail@cisco.com
+> +> Subject: [AVT] Requirements draft on video control
+> +>
+> +>
+> +> Attached you will find draft-basso-avt-videoconreq-00.txt
+> +>
+> +> Abstract:
+> +>
+> +> A variety of communication services such as video
+> +> conferencing and video messaging rely on the capability of video
+> +> encoders and decoders to exchange control commands. This document
+> +> outlines this set of commands as well as the requirements for
+> +> their transport.
+> +>
+> +> Comments are more than welcome.
+> +>
+> +>
+> +>
+> +>
+> +>
+> +> Andrea Basso
+> +> NMS Communications
+> +> (732) 936-2118
+> +> (See attached file: draft-basso-avt-videoconreq-00.zip)
+> +>
+>=20
+>=20
+>=20
+>=20
+>=20
+>=20

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Gary,

Thanks for the comments. Definitely we need to add consistency in the terms 
we are using in the draft.

>Andrea et al,
>
>Perhaps I was having some trouble understanding the purpose of this ID.
>I thought it was some sort of draft of a formal specification, rather
>than just an expression of needs to be taken as input by the group.  So
>I criticized the language more heavily than necessary.


So now that this is clarified we need to discuss the requirements that are 
specified in that draft
and see if people think that these are legitimate requirements that need to 
be addressed or not.

nermeen




>In regard to the "intra frames" = "inter frames" mix-up:
>
>+> >intra frames are also known as inter frames, which is
>+> >definitely not the case
>+>
>+>  I do not think the text says this.  Here is the sentence:
>+>
>+>      Current coding schemes such as H.261 [2], H.263 [3], MPEG-1, 2,4
>+>       [5], H.264 [6] can encode video pictures as reference
>+> frames, also
>+>       known as intra frames or predicted frames, also known as inter
>+>       frames.
>
>It seems like what we have is a scoping problem.  To what set of words
>does the first "also known as" phrase apply?  To me, when you said "A,
>also known as B or C, also known as D", I interpreted this as saying
>that A, B, C, and D are all synonyms (with the first "also known as"
>applying to the "B or C").  Apparently that's not what you meant.
>
>Also, the way the term "reference frame" is used in this document may
>have contributed to my confusion.  As I noted in my original message,
>that term is used differently here than it is in some other video coding
>discussions.
>
>Best Regards,
>
>Gary Sullivan
>
>
>+> -----Original Message-----
>+> From: Andrea Basso [mailto:Andrea_Basso@nmss.com]
>+> Sent: Wednesday, July 09, 2003 12:17 PM
>+> To: Gary Sullivan
>+> Cc: Andrea Basso; avt@ietf.org; casner@acm.org;
>+> csp@csperkins.org; jo@tzi.uni-bremen.de;
>+> magnus.westerlund@ericsson.com; mmusic@ietf.org;
>+> nismail@cisco.com; Orit Levin; Roni Even
>+> Subject: RE: [AVT] Requirements draft on video control
>+>
>+>
>+>
>+> Gary,
>+> here are some comments.
>+>
>+>
>+> > Some of it seems like it could use a bit of updating in that regard
>+> > (e.g., videofastupdateGOB).
>+> > Draft Recommendation H.241 is one good place to look for such
>+> > information.
>+>
>+> H.241 is very focused on H.264 and in very early stages in addressing
>+> Commands and Indications applicable to all codecs.
>+>  If you look at the H.241 draft section 6 says:
>+>
>+>
>+>
>+> 6      Commands and Indications
>+>
>+>
>+>
>+> 6.1    C&I applicable to all video codecs
>+>
>+> For further study.
>+>
>+>
>+> We plan to monitor the evolution the H.241 and to update the
>+> ID accordingly
>+> if needed.
>+>
>+>
>+> >intra frames are also known as inter frames, which is
>+> >definitely not the case
>+>
>+>  I do not think the text says this.  Here is the sentence:
>+>
>+>      Current coding schemes such as H.261 [2], H.263 [3], MPEG-1, 2,4
>+>       [5], H.264 [6] can encode video pictures as reference
>+> frames, also
>+>       known as intra frames or predicted frames, also known as inter
>+>       frames.
>+>
>+>
>+> >The terms "picture" and "frame" are also kind of
>+> >mixed up.
>+>
>+> For progressive video, a picture is identical to a frame.
>+> The difference
>+> appears for  interlaced video only.
>+> The new text will use the term  'picture' only.
>+>
>+>
>+> >The characterization of a "slice" or "GOB" as being a
>+> "stripe" is not
>+> >really quite right.
>+>
>+> The text does not say "image stripe" says "stripe" and in
>+> particular it
>+> does not imply that such stripe goes border-to-border in the
>+> image (i.e.
>+> can cover a partial macroblock row) nor that is should only include a
>+> single  macroblock row (i.e., can cover multiple partial
>+> rows as in H.261).
>+> Clarifications will be addressed in the new version of the draft.
>+>
>+>
>+> -A
>+>
>+> Andrea Basso
>+> NMS Communications
>+> (732) 936-2118
>+>
>+>
>+>
>+>
>+>
>+>                       "Gary Sullivan"
>+>
>+>                       <garysull@windows.mic        To:
>+> "Andrea Basso" <Andrea_Basso@nmss.com>, <avt@ietf.org>,
>+>                       rosoft.com>
>+> <avt-admin@ietf.org>, <mmusic@ietf.org>
>+>
>+>                                                    cc:
>+> <casner@acm.org>, <jo@tzi.uni-bremen.de>,
>+>                       07/08/2003 08:03 PM
>+> <magnus.westerlund@ericsson.com>, <csp@csperkins.org>, "Orit
>+> Levin"
>+>
>+> <orit@radvision.com>, "Roni Even" <roni.even@polycom.co.il>,
>+>
>+>
>+> <nismail@cisco.com>
>+>
>+>                                                    Subject:
>+> RE: [AVT] Requirements draft on video control
>+>
>+>
>+>
>+>
>+>
>+>
>+>
>+> Much of the content of this ID will look familiar to those with
>+> experience with ITU-T systems control specifications (such as H.245).
>+>
>+> Some of it seems like it could use a bit of updating in that regard
>+> (e.g., videofastupdateGOB).
>+> Draft Recommendation H.241 is one good place to look for such
>+> information.
>+>
>+> Section 3 is a bit confused in its terminology.  For example
>+> it seems to
>+> say that intra frames are also known as inter frames, which is
>+> definitely not the case.  It mixes the terms "predictive" and
>+> "prediction" and seems to consider a "reference" frame to be
>+> synonymous
>+> with an intra frame.  The terms "picture" and "frame" are
>+> also kind of
>+> mixed up.
>+>
>+> A more consistent terminology would be as follows:
>+>
>+> An intra picture is a picture that can be decoded without
>+> first decoding
>+> any other picture.
>+>
>+> A predicted (or non-intra) picture is a picture that may require data
>+> from one or more previously-decoded pictures in order to be properly
>+> decoded.
>+>
>+> A reference picture is a picture that is stored in the
>+> decoder for use
>+> as a reference in the decoding process of some subsequent
>+> picture in the
>+> bitstream.
>+>
>+> A non-reference picture is a picture that is not used as a
>+> reference for
>+> the decoding process of any other picture in the bitstream.
>+>
>+> The concepts of intra versus non-Intra and reference versus
>+> non-reference are independent.  A particular picture can (in
>+> general) be
>+> any one of the four types (intra reference, non-intra
>+> reference, intra
>+> non-reference, non-intra non-reference).
>+>
>+> A "fast update", also known as an "instantaneous decoder refresh",
>+> involves sending an intra picture and thereafter refraining
>+> from using
>+> any picture sent prior to that intra picture as a reference for the
>+> decoding process of any subsequent picture sent in the stream.
>+>
>+> In particular it is worth noting that some concepts that
>+> applied to some
>+> older codecs are not really valid in general and should be avoided
>+> (e.g., that a non-reference picture is called a B picture or that an
>+> intra picture is the same thing as a fast update or that an intra
>+> picture is always a reference picture).
>+>
>+> The characterization of a "slice" or "GOB" as being a "stripe" is not
>+> really quite right.  For example, a single slice in MPEG-1,
>+> H.263 Annex
>+> O, or MPEG-4 can consist of a few macroblocks at the right
>+> edge of one
>+> row and a few macroblocks at the left edge of the next row (i.e., two
>+> distinct rectangular regions quite far apart from each other in the
>+> picture can be in a single slice).  A GOB in H.261 CIF
>+> consists of THREE
>+> partial rows of macroblocks extending only halfway across a picture.
>+> And in H.264/AVC, a slice can be ANY collection of
>+> macroblocks scattered
>+> around absolutely anywhere in the picture (by use of a
>+> feature known as
>+> a "slice group map").
>+>
>+> In regard to section 5.1 VideoFreezePicture, I believe H.262
>+> (also known
>+> as MPEG-2 Video) also supports a freeze picture release
>+> within the ITU-T
>+> extension.
>+>
>+> It is also possible to obtain random access recovery without a fast
>+> update.  This is sometimes called "gradual decoder refresh".  See for
>+> example the recovery point SEI message in H.264/AVC.
>+>
>+> Best Regards,
>+>
>+> Gary Sullivan
>+>
>+>
>+> +> -----Original Message-----
>+> +> From: avt-admin@ietf.org [mailto:avt-admin@ietf.org] On
>+> +> Behalf Of Andrea Basso
>+> +> Sent: Monday, July 07, 2003 2:34 PM
>+> +> To: avt@ietf.org; avt-admin@ietf.org; mmusic@ietf.org
>+> +> Cc: casner@acm.org; jo@tzi.uni-bremen.de;
>+> +> magnus.westerlund@ericsson.com; csp@csperkins.org; Orit
>+> +> Levin; Roni Even; nismail@cisco.com
>+> +> Subject: [AVT] Requirements draft on video control
>+> +>
>+> +>
>+> +> Attached you will find draft-basso-avt-videoconreq-00.txt
>+> +>
>+> +> Abstract:
>+> +>
>+> +> A variety of communication services such as video
>+> +> conferencing and video messaging rely on the capability of video
>+> +> encoders and decoders to exchange control commands. This document
>+> +> outlines this set of commands as well as the requirements for
>+> +> their transport.
>+> +>
>+> +> Comments are more than welcome.
>+> +>
>+> +>
>+> +>
>+> +>
>+> +>
>+> +> Andrea Basso
>+> +> NMS Communications
>+> +> (732) 936-2118
>+> +> (See attached file: draft-basso-avt-videoconreq-00.zip)
>+> +>
>+>
>+>
>+>
>+>
>+>
>+>
>
>_______________________________________________
>Audio/Video Transport Working Group
>avt@ietf.org
>https://www1.ietf.org/mailman/listinfo/avt


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From: Aravind Narasimhan <aravind.narasimhan@sun.com>
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Subject: Re: [MMUSIC] Aggregate Control URI
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Comments line:

Magnus Westerlund wrote:

> Hi,
>
> A few words in relation to this. When I filed the bug I was thinking 
> of such a case that you try to aggregate two different media that the 
> server did not offer as an aggregated session. However during 
> discussions I have come to the conclusion that it will be difficult to 
> use. However the aggregated control URI resolution may have more usage 
> when it comes to session that are supposed to be used where the 
> aggregated control URL is missing. I do think it is good to have 
> stated a direction on how this is resolved in cased when information 
> is missing but the server allows it.
>
> Note that a server can always refuse to perform aggregation of a media 
> with another, by responding to a SETUP request trying to aggregate 
> with a "459 Aggregate operation not allowed" error code. In that case 
> the client will have to perform synchronization, etc. locally using 
> two non-aggregated sessions.
>
> "If an Aggregate control URI is not specified in the session 
> description, a client MUST create an URI for aggregate control of the 
> session."
>
> I don't think this formulation is good. The reason a session 
> description does not give a aggregated control URI is that it does not 
> desire the media to be aggregated. I would reformulate the sentence into:
>
> If an Aggregate control URI is not specified in the session 
> description, it is probably a indication that non-aggregated control 
> SHOULD be used. However a client MAY try to SETUP the session in 
> aggregated control. If the server refuse to aggregate the specified 
> media, the server SHALL use the 459 error code. If the server allows 
> the aggregation, then the client MUST create an URI for aggregate 
> control of the session. This URI MUST contain the servers host address ...
>
> As a conclusion, I don't see a problem with this resolution, although 
> it is not what we had discussed. So I can understand any comments to 
> this. What do you think of the updated text? 

I think this works.  My only comment is that I think we need clarify the 
definition of exactly what aggregate control means.  The spec. is till 
unclear about this in many places.  I think it is important to make sure 
that we re-check the use of the phrases "aggregate control" and 
"non-aggregate control" within the spec.  Specifically aggregate control 
should be anything that happens within a session, whether a session has 
0, 1 or more media.  "Non-aggregate control" should be anything that 
happens between multiple sessions, regardless of how many media 
resources each session has.  What we need to clearly state is that RTSP 
only deals with specifying aggregate control of media through a RTSP 
session, and not with other problem of non-aggregate control of multiple 
sessions.

Do people agree with this interpretation?

Thanks

Aravind


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Aravind Narasimhan wrote:
 >  Specifically aggregate control
> should be anything that happens within a session, whether a session has 
> 0, 1 or more media.  "Non-aggregate control" should be anything that 
> happens between multiple sessions, regardless of how many media 
> resources each session has.  What we need to clearly state is that RTSP 
> only deals with specifying aggregate control of media through a RTSP 
> session, and not with other problem of non-aggregate control of multiple 
> sessions.
> 
> Do people agree with this interpretation?

No, not really.  Aggregate control to me has meant a method of controlling all
streams in a session simultaneously.  This can happen only if there is an
a=control statement before any media.

Non aggregate control has meant individual control of streams within a session.
These use the a=control statement required by the media.

I guess I do not understand where multiple sessions come in.

Can you enlighten me as to where I'm wrong ?

Bill May
Cisco Systems


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Thread-Topic: [AVT] Requirements draft on video control
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From: "Gary Sullivan" <garysull@windows.microsoft.com>
To: "Andrea Basso" <Andrea_Basso@nmss.com>, <avt@ietf.org>,
        <avt-admin@ietf.org>, <mmusic@ietf.org>
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Subject: [MMUSIC] RE: [AVT] Requirements draft on video control
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Much of the content of this ID will look familiar to those with
experience with ITU-T systems control specifications (such as H.245).

Some of it seems like it could use a bit of updating in that regard
(e.g., videofastupdateGOB).
Draft Recommendation H.241 is one good place to look for such
information.

Section 3 is a bit confused in its terminology.  For example it seems to
say that intra frames are also known as inter frames, which is
definitely not the case.  It mixes the terms "predictive" and
"prediction" and seems to consider a "reference" frame to be synonymous
with an intra frame.  The terms "picture" and "frame" are also kind of
mixed up.

A more consistent terminology would be as follows:

An intra picture is a picture that can be decoded without first decoding
any other picture.

A predicted (or non-intra) picture is a picture that may require data
from one or more previously-decoded pictures in order to be properly
decoded.

A reference picture is a picture that is stored in the decoder for use
as a reference in the decoding process of some subsequent picture in the
bitstream.

A non-reference picture is a picture that is not used as a reference for
the decoding process of any other picture in the bitstream.

The concepts of intra versus non-Intra and reference versus
non-reference are independent.  A particular picture can (in general) be
any one of the four types (intra reference, non-intra reference, intra
non-reference, non-intra non-reference).

A "fast update", also known as an "instantaneous decoder refresh",
involves sending an intra picture and thereafter refraining from using
any picture sent prior to that intra picture as a reference for the
decoding process of any subsequent picture sent in the stream.

In particular it is worth noting that some concepts that applied to some
older codecs are not really valid in general and should be avoided
(e.g., that a non-reference picture is called a B picture or that an
intra picture is the same thing as a fast update or that an intra
picture is always a reference picture).

The characterization of a "slice" or "GOB" as being a "stripe" is not
really quite right.  For example, a single slice in MPEG-1, H.263 Annex
O, or MPEG-4 can consist of a few macroblocks at the right edge of one
row and a few macroblocks at the left edge of the next row (i.e., two
distinct rectangular regions quite far apart from each other in the
picture can be in a single slice).  A GOB in H.261 CIF consists of THREE
partial rows of macroblocks extending only halfway across a picture.
And in H.264/AVC, a slice can be ANY collection of macroblocks scattered
around absolutely anywhere in the picture (by use of a feature known as
a "slice group map").

In regard to section 5.1 VideoFreezePicture, I believe H.262 (also known
as MPEG-2 Video) also supports a freeze picture release within the ITU-T
extension.

It is also possible to obtain random access recovery without a fast
update.  This is sometimes called "gradual decoder refresh".  See for
example the recovery point SEI message in H.264/AVC.

Best Regards,

Gary Sullivan


+> -----Original Message-----
+> From: avt-admin@ietf.org [mailto:avt-admin@ietf.org] On=20
+> Behalf Of Andrea Basso
+> Sent: Monday, July 07, 2003 2:34 PM
+> To: avt@ietf.org; avt-admin@ietf.org; mmusic@ietf.org
+> Cc: casner@acm.org; jo@tzi.uni-bremen.de;=20
+> magnus.westerlund@ericsson.com; csp@csperkins.org; Orit=20
+> Levin; Roni Even; nismail@cisco.com
+> Subject: [AVT] Requirements draft on video control
+>=20
+>=20
+> Attached you will find draft-basso-avt-videoconreq-00.txt
+>=20
+> Abstract:
+>=20
+> A variety of communication services such as video
+> conferencing and video messaging rely on the capability of video
+> encoders and decoders to exchange control commands. This document
+> outlines this set of commands as well as the requirements for
+> their transport.
+>=20
+> Comments are more than welcome.
+>=20
+>=20
+>=20
+>=20
+>=20
+> Andrea Basso
+> NMS Communications
+> (732) 936-2118
+> (See attached file: draft-basso-avt-videoconreq-00.zip)
+>=20

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To: "Gary Sullivan" <garysull@windows.microsoft.com>
Cc: "Andrea Basso" <Andrea_Basso@nmss.com>, avt@ietf.org, casner@acm.org,
        csp@csperkins.org, jo@tzi.uni-bremen.de,
        magnus.westerlund@ericsson.com, mmusic@ietf.org, nismail@cisco.com,
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Subject: [MMUSIC] RE: [AVT] Requirements draft on video control
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Gary,
here are some comments.


> Some of it seems like it could use a bit of updating in that regard
> (e.g., videofastupdateGOB).
> Draft Recommendation H.241 is one good place to look for such
> information.

H.241 is very focused on H.264 and in very early stages in addressing
Commands and Indications applicable to all codecs.
 If you look at the H.241 draft section 6 says:



6      Commands and Indications



6.1    C&I applicable to all video codecs

For further study.


We plan to monitor the evolution the H.241 and to update the ID accordingly
if needed.


>intra frames are also known as inter frames, which is
>definitely not the case

 I do not think the text says this.  Here is the sentence:

     Current coding schemes such as H.261 [2], H.263 [3], MPEG-1, 2,4
      [5], H.264 [6] can encode video pictures as reference frames, also
      known as intra frames or predicted frames, also known as inter
      frames.


>The terms "picture" and "frame" are also kind of
>mixed up.

For progressive video, a picture is identical to a frame. The difference
appears for  interlaced video only.
The new text will use the term  'picture' only.


>The characterization of a "slice" or "GOB" as being a "stripe" is not
>really quite right.

The text does not say "image stripe" says "stripe" and in particular it
does not imply that such stripe goes border-to-border in the image (i.e.
can cover a partial macroblock row) nor that is should only include a
single  macroblock row (i.e., can cover multiple partial rows as in H.261).
Clarifications will be addressed in the new version of the draft.


-A

Andrea Basso
NMS Communications
(732) 936-2118



                                                                                                                               
                      "Gary Sullivan"                                                                                          
                      <garysull@windows.mic        To:       "Andrea Basso" <Andrea_Basso@nmss.com>, <avt@ietf.org>,           
                      rosoft.com>                   <avt-admin@ietf.org>, <mmusic@ietf.org>                                    
                                                   cc:       <casner@acm.org>, <jo@tzi.uni-bremen.de>,                         
                      07/08/2003 08:03 PM           <magnus.westerlund@ericsson.com>, <csp@csperkins.org>, "Orit Levin"        
                                                    <orit@radvision.com>, "Roni Even" <roni.even@polycom.co.il>,               
                                                    <nismail@cisco.com>                                                        
                                                   Subject:  RE: [AVT] Requirements draft on video control                     
                                                                                                                               





Much of the content of this ID will look familiar to those with
experience with ITU-T systems control specifications (such as H.245).

Some of it seems like it could use a bit of updating in that regard
(e.g., videofastupdateGOB).
Draft Recommendation H.241 is one good place to look for such
information.

Section 3 is a bit confused in its terminology.  For example it seems to
say that intra frames are also known as inter frames, which is
definitely not the case.  It mixes the terms "predictive" and
"prediction" and seems to consider a "reference" frame to be synonymous
with an intra frame.  The terms "picture" and "frame" are also kind of
mixed up.

A more consistent terminology would be as follows:

An intra picture is a picture that can be decoded without first decoding
any other picture.

A predicted (or non-intra) picture is a picture that may require data
from one or more previously-decoded pictures in order to be properly
decoded.

A reference picture is a picture that is stored in the decoder for use
as a reference in the decoding process of some subsequent picture in the
bitstream.

A non-reference picture is a picture that is not used as a reference for
the decoding process of any other picture in the bitstream.

The concepts of intra versus non-Intra and reference versus
non-reference are independent.  A particular picture can (in general) be
any one of the four types (intra reference, non-intra reference, intra
non-reference, non-intra non-reference).

A "fast update", also known as an "instantaneous decoder refresh",
involves sending an intra picture and thereafter refraining from using
any picture sent prior to that intra picture as a reference for the
decoding process of any subsequent picture sent in the stream.

In particular it is worth noting that some concepts that applied to some
older codecs are not really valid in general and should be avoided
(e.g., that a non-reference picture is called a B picture or that an
intra picture is the same thing as a fast update or that an intra
picture is always a reference picture).

The characterization of a "slice" or "GOB" as being a "stripe" is not
really quite right.  For example, a single slice in MPEG-1, H.263 Annex
O, or MPEG-4 can consist of a few macroblocks at the right edge of one
row and a few macroblocks at the left edge of the next row (i.e., two
distinct rectangular regions quite far apart from each other in the
picture can be in a single slice).  A GOB in H.261 CIF consists of THREE
partial rows of macroblocks extending only halfway across a picture.
And in H.264/AVC, a slice can be ANY collection of macroblocks scattered
around absolutely anywhere in the picture (by use of a feature known as
a "slice group map").

In regard to section 5.1 VideoFreezePicture, I believe H.262 (also known
as MPEG-2 Video) also supports a freeze picture release within the ITU-T
extension.

It is also possible to obtain random access recovery without a fast
update.  This is sometimes called "gradual decoder refresh".  See for
example the recovery point SEI message in H.264/AVC.

Best Regards,

Gary Sullivan


+> -----Original Message-----
+> From: avt-admin@ietf.org [mailto:avt-admin@ietf.org] On
+> Behalf Of Andrea Basso
+> Sent: Monday, July 07, 2003 2:34 PM
+> To: avt@ietf.org; avt-admin@ietf.org; mmusic@ietf.org
+> Cc: casner@acm.org; jo@tzi.uni-bremen.de;
+> magnus.westerlund@ericsson.com; csp@csperkins.org; Orit
+> Levin; Roni Even; nismail@cisco.com
+> Subject: [AVT] Requirements draft on video control
+>
+>
+> Attached you will find draft-basso-avt-videoconreq-00.txt
+>
+> Abstract:
+>
+> A variety of communication services such as video
+> conferencing and video messaging rely on the capability of video
+> encoders and decoders to exchange control commands. This document
+> outlines this set of commands as well as the requirements for
+> their transport.
+>
+> Comments are more than welcome.
+>
+>
+>
+>
+>
+> Andrea Basso
+> NMS Communications
+> (732) 936-2118
+> (See attached file: draft-basso-avt-videoconreq-00.zip)
+>






_______________________________________________
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Date: Wed, 9 Jul 2003 11:53:39 -0700 (PDT)
To: "Rosen, Brian" <Brian.Rosen@marconi.com>
Cc: "'Yutaka Takeda'" <takeday@kmerl.com>, sip@ietf.org, mmusic@ietf.org
Subject: RE: [MMUSIC] Re: [Sip] Appropriate usage of SIP and RTSP
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Hmm. I'd always thought of SIP as a rendezvous
protocol so this seems perfectly natural to me.
Is the general problem here that the SDP
announcement for an RTSP controlled session isn't
defined? Or is the issue that people would like to
piggyback both the RTSP and RTP session
information in the SIP SDP? Or both?=20

Of course if the announcement for RTSP is not
specified, it sort of begs the question of why
you'd want to just define RTSP semantics... why
not HTTP semantics, etc too? (in which case, it
seems to me that an over-loaded SIP SDP
announcment is probably the wrong thing to do).

=09       Mike

Rosen, Brian writes:
 > I've been thinking for a long time about what an appropriate
 > mechanism to provide a voice/videomail client on a sipphone
 > would be.  It's really clear that you record and play messages
 > with VCR like functionality.  For that, you need start/stop/pause/
 > rewind/fast forward, and so I was thinking RTSP.  On the other
 > hand, you surely establish the session to the voicemail server
 > with a sip call.
 >=20
 > Thus, I like the way Jonathan is thinking, but you also need
 > message selection/creation/deletion functions, and for those
 > I was thinking KPML, and then you wonder if you just use that
 > as the signalling mechanism for the record/play, and I get
 > confused.
 >=20
 > Brian
 >=20
 > > -----Original Message-----
 > > From: Yutaka Takeda [mailto:takeday@kmerl.com]
 > > Sent: Wednesday, July 09, 2003 2:11 PM
 > > To: sip@ietf.org; mmusic@ietf.org
 > > Subject: RE: [MMUSIC] Re: [Sip] Appropriate usage of SIP and RTSP
 > >=20
 > >=20
 > > The applications that have need for SIP and RTSP features I
 > > can imagine are:
 > >=20
 > > - Voice&video mail (similar to 'sipum' but VM server is in=20
 > > the SIP phone)
 > > - Personal broadcast station from my PC at home.
 > > - Watching video recorded with VCR at home or office from remote..=
.
 > >=20
 > > What I am not sure is if RTSP has any solution or a framework for =
a
 > > RTSP server behind a NAT. If not, the solution is likely to=20
 > > be a repeat
 > > of what SIP provides. I thought TURN could be used in order=20
 > > for signaling
 > > message to reach RTSP server behind a NAT, but I noticed that=20
 > > it is not=20
 > > applicable (purposefully) for a server running behind a NAT becaus=
e of
 > > a security consideration. Lots of issues for RTSP in this area alo=
ne?
 > >=20
 > > I believe a lot of people are interested in this discussion.
 > >=20
 > > Best regards,
 > > Yutaka
 > >=20
 > >=20
 > > > -----Original Message-----
 > > > From: Magnus Westerlund [mailto:magnus.westerlund@ericsson.com]
 > > > Sent: Wednesday, July 09, 2003 5:53 AM
 > > > To: Pianigiani, Jacopo (Jacopo)
 > > > Cc: sip@ietf.org; mmusic@ietf.org
 > > > Subject: [MMUSIC] Re: [Sip] Appropriate usage of SIP and RTSP
 > > >=20
 > > >=20
 > > > Hi,
 > > >=20
 > > > When it comes to IMS and 3G terminals, most will already=20
 > > > before having=20
 > > > an IMS functionality have support for PSS. PSS is=20
 > > > Packet-based Streaming=20
 > > > Service which is an umbrella kind of standard for streaming serv=
ice=20
 > > > defined in 3GPP targeted at low bit-rates and mobile networks.=20=

 > > > Specification available from Rel 4 in TS 26.233 and TS=20
 > > > 26.234. Already=20
 > > > today there exist GSM/GPRS phones that has a PSS client.
 > > >=20
 > > > So I think that dual stack implementations will not be that=20
 > > > impossible=20
 > > > to foresee.
 > > >=20
 > > > However I think the main issue in this discussion is to=20
 > > look at what=20
 > > > applications that has need for SIP-RTSP interactions. Based=20
 > > > on this we=20
 > > > can see if there is solutions easily available or not.
 > > >=20
 > > > I can agree with Rosenberg that if we where going to design a RT=
SP=20
 > > > functionality protocol today, looking at SIP for session=20
 > > > establishment=20
 > > > would be interesting. However that opportunity has passed=20
 > > as RTSP has=20
 > > > started to be deployed in increasing numbers. I think even=20
 > > the latest=20
 > > > Windows media player does support RTSP.
 > > >=20
 > > >=20
 > > > Best Regards
 > > >=20
 > > > Magnus Westerlund
 > > >=20
 > > >=20
 > > > Pianigiani, Jacopo (Jacopo) wrote:
 > > > > Hello all,
 > > > > In my undertanding RTSP is suitable for broadcast, unicast=20
 > > > or multicast streams distribution. The RTSP protocol was=20
 > > > ideated for typical content delivery, and in effect for this=20
 > > > application could be more than suitable. But referring to an=20
 > > > IMS domain, in my point of view adopting RSTP as media=20
 > > > streams control, would imply adopting at least a double=20
 > > > protocol stack in the terminal equipment. The IMS concept was=20=

 > > > mainly driven by the concept - in my understanding - of=20
 > > > simplifying the terminal (making it simpler from a protocol=20
 > > > stack implementation means lowering costs and increasing=20
 > > > penetration on the market) by adopting a single protocol=20
 > > > stack in the terminal, and having the RAN and the core=20
 > > > evolving toward a unified transport mechanism for which an=20
 > > > almost unified level of control on the network resources=20
 > > > allocated to a session (whatever session we refer to, voice ,=20=

 > > > multimedia p-t-t call, web browsing, multimedia session with=20
 > > > voice call and dynamic web pages).
 > > > > So in this sense, my understanding is that the RTSP could=20
 > > > be suitable for media content, but it would imply again new=20
 > > > complexity on the IMS UMTS/CDMA terminal itself, which is=20
 > > > against the idea of IMS of enhancing the services the user=20
 > > > can access by having an homogeneous protocol stack on the=20
 > > > terminal itself for all types of services.
 > > > >=20
 > > > > After all, the RTSP , apart from content delivery (of=20
 > > > streams), could not definitely handle appropriately sessions=20
 > > > like Voice calls + Interactive Web Pages.=20
 > > > > Regards
 > > > >=20
 > > > > Jacopo Pianigiani
 > > > > Lucent Technologies - Italy
 > > > > =E839 335 7350536
 > > > >=20
 > > > > -----Original Message-----
 > > > > From: Paolo Asprino [mailto:asprino@coritel.it]
 > > > > Sent: Wednesday, July 09, 2003 9:40 AM
 > > > > To: NAKAMURA, Hidefumi; sip@ietf.org; mmusic@ietf.org
 > > > > Subject: Re: [Sip] Appropriate usage of SIP and RTSP
 > > > >=20
 > > > >=20
 > > > > Hi all
 > > > >=20
 > > > > I'm thinking a solution to join SIP and RTSP in the 3G IMS dom=
ain.
 > > > > In particular in the IMS, I think that to provide multilmedia
 > > > > service (i.e video on demand), one can estabilish a=20
 > > > subscription to the service by SIP and then activate the=20
 > > > service with RTSP by DIGEST autentication with the=20
 > > > > parameters exchanged early during the subscription=20
 > > > (username and password)=20
 > > > >=20
 > > > > What do you think about that?
 > > > >=20
 > > > > Best Regards=20
 > > > >=20
 > > > > ----- Original Message -----=20
 > > > > From: "NAKAMURA, Hidefumi" <nakamura.hidefumi@lab.ntt.co.jp>
 > > > > To: <sip@ietf.org>; <mmusic@ietf.org>
 > > > > Cc: <hidefumi.nakamura@staff.east.ntt.co.jp>
 > > > > Sent: Monday, July 07, 2003 9:49 AM
 > > > > Subject: [Sip] Appropriate usage of SIP and RTSP
 > > > >=20
 > > > >=20
 > > > >=20
 > > > >>Hi, all.
 > > > >>
 > > > >>I have a question about the relationship between SIP and RTSP.=
=20
 > > > >>
 > > > >>In RFC3261, there is a description that says=20
 > > > >>   "SIP is not a vertically integrated communications=20
 > > > system.  SIP is
 > > > >>   rather a component that can be used with other IETF=20
 > > protocols to
 > > > >>   build a complete multimedia architecture.  Typically, these=

 > > > >>   architectures will include protocols such as the=20
 > > > Real-time Transport
 > > > >>   Protocol (RTP) (RFC 1889 [28]) for transporting=20
 > > > real-time data and
 > > > >>   providing QoS feedback, the Real-Time streaming protocol=20=

 > > > (RTSP) (RFC
 > > > >>   2326 [29]) for controlling delivery of streaming media, ...=
"
 > > > >>   (RFC3261 Section 2)
 > > > >>
 > > > >>However, my understanding is that both SIP and RTSP have=20
 > > > the capability
 > > > >>for "discovery of UAs or media streams."
 > > > >>If I use SIP to establish a stream session and use RTSP to con=
trol
 > > > >>the stream, there will be redundant sequences, i.e.=20
 > > > INVITE-OK-ACK and
 > > > >>SETUP-OK.
 > > > >>
 > > > >>Was there any discussion on how to use these two protocols=20
 > > > appropriately?
 > > > >>
 > > > >>With SIP application server, network providers can provide var=
ious
 > > > >>services on contents delivery while we will not be able to=20
 > > > do so only
 > > > >>with RTSP, I think.  On the other hand, RTSP has enough=20
 > > > capability for
 > > > >>discovery of media streams and for negotiation of SDPs.
 > > > >>So, I think, for the simple delivery of contents, RTSP is=20
 > > > appropriate to
 > > > >>use, and for various session control services regarding conten=
ts
 > > > >>delivery, SIP with RTSP is appropriate to use.
 > > > >>
 > > > >>Any opinions?
 > > > >>
 > > > >>I wonder why no contents delivery server seems to prepare=20
 > > > SIP stack now.=20
 > > > >>Is it because, up to now, there exists only a simple=20
 > > > contents delivery
 > > > >>service?
 > > > >>
 > > > >>best regards,
 > > > >>
 > > > >>--=20
 > > > >>NAKAMURA, Hidefumi=20
 > > > >>NTT ServiceIntegration /NetworkServiceSystems Labs.
 > > > >>tel: +81(422)59 3904; fax:+81(422)60 4012
 > > > >>---
 > > > >>
 > > > >>
 > > > >>
 > > > >>_______________________________________________
 > > > >>Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
 > > > >>This list is for NEW development of the core SIP Protocol
 > > > >>Use sip-implementors@cs.columbia.edu for questions on current =
sip
 > > > >>Use sipping@ietf.org for new developments on the=20
 > > application of sip
 > > > >>
 > > > >=20
 > > > >=20
 > > > >=20
 > > > > ---
 > > > > Outgoing mail is certified Virus Free.
 > > > > Checked by AVG anti-virus system (http://www.grisoft.com).
 > > > > Version: 6.0.495 / Virus Database: 294 - Release Date:=20
 > > > 30/06/2003J*fj)bz=09b=B2=D8m=B6>?=FF=0C> > 0=D6'=AD~S=E0=FEf=A2-=
f=A7=FEX=AC=B6)=DF=A3=FB"=A58b=B2X=AC=B6+=1F=A2=B3DY=D7=AF
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=AE=C7,r?n(tm)=B8sy=DBY=A2=BA=AEz=CBb=A2{(=9D=CB=AB
 > > > =AD=E9=ED=B2*T=B1=EB"=A6~=A7''=AD~S=E0~S=E7{=07^=BD=E9h=A6g=A7=B6=
=CA'=B6=17s=A6(tm)bq=ABb=A2z=1F
 > > > >=20
 > > > > _______________________________________________
 > > > > Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
 > > > > This list is for NEW development of the core SIP Protocol
 > > > > Use sip-implementors@cs.columbia.edu for questions on current =
sip
 > > > > Use sipping@ietf.org for new developments on the=20
 > > application of sip
 > > > >=20
 > > >=20
 > > >=20
 > > > --=20
 > > >=20
 > > > Magnus Westerlund
 > > >=20
 > > > Multimedia Technologies, Ericsson Research EAB/TVA/A
 > > >=20
 > > ------------------------------------------------------------------=
----
 > > > Ericsson AB                | Phone +46 8 4048287
 > > > Torshamsgatan 23           | Fax   +46 8 7575550
 > > > S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.=
com
 > > >=20
 > > >=20
 > > > _______________________________________________
 > > > mmusic mailing list
 > > > mmusic@ietf.org
 > > > https://www1.ietf.org/mailman/listinfo/mmusic
 > > >=20
 > >=20
 > > _______________________________________________
 > > mmusic mailing list
 > > mmusic@ietf.org
 > > https://www1.ietf.org/mailman/listinfo/mmusic
 > >=20
 >=20
 > _______________________________________________
 > Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
 > This list is for NEW development of the core SIP Protocol
 > Use sip-implementors@cs.columbia.edu for questions on current sip
 > Use sipping@ietf.org for new developments on the application of sip

_______________________________________________
mmusic mailing list
mmusic@ietf.org
https://www1.ietf.org/mailman/listinfo/mmusic



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Today's Topics:

   1. [ rtspspec-Bugs-678107 ] Change of Proxy-Require header (SourceForge.net)

--__--__--

Message: 1
To: noreply@sourceforge.net
From: "SourceForge.net" <noreply@sourceforge.net>
Date: Thu, 10 Jul 2003 02:42:58 -0700
Subject: [rtspspec-bugs] [ rtspspec-Bugs-678107 ] Change of Proxy-Require header

Bugs item #678107, was opened at 2003-01-31 13:43
Message generated for change (Comment added) made by magwes
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=377744&aid=678107&group_id=23194

Category: General
>Group: Resolved - Need write up
Status: Open
Resolution: None
Priority: 5
Submitted By: Magnus Westerlund (magwes)
>Assigned to: Magnus Westerlund (magwes)
Summary: Change of Proxy-Require header

Initial Comment:
Current text: Says that proxy-require applies to both
proxy and server.

New Proposal: The feature tags in a "Proxy-require"
header will only apply to the proxies, and not the
server. For feature that the server must support the
"Require" header shall be used. If required feature
support from both proxy and server both "Proxy-Require"
and "Require" must be used.

Pro:
- Align with SIP's usage of header
- Makes it possible to create features tags for proxy
only functionality. Otherwise all servers will be
mandated to also know about proxy only features.

Cons: 
- Backwards compatibility. (Actually this does not
matter much as: A old server implementing the old way
would also not work with any new feature tags for
proxies. So it will block operation independent of
changed semantics or not.)


----------------------------------------------------------------------

>Comment By: Magnus Westerlund (magwes)
Date: 2003-07-10 11:42

Message:
Logged In: YES 
user_id=302620

Whas resolved at the telecon january 22 2003. 
Resolution: Proxy-require shall only apply to proxies not
servers. 

Needs to be changed in the specification. Should also
clarify that a feature tag can be of type, proxy, server or
both. 

----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=377744&aid=678107&group_id=23194




End of Rtspspec-bugs Digest


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To: Bill May <wmay@cisco.com>
CC: Aravind Narasimhan <aravind.narasimhan@sun.com>, mmusic@ietf.org
Subject: Re: [MMUSIC] Aggregate Control URI
References: <20030630174155.GC25404@real.com> <3F042CF2.5050307@ericsson.com> <3F0DDBB0.2040001@sun.com> <3F0DE007.2020505@cisco.com>
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Hi Aravind and Bill,

My view on aggregated control has been that this is a media session 
which has at least 2 media. That forces a server to run these under 
aggregated control according to the new spec. Non-aggregated control is 
when a session has only 1 media. However I agree that this is not a 
watertight definition as a client could potentially use the aggregated 
control URL to control a session with only a single media. However there 
is some clear differences in behaviour between a session with 1 media 
and another with 2 media.

I do agree that we need to resolve this and use it consistently through 
the draft. What we need to express in the draft, I believe is the 
differences between a 1 media session and a 2 or more media session. 
Then we can of course better explain that using multiple 1 media 
sessions allow the client maximal control of how to handle the media. 
Then we must also clarify how the aggregated and non-aggregated control 
URI fit.

Best Regards

Magnus

Bill May wrote:

> 
> 
> Aravind Narasimhan wrote:
>  >  Specifically aggregate control
> 
>> should be anything that happens within a session, whether a session 
>> has 0, 1 or more media.  "Non-aggregate control" should be anything 
>> that happens between multiple sessions, regardless of how many media 
>> resources each session has.  What we need to clearly state is that 
>> RTSP only deals with specifying aggregate control of media through a 
>> RTSP session, and not with other problem of non-aggregate control of 
>> multiple sessions.
>>
>> Do people agree with this interpretation?
> 
> 
> No, not really.  Aggregate control to me has meant a method of 
> controlling all
> streams in a session simultaneously.  This can happen only if there is an
> a=control statement before any media.
> 
> Non aggregate control has meant individual control of streams within a 
> session.
> These use the a=control statement required by the media.
> 
> I guess I do not understand where multiple sessions come in.
> 
> Can you enlighten me as to where I'm wrong ?
> 
> Bill May
> Cisco Systems
> 

-- 

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com


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To: jo@informatik.uni-bremen.de, csp@csperkins.org, mmusic@ietf.org
From: Yuji Nomura <nom@flab.fujitsu.co.jp>
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Subject: [MMUSIC] draft-nomura-mmusic-img-requirements-01.txt
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Hi,

I submitted following I-D in June, and it is now available at
the official web site. Please update the MMUSIC Agenda for the 57th IETF.

http://www.ietf.org/internet-drafts/draft-nomura-mmusic-img-requirements-01.txt

Title: Protocol Requirements for Internet Media Guides

Filename:  draft-nomura-mmusic-img-requirements-01.txt

Abstract:

   This memo specifies requirements for a protocol for accessing and
   updating Internet Media Guide (IMG) information for media-on-demand
   and multicast applications. These requirements are designed to guide
   development of an IMG protocol for efficient and scalable delivery.

Comments are appreciated.
----------
Yuji Nomura

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Subject: Re: [MMUSIC] Re: [Sip] Appropriate usage of SIP and RTSP
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In many ways, this problem is similar to the far end camera control issues.
Real time responses is needed, It is a 1:1 relationship between the
controller and controlee, the control protocol needs to be extensible.

On 7/9/03 11:40, "Rosen, Brian" <Brian.Rosen@marconi.com> wrote:

> I've been thinking for a long time about what an appropriate
> mechanism to provide a voice/videomail client on a sipphone
> would be.  It's really clear that you record and play messages
> with VCR like functionality.  For that, you need start/stop/pause/
> rewind/fast forward, and so I was thinking RTSP.  On the other
> hand, you surely establish the session to the voicemail server
> with a sip call.
>=20
> Thus, I like the way Jonathan is thinking, but you also need
> message selection/creation/deletion functions, and for those
> I was thinking KPML, and then you wonder if you just use that
> as the signalling mechanism for the record/play, and I get
> confused.
>=20
> Brian
>=20
>> -----Original Message-----
>> From: Yutaka Takeda [mailto:takeday@kmerl.com]
>> Sent: Wednesday, July 09, 2003 2:11 PM
>> To: sip@ietf.org; mmusic@ietf.org
>> Subject: RE: [MMUSIC] Re: [Sip] Appropriate usage of SIP and RTSP
>>=20
>>=20
>> The applications that have need for SIP and RTSP features I
>> can imagine are:
>>=20
>> - Voice&video mail (similar to 'sipum' but VM server is in
>> the SIP phone)
>> - Personal broadcast station from my PC at home.
>> - Watching video recorded with VCR at home or office from remote...
>>=20
>> What I am not sure is if RTSP has any solution or a framework for a
>> RTSP server behind a NAT. If not, the solution is likely to
>> be a repeat
>> of what SIP provides. I thought TURN could be used in order
>> for signaling
>> message to reach RTSP server behind a NAT, but I noticed that
>> it is not=20
>> applicable (purposefully) for a server running behind a NAT because of
>> a security consideration. Lots of issues for RTSP in this area alone?
>>=20
>> I believe a lot of people are interested in this discussion.
>>=20
>> Best regards,
>> Yutaka
>>=20
>>=20
>>> -----Original Message-----
>>> From: Magnus Westerlund [mailto:magnus.westerlund@ericsson.com]
>>> Sent: Wednesday, July 09, 2003 5:53 AM
>>> To: Pianigiani, Jacopo (Jacopo)
>>> Cc: sip@ietf.org; mmusic@ietf.org
>>> Subject: [MMUSIC] Re: [Sip] Appropriate usage of SIP and RTSP
>>>=20
>>>=20
>>> Hi,
>>>=20
>>> When it comes to IMS and 3G terminals, most will already
>>> before having=20
>>> an IMS functionality have support for PSS. PSS is
>>> Packet-based Streaming
>>> Service which is an umbrella kind of standard for streaming service
>>> defined in 3GPP targeted at low bit-rates and mobile networks.
>>> Specification available from Rel 4 in TS 26.233 and TS
>>> 26.234. Already
>>> today there exist GSM/GPRS phones that has a PSS client.
>>>=20
>>> So I think that dual stack implementations will not be that
>>> impossible=20
>>> to foresee.
>>>=20
>>> However I think the main issue in this discussion is to
>> look at what=20
>>> applications that has need for SIP-RTSP interactions. Based
>>> on this we=20
>>> can see if there is solutions easily available or not.
>>>=20
>>> I can agree with Rosenberg that if we where going to design a RTSP
>>> functionality protocol today, looking at SIP for session
>>> establishment=20
>>> would be interesting. However that opportunity has passed
>> as RTSP has=20
>>> started to be deployed in increasing numbers. I think even
>> the latest=20
>>> Windows media player does support RTSP.
>>>=20
>>>=20
>>> Best Regards
>>>=20
>>> Magnus Westerlund
>>>=20
>>>=20
>>> Pianigiani, Jacopo (Jacopo) wrote:
>>>> Hello all,
>>>> In my undertanding RTSP is suitable for broadcast, unicast
>>> or multicast streams distribution. The RTSP protocol was
>>> ideated for typical content delivery, and in effect for this
>>> application could be more than suitable. But referring to an
>>> IMS domain, in my point of view adopting RSTP as media
>>> streams control, would imply adopting at least a double
>>> protocol stack in the terminal equipment. The IMS concept was
>>> mainly driven by the concept - in my understanding - of
>>> simplifying the terminal (making it simpler from a protocol
>>> stack implementation means lowering costs and increasing
>>> penetration on the market) by adopting a single protocol
>>> stack in the terminal, and having the RAN and the core
>>> evolving toward a unified transport mechanism for which an
>>> almost unified level of control on the network resources
>>> allocated to a session (whatever session we refer to, voice ,
>>> multimedia p-t-t call, web browsing, multimedia session with
>>> voice call and dynamic web pages).
>>>> So in this sense, my understanding is that the RTSP could
>>> be suitable for media content, but it would imply again new
>>> complexity on the IMS UMTS/CDMA terminal itself, which is
>>> against the idea of IMS of enhancing the services the user
>>> can access by having an homogeneous protocol stack on the
>>> terminal itself for all types of services.
>>>>=20
>>>> After all, the RTSP , apart from content delivery (of
>>> streams), could not definitely handle appropriately sessions
>>> like Voice calls + Interactive Web Pages.
>>>> Regards
>>>>=20
>>>> Jacopo Pianigiani
>>>> Lucent Technologies - Italy
>>>> =E839 335 7350536
>>>>=20
>>>> -----Original Message-----
>>>> From: Paolo Asprino [mailto:asprino@coritel.it]
>>>> Sent: Wednesday, July 09, 2003 9:40 AM
>>>> To: NAKAMURA, Hidefumi; sip@ietf.org; mmusic@ietf.org
>>>> Subject: Re: [Sip] Appropriate usage of SIP and RTSP
>>>>=20
>>>>=20
>>>> Hi all
>>>>=20
>>>> I'm thinking a solution to join SIP and RTSP in the 3G IMS domain.
>>>> In particular in the IMS, I think that to provide multilmedia
>>>> service (i.e video on demand), one can estabilish a
>>> subscription to the service by SIP and then activate the
>>> service with RTSP by DIGEST autentication with the
>>>> parameters exchanged early during the subscription
>>> (username and password)
>>>>=20
>>>> What do you think about that?
>>>>=20
>>>> Best Regards=20
>>>>=20
>>>> ----- Original Message -----
>>>> From: "NAKAMURA, Hidefumi" <nakamura.hidefumi@lab.ntt.co.jp>
>>>> To: <sip@ietf.org>; <mmusic@ietf.org>
>>>> Cc: <hidefumi.nakamura@staff.east.ntt.co.jp>
>>>> Sent: Monday, July 07, 2003 9:49 AM
>>>> Subject: [Sip] Appropriate usage of SIP and RTSP
>>>>=20
>>>>=20
>>>>=20
>>>>> Hi, all.
>>>>>=20
>>>>> I have a question about the relationship between SIP and RTSP.
>>>>>=20
>>>>> In RFC3261, there is a description that says
>>>>>   "SIP is not a vertically integrated communications
>>> system.  SIP is
>>>>>   rather a component that can be used with other IETF
>> protocols to
>>>>>   build a complete multimedia architecture.  Typically, these
>>>>>   architectures will include protocols such as the
>>> Real-time Transport
>>>>>   Protocol (RTP) (RFC 1889 [28]) for transporting
>>> real-time data and
>>>>>   providing QoS feedback, the Real-Time streaming protocol
>>> (RTSP) (RFC
>>>>>   2326 [29]) for controlling delivery of streaming media, ..."
>>>>>   (RFC3261 Section 2)
>>>>>=20
>>>>> However, my understanding is that both SIP and RTSP have
>>> the capability
>>>>> for "discovery of UAs or media streams."
>>>>> If I use SIP to establish a stream session and use RTSP to control
>>>>> the stream, there will be redundant sequences, i.e.
>>> INVITE-OK-ACK and
>>>>> SETUP-OK.
>>>>>=20
>>>>> Was there any discussion on how to use these two protocols
>>> appropriately?
>>>>>=20
>>>>> With SIP application server, network providers can provide various
>>>>> services on contents delivery while we will not be able to
>>> do so only
>>>>> with RTSP, I think.  On the other hand, RTSP has enough
>>> capability for
>>>>> discovery of media streams and for negotiation of SDPs.
>>>>> So, I think, for the simple delivery of contents, RTSP is
>>> appropriate to
>>>>> use, and for various session control services regarding contents
>>>>> delivery, SIP with RTSP is appropriate to use.
>>>>>=20
>>>>> Any opinions?
>>>>>=20
>>>>> I wonder why no contents delivery server seems to prepare
>>> SIP stack now.=20
>>>>> Is it because, up to now, there exists only a simple
>>> contents delivery
>>>>> service?
>>>>>=20
>>>>> best regards,
>>>>>=20
>>>>> --=20
>>>>> NAKAMURA, Hidefumi
>>>>> NTT ServiceIntegration /NetworkServiceSystems Labs.
>>>>> tel: +81(422)59 3904; fax:+81(422)60 4012
>>>>> ---
>>>>>=20
>>>>>=20
>>>>>=20
>>>>> _______________________________________________
>>>>> Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
>>>>> This list is for NEW development of the core SIP Protocol
>>>>> Use sip-implementors@cs.columbia.edu for questions on current sip
>>>>> Use sipping@ietf.org for new developments on the
>> application of sip
>>>>>=20
>>>>=20
>>>>=20
>>>>=20
>>>> ---
>>>> Outgoing mail is certified Virus Free.
>>>> Checked by AVG anti-virus system (http://www.grisoft.com).
>>>> Version: 6.0.495 / Virus Database: 294 - Release Date:
>>> 30/06/2003J*fj)bz    b=B2=D8m=B6>?=FF=0C> > 0=D6'=AD~S=E0=FEf=A2-f=A7=FEX=AC=B6)=DF=A3=FB"=A58b=B2X=AC=B6+=1F=A2=B3DY=D7=AF
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>>> =AD=E9=ED=B2*T=B1=EB"=A6~=A7''=AD~S=E0~S=E7{=07^=BD=E9h=A6g=A7=B6=CA'=B6=17s=A6(tm)bq=ABb=A2z=1F
>>>>=20
>>>> _______________________________________________
>>>> Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
>>>> This list is for NEW development of the core SIP Protocol
>>>> Use sip-implementors@cs.columbia.edu for questions on current sip
>>>> Use sipping@ietf.org for new developments on the
>> application of sip
>>>>=20
>>>=20
>>>=20
>>> --=20
>>>=20
>>> Magnus Westerlund
>>>=20
>>> Multimedia Technologies, Ericsson Research EAB/TVA/A
>>>=20
>> ----------------------------------------------------------------------
>>> Ericsson AB                | Phone +46 8 4048287
>>> Torshamsgatan 23           | Fax   +46 8 7575550
>>> S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com
>>>=20
>>>=20
>>> _______________________________________________
>>> mmusic mailing list
>>> mmusic@ietf.org
>>> https://www1.ietf.org/mailman/listinfo/mmusic
>>>=20
>>=20
>> _______________________________________________
>> mmusic mailing list
>> mmusic@ietf.org
>> https://www1.ietf.org/mailman/listinfo/mmusic
>>=20
>=20
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic
>=20


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Date: Fri, 11 Jul 2003 10:40:35 -0400
From: Aravind Narasimhan <aravind.narasimhan@sun.com>
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Subject: Re: [MMUSIC] Aggregate Control URI
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Hi Bill,

comments inline:

Bill May wrote:

>
>
> Aravind Narasimhan wrote:
> >  Specifically aggregate control
>
>> should be anything that happens within a session, whether a session 
>> has 0, 1 or more media.  "Non-aggregate control" should be anything 
>> that happens between multiple sessions, regardless of how many media 
>> resources each session has.  What we need to clearly state is that 
>> RTSP only deals with specifying aggregate control of media through a 
>> RTSP session, and not with other problem of non-aggregate control of 
>> multiple sessions.
>>
>> Do people agree with this interpretation?
>
>
> No, not really.  Aggregate control to me has meant a method of 
> controlling all
> streams in a session simultaneously.  This can happen only if there is an
> a=control statement before any media.

The a=control attribute at the session level of an SDP description 
indicates that URL that should be used for aggregate control of the 
presentation that is being described.  While this is what the client 
should use for aggregate control of the presentation, this is not a 
normative requirement from the RTSP spec.  For one thing RTSP and SDP 
are not tied together.  You could potentially use a different standard 
for describing a session.  Secondly, as Tom and Magnus have mentioned, a 
user may try to aggregate multiple streams in one RTSP session, where 
there isnt a unified presentaiton description, or where someone has 
ignored to put a session level aggregate control URL in the SDP.  Now 
the server has the right to say that it cannot aggregate the given media 
URLs in a session, but it does not make sense for the server to allow 
two or more streams to be part of a session where each stream within the 
session is going ot be controlled separately in a non-aggregate fashion.

In the RTSP concalls of late, there was a general trend towards a 
consensus that within a RTSP session, all streams should be "aggregately 
controlled."  In other words, once part of a session, an individual 
media stream will be tied to the timeline of the session and will be 
controlled in conjunction with the rest of the streams in the session.  
So control methods such as PAUSE, PLAY would apply collectively to all 
streams within the session.  The upshot of this is that you cannot just 
PLAY or PAUSE a single media stream within a session. 

>
> Non aggregate control has meant individual control of streams within a 
> session.
> These use the a=control statement required by the media.
>
> I guess I do not understand where multiple sessions come in.


To achieve the notion of "non-aggregate control", or may be the more 
appropriate term is "independent control" the consensus was that the 
onus should be on the client to set up multiple RTSP sessions, each with 
one or more media streams and manage them in a non-aggregate fashion.  
To try to clearly specify the mechanisms of "non-aggregate" control of 
individual media streams within a single session would probably cloud 
and confuse the spec unnecessarily, since the functionality is easily 
achievable by having multiple RTSP sessions that are controlled 
independently.  If this becomes a very serious requirement, someone can 
write an extension to RTSP that describes how two independent RTSP 
sessions can be controlled in a coordinated, yet non-aggregate fashion.

> Can you enlighten me as to where I'm wrong ?

Now there is an effort underway to establish the MUTE/UNMUTE methods to 
temporarily "silence/unsilence" individual streams within a RTSP session 
as a extension to RTSP.  In this case, however, the streams would still 
be tied to the timeline of the RTSP Session, where PLAY and PAUSE on the 
session would supercede the MUTE/UNMUTE methods.

But I can see where my definitions for aggregate control and 
non-aggregate control could be a bit ambiguous, since obviously, there 
are methods such as SETUP and TEARDOWN, and even MUTE and UNMUTE that 
can work on individual media streams within a session.  I'll see if I 
can clean it up to take these methods into account.  We may just have to 
come up with more appropriate terminology.

Aravind




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Hi Philippe,


I have now had time to read your requirements draft and has some 
comments about this. I also have been rather heavily involved in the 
work within 3GPP to define bit-rate and content-rate adaptation so I 
have some comments based on this work.

First, the goal of the stream switching work is in my opinion to:
- Enable the receiver to receive interrupt free media at highest 
possible quality.

To enable this the complete system must ensure the following things:
- Congestion Control or rather adapting transmission rates to available 
network rate => avoiding high packet loss rates that severely effect 
quality.
- Avoid that the receivers buffers either under flow (causes interrupt) 
or overflow (show up as packet loss).

Based on this one can arrive at the conclusion that the media or content 
rate must be adapted, otherwise the underflow condition will be 
impossible to avoid. If one performs content adaptation towards lower 
bit-rates one must also perform adaptation towards higher rates.

This I think is the basic requirement and assumptions that apply to your 
requirements draft.

Based on this any solution can be divided up into different 
functionality blocks:

- Transmission rate control, this functionality ensures that a sender 
does not send more data then the network can transport without being to 
unfair, or overflow network buffers.

- Receiver buffer control, this functionality ensure that one does not 
overflow the client's receiver buffers.

- Content rate control, functionality to ensure that the transmitted 
date fits the available network rate, while at the same time ensure that 
the receiver buffer does not underflow.

Based on this functionality blocks one can use one or several 
protocols/solutions to realize them. They do not need to be separate and 
can utilize information enabled by any of the other functionality 
blocks. However I believe that all parts must be present to have a 
complete solution. Also how to realize the solutions is a not fixed by 
this.

I would suggest that one tries to group the requirements regarding which 
of the functionalities they address.

When one comes to solution one must start discussing what control 
paradigm one desires, as it will heavily influence the solution. Three 
different ones are:
- Server controlled: In this the server is the responsible for all 
decisions regarding the adaptation. The client simply reports certain 
measurements that the server interprets.

- Client controlled: The client makes the decisions and interpretations 
of what it see. Then it issues commands to the server that it must 
follow. The server is a simple slave.

- Hybrid control: In a hybrid control scenario both client and servers 
makes decisions and interpretations of the data.

I will not try to compare these solutions this if for future 
discussions. If one is interested in a server controlled solution one 
can look at the latest proposal in 3GPP SA4: 
http://www.3gpp.org/ftp/tsg_sa/WG4_CODEC/TSGS4_27/Docs/S4-030501.zip
Look at the buffer reporting mode variant. This proposal provides 
receiver buffer control and content rate control. The transmission rate 
control is handled through RTCP reports with enabled extended reports of 
packet loss vectors.


Some more direct comments on the draft:

1. Introduction: The encoding could be done in real time allowing 
maximum flexibility in the produced content rate. However this is may 
not result in optimal encodings and are also very resource demanding for 
a server.

2. Section 2.1.1 and 2.1.2: I think the behaviour in this case should 
really be depending on the operators policies. I would not like to have 
my expensively paid on demand video reduced in quality if this network 
is of the type you describe. However I can see that we should enable this.

3. Section 2.2: I think you need to be a bit more clear that this is one 
example of a service. Also the AMR rate of 5 kbps is a bit to low. The 
4.75 kbps mode has a quality that is not the best. However to achieve 
this bit-rate you must only send one AMR packet every 1.28 seconds, 
which means 64 amr frames per packet. This is not realistic as every 
packet will be required to reach the receiver to achieve acceptable 
quality. I would think that reasonable AMR qualities are using at least 
10 packet every second, meaning that a header overhead of 3 kbps.

4. Section 2.5: I think this section assumes something that are not 
quite true. First the impossibility to signal this rate switch using 
current protocols. I claim it is possible but most likely not supported 
by any available client. To signal the rate switch in SDP you present 
one different RTP payload types for each codec and configuration, most 
likely at least 4 maybe 5. The 40 and 50 kbps AAC stereo may be possible 
to encode using the same AAC configuration. The declared payload types 
are present in a SDP. A client shall not accept the session and setup 
the media stream unless it can handle all these codecs. If it has setup 
this media stream it has in fact accepted that any of the codec may be 
used in the media stream.

The server can here use different strategies when switching. The most 
likely one is to use a single SSRC and in the same RTP sequence number 
and timestamp space send the selected media quality. When the server 
switched this will be indicated by the new RTP PT. This has a slight 
problem as RTP/RTCP does not handle switched RTP TS rate perfectly. The 
client may in fact lose synchronization until it receives a RTCP packet 
after the switch has taken place. This happens if the packet where the 
RTP TS rate switches is lost. This is not a problem as long as the RTP 
TS rate before and after the payload type switch has the same TS rate. 
In other words not a problem for any video codec which all runs at 
90000. This is more a problem for audio codecs. I would in fact try to 
address this problem with audio codecs by ensuring that any audio codec 
is allowed to select a RTP TS rate that is a even rate multiple of its 
native value. This would allow audio codecs to run at a the smallest 
common denominator rate.

The other strategy at points of switching would be to use different 
SSRCs. This would violate the semantics that a SSRC represents a certain 
source. This also has some problems with the synchronization of the 
different SSRCs. This can't be done in RTSP as RTSP due to an erroneous 
definition of RTP-Info did not map each synchronization information to 
the SSRC. This can only be fixed through a new header due to backwards 
compatibility problems. Otherwise RTCP could be used. By sending SR for 
all SSRC one could in fact ensure that the synchronization is available. 
It will utilize more RTCP bandwidth.

5. Section 3.1.2: I don't think you should mix congestion control with 
adaptation control that hard. In my opinion, how drastic a content rate 
change is needed and how much depends on the clients buffer status.

6. Section 3.2.1: I think this directly falls under Transmission rate 
control and is a function of the congestion control mechanism.

7. Section 3.2.2.1: I don't think that this is a valid requirement. This 
is clearly an option that must be available. The controlling entity can 
trade off sending new data against retransmitting lost data. This trade 
off needs to be available to maximize quality. Further this can be done 
without causing congestion as long as the sender keeps to the available 
network rate. This is why splitting the functionality into different 
functionality blocks are so important. By having this model one can see 
that a server can have network rate N(t), content rate C(t) and 
retransmission rate R(t). The controlling entity must ensure that 
C(t)+R(t) <= N(t). Further the clients buffer allows that on short time 
scales R(t) can be equal to N(t) as long as enough data are available in 
the clients buffer.

8. Section 3.7: I don't think we can deploy a solution for switching 
that gives full functionality and at the same time is backwards 
compatible. However think on how one can maintain some of the 
functionality and being backwards compatible may be a worth the effort. 
However this is rather a design evaluation criteria than a requirement.



Best Regards

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com


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To: Aravind Narasimhan <aravind.narasimhan@sun.com>
CC: Magnus Westerlund <magnus.westerlund@ericsson.com>, mmusic@ietf.org
Subject: Re: [MMUSIC] Aggregate Control URI
References: <20030630174155.GC25404@real.com> <3F042CF2.5050307@ericsson.com> <3F0DDBB0.2040001@sun.com> <3F0DE007.2020505@cisco.com> <3F0ECC63.6020900@sun.com>
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Aravind Narasimhan wrote:
>  Secondly, as Tom and Magnus have mentioned, a 
> user may try to aggregate multiple streams in one RTSP session, where 
> there isnt a unified presentaiton description, or where someone has 
> ignored to put a session level aggregate control URL in the SDP.  Now 
> the server has the right to say that it cannot aggregate the given media 
> URLs in a session, 

I will agree with this; however, it does not make sense for the client
to create it's own aggregate URLS where the server does not specify one
(given the SDP case).

 > but it does not make sense for the server to allow
> two or more streams to be part of a session where each stream within the 
> session is going ot be controlled separately in a non-aggregate fashion.

I'm sorry, but I do not understand.

I can see a scenario where you might want to stop the video, but still maintain
the audio.  In this case, you have 2 or more streams running, and the client
wishes to stop 1 of them.  This is a perfectly legal scenario.

Another would be a fast forward application, where you pause 1 or more streams
while changing speeds on another.

Can you please expand on why it doesn't make sense to allow streams to
be controlled seperately ?  I've done most of my work on the player side with
the idea that the streams could be seperate, so most likely I'm missing
something.

> In the RTSP concalls of late, there was a general trend towards a 
> consensus that within a RTSP session, all streams should be "aggregately 
> controlled."  In other words, once part of a session, an individual 
> media stream will be tied to the timeline of the session and will be 
> controlled in conjunction with the rest of the streams in the session.  
> So control methods such as PAUSE, PLAY would apply collectively to all 
> streams within the session.  The upshot of this is that you cannot just 
> PLAY or PAUSE a single media stream within a session.

Why ?  To me, aggregate (or control of the entire session) control and
non-aggregate control (or control based on each stream) can be used
at the same time, and should be allowed.

Perhaps I do not understand the argument why control over streams
in a session is so difficult.  Can you point me to some information about
this ?

The only thing I could see is that you might want to discourage changes
to the overall timeline, ie:one stream going back 10 seconds from the
rest of the presentation.

But it would seem to me that would be an easy thing to prevent.

> To achieve the notion of "non-aggregate control", or may be the more 
> appropriate term is "independent control" the consensus was that the 
> onus should be on the client to set up multiple RTSP sessions, each with 
> one or more media streams and manage them in a non-aggregate fashion.  

That seems non-intuitive to me -keeping twice as much information as
needed.

> To try to clearly specify the mechanisms of "non-aggregate" control of 
> individual media streams within a single session would probably cloud 
> and confuse the spec unnecessarily, since the functionality is easily 
> achievable by having multiple RTSP sessions that are controlled 
> independently.  If this becomes a very serious requirement, someone can 
> write an extension to RTSP that describes how two independent RTSP 
> sessions can be controlled in a coordinated, yet non-aggregate fashion.

I guess I'm not understanding why this would be difficult.  The only
limitation would be that the timeline must be consistent across all
streams.  Otherwise, control the streams to your heart's content.

I apologize for being so dense.

> Now there is an effort underway to establish the MUTE/UNMUTE methods to 
> temporarily "silence/unsilence" individual streams within a RTSP session 
> as a extension to RTSP.  In this case, however, the streams would still 
> be tied to the timeline of the RTSP Session, where PLAY and PAUSE on the 
> session would supercede the MUTE/UNMUTE methods.

I'm not sure that this buys you anything, if all a MUTE is is a PAUSE to
an individual streams.  It does sound like over-complicating (adding more
states and breaking backward compatibility) to avoid a couple of sentences.

> But I can see where my definitions for aggregate control and 
> non-aggregate control could be a bit ambiguous, since obviously, there 
> are methods such as SETUP and TEARDOWN, and even MUTE and UNMUTE that 
> can work on individual media streams within a session.  I'll see if I 
> can clean it up to take these methods into account.  We may just have to 
> come up with more appropriate terminology.

Most likely that is why I do not understand.

Bill


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Subject: RE: [MMUSIC] RTP denial of service
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Jonathan:

Thanks for this timely work. I finally got a chance to review it, along with
the email trail.

Magnus asked a good question: doesn't STUN (RFC3489) require TLS ? See
section 9.2:
   In order to ensure interoperability, this
   specification describes a TLS-based mechanism.  This mechanism,
   described in this section, MUST be implemented by clients and
   servers.

I suspect that some RTSP thin clients (those embedded in low-power devices)
may not have enough resources (CPU and/or bandwidth) to run TLS... at the
minimal, it adds more work to implementors of RTSP.


Now, in section 5 of:
http://www.ietf.org/internet-drafts/draft-rosenberg-mmusic-rtp-denialofservi
ce-00.txt

You seem to imply that RTSP already follows Offer/Answer exchanges? I'd like
to hear more on this subject...

Thanks,
- thomas
-----Original Message-----
From: Jonathan Rosenberg [mailto:jdrosen@dynamicsoft.com]
Sent: Tuesday, July 01, 2003 10:16 PM
To: mmusic@ietf.org
Subject: [MMUSIC] RTP denial of service


Folks,

I'd like to draw your attention to the following I-D that I submitted 
recently:

http://www.ietf.org/internet-drafts/draft-rosenberg-mmusic-rtp-denialofservi
ce-00.txt

This draft describes a denial-of-service attack using RTP. This attack 
can be launched using any protocol that uses an offer/answer-like SDP 
exchange, including SIP and RTSP. The draft also discusses ICE as a 
solution to the problem.

Comments welcome.

Thanks,
Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com



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Bill:

Based on my understanding of the discussions during the past RTSP tele
conferences, I'd like to make a couple of  comments. 

See below.

- thomas

>  -----Original Message-----
> From: 	Bill May [mailto:wmay@cisco.com] 
> Sent:	Friday, July 11, 2003 10:17 AM
> To:	Aravind Narasimhan
> Cc:	Magnus Westerlund; mmusic@ietf.org
> Subject:	Re: [MMUSIC] Aggregate Control URI
> 
> 
> 
> Aravind Narasimhan wrote:
> >  Secondly, as Tom and Magnus have mentioned, a 
> > user may try to aggregate multiple streams in one RTSP session, where 
> > there isnt a unified presentaiton description, or where someone has 
> > ignored to put a session level aggregate control URL in the SDP.  Now 
> > the server has the right to say that it cannot aggregate the given media
> 
> > URLs in a session, 
> 
> I will agree with this; however, it does not make sense for the client
> to create it's own aggregate URLS where the server does not specify one
> (given the SDP case).
	[Thomas Zeng]  The bottom line is that PLAY is always an "aggregate"
operation. Regardless of the control URI in the PLAY request, the sessionID
will uniquely identify the media streams affected by the PLAY request.  That
is the spirit of draft-ietf-mmusic-rfc2326bis-04 (see section 11.4).  In
your case, if the SDP does not intend to support aggregate control (assume
that the SDP does have more than one media tracks), it should NOT have used
RTSP in the media level control URL.

>  > but it does not make sense for the server to allow
> > two or more streams to be part of a session where each stream within the
> 
> > session is going ot be controlled separately in a non-aggregate fashion.
> 
> I'm sorry, but I do not understand.
> 
> 
> I can see a scenario where you might want to stop the video, but still
> maintain
> the audio.  In this case, you have 2 or more streams running, and the
> client
> wishes to stop 1 of them.  This is a perfectly legal scenario.
	[Thomas Zeng]  There are two ways to do what you want here: 1) issue
teardown on the audio track. 2) perform a MUTE on the audio track.

> Another would be a fast forward application, where you pause 1 or more
> streams
> while changing speeds on another.
	[Thomas Zeng]  Again, you would use MUTE to pause 1 or more streams,
then use PLAY with range to seek.

> Can you please expand on why it doesn't make sense to allow streams to
> be controlled seperately ?  I've done most of my work on the player side
> with
> the idea that the streams could be seperate, so most likely I'm missing
> something.
	[Thomas Zeng]  If two streams belong to same RTSP session, and you
issue PLAY on one stream, what would be the state of the overall session ?
what would be the NPT  (Normal Play Time) of the session? If I recall
correctly, if PLAY/PAUSE were allowed on each track in a mutli-tracked RTSP
session, the RTSP state machine would break.

> > In the RTSP concalls of late, there was a general trend towards a 
> > consensus that within a RTSP session, all streams should be "aggregately
> 
> > controlled."  In other words, once part of a session, an individual 
> > media stream will be tied to the timeline of the session and will be 
> > controlled in conjunction with the rest of the streams in the session.  
> > So control methods such as PAUSE, PLAY would apply collectively to all 
> > streams within the session.  The upshot of this is that you cannot just 
> > PLAY or PAUSE a single media stream within a session.
> 
> Why ?  To me, aggregate (or control of the entire session) control and
> non-aggregate control (or control based on each stream) can be used
> at the same time, and should be allowed.
	[Thomas Zeng]  Yes, you are right here. The decision by the RTSP
task force was to let PLAY/PAUSE be aggregate, while SETUP/TEARDOWN and
MUTE/UNMUTE be non-aggregate (note MUTE/UNMUTE is defined as an extension to
RTSP core spec).

> Perhaps I do not understand the argument why control over streams
> in a session is so difficult.  Can you point me to some information about
> this ?
> 
> The only thing I could see is that you might want to discourage changes
> to the overall timeline, ie:one stream going back 10 seconds from the
> rest of the presentation.
> 
> But it would seem to me that would be an easy thing to prevent.
> 
> > To achieve the notion of "non-aggregate control", or may be the more 
> > appropriate term is "independent control" the consensus was that the 
> > onus should be on the client to set up multiple RTSP sessions, each with
> 
> > one or more media streams and manage them in a non-aggregate fashion.  
> 
> That seems non-intuitive to me -keeping twice as much information as
> needed.
> 
> > To try to clearly specify the mechanisms of "non-aggregate" control of 
> > individual media streams within a single session would probably cloud 
> > and confuse the spec unnecessarily, since the functionality is easily 
> > achievable by having multiple RTSP sessions that are controlled 
> > independently.  If this becomes a very serious requirement, someone can 
> > write an extension to RTSP that describes how two independent RTSP 
> > sessions can be controlled in a coordinated, yet non-aggregate fashion.
> 
> I guess I'm not understanding why this would be difficult.  The only
> limitation would be that the timeline must be consistent across all
> streams.  Otherwise, control the streams to your heart's content.
	[Thomas Zeng]  Here the concern is on RTSP state machine.
> I apologize for being so dense.
> 
> > Now there is an effort underway to establish the MUTE/UNMUTE methods to 
> > temporarily "silence/unsilence" individual streams within a RTSP session
> 
> > as a extension to RTSP.  In this case, however, the streams would still 
> > be tied to the timeline of the RTSP Session, where PLAY and PAUSE on the
> 
> > session would supercede the MUTE/UNMUTE methods.
> 
> I'm not sure that this buys you anything, if all a MUTE is is a PAUSE to
> an individual streams.  It does sound like over-complicating (adding more
> states and breaking backward compatibility) to avoid a couple of
> sentences.
> 
> > But I can see where my definitions for aggregate control and 
> > non-aggregate control could be a bit ambiguous, since obviously, there 
> > are methods such as SETUP and TEARDOWN, and even MUTE and UNMUTE that 
> > can work on individual media streams within a session.  I'll see if I 
> > can clean it up to take these methods into account.  We may just have to
> 
> > come up with more appropriate terminology.
> 
> Most likely that is why I do not understand.
> 
> Bill
> 
> 
> _______________________________________________
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	(envelope-from csp@csperkins.org)
Date: Sun, 13 Jul 2003 15:20:30 +0200
From: Colin Perkins <csp@csperkins.org>
To: mmusic@ietf.org
Subject: Re: [MMUSIC] I-D ACTION:draft-ietf-mmusic-sdp-bwparam-04.txt
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A number of people raised concerns with the previous version of this draft.
Does this revision address those concerns?

Colin



--> Internet-Drafts@ietf.org writes:
> A New Internet-Draft is available from the on-line Internet-Drafts
> directories. This draft is a work item of the Multiparty Multimedia
> Session Control Working Group of the IETF.
> 
> 	Title		: A Transport Independent Bandwidth Modifier for the 
>                           Session Description Protocol (SDP)
> 	Author(s)	: M. Westerlund
> 	Filename	: draft-ietf-mmusic-sdp-bwparam-04.txt
> 	Pages		: 18
> 	Date		: 2003-6-26
> 	
> The existing Session Description Protocol (SDP) bandwidth modifiers
> and their values include the bandwidth needed also for the transport
> and IP layers. When using SDP with protocols like the Session
> Announcement Protocol (SAP), the Session Initiation Protocol (SIP)
> and the Real-Time Streaming Protocol (RTSP) and when the involved
> hosts reside in networks running different IP versions, the
> interpretation of what lower layer bandwidths are included is not
> clear. This document defines a bandwidth modifier that does not
> include transport overhead; instead an additional packet rate
> attribute is defined. The transport independent bit-rate value
> together with the maximum packet rate can then be used to calculate
> the real bit-rate over the transport actually used.
> 
> A URL for this Internet-Draft is:
> http://www.ietf.org/internet-drafts/draft-ietf-mmusic-sdp-bwparam-04.txt
> 
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> or ftp://ftp.ietf.org/ietf/1shadow-sites.txt
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> 
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> Send a message to:
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-- 
Colin Perkins
csp@csperkins.org

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This is an automatic digest of bugs submitted and changed on the RTSP bug tracker.  To see a list of bugs, visit:

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Today's Topics:

   1. [ rtspspec-Bugs-770522 ] Request to response time is not limited. (SourceForge.net)

--__--__--

Message: 1
To: noreply@sourceforge.net
From: "SourceForge.net" <noreply@sourceforge.net>
Date: Sun, 13 Jul 2003 07:00:04 -0700
Subject: [rtspspec-bugs] [ rtspspec-Bugs-770522 ] Request to response time is not limited.

Bugs item #770522, was opened at 2003-07-13 16:00
Message generated for change (Tracker Item Submitted) made by Item Submitter
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=377744&aid=770522&group_id=23194

Category: None
Group: Fix for DS - Need WG Input
Status: Open
Resolution: None
Priority: 5
Submitted By: Magnus Westerlund (magwes)
Assigned to: Nobody/Anonymous (nobody)
Summary: Request to response time is not limited.

Initial Comment:
The time a server is expected to respond to a request
in is not defined. This may create interoperability
issues that a certain client timesout while another
will wait. We should define some time limits for this.
Then a server can know that a request needs to be
adressed in a certain time. If the server processing
takes to long time the server can send a 1xx code to
indicate the request as being under processing. 

The SIP spec can provide hints on how to solve this.
 

----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=377744&aid=770522&group_id=23194




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Subject: Re: [MMUSIC] stream switching
To: Magnus Westerlund <magnus.westerlund@ericsson.com>
Cc: mmusic@ietf.org
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Magnus, you wrote:

>Hi Philippe,
>

   Hi Magnus, thank you for the feedback! It will definetely help
   me in the job of improving this draft.

>
>I have now had time to read your requirements draft and has some
>comments about this. I also have been rather heavily involved in the
>work within 3GPP to define bit-rate and content-rate adaptation so I
>have some comments based on this work.
>
>First, the goal of the stream switching work is in my opinion to:
>- Enable the receiver to receive interrupt free media at highest
>possible quality.
>

   sure, if this is not obvious from the "requirement" draft then I
   need to reword the introduction!

>To enable this the complete system must ensure the following things:
>- Congestion Control or rather adapting transmission rates to available
>network rate => avoiding high packet loss rates that severely effect
>quality.

   yes

>- Avoid that the receivers buffers either under flow (causes interrupt)
>or overflow (show up as packet loss).
>

   yes, this is fundamental for seamless-ness

>Based on this one can arrive at the conclusion that the media or content
>rate must be adapted, otherwise the underflow condition will be
>impossible to avoid. If one performs content adaptation towards lower
>bit-rates one must also perform adaptation towards higher rates.
>

   I am not sure about this "must", could it be that your are
   considering differently media rate and transmission rate ?

   because I am not considering changing the transmission rate (as a
   end-to-end application issue) => stream switching is only about
   changing the *media* rate.

   what I want to mean is you dont *need* to increase the media rate
   to avoid undeflows but instead you may *want* to increase the
   media rate in order to improve the user experience in terms of
   image quality...

>This I think is the basic requirement and assumptions that apply to your
>requirements draft.
>
>Based on this any solution can be divided up into different
>functionality blocks:
>
>- Transmission rate control, this functionality ensures that a sender
>does not send more data then the network can transport without being to
>unfair, or overflow network buffers.
>

   hum, again i prefer the term "media rate control" if you dont mind?

>- Receiver buffer control, this functionality ensure that one does not
>overflow the client's receiver buffers.
>

   yes, not sure there is much to "do" there in terms of IETF spec?


>- Content rate control, functionality to ensure that the transmitted
>date fits the available network rate, while at the same time ensure that
>the receiver buffer does not underflow.
>

   yes! this is stream switching principle, but again it is about
   "media rate", not changing the transmission rate.

>Based on this functionality blocks one can use one or several
>protocols/solutions to realize them. They do not need to be separate and
>can utilize information enabled by any of the other functionality
>blocks. However I believe that all parts must be present to have a
>complete solution. Also how to realize the solutions is a not fixed by
>this.
>
>I would suggest that one tries to group the requirements regarding which
>of the functionalities they address.
>

   Which groups would you suggest ?


>When one comes to solution one must start discussing what control
>paradigm one desires, as it will heavily influence the solution. Three
>different ones are:
>- Server controlled: In this the server is the responsible for all
>decisions regarding the adaptation. The client simply reports certain
>measurements that the server interprets.
>
>- Client controlled: The client makes the decisions and interpretations
>of what it see. Then it issues commands to the server that it must
>follow. The server is a simple slave.
>

   slave, yes, but a slave that *could* refuse to obey ;-) e.g. as
   discussed in my draft for rate control a server must be allowed to
   deny a request for a higher data rate...


>- Hybrid control: In a hybrid control scenario both client and servers
>makes decisions and interpretations of the data.
>
>I will not try to compare these solutions this if for future
>discussions. If one is interested in a server controlled solution one
>can look at the latest proposal in 3GPP SA4:
>http://www.3gpp.org/ftp/tsg_sa/WG4_CODEC/TSGS4_27/Docs/S4-030501.zip
>Look at the buffer reporting mode variant. This proposal provides
>receiver buffer control and content rate control. The transmission rate
>control is handled through RTCP reports with enabled extended reports of
>packet loss vectors.
>

   I have to say that using such RTCP extensions looks very much like
   "client control" to me ;-) but I dont really care about the
   terminology ;-)


>
>Some more direct comments on the draft:
>
>1. Introduction: The encoding could be done in real time allowing
>maximum flexibility in the produced content rate. However this is may
>not result in optimal encodings and are also very resource demanding for
>a server.
>


   yes, I did not mention this possibility because in large scale
   media distribution this would effectively require one "production"
   encoder per client, which is -even in several years from now- way
   beyond the cost points for this type of products.


>2. Section 2.1.1 and 2.1.2: I think the behaviour in this case should
>really be depending on the operators policies. I would not like to have
>my expensively paid on demand video reduced in quality if this network
>is of the type you describe. However I can see that we should enable this.


   Yes, you are right, all this assumes the correct commercial
   agreements are in place. Our experience is however that a end user
   always prefers a continuous playback, even a degraded one,
   providing that the degradation is "resonable", all other solutions
   including "freezes" for rebuffereing are not acceptable for the
   wide public who is accustomed to TV ;-(

From an IETF point of view (hey, just giving my own opinion ;-)
I think it would be a good idea that implementations *by default*
would "behave a la TFRC" rather than what we have today,
because otherwise -as sally floyd pointed out this morning-
we would run into rather nasty trouble.


>
>3. Section 2.2: I think you need to be a bit more clear that this is one
>example of a service. Also the AMR rate of 5 kbps is a bit to low. The
>4.75 kbps mode has a quality that is not the best. However to achieve
>this bit-rate you must only send one AMR packet every 1.28 seconds,
>which means 64 amr frames per packet. This is not realistic as every
>packet will be required to reach the receiver to achieve acceptable
>quality. I would think that reasonable AMR qualities are using at least
>10 packet every second, meaning that a header overhead of 3 kbps.
>

   right.

>4. Section 2.5: I think this section assumes something that are not
>quite true. First the impossibility to signal this rate switch using
>current protocols.

   What *is* impossible is to find a comprehensive spec for stream
   switching !-) and it is my intention to provide one, i would love to
   "use the current protocols"!

>I claim it is possible but most likely not supported
>by any available client.

   And that would be the point in writing that spec...

>To signal the rate switch in SDP you present
>one different RTP payload types for each codec and configuration, most
>likely at least 4 maybe 5. The 40 and 50 kbps AAC stereo may be possible
>to encode using the same AAC configuration. The declared payload types
>are present in a SDP. A client shall not accept the session and setup
>the media stream unless it can handle all these codecs. If it has setup
>this media stream it has in fact accepted that any of the codec may be
>used in the media stream.
>

   well, I completely agree that *that* may be a solution to stream
   switching, the point then would be to document it!-)


>The server can here use different strategies when switching. The most
>likely one is to use a single SSRC and in the same RTP sequence number
>and timestamp space send the selected media quality.

   agreed, this is a very nice possibility...that obvioulsy we would
   need to *seriouly* document ... because this is not the "default"
   thing at all from existing specs, right?


>When the server
>switched this will be indicated by the new RTP PT. This has a slight
>problem as RTP/RTCP does not handle switched RTP TS rate perfectly. The
>client may in fact lose synchronization until it receives a RTCP packet
>after the switch has taken place.

   right! that is a key issue!

>This happens if the packet where the
>RTP TS rate switches is lost. This is not a problem as long as the RTP
>TS rate before and after the payload type switch has the same TS rate.
>In other words not a problem for any video codec which all runs at
>90000.

   yes, not a problem *if* (as mentionned above) you mandate the same
   RTPTS space for all streams ...

>This is more a problem for audio codecs. I would in fact try to
>address this problem with audio codecs by ensuring that any audio codec
>is allowed to select a RTP TS rate that is a even rate multiple of its
>native value. This would allow audio codecs to run at a the smallest
>common denominator rate.
>

   Is it always possible/efficient?

>The other strategy at points of switching would be to use different
>SSRCs. This would violate the semantics that a SSRC represents a certain
>source. This also has some problems with the synchronization of the
>different SSRCs. This can't be done in RTSP as RTSP due to an erroneous
>definition of RTP-Info did not map each synchronization information to
>the SSRC. This can only be fixed through a new header due to backwards
>compatibility problems. Otherwise RTCP could be used. By sending SR for
>all SSRC one could in fact ensure that the synchronization is available.
>It will utilize more RTCP bandwidth.
>

Hum, so we should disregard this option?

>5. Section 3.1.2: I don't think you should mix congestion control with
>adaptation control that hard. In my opinion, how drastic a content rate
>change is needed and how much depends on the clients buffer status.
>

sorry, I do not understand that one?

>6. Section 3.2.1: I think this directly falls under Transmission rate
>control and is a function of the congestion control mechanism.
>
>7. Section 3.2.2.1: I don't think that this is a valid requirement. This
>is clearly an option that must be available. The controlling entity can
>trade off sending new data against retransmitting lost data. This trade
>off needs to be available to maximize quality. Further this can be done
>without causing congestion as long as the sender keeps to the available
>network rate. This is why splitting the functionality into different
>functionality blocks are so important. By having this model one can see
>that a server can have network rate N(t), content rate C(t) and
>retransmission rate R(t). The controlling entity must ensure that
>C(t)+R(t) <= N(t). Further the clients buffer allows that on short time
>scales R(t) can be equal to N(t) as long as enough data are available in
>the clients buffer.


   fully aggreed, the point was to explain that FEC increases the
   data rate (which a lot of people seem not to be aware of !-) but I
   agree recommending "not using FEC" is too blunt


>
>8. Section 3.7: I don't think we can deploy a solution for switching
>that gives full functionality and at the same time is backwards
>compatible. However think on how one can maintain some of the
>functionality and being backwards compatible may be a worth the effort.
>However this is rather a design evaluation criteria than a requirement.
>

   do you mean it is not appropriate to have backward compatibility as
   a requirement?





Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com



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Hi Phillipe,

I hope that I can clarify anything that was unclear. I also has some 
further comments, see below.

philippe.gentric@philips.com wrote:

>Magnus, you wrote:
>  
>
>>To enable this the complete system must ensure the following things:
>>- Congestion Control or rather adapting transmission rates to available
>>network rate => avoiding high packet loss rates that severely effect
>>quality.
>>    
>>
>
>   yes
>
>  
>
>>- Avoid that the receivers buffers either under flow (causes interrupt)
>>or overflow (show up as packet loss).
>>
>>    
>>
>
>   yes, this is fundamental for seamless-ness
>
>  
>
>>Based on this one can arrive at the conclusion that the media or content
>>rate must be adapted, otherwise the underflow condition will be
>>impossible to avoid. If one performs content adaptation towards lower
>>bit-rates one must also perform adaptation towards higher rates.
>>
>>    
>>
>
>   I am not sure about this "must", could it be that your are
>   considering differently media rate and transmission rate ?
>  
>

What I mean is that if the available transmission rate is less the media 
rate then you on some time scale if nothing changes you will empty your 
buffer. Therefore you "must" change the media rate to avoid this or have 
interrupts. I don't know about any other solution.

>   because I am not considering changing the transmission rate (as a
>   end-to-end application issue) => stream switching is only about
>   changing the *media* rate.
>

I don't think you can exclude the transmission rate from the equation. 
In my opinion you need to consider transmission rate, receiver buffers, 
and the media rate all together.

>
>   what I want to mean is you dont *need* to increase the media rate
>   to avoid undeflows but instead you may *want* to increase the
>   media rate in order to improve the user experience in terms of
>   image quality...
>
I am not sure what you mean, but I guess the following. In cases you are 
not transmission rate limited one is not required to increase the media 
rate, however it is commonly desired. I can agree that there are some 
need to allow the receiver to specify what is allowed in respect to 
media rate modifications.

>
>  
>
>>This I think is the basic requirement and assumptions that apply to your
>>requirements draft.
>>
>>Based on this any solution can be divided up into different
>>functionality blocks:
>>
>>- Transmission rate control, this functionality ensures that a sender
>>does not send more data then the network can transport without being to
>>unfair, or overflow network buffers.
>>
>>    
>>
>
>   hum, again i prefer the term "media rate control" if you dont mind?
>

No, I don't think you completely understand. In a system where the 
buffer space is known you don't have to transmit the data in the same 
rate as the media rate. Due to the buffer one can during some parts of 
the session transmit data at rates that are both higher and lower than 
the media rate. However when doing this you need to ensure that you are 
not under or overflowing the receiver buffer. What you try to do is to 
simplify this system to basically say that the transmission rate is 
equal to media rate which I think prevents better performance.

If any one does not understand this, please prod me and I will try to 
provide a better explanation of the complete system.

>
>  
>
>>- Receiver buffer control, this functionality ensure that one does not
>>overflow the client's receiver buffers.
>>
>>    
>>
>
>   yes, not sure there is much to "do" there in terms of IETF spec?
>

There is nothing in IETF that allows feedback or even specification 
about the receiver buffers to or by the sending side. This is analogous 
to TCP's receiver window that allow to control the flow of media.

>
>
>  
>
>>- Content rate control, functionality to ensure that the transmitted
>>date fits the available network rate, while at the same time ensure that
>>the receiver buffer does not underflow.
>>
>>    
>>
>
>   yes! this is stream switching principle, but again it is about
>   "media rate", not changing the transmission rate. 
>

This I can agree is what you describe as media rate control. By 
selecting or controlling the media rate one can meet the requirements of 
transmission rate and receiver buffers.

>
>  
>
>>Based on this functionality blocks one can use one or several
>>protocols/solutions to realize them. They do not need to be separate and
>>can utilize information enabled by any of the other functionality
>>blocks. However I believe that all parts must be present to have a
>>complete solution. Also how to realize the solutions is a not fixed by
>>this.
>>
>>I would suggest that one tries to group the requirements regarding which
>>of the functionality's they address.
>>
>>    
>>
>
>   Which groups would you suggest ?
>

Some suggestions would be:

Media requirements: Requirements to prevent the media from being 
corrupted or worsen quality, like limited packet losses, gap free 
switching, RAP,etc.

Signalling requirements: Requirements that are a related to what the 
signalling mechanism needs to achieve.

System requirements: Requirements that have more general feeling, like 
backwards compatibility, etc.
 

>
>
>  
>
>>When one comes to solution one must start discussing what control
>>paradigm one desires, as it will heavily influence the solution. Three
>>different ones are:
>>- Server controlled: In this the server is the responsible for all
>>decisions regarding the adaptation. The client simply reports certain
>>measurements that the server interprets.
>>
>>- Client controlled: The client makes the decisions and interpretations
>>of what it see. Then it issues commands to the server that it must
>>follow. The server is a simple slave.
>>
>>    
>>
>
>   slave, yes, but a slave that *could* refuse to obey ;-) e.g. as
>   discussed in my draft for rate control a server must be allowed to
>   deny a request for a higher data rate...
>
>  
>
In a true client control paradigm, this may not even be true. But the 
basic point is that the requirements may motivate the choice, but we 
should not choice a a paradigm and then write the requirements to fulfil 
them. I have a rather long list of comments to when this discussion 
needs to be started.

>  
>
>>- Hybrid control: In a hybrid control scenario both client and servers
>>makes decisions and interpretations of the data.
>>
>>I will not try to compare these solutions this if for future
>>discussions. If one is interested in a server controlled solution one
>>can look at the latest proposal in 3GPP SA4:
>>http://www.3gpp.org/ftp/tsg_sa/WG4_CODEC/TSGS4_27/Docs/S4-030501.zip
>>Look at the buffer reporting mode variant. This proposal provides
>>receiver buffer control and content rate control. The transmission rate
>>control is handled through RTCP reports with enabled extended reports of
>>packet loss vectors.
>>
>>    
>>
>
>   I have to say that using such RTCP extensions looks very much like
>   "client control" to me ;-) but I dont really care about the
>   terminology ;-)
>

Actually the mechanism in my opinion is very server controlled. The 
client provides the server side with some parameters telling it what to 
achieve. Then the client provides regular feedback to allow the server 
to run the algorithms and control the whole system.

>
>
>  
>
>>Some more direct comments on the draft:
>>
>>1. Introduction: The encoding could be done in real time allowing
>>maximum flexibility in the produced content rate. However this is may
>>not result in optimal encodings and are also very resource demanding for
>>a server.
>>
>>    
>>
>
>
>   yes, I did not mention this possibility because in large scale
>   media distribution this would effectively require one "production"
>   encoder per client, which is -even in several years from now- way
>   beyond the cost points for this type of products.
>  
>
I think that spending two sentences on this is useful, just to make it 
clear that it has been considered but has significant problems.

>
>  
>
>>2. Section 2.1.1 and 2.1.2: I think the behaviour in this case should
>>really be depending on the operators policies. I would not like to have
>>my expensively paid on demand video reduced in quality if this network
>>is of the type you describe. However I can see that we should enable this.
>>    
>>
>
>
>   Yes, you are right, all this assumes the correct commercial
>   agreements are in place. Our experience is however that a end user
>   always prefers a continuous playback, even a degraded one,
>   providing that the degradation is "resonable", all other solutions
>   including "freezes" for rebuffereing are not acceptable for the
>   wide public who is accustomed to TV ;-(
>
>From an IETF point of view (hey, just giving my own opinion ;-)
>I think it would be a good idea that implementations *by default*
>would "behave a la TFRC" rather than what we have today,
>because otherwise -as sally floyd pointed out this morning-
>we would run into rather nasty trouble.
>

Yes, I agree that over any best effort network you need some type of 
congestion avoidance. So default behaviour is good, however we must also 
allow for systems that has QoS agreements.

>
>
>  
>
>>3. Section 2.2: I think you need to be a bit more clear that this is one
>>example of a service. Also the AMR rate of 5 kbps is a bit to low. The
>>4.75 kbps mode has a quality that is not the best. However to achieve
>>this bit-rate you must only send one AMR packet every 1.28 seconds,
>>which means 64 amr frames per packet. This is not realistic as every
>>packet will be required to reach the receiver to achieve acceptable
>>quality. I would think that reasonable AMR qualities are using at least
>>10 packet every second, meaning that a header overhead of 3 kbps.
>>
>>    
>>
>
>   right.
>
>  
>
>>4. Section 2.5: I think this section assumes something that are not
>>quite true. First the impossibility to signal this rate switch using
>>current protocols.
>>    
>>
>
>   What *is* impossible is to find a comprehensive spec for stream
>   switching !-) and it is my intention to provide one, i would love to
>   "use the current protocols"!
>
>  
>
>>I claim it is possible but most likely not supported
>>by any available client.
>>    
>>
>
>   And that would be the point in writing that spec...
>
>  
>
>>To signal the rate switch in SDP you present
>>one different RTP payload types for each codec and configuration, most
>>likely at least 4 maybe 5. The 40 and 50 kbps AAC stereo may be possible
>>to encode using the same AAC configuration. The declared payload types
>>are present in a SDP. A client shall not accept the session and setup
>>the media stream unless it can handle all these codecs. If it has setup
>>this media stream it has in fact accepted that any of the codec may be
>>used in the media stream.
>>
>>    
>>
>
>   well, I completely agree that *that* may be a solution to stream
>   switching, the point then would be to document it!-)
>  
>

Good, then you should rather document this deficiency rather than 
claiming that it is possible.

>
>  
>
>>The server can here use different strategies when switching. The most
>>likely one is to use a single SSRC and in the same RTP sequence number
>>and timestamp space send the selected media quality.
>>    
>>
>
>   agreed, this is a very nice possibility...that obvioulsy we would
>   need to *seriouly* document ... because this is not the "default"
>   thing at all from existing specs, right?
>
>  
>

I have seen it as being the default behaviour, however this is nothing 
that has been thoroughly discussed in AVT and the RTP spec not be that 
clear on this point. Documenting this would be a good thing.

>  
>
>>When the server
>>switched this will be indicated by the new RTP PT. This has a slight
>>problem as RTP/RTCP does not handle switched RTP TS rate perfectly. The
>>client may in fact lose synchronization until it receives a RTCP packet
>>after the switch has taken place.
>>    
>>
>
>   right! that is a key issue!
>
>  
>
>>This happens if the packet where the
>>RTP TS rate switches is lost. This is not a problem as long as the RTP
>>TS rate before and after the payload type switch has the same TS rate.
>>In other words not a problem for any video codec which all runs at
>>90000.
>>    
>>
>
>   yes, not a problem *if* (as mentioned above) you mandate the same
>   RTPTS space for all streams ...
>
>  
>
>>This is more a problem for audio codecs. I would in fact try to
>>address this problem with audio codecs by ensuring that any audio codec
>>is allowed to select a RTP TS rate that is a even rate multiple of its
>>native value. This would allow audio codecs to run at a the smallest
>>common denominator rate.
>>
>>    
>>
>
>   Is it always possible/efficient?
>

No, not for the currently specified RTP payload formats. It is something 
I will recommend in future payload formats to allow for this functionality.

>
>  
>
>>The other strategy at points of switching would be to use different
>>SSRCs. This would violate the semantics that a SSRC represents a certain
>>source. This also has some problems with the synchronization of the
>>different SSRCs. This can't be done in RTSP as RTSP due to an erroneous
>>definition of RTP-Info did not map each synchronization information to
>>the SSRC. This can only be fixed through a new header due to backwards
>>compatibility problems. Otherwise RTCP could be used. By sending SR for
>>all SSRC one could in fact ensure that the synchronization is available.
>>It will utilize more RTCP bandwidth.
>>
>>    
>>
>
>Hum, so we should disregard this option?
>

I think so.

>
>  
>
>>5. Section 3.1.2: I don't think you should mix congestion control with
>>adaptation control that hard. In my opinion, how drastic a content rate
>>change is needed and how much depends on the clients buffer status.
>>
>>    
>>
>
>sorry, I do not understand that one?
>

This has to do with the complete system that a sender can transmit at 
one rate, while the media rate has another rate. The discrepancy is 
handled by the receiver buffer. Therefore the control of the media rate 
can be performed more drastic or not depending on what the buffer status 
is. An almost empty receiver buffer needs to be handled quickly and 
drastically, probably be reducing the media rate significantly. If the 
buffer are rather full the handling of this can be much less drastic, a 
small discrepancy can simply be tried to waited out. Or the quality 
change can be minimal.

>  
>
>
>  
>
>>8. Section 3.7: I don't think we can deploy a solution for switching
>>that gives full functionality and at the same time is backwards
>>compatible. However think on how one can maintain some of the
>>functionality and being backwards compatible may be a worth the effort.
>>However this is rather a design evaluation criteria than a requirement.
>>
>>    
>>
>
>   do you mean it is not appropriate to have backward compatibility as
>   a requirement?
>
>  
>

It might, however I think it should be further considered. I think 
listing the level as critical is to high level.

Cheers

Magnus Westerlund



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To: mmusic@ietf.org
Cc: csp@csperkins.org
X-face: #V(jdpv[lI!TNUU=2*oh:="#suS*ponXW"yr6G;~L}<xZn_2^0)V{jqdc4y}@2b]ffd}SY#
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From: Pekka Pessi <pessi@iki.fi>
Reply-To: pessi@iki.fi
In-Reply-To: <200305231412.KAA06476@ietf.org> ("Internet-Drafts@ietf.org"'s
 message of "Fri, 23 May 2003 10:12:53 -0400")
References: <200305231412.KAA06476@ietf.org>
Date: Mon, 14 Jul 2003 18:05:41 +0300
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Subject: [MMUSIC] Inconsistency in draft-ietf-mmusic-sdp-new-13.txt
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	Hello all,

	In the sdp-new, there seems to be a contradiction between the
	ABNF definition of "token-char" and comments after the
	definition:

      token-char =          %x21 / %x23-27 / %x2A-2B / %x2D-2E / %x30-39
                            / %x41-5A / %x5E-7E
                            ; definition from RFC 2045 -
                            ; "any (US-ASCII) CHAR except SPACE, CTLs,
                            ; or tspecials".
                            ; the tspecials are ()<>@,;:

	According to the ABNF, the tspecials include quote (%22, "),
	slash (%2F, /), equal (%3D, =), question mark (%3f, ?), square
	brackets (%5B, [ and %5D, ]), and backslash (%5C, \), too:

                            ; the tspecials are ()/<>@,;:"=?[\]

	As it looks like that the sdp-new-14 is recycled once more, so
	it is possible to fix the comment there (or ABNF, if that is
	more appropriate).

					--Pekka

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Subject: [MMUSIC] RTSP & NAT discussion on wednesday and thursday.
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Hi,

On wednesday at dinner time there will be a as proposed in the MMUSIC 
agenda an RTSP discussion meeting. The preliminary meeting place is in 
the main foyer near the registration counter at 17.30-17.40. We will try 
to put together an agenda for this meeting during tomorrow.

However this mail is about something else, namely the RTSP and NAT 
traversal document. This is a preparation for what will be further 
discussed during wednesday and thursday and concerns open issues.

Issue number one: What is the goal of the RTSP & NAT document. This has 
previous been communicated as documenting solutions that do not require 
further standardization and to give guidelines for RTSP ALGs and how to 
handle firewalls.

However it is evident that we need a solution for traversal of symmetric 
NATs for RTSP. As all known possible solutions requires server side 
extensions to work, further requirements for this work should be 
considered.

Possible other considerations for this work is:

- Enable RTSP servers to be placed behind a NAT. Will allow for 
implementing RTSP server for other purposes than on-demand content and 
provide a richer usage of RTSP.

- Provide mitigation of the RTP DoS attack threat. It can't be 
completely solved, however it can be severely limited to only be 
possible to perform by attackers that can hijack traffic inside a 
network. And as a an attacker having this possibilities can do many 
other really bad stuff, this is probably enough.

- Do not worsen security. We should do anything to avoid worsening 
security for RTSP.

- Have only a single solution to provide interoperability and incentive 
to implement this solution.

- Consider complexity of operations and implementation for any proposal.

- Time to availability of solution.

So please consider if you have any further requirements that should be 
consider for this work. We should in the next weeks have some consensus 
on what work we should perform regarding the solution for symmetric NATs 
and RTSP. The result of this discussion will be used to decide on what 
solution to select.

The current proposals to a solution for the symmetric NAT traversal are:

- Symmetric RTP
- Co-located STUN
- ICE for RTSP


They are documented in the draft-ietf-mmusic-rtsp-nat-01.txt. Please 
read and comment so that we can start putting an analysis together.

Best Regards

Magnus






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From: Bill May <wmay@cisco.com>
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Subject: Re: [MMUSIC] Aggregate Control URI
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Thomas,

I think that we can agree that this new specification would not be
backward compatible with existing RTSP session.

To me, it does not seem like for good reason.  Not enough bang for the
buck, but perhaps I am still missing something.

As long as you are aware of this and have done so intentionally, that's
cool.  But IMO, I would not not be making these changes (adding MUTE,
requiring PLAY/PAUSE to be aggregate as opposed to stream based) in
order to make wording or a state machine clearer.

In fact, the MUTE complicates the state machine in the exact same way
that a non-aggregate PAUSE does.

More below:

Thomas Zeng wrote:
>>I can see a scenario where you might want to stop the video, but still
>>maintain
>>the audio.  In this case, you have 2 or more streams running, and the
>>client
>>wishes to stop 1 of them.  This is a perfectly legal scenario.
> 
> 	[Thomas Zeng]  There are two ways to do what you want here: 1) issue
> teardown on the audio track. 2) perform a MUTE on the audio track.

Doesn't teardown now need to be aggregate ?  So that wouldn't work.


>>Can you please expand on why it doesn't make sense to allow streams to
>>be controlled seperately ?  I've done most of my work on the player side
>>with
>>the idea that the streams could be seperate, so most likely I'm missing
>>something.
> 
> 	[Thomas Zeng]  If two streams belong to same RTSP session, and you
> issue PLAY on one stream, what would be the state of the overall session ?
> what would be the NPT  (Normal Play Time) of the session? If I recall
> correctly, if PLAY/PAUSE were allowed on each track in a mutli-tracked RTSP
> session, the RTSP state machine would break.

I'm not sure that I understand why the state of the session is important.
The server would be issueing the required streams.

The NPT of the session would be whatever the player decided it would be -
it can derive this from the RTPInfo, and decide how it wants to deal with it.

Are you defining a specification on how to develop a server (which is what
a state machine would imply) ?  Or a method of interoperability ?


>>Why ?  To me, aggregate (or control of the entire session) control and
>>non-aggregate control (or control based on each stream) can be used
>>at the same time, and should be allowed.
> 
> 	[Thomas Zeng]  Yes, you are right here. The decision by the RTSP
> task force was to let PLAY/PAUSE be aggregate, while SETUP/TEARDOWN and
> MUTE/UNMUTE be non-aggregate (note MUTE/UNMUTE is defined as an extension to
> RTSP core spec).

I'm not sure I understand still why MUTE is needed.  All it does is PAUSE
a single stream.  The MUTE complicates the RTSP server state machine in exactly
the same way that a non-aggregate PAUSE down.

It's the same thing called something different.


>>I guess I'm not understanding why this would be difficult.  The only
>>limitation would be that the timeline must be consistent across all
>>streams.  Otherwise, control the streams to your heart's content.
> 
> 	[Thomas Zeng]  Here the concern is on RTSP state machine.

Which still has the same complications with the MUTE.

Bill May


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From: Tom Marshall <tmarshall@real.com>
To: Magnus Westerlund <magnus.westerlund@ericsson.com>
Cc: mmusic@ietf.org
Subject: Re: [MMUSIC] RTSP & NAT discussion on wednesday and thursday.
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> So please consider if you have any further requirements that should be=20
> consider for this work. We should in the next weeks have some consensus=
=20
> on what work we should perform regarding the solution for symmetric NATs=
=20
> and RTSP. The result of this discussion will be used to decide on what=20
> solution to select.

Perhaps I misread this, but it sounds like you are saying that we should
agree on one traversal solution.  I thought the RTSP NAT document was
intended (and does) present the various NAT traversal solutions along with
their strengths and weaknesses, and let the implemetors decide which to use?

--=20
=2E..if the church put in half the time on covetousness that it does on lus=
t,
 this would be a better world.
        -- Garrison Keillor, "Lake Wobegon Days"

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Tom Marshall wrote:

>  > So please consider if you have any further requirements that should be
>  > consider for this work. We should in the next weeks have some consensus
>  > on what work we should perform regarding the solution for symmetric NATs
>  > and RTSP. The result of this discussion will be used to decide on what
>  > solution to select.
> 
> Perhaps I misread this, but it sounds like you are saying that we should
> agree on one traversal solution.  I thought the RTSP NAT document was
> intended (and does) present the various NAT traversal solutions along with
> their strengths and weaknesses, and let the implemetors decide which to 
> use?

You need to be really careful with approaches like that. The problem 
is interoperability. Unless you agree on a mandatory to implement 
mechanism, you will have problems. Furthermore, it makes it hard to 
use the same client in deployments where one solution vs. another 
would be the optimal one. We have suffered alot on both these points 
in sip, where sip clients work in specific cases dependenting on which 
nat solution they have used. It has been a real barrier to deployment.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com


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Hi Bill,


Bill May wrote:

> Thomas,
>
> I think that we can agree that this new specification would not be
> backward compatible with existing RTSP session. 


To my knowledge the changes result in a subset of the functionality that 
RFC 2326 specifies. This subset is working in this regard the same way 
the original specification. In our discussion there where no 
implementations that actually use the functionality of having individual 
PLAY/PAUSE in a aggregated session. The reason of the change was 
basically get the protocol to be interoperable. There where so many 
strange things when you allow individual media control within an 
aggregated session. By requiring all media control methods (PLAY and 
PAUSE) to work on the aggregated the whole issue was resolved and 
everything becomes consistent. So the interoperability issues of this 
change seem minor and the client will get clear indications through 
error codes that it attempts something not allowed by the server.

>
>
> To me, it does not seem like for good reason.  Not enough bang for the
> buck, but perhaps I am still missing something.
>
> As long as you are aware of this and have done so intentionally, that's
> cool.  But IMO, I would not not be making these changes (adding MUTE,
> requiring PLAY/PAUSE to be aggregate as opposed to stream based) in
> order to make wording or a state machine clearer.
>
> In fact, the MUTE complicates the state machine in the exact same way
> that a non-aggregate PAUSE does. 


No it doesn't. As MUTE/UNMUTE only switch on and off the media delivery 
and do not effect the timing of the state and in what state machine 
state it is, it does not complicate things.

>
>
> More below:
>
> Thomas Zeng wrote:
>
>>> I can see a scenario where you might want to stop the video, but still
>>> maintain
>>> the audio.  In this case, you have 2 or more streams running, and the
>>> client
>>> wishes to stop 1 of them.  This is a perfectly legal scenario.
>>
>>
>>     [Thomas Zeng]  There are two ways to do what you want here: 1) issue
>> teardown on the audio track. 2) perform a MUTE on the audio track.
>
>
> Doesn't teardown now need to be aggregate ?  So that wouldn't work. 


Teardown can be used both aggregated and non aggregated.

>
>
>
>>> Can you please expand on why it doesn't make sense to allow streams to
>>> be controlled separately ?  I've done most of my work on the player 
>>> side
>>> with
>>> the idea that the streams could be seperate, so most likely I'm missing
>>> something.
>>
>>
>>     [Thomas Zeng]  If two streams belong to same RTSP session, and you
>> issue PLAY on one stream, what would be the state of the overall 
>> session ?
>> what would be the NPT  (Normal Play Time) of the session? If I recall
>> correctly, if PLAY/PAUSE were allowed on each track in a 
>> mutli-tracked RTSP
>> session, the RTSP state machine would break.
>
>
> I'm not sure that I understand why the state of the session is important.
> The server would be issueing the required streams. 


Have you tried to implement a correct minimal implementation of the RFC 
2326 defined RTSP server? If you had I don't think you would ask this 
question. When I performed the implementation this resulted in a 50+ 
questions regarding how things should work that directly related to 
expected behaviour and interoperability.

>
>
> The NPT of the session would be whatever the player decided it would be -
> it can derive this from the RTPInfo, and decide how it wants to deal 
> with it. 


I don't think it is this simple. In a session with two aggregated 
session you will have actually three different playout clocks if you 
allow individual PLAY/PAUSE.
- The aggregated session playout time
- Media 1 playout time
- media 2 playout time.

When you perform an individual PLAY on a pause media using the media URL 
what should happened, what timers should be started? If you after that 
performs an aggregated PLAY, does that replace the previous media 
playout, or does it only start all not already running media? This is a 
rat hole.

>
>
> Are you defining a specification on how to develop a server (which is 
> what
> a state machine would imply) ?  Or a method of interoperability ?


This is a interoperability problem and a fix to a under specified part 
of RTSP.

>
>
>>> Why ?  To me, aggregate (or control of the entire session) control and
>>> non-aggregate control (or control based on each stream) can be used
>>> at the same time, and should be allowed.
>>
>>
>>     [Thomas Zeng]  Yes, you are right here. The decision by the RTSP
>> task force was to let PLAY/PAUSE be aggregate, while SETUP/TEARDOWN and
>> MUTE/UNMUTE be non-aggregate (note MUTE/UNMUTE is defined as an 
>> extension to
>> RTSP core spec).
>
>
> I'm not sure I understand still why MUTE is needed.  All it does is PAUSE
> a single stream.  The MUTE complicates the RTSP server state machine 
> in exactly
> the same way that a non-aggregate PAUSE down.
>
> It's the same thing called something different.


Not exactly the same thing. You are correct that MUTE can be realized 
using one RTSP session per media and do all media synchronization at the 
client side. The MUTE/UNMUTE proposal is a separate extension draft and 
will  need further review. You might be correct that MUTE/UNMUTE are not 
in fact needed.


Best Regards

Magnus Westerlund


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From: Magnus Westerlund <magnus.westerlund@ericsson.com>
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To: Jonathan Rosenberg <jdrosen@dynamicsoft.com>
CC: Tom Marshall <tmarshall@real.com>, mmusic@ietf.org
Subject: Re: [MMUSIC] RTSP & NAT discussion on wednesday and thursday.
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Hi Tom and Jonathan,

My goal is in regards to the symmetric NAT solution which requires 
server modifications to only have one solution. However when it comes to 
solution that can be implemented at the client side without server 
modifications or simply servers running the updated RTSP they will all 
be documented.

Best Regards

Magnus

Jonathan Rosenberg wrote:

>
>
> Tom Marshall wrote:
>
>>  > So please consider if you have any further requirements that 
>> should be
>>  > consider for this work. We should in the next weeks have some 
>> consensus
>>  > on what work we should perform regarding the solution for 
>> symmetric NATs
>>  > and RTSP. The result of this discussion will be used to decide on 
>> what
>>  > solution to select.
>>
>> Perhaps I misread this, but it sounds like you are saying that we should
>> agree on one traversal solution.  I thought the RTSP NAT document was
>> intended (and does) present the various NAT traversal solutions along 
>> with
>> their strengths and weaknesses, and let the implemetors decide which 
>> to use?
>
>
> You need to be really careful with approaches like that. The problem 
> is interoperability. Unless you agree on a mandatory to implement 
> mechanism, you will have problems. Furthermore, it makes it hard to 
> use the same client in deployments where one solution vs. another 
> would be the optimal one. We have suffered alot on both these points 
> in sip, where sip clients work in specific cases dependenting on which 
> nat solution they have used. It has been a real barrier to deployment.
>
> -Jonathan R.
>


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Subject: Re: [MMUSIC] Aggregate Control URI
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> >>    [Thomas Zeng]  There are two ways to do what you want here: 1) issue
> >>teardown on the audio track. 2) perform a MUTE on the audio track.
> >
> >
> >Doesn't teardown now need to be aggregate ?  So that wouldn't work.=20
>=20
>=20
> Teardown can be used both aggregated and non aggregated.

I was under the impression that RTSP/1.0 only allowed aggregate TEARDOWN,
while RTSP/1.1 will allow both aggregate and non-aggregate TEARDOWN.

> >I'm not sure I understand still why MUTE is needed.  All it does is PAUSE
> >a single stream.  The MUTE complicates the RTSP server state machine=20
> >in exactly
> >the same way that a non-aggregate PAUSE down.
> >
> >It's the same thing called something different.
>=20
>=20
> Not exactly the same thing. You are correct that MUTE can be realized=20
> using one RTSP session per media and do all media synchronization at the=
=20
> client side. The MUTE/UNMUTE proposal is a separate extension draft and=
=20
> will  need further review. You might be correct that MUTE/UNMUTE are not=
=20
> in fact needed.

I believe we have recently agreed that the RTP time continues while in the
PAUSE state.  Wouldn't this make MUTE and PAUSE pretty much identical?  What
would be the remaining difference(s)?

--=20
One good reason why computers can do more work than people is that they
never have to stop and answer the phone.

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>
>I believe we have recently agreed that the RTP time continues while in the
>PAUSE state.  Wouldn't this make MUTE and PAUSE pretty much identical?  What
>would be the remaining difference(s)?

RTP time continues indeed, but not NPT, whereas I understand MUTE to 
say that NPT is advancing, whereas when paused it is not.  So, after 
play/pause a subsequent play will start where you paused (with RTP 
timestamps advanced by the duration of the pause, but the media 
continuous);  play/mute and then subsequent unmute would unmute 
material that is later in the source content by the the muted 
duration.

right?
-- 
David Singer
Apple Computer/QuickTime

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To: Dave Singer <singer@apple.com>
CC: mmusic@ietf.org
Subject: Re: [MMUSIC] Aggregate Control URI
References: <72263E8E8622D611975C0002B32C19D84A7C57@misty.packetvideo.com> <3F12EB45.7080003@cisco.com> <3F13B2A1.7000000@ericsson.com> <20030715080822.GB25484@real.com> <p05210645bb396c77c1b2@[81.160.227.51]>
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>>
>> I believe we have recently agreed that the RTP time continues while 
>> in the
>> PAUSE state.  Wouldn't this make MUTE and PAUSE pretty much 
>> identical?  What
>> would be the remaining difference(s)?
>
>
> RTP time continues indeed, but not NPT, whereas I understand MUTE to 
> say that NPT is advancing, whereas when paused it is not.  So, after 
> play/pause a subsequent play will start where you paused (with RTP 
> timestamps advanced by the duration of the pause, but the media 
> continuous);  play/mute and then subsequent unmute would unmute 
> material that is later in the source content by the the muted duration.
>
> right? 


Yes, MUTE only specifies that delivery is not performed. If you are in 
PLAY state the NPT time continues to run.

Cheers

Magnus Westerlund


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Subject: Re: [MMUSIC] Aggregate Control URI
To: Magnus Westerlund <magnus.westerlund@ericsson.com>
Cc: mmusic@ietf.org, Bill May <wmay@cisco.com>
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>> I'm not sure I understand still why MUTE is needed.  All it does is PAUSE
>> a single stream.  The MUTE complicates the RTSP server state machine
>> in exactly
>> the same way that a non-aggregate PAUSE down.
>>
>> It's the same thing called something different.
>
>Not exactly the same thing. You are correct that MUTE can be realized
>using one RTSP session per media and do all media synchronization at the
>client side. The MUTE/UNMUTE proposal is a separate extension draft and
>will  need further review. You might be correct that MUTE/UNMUTE are not
>in fact needed.

one difference/advantage is the need to specify a target media time with PLAY,
with MUTE/UNMUTE it could be optional:

for example if I was to SETUP 2 audio streams and MUTE one from the start,
I want to be able after some playback time to send MUTE on the one playing
and UNMUTE on the other one, simultaneously (queued RTSP commands)
, without specifying the target time:
i.e. for the server it means "now" or "asap", and it should make sure that the media
is sent in a way that there is "no gap".

=> it is "aggregate control" in the sense that the server must be aware of the NPT relationship
between these two streams

=> it is like when you aggregate PLAY audio and video
the server must send audio and video data that are at the same (NPT) media time.

(BTW this would also be a useful step for stream switching;-)

regards,


Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com


                                                                                                                                           
                                                                                                                                           
                                                       To:   Bill May <wmay@cisco.com>                                                     
                                                       cc:   mmusic@ietf.org                                                               
                                                        (bcc: Philippe Gentric/MP4-SUR/CE/PHILIPS)                                         
                                                       Subject:    Re: [MMUSIC] Aggregate Control URI                                      
               Magnus Westerlund                                                                                                           
               <magnus.westerlund@ericsson.            Classification:                                                                     
               com>                                                                                                                        
                                                                                                                                           
               Sent by:                                                                                                                    
               mmusic-admin@ietf.org                                                                                                       
                                                                                                                                           
               15/07/2003 09:52                                                                                                            
                                                                                                                                           
                                                                                                                                           




Hi Bill,


Bill May wrote:

> Thomas,
>
> I think that we can agree that this new specification would not be
> backward compatible with existing RTSP session.


To my knowledge the changes result in a subset of the functionality that
RFC 2326 specifies. This subset is working in this regard the same way
the original specification. In our discussion there where no
implementations that actually use the functionality of having individual
PLAY/PAUSE in a aggregated session. The reason of the change was
basically get the protocol to be interoperable. There where so many
strange things when you allow individual media control within an
aggregated session. By requiring all media control methods (PLAY and
PAUSE) to work on the aggregated the whole issue was resolved and
everything becomes consistent. So the interoperability issues of this
change seem minor and the client will get clear indications through
error codes that it attempts something not allowed by the server.

>
>
> To me, it does not seem like for good reason.  Not enough bang for the
> buck, but perhaps I am still missing something.
>
> As long as you are aware of this and have done so intentionally, that's
> cool.  But IMO, I would not not be making these changes (adding MUTE,
> requiring PLAY/PAUSE to be aggregate as opposed to stream based) in
> order to make wording or a state machine clearer.
>
> In fact, the MUTE complicates the state machine in the exact same way
> that a non-aggregate PAUSE does.


No it doesn't. As MUTE/UNMUTE only switch on and off the media delivery
and do not effect the timing of the state and in what state machine
state it is, it does not complicate things.

>
>
> More below:
>
> Thomas Zeng wrote:
>
>>> I can see a scenario where you might want to stop the video, but still
>>> maintain
>>> the audio.  In this case, you have 2 or more streams running, and the
>>> client
>>> wishes to stop 1 of them.  This is a perfectly legal scenario.
>>
>>
>>     [Thomas Zeng]  There are two ways to do what you want here: 1) issue
>> teardown on the audio track. 2) perform a MUTE on the audio track.
>
>
> Doesn't teardown now need to be aggregate ?  So that wouldn't work.


Teardown can be used both aggregated and non aggregated.

>
>
>
>>> Can you please expand on why it doesn't make sense to allow streams to
>>> be controlled separately ?  I've done most of my work on the player
>>> side
>>> with
>>> the idea that the streams could be seperate, so most likely I'm missing
>>> something.
>>
>>
>>     [Thomas Zeng]  If two streams belong to same RTSP session, and you
>> issue PLAY on one stream, what would be the state of the overall
>> session ?
>> what would be the NPT  (Normal Play Time) of the session? If I recall
>> correctly, if PLAY/PAUSE were allowed on each track in a
>> mutli-tracked RTSP
>> session, the RTSP state machine would break.
>
>
> I'm not sure that I understand why the state of the session is important.
> The server would be issueing the required streams.


Have you tried to implement a correct minimal implementation of the RFC
2326 defined RTSP server? If you had I don't think you would ask this
question. When I performed the implementation this resulted in a 50+
questions regarding how things should work that directly related to
expected behaviour and interoperability.

>
>
> The NPT of the session would be whatever the player decided it would be -
> it can derive this from the RTPInfo, and decide how it wants to deal
> with it.


I don't think it is this simple. In a session with two aggregated
session you will have actually three different playout clocks if you
allow individual PLAY/PAUSE.
- The aggregated session playout time
- Media 1 playout time
- media 2 playout time.

When you perform an individual PLAY on a pause media using the media URL
what should happened, what timers should be started? If you after that
performs an aggregated PLAY, does that replace the previous media
playout, or does it only start all not already running media? This is a
rat hole.

>
>
> Are you defining a specification on how to develop a server (which is
> what
> a state machine would imply) ?  Or a method of interoperability ?


This is a interoperability problem and a fix to a under specified part
of RTSP.

>
>
>>> Why ?  To me, aggregate (or control of the entire session) control and
>>> non-aggregate control (or control based on each stream) can be used
>>> at the same time, and should be allowed.
>>
>>
>>     [Thomas Zeng]  Yes, you are right here. The decision by the RTSP
>> task force was to let PLAY/PAUSE be aggregate, while SETUP/TEARDOWN and
>> MUTE/UNMUTE be non-aggregate (note MUTE/UNMUTE is defined as an
>> extension to
>> RTSP core spec).
>
>
> I'm not sure I understand still why MUTE is needed.  All it does is PAUSE
> a single stream.  The MUTE complicates the RTSP server state machine
> in exactly
> the same way that a non-aggregate PAUSE down.
>
> It's the same thing called something different.


Not exactly the same thing. You are correct that MUTE can be realized
using one RTSP session per media and do all media synchronization at the
client side. The MUTE/UNMUTE proposal is a separate extension draft and
will  need further review. You might be correct that MUTE/UNMUTE are not
in fact needed.


Best Regards

Magnus Westerlund


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Subject: Re: [MMUSIC] RTSP & NAT discussion on wednesday and thursday.
To: Magnus Westerlund <magnus.westerlund@ericsson.com>
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        Tom Marshall <tmarshall@real.com>
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Magnus,

I totally agree with Jonathan,

if we leave the door open to several solutions
you can be sure each of them will be implemented
(because when you have a hammer all the problems are nails;-)
and we will create even more trouble than we already have,
plus a lot of burden on implementers and IOT

plus the risk that we actually produce a mess that will simply not work,
e.g. the problem is that some solutions are aggresive to others
for example an ALG kills STUN, as simple as that
(I have seen that happen recently;-(


So I would really hope we would decide to choose ONE solution,
even if takes longer and creates a few more unhappy people.

regards,


Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com


                                                                                                                                           
                                                                                                                                           
                                                       To:   Jonathan Rosenberg <jdrosen@dynamicsoft.com>                                  
                                                       cc:   Tom Marshall <tmarshall@real.com>                                             
                                                        mmusic@ietf.org                                                                    
                                                        (bcc: Philippe Gentric/MP4-SUR/CE/PHILIPS)                                         
               Magnus Westerlund                       Subject:    Re: [MMUSIC] RTSP & NAT discussion on wednesday and thursday.           
               <magnus.westerlund@ericsson.                                                                                                
               com>                                    Classification:                                                                     
                                                                                                                                           
               Sent by:                                                                                                                    
               mmusic-admin@ietf.org                                                                                                       
                                                                                                                                           
               15/07/2003 10:00                                                                                                            
                                                                                                                                           
                                                                                                                                           




Hi Tom and Jonathan,

My goal is in regards to the symmetric NAT solution which requires
server modifications to only have one solution. However when it comes to
solution that can be implemented at the client side without server
modifications or simply servers running the updated RTSP they will all
be documented.

Best Regards

Magnus

Jonathan Rosenberg wrote:

>
>
> Tom Marshall wrote:
>
>>  > So please consider if you have any further requirements that
>> should be
>>  > consider for this work. We should in the next weeks have some
>> consensus
>>  > on what work we should perform regarding the solution for
>> symmetric NATs
>>  > and RTSP. The result of this discussion will be used to decide on
>> what
>>  > solution to select.
>>
>> Perhaps I misread this, but it sounds like you are saying that we should
>> agree on one traversal solution.  I thought the RTSP NAT document was
>> intended (and does) present the various NAT traversal solutions along
>> with
>> their strengths and weaknesses, and let the implemetors decide which
>> to use?
>
>
> You need to be really careful with approaches like that. The problem
> is interoperability. Unless you agree on a mandatory to implement
> mechanism, you will have problems. Furthermore, it makes it hard to
> use the same client in deployments where one solution vs. another
> would be the optimal one. We have suffered alot on both these points
> in sip, where sip clients work in specific cases dependenting on which
> nat solution they have used. It has been a real barrier to deployment.
>
> -Jonathan R.
>


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From: Thomas Zeng <zeng@PacketVideo.COM>
To: Tom Marshall <tmarshall@real.com>,
        Magnus Westerlund
	 <magnus.westerlund@ericsson.com>
Cc: mmusic@ietf.org
Subject: RE: [MMUSIC] RTSP & NAT discussion on wednesday and thursday.
Date: Tue, 15 Jul 2003 02:25:55 -0700
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Dear Tom:

Yes, we have presented "various NAT traversal solutions along with their
strengths and weaknesses", but some of these solutions happen to require
protocol development (e.g. port co-Located STUN). 

Correct me if I am wrong, but I think none of the off-the-shelf, UDP based
solutions (e.g.,, STUN) work for Symmetric NAT, yet Symmetric NATs are
rather common. Here I don't count TURN and ICE yet since they are only IDs,
and even when they do become RFCs, their complexity seems to be high enough
such that implementors will, as a knee-jerky reaction, fall back to TCP
tunnelling for NAT traversal.

Perhaps  TCP tunnelling is acceptable (Magnus would disgree with me), or
perhaps we could develope a UDP based solution whose complexity is not much
worse than TCP tunnelling?

Then there is RTP DoS problem ...

Hence the change of direction, so to speak.

Cheers,
- thomas





-----Original Message-----
From: Tom Marshall [mailto:tmarshall@real.com]
Sent: Monday, July 14, 2003 11:14 AM
To: Magnus Westerlund
Cc: mmusic@ietf.org
Subject: Re: [MMUSIC] RTSP & NAT discussion on wednesday and thursday.


> So please consider if you have any further requirements that should be 
> consider for this work. We should in the next weeks have some consensus 
> on what work we should perform regarding the solution for symmetric NATs 
> and RTSP. The result of this discussion will be used to decide on what 
> solution to select.

Perhaps I misread this, but it sounds like you are saying that we should
agree on one traversal solution.  I thought the RTSP NAT document was
intended (and does) present the various NAT traversal solutions along with
their strengths and weaknesses, and let the implemetors decide which to use?

-- 
...if the church put in half the time on covetousness that it does on lust,
 this would be a better world.
        -- Garrison Keillor, "Lake Wobegon Days"

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From: Tom Marshall <tmarshall@real.com>
To: Thomas Zeng <zeng@PacketVideo.COM>
Cc: Magnus Westerlund <magnus.westerlund@ericsson.com>, mmusic@ietf.org
Subject: Re: [MMUSIC] RTSP & NAT discussion on wednesday and thursday.
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On Tue, Jul 15, 2003 at 02:25:55AM -0700, Thomas Zeng wrote:
> Dear Tom:
>=20
> Yes, we have presented "various NAT traversal solutions along with their
> strengths and weaknesses", but some of these solutions happen to require
> protocol development (e.g. port co-Located STUN).=20
>=20
> Correct me if I am wrong, but I think none of the off-the-shelf, UDP based
> solutions (e.g.,, STUN) work for Symmetric NAT, yet Symmetric NATs are
> rather common. Here I don't count TURN and ICE yet since they are only ID=
s,
> and even when they do become RFCs, their complexity seems to be high enou=
gh
> such that implementors will, as a knee-jerky reaction, fall back to TCP
> tunnelling for NAT traversal.
>=20
> Perhaps  TCP tunnelling is acceptable (Magnus would disgree with me), or
> perhaps we could develope a UDP based solution whose complexity is not mu=
ch
> worse than TCP tunnelling?
>=20
> Then there is RTP DoS problem ...
>=20
> Hence the change of direction, so to speak.

I believe these are all good arguments for documenting and supporting
Symmetric RTP in the draft:

 - Works through Symmetric NAT.
 - Works through ALGs.
 - Very simple to implement.
 - Does not change DoS threat level.

I believe that Symmetric RTP should be presented as a simple and basic NAT
traversal solution for the case where the server is in the open and the
client may be behind a NAT (the client need not know or care, because using
Symmetric RTP will not break things if it's not really behind a NAT).  We
can then continue on with the more complex cases, such as servers behind
NATs.

--=20
Apathy Club meeting this Friday.  If you want to come, you're not invited.

--cWoXeonUoKmBZSoM
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Subject: Re: [MMUSIC] RTSP & NAT discussion on wednesday and thursday.
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inline.

Tom Marshall wrote:

> On Tue, Jul 15, 2003 at 02:25:55AM -0700, Thomas Zeng wrote:
>  > Dear Tom:
>  >
>  > Yes, we have presented "various NAT traversal solutions along with their
>  > strengths and weaknesses", but some of these solutions happen to require
>  > protocol development (e.g. port co-Located STUN).
>  >
>  > Correct me if I am wrong, but I think none of the off-the-shelf, UDP 
> based
>  > solutions (e.g.,, STUN) work for Symmetric NAT, yet Symmetric NATs are
>  > rather common. Here I don't count TURN and ICE yet since they are 
> only IDs,
>  > and even when they do become RFCs, their complexity seems to be high 
> enough
>  > such that implementors will, as a knee-jerky reaction, fall back to TCP
>  > tunnelling for NAT traversal.
>  >
>  > Perhaps  TCP tunnelling is acceptable (Magnus would disgree with me), or
>  > perhaps we could develope a UDP based solution whose complexity is 
> not much
>  > worse than TCP tunnelling?
>  >
>  > Then there is RTP DoS problem ...
>  >
>  > Hence the change of direction, so to speak.
> 
> I believe these are all good arguments for documenting and supporting
> Symmetric RTP in the draft:
> 
>  - Works through Symmetric NAT.
>  - Works through ALGs.
>  - Very simple to implement.
>  - Does not change DoS threat level.

How do you arrive at that? Symmetric RTP has the problem I outlined in 
my draft. I just need to spoof the source of an IP packet, and then I 
can launch the attack.

-Jonathan R.


-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com


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Cc: Thomas Zeng <zeng@PacketVideo.COM>,
        Magnus Westerlund <magnus.westerlund@ericsson.com>, mmusic@ietf.org
Subject: Re: [MMUSIC] RTSP & NAT discussion on wednesday and thursday.
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> >I believe these are all good arguments for documenting and supporting
> >Symmetric RTP in the draft:
> >
> > - Works through Symmetric NAT.
> > - Works through ALGs.
> > - Very simple to implement.
> > - Does not change DoS threat level.
>=20
> How do you arrive at that? Symmetric RTP has the problem I outlined in=20
> my draft. I just need to spoof the source of an IP packet, and then I=20
> can launch the attack.

A proper implementation on the server side will only accept a Symmetric RTP
packet which originates from the same IP as the RTSP control connection (and
yes, we should make sure to document this prominently).  Note that a client
could send a flood of media packets to another client on its own network,
but this is something that it can already do.  Thus the DoS threat level
remains unchanged.

--=20
For my birthday I got a humidifier and a de-humidifier...  I put them in
the same room and let them fight it out.
        -- Steven Wright

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CC: mmusic@ietf.org, Bill May <wmay@cisco.com>
Subject: Re: [MMUSIC] Aggregate Control URI
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Hi Philippe,

See below:

philippe.gentric@philips.com wrote:

>>>I'm not sure I understand still why MUTE is needed.  All it does is PAUSE
>>>a single stream.  The MUTE complicates the RTSP server state machine
>>>in exactly
>>>the same way that a non-aggregate PAUSE down.
>>>
>>>It's the same thing called something different.
>>>      
>>>
>>Not exactly the same thing. You are correct that MUTE can be realized
>>using one RTSP session per media and do all media synchronization at the
>>client side. The MUTE/UNMUTE proposal is a separate extension draft and
>>will  need further review. You might be correct that MUTE/UNMUTE are not
>>in fact needed.
>>    
>>
>
>one difference/advantage is the need to specify a target media time with PLAY,
>with MUTE/UNMUTE it could be optional:
>
>for example if I was to SETUP 2 audio streams and MUTE one from the start,
>I want to be able after some playback time to send MUTE on the one playing
>and UNMUTE on the other one, simultaneously (queued RTSP commands)
>

It is not queued RTSP commands, it is pipelined commands.

>, without specifying the target time:
>i.e. for the server it means "now" or "asap", and it should make sure that the media
>is sent in a way that there is "no gap".
>

Yes, not specifying a range for MUTE will make it happend directly. So 
by unmuting before muteing will ensure seamless switching.

>
>=> it is "aggregate control" in the sense that the server must be aware of the NPT relationship
>between these two streams
>

If the media streams that a client are muteing and unmuting is in the 
same session they are running using the same NPT timestamp.

>
>=> it is like when you aggregate PLAY audio and video
>the server must send audio and video data that are at the same (NPT) media time.
>  
>
Yes,

>(BTW this would also be a useful step for stream switching;-)
>

I don't know that. The SETUP overhead is considerable.

Best Regards

Magnus Westerlund



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Tom Marshall wrote:

>  > >I believe these are all good arguments for documenting and supporting
>  > >Symmetric RTP in the draft:
>  > >
>  > > - Works through Symmetric NAT.
>  > > - Works through ALGs.
>  > > - Very simple to implement.
>  > > - Does not change DoS threat level.
>  >
>  > How do you arrive at that? Symmetric RTP has the problem I outlined in
>  > my draft. I just need to spoof the source of an IP packet, and then I
>  > can launch the attack.
> 
> A proper implementation on the server side will only accept a Symmetric RTP
> packet which originates from the same IP as the RTSP control connection 
> (and
> yes, we should make sure to document this prominently).

That doesnt work with a nat that has more than one public IP. The RTP 
and RTSP requests might NAT to different addresses.

> Note that a client
> could send a flood of media packets to another client on its own network,
> but this is something that it can already do.  Thus the DoS threat level
> remains unchanged.

It still seems like a problem, though.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com


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This is an automatic digest of bugs submitted and changed on the RTSP bug tracker.  To see a list of bugs, visit:

http://sf.net/projects/rtspspec

When replying, please make your Subject line more specific than "Re: Rtspspec-bugs digest"



Today's Topics:

   1. [ rtspspec-Bugs-771638 ] a=range in SDP to indicate live media (SourceForge.net)
   2. [ rtspspec-Feature Requests-522607 ] Need END_OF_STREAM request (SourceForge.net)

--__--__--

Message: 1
To: noreply@sourceforge.net
From: "SourceForge.net" <noreply@sourceforge.net>
Date: Tue, 15 Jul 2003 07:46:51 -0700
Subject: [rtspspec-bugs] [ rtspspec-Bugs-771638 ] a=range in SDP to indicate live media

Bugs item #771638, was opened at 2003-07-15 16:46
Message generated for change (Tracker Item Submitted) made by Item Submitter
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=377744&aid=771638&group_id=23194

Category: None
Group: Fix for DS - Need WG Input
Status: Open
Resolution: None
Priority: 5
Submitted By: Magnus Westerlund (magwes)
Assigned to: Nobody/Anonymous (nobody)
Summary: a=range in SDP to indicate live media

Initial Comment:
Today there is some confusion on how a client should
know that media is live. To be able to indicate this in
SDP the following is proposed:

Use a=range with any timeformet but in open ended style
will indicate that the media is live, e.g.
a=range:npt=0- or a=range:npt=now-. This makes it
possible to use also for sessions using SMTPE or UTC
times. 





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You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=377744&aid=771638&group_id=23194


--__--__--

Message: 2
To: noreply@sourceforge.net
From: "SourceForge.net" <noreply@sourceforge.net>
Date: Tue, 15 Jul 2003 08:25:05 -0700
Subject: [rtspspec-bugs] [ rtspspec-Feature Requests-522607 ] Need END_OF_STREAM request

Feature Requests item #522607, was opened at 2002-02-25 20:49
Message generated for change (Comment added) made by magwes
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=377747&aid=522607&group_id=23194

Category: None
>Group: Protocol Extension
Status: Open
Priority: 5
Submitted By: Thomas M Zeng (zengtm)
Assigned to: Nobody/Anonymous (nobody)
Summary: Need END_OF_STREAM request

Initial Comment:
Currently there is no way for Server to inform Client 
the completion of a presentation (VOD or Live) without 
issuing a TEARDOWN and thus release reources. What if 
the player wants to use the same resources (pertinent 
to its sessionID) to watch another clip? It would be 
wasteful to teardown and then acquire another 
sessionID immediately.

Would like to see a END_OF_STREAM method added on the 
S->C direction. E.g.:

END_OF_STREAM <p_URI> or <track_URL> RTSP/1.0
SESSION: <session_ID>
REASON: <text describing reason of EOS>




----------------------------------------------------------------------

>Comment By: Magnus Westerlund (magwes)
Date: 2003-07-15 17:24

Message:
Logged In: YES 
user_id=302620

I think this issues should be further discussed. However I
think this clearly is an protocol extension, not part of the
core. It would solve the problem for live and also enable
this to be clear in other scenarios.

The basic semantics is: The server has/will have fulfilled
the PLAY request. 

Putting this into RTSP has the advantage that it becomes
media transport agnostic, however the indication may also be
suitable to put into a media transport protocol. 

Further consideration on this is necessary. If someone has
need, please write up an draft to be an RTSP extension or go
to RTP, etc to put the functionality in. 

----------------------------------------------------------------------

Comment By: Jason Lango (jasonlango)
Date: 2002-03-14 01:55

Message:
Logged In: YES 
user_id=223672

If this makes it into the spec, it would be a useful
addition to know the last packet sequence numbers expected
for each track (to identify packet loss at the end of
stream)

Perhaps this could be conveyed in an RTP-Info header?

i.e.

END_OF_STREAM <p_URI> RTSP/1.0
Session: <session_ID>
RTP-Info: <track1_URL>;seqno=1234567,<track2_URL>;seqno=...
...


----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=377747&aid=522607&group_id=23194




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From: Tom Marshall <tmarshall@real.com>
To: Jonathan Rosenberg <jdrosen@dynamicsoft.com>
Cc: mmusic@ietf.org
Subject: Re: [MMUSIC] RTSP & NAT discussion on wednesday and thursday.
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> > > >I believe these are all good arguments for documenting and supporting
> > > >Symmetric RTP in the draft:
> > > >
> > > > - Works through Symmetric NAT.
> > > > - Works through ALGs.
> > > > - Very simple to implement.
> > > > - Does not change DoS threat level.
> > >
> > > How do you arrive at that? Symmetric RTP has the problem I outlined in
> > > my draft. I just need to spoof the source of an IP packet, and then I
> > > can launch the attack.
> >
> >A proper implementation on the server side will only accept a Symmetric =
RTP
> >packet which originates from the same IP as the RTSP control connection=
=20
> >(and
> >yes, we should make sure to document this prominently).
>=20
> That doesnt work with a nat that has more than one public IP. The RTP=20
> and RTSP requests might NAT to different addresses.

That is correct.  In such a case, a more complex mechanism would be needed.=
=20
However, I have yet to enounter or even hear of such a NAT setup.  I think
it's safe to say that this is a rare corner case.

Symmetric RTP is a very simple solution that works in the vast majority of
implemented NATs (my guess is 99% or so) when the server is in the open and
the client is behind a NAT (or not).  I'm not trying to convince anyone
otherwise.  I'm only saying that there is a very heavy penalty in terms of
implementation complexity to get that extra 1% and we should keep a simple
option available for those who don't need to handle all of the possible
scenarios and corner cases.

> >Note that a client
> >could send a flood of media packets to another client on its own network,
> >but this is something that it can already do.  Thus the DoS threat level
> >remains unchanged.
>=20
> It still seems like a problem, though.

How so?

--=20
Logic is a systematic method of coming to the wrong conclusion with
confidence.

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inline.

Tom Marshall wrote:


>  > That doesnt work with a nat that has more than one public IP. The RTP
>  > and RTSP requests might NAT to different addresses.
> 
> That is correct.  In such a case, a more complex mechanism would be needed.
> However, I have yet to enounter or even hear of such a NAT setup.  I think
> it's safe to say that this is a rare corner case.
> 
> Symmetric RTP is a very simple solution that works in the vast majority of
> implemented NATs (my guess is 99% or so) when the server is in the open and
> the client is behind a NAT (or not).  I'm not trying to convince anyone
> otherwise.  I'm only saying that there is a very heavy penalty in terms of
> implementation complexity to get that extra 1% and we should keep a simple
> option available for those who don't need to handle all of the possible
> scenarios and corner cases.

I agree its the simplest solution in the cases where it works (though 
there is still that dos attack). The real issue is whether the group 
is interested in some of the other areas of applicability where the 
mechanism will not work, such as where the RTSP server is not in the 
open. If those are areas where you want RTSP to function, you would 
end up having two solutions, and you will have all the problems of 
figuring out which one to use. I've been down that route with SIP, and 
its not a pleasant one.

-Jonathan R.


-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com


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--> Pekka Pessi <pessi@iki.fi> writes:
> 	Hello all,
> 
> 	In the sdp-new, there seems to be a contradiction between the
> 	ABNF definition of "token-char" and comments after the
> 	definition:
> 
>       token-char =          %x21 / %x23-27 / %x2A-2B / %x2D-2E / %x30-39
>                             / %x41-5A / %x5E-7E
>                             ; definition from RFC 2045 -
>                             ; "any (US-ASCII) CHAR except SPACE, CTLs,
>                             ; or tspecials".
>                             ; the tspecials are ()<>@,;:
> 
> 	According to the ABNF, the tspecials include quote (%22, "),
> 	slash (%2F, /), equal (%3D, =), question mark (%3f, ?), square
> 	brackets (%5B, [ and %5D, ]), and backslash (%5C, \), too:
> 
>                             ; the tspecials are ()/<>@,;:"=?[\]
> 
> 	As it looks like that the sdp-new-14 is recycled once more, so
> 	it is possible to fix the comment there (or ABNF, if that is
> 	more appropriate).

I'd like to solicit opinions from implementors about this. Please state
your preference for either:

 1) Leave the ABNF for token-char as-is, but remove the comment

 2) Change the ABNF for token-char to be:

	token-char = %x21-27 / %x2A-2B / %x2D-2F / %x30-39 / %x3D / %x3F / %x41-5B
                    / %x5C-%x5D / %x5E-7E

    adding the characters mentioned above.

-- 
Colin Perkins
csp@csperkins.org

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Date: Wed, 16 Jul 2003 09:57:44 +0200
From: Colin Perkins <csp@csperkins.org>
To: Belling Thomas <thomas.belling@siemens.com>
Cc: magnus.westerlund@ericsson.com, thomas.belling@siemens.com,
        mmusic@ietf.org
Subject: Re: [MMUSIC] RTP bandwidth for multiple media streams
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Thanks. These changes look reasonable: comments from the group?
Colin

--> Belling Thomas <thomas.belling@siemens.com> writes:
> Dear Colin
>=20
> I would like to suggest the following additions to the SDP new draft
> (denoted by ">>> <<<")
>=20
> Alternatively, removing the <number of ports> and the corresponding
> explanations from page 19f is acceptable to me, if nobody has concerns
> with respect to the backward compatibility.
>=20
> Thanks, Thomas
>=20
>=20
>=20
> On page 13f:
>=20
>    Bandwidth
>=20
>       b=3D<modifier>:<bandwidth-value>
>=20
> ...
>=20
>       Two modifiers are initially defined:
>=20
>         CT  Conference Total
>             If the bandwidth of a session or media in a session is
>             different from the bandwidth implicit from the scope, a
>             "b=3DCT:..." line should be supplied for the session giving
>             the proposed upper limit to the bandwidth used.  The primary
>             purpose of this is to give an approximate idea as to whether
>             two or more sessions can co-exist simultaneously.
> >>>         For RTP, if several RTP sessions are part of the conference,
>             the conference total refers to total bandwidth of all RTP
>             sessions. <<<
>            =20
>=20
>         AS  Application-Specific Maximum
>             The bandwidth is interpreted to be application-specific (it
>             will be the application's concept of maximum bandwidth).
>             Normally this will coincide with what is set on the
>             application's "maximum bandwidth" control if applicable.
>             For RTP based applications, AS gives the RTP "session
>             bandwidth" as defined in section 6.2 of [RFC1889].
>=20
>       Note that CT gives a total bandwidth figure for all the media at
>       all sites.  AS gives a bandwidth figure for a single media at a
>       single site, although there may be many sites sending
>       simultaneously.
>=20
>=20
>=20
>=20
>=20
>=20
>=20
> On page 19f:
>=20
>    Media Announcements
>=20
>       m=3D<media> <port> <transport> <fmt list>
>=20
>       ...
>=20
>       The second sub-field is the transport port to which the media
>       stream is sent. The meaning of the transport port depends on the
>       network being used as specified in the relevant "c=3D" field, and on
>       the transport protocol defined in the third sub-field.  Other
>       ports used by the media application (such as the RTCP port
>       [RFC1889]) MAY be derived algorithmically from the base media port
>       or MAY be specified in a separate attribute (e.g. "a=3Drtcp:" as
>       defined in [RTCPSDP]).
>=20
>       For applications where hierarchically encoded streams are being
>       sent to a unicast address, it may be necessary to specify multiple
>       transport ports.  This is done using a similar notation to that
>       used for IP multicast addresses in the "c=3D" field:
>=20
>=20
>          m=3D<media> <port>/<number of ports> <transport> <fmt list>
>=20
>       In such a case, the ports used depend on the transport protocol.
>       For RTP, the default is that only the even numbered ports are used
>       for data and the corresponding one-higher odd port is used for
> >>>   RTCP >>> belonging to this RTP session, and the <number of ports>
> >denotes the number of RTP sessions<<<.  For example:
>=20
>          m=3Dvideo 49170/2 RTP/AVP 31
>=20
>       would specify that ports 49170 and 49171 form one RTP/RTCP pair
>       and 49172 and 49173 form the second RTP/RTCP pair. RTP/AVP is the
>       transport protocol and 31 is the format (see below). If non-
>       contiguous ports are required, they must be signalled using a
>       separate attribute (e.g. "a=3Drtcp:" as defined in [RTCPSDP])
>       ...
>=20
>=20
> -----Urspr=FCngliche Nachricht-----
> Von: Colin Perkins [mailto:csp@csperkins.org]
> Gesendet: Mittwoch, 25. Juni 2003 19:03
> An: Magnus Westerlund
> Cc: thomas.belling@siemens.com; mmusic@ietf.org
> Betreff: Re: AW: [MMUSIC] RTP bandwidth for multiple media streams
>=20
>=20
> Can you suggest explicit wording changes to clarify the draft? There is
> probably still time to incorporate minor edits for clarification.
>=20
> Colin
>=20
>=20
>=20
> --> Magnus
> Westerlund<magnus.westerlund@ericsson.com> writes:
> > Hi Thomas,
> >=20
> > Even more inline:
> >=20
> > Belling Thomas wrote:
> > > Hi Magnus,
> > >=20
> > > My answers are inline
> > >=20
> > >=20
> > > -----Urspr=FCngliche Nachricht-----
> > > Von: Magnus Westerlund [mailto:magnus.westerlund@ericsson.com]
> > > Gesendet: Montag, 23. Juni 2003 09:27
> > > An: Belling Thomas
> > > Cc: 'mmusic@ietf.org'
> > > Betreff: Re: [MMUSIC] RTP bandwidth for multiple media streams
> > >=20
> > >=20
> > > Hi,
> > >=20
> > > I would agree with the interpretation, at least when it comes to b=3D=
AS
> > > as it clearly specifies that this is the RTP session bandwidth. When
> > > one uses a m=3D line with port/2 it becomes two RTP sessions. However=
 I
> > > am not certain over how one should in this case interpret any of the
> > > other bandwidth attributes.
> > >=20
> > > [Thomas] Fine, but is that 100 Percent clear from the wording of the
> > > RFCs and draft-ietf-mmusic-sdp-new-12? It would prefere a
> > > clarification there
> >=20
> > Yes, this should probably be clarified. I don't think it is obvious.
> >=20
> > >=20
> > > The available bandwidth modifiers are:
> > > CT
> > > RR
> > > RS
> > >=20
> > > Lets look at them:
> > >=20
> > > CT is defined in draft-ietf-mmusic-sdp-new-12 as:
> > >          CT  Conference Total
> > >              If the bandwidth of a session or media in a session is
> > >              different from the bandwidth implicit from the scope, a
> > >              "b=3DCT:..." line should be supplied for the session
> > >              giving the proposed upper limit to the bandwidth used.=20
> > >              The primary purpose of this is to give an approximate
> > >              idea as to whether two or more sessions can co-exist
> > >              simultaneously.
> > >=20
> > > Based on this I would interpret that a given CT value should be for
> > > the complete media, i.e. counting the total of both RTP sessions.
> > >=20
> > > [Thomas] I agree that this is an interpretation in line with my
> > > understanding of the intentions of the CT bandwidth modifier.
> > > However, the wording is not so clear. What is a "session"? If you
> > > understand"RTP session", this would contradict your interpretation.
> > > As an aside: 3GPP ignores this parameter, so from that perspective a
> > > clarification is less urgent than for the AS modifier.
> >=20
> > Yes, the session in the quote is a bit unclear. I think it is a larger=
=20
> > session concept, like the complete streaming session, or probably when=
=20
> > it was written the conferencing session with all the media included. On
> > media level the text indicates the complete media, which in this case
> > is transported over several RTP sessions. So based on these two=20
> > interpretations I arrive at my conclusion.
> >=20
> > > When it concerns TIAS I will do the same interpretation that the=20
> > > bandwidth value apply per RTP session.
> > >=20
> > > [Thomas] Makes sense if you take TIAS as a kind of refinement of the
> > > AS modifier. I did not yet read the draft with that question in mind,
> > > and the draft is still in a stage where this can be clarified.
> >=20
> > Yes, it can still be modified. I have made an update and I did not=20
> > address the issue. The reason being is that I think the SDP draft
> > should=20
> >   first address this. Based on this clarification I would add to the=20
> > TIAS draft if necessary.
> >=20
> > >=20
> > > My concern is that this simplistic model is probably not what you
> > > would like if you would actually use this functionality. If one uses
> > > multiple RTP sessions for a single media you are probably doing some
> > > form of scalability, etc., and would like to specify the values
> > > independently per RTP session. Fortunately there exist today
> > > alternatives to achieve this behaviour today. With the help of
> > > grouping of media lines it is possible to specify that several m=3D
> > > lines are part of the same media. Using FID there is only a pitfall
> > > with the following sentence:"A media agent handling a media flow that
> > > comprises several "m"
> > >     lines MUST send a copy of the media to every "m" line part of the
> > >     flow as long as the codecs and the direction attribute present in
> > >     a particular "m" line allow it."
> > >=20
> > > If that is a problem it might be easier to define a new grouping=20
> > > attribute for that situation.
> > > Finally I have a question to the group, has anyone seen that "m=3D
> > > port/2..." ever been used. And in that case how.
> > >=20
> > > [Thomas] Take the simple example of stereo sound. Why not use the "m=
=3D
> > > port/2 " notification for that? Something in that direction might
> > > have been the original motification. From a 3GPP perspective, where
> > > this relates to thev bandwidth on the air and possibly the rate
> > > charged for a service, we should have a clear understanding as this
> > > possibility exists and might also be misused otherwise.
> >=20
> > I don't think stereo is a good example. First reason is that you=20
> > normally don't split left and right channel into different packets,=20
> > unless they are really big, reasons are like synchronization. Therefore
> > most audio codecs are possible to transport over RTP using a single=20
> > source. The sample based codec normally only specify that every other=20
> > sample is left  and the other are right. Frame based codec normally
> > have more advanced schemes where they encode left and right together to
> > take advantage of the similarities between channels.
> >=20
> > My thinking is actually along the lines, if no one uses it, why not=20
> > remove it, we will still have to if no implementations are identified=20
> > when going to draft standard.
> >=20
> >=20
> > Best Regards
> >=20
> > Magnus Westerlund
> >=20
> > Multimedia Technologies, Ericsson Research EAB/TVA/A
> > ----------------------------------------------------------------------
> > Ericsson AB                | Phone +46 8 4048287
> > Torshamsgatan 23           | Fax   +46 8 7575550
> > S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com
> >=20
> >=20
> > _______________________________________________
> > mmusic mailing list
> > mmusic@ietf.org
> > https://www1.ietf.org/mailman/listinfo/mmusic
> >=20
>=20
>=20
> --=20
> Colin Perkins
> csp@csperkins.org
>=20


--=20
Colin Perkins
csp@csperkins.org

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From: Tom Marshall <tmarshall@real.com>
To: Jonathan Rosenberg <jdrosen@dynamicsoft.com>
Cc: mmusic@ietf.org
Subject: Re: [MMUSIC] RTSP & NAT discussion on wednesday and thursday.
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> > > That doesnt work with a nat that has more than one public IP. The RTP
> > > and RTSP requests might NAT to different addresses.
> >
> >That is correct.  In such a case, a more complex mechanism would be need=
ed.
> >However, I have yet to enounter or even hear of such a NAT setup.  I thi=
nk
> >it's safe to say that this is a rare corner case.
> >
> >Symmetric RTP is a very simple solution that works in the vast majority =
of
> >implemented NATs (my guess is 99% or so) when the server is in the open =
and
> >the client is behind a NAT (or not).  I'm not trying to convince anyone
> >otherwise.  I'm only saying that there is a very heavy penalty in terms =
of
> >implementation complexity to get that extra 1% and we should keep a simp=
le
> >option available for those who don't need to handle all of the possible
> >scenarios and corner cases.
>=20
> I agree its the simplest solution in the cases where it works (though=20
> there is still that dos attack). The real issue is whether the group=20
> is interested in some of the other areas of applicability where the=20
> mechanism will not work, such as where the RTSP server is not in the=20
> open. If those are areas where you want RTSP to function, you would=20
> end up having two solutions, and you will have all the problems of=20
> figuring out which one to use. I've been down that route with SIP, and=20
> its not a pleasant one.

Regarding the dos attack, I maintain that the threat does not change from
the current usage without NAT traversal (provided the server enforces the
destination address constraint).  Please provide an example of a case where
the threat is increased if you believe otherwise.

Please correct me if I'm wrong (I'm not very familiar with SIP), but my
understanding is that SIP is primarily intended to be used in a peer to peer
model while RTSP is primarily intended to be used in a client server model.=
=20
I suspect this is probably a big reason for the unpleasantness that you
mention.

For specific applications (such as ours), Symmetric RTP will cover about 99%
of the cases.  The remaining 1% are covered with TCP interleaving.  This has
been shown to be true with a similar mechanism in our proprietary RDT
transport.  It's unlikely that the added implementation complexity for the
other solutions will be worth the effort.  Therefore, Symmetric RTP is very
attractive in a real world application.

--=20
Most people are too busy to have time for anything important.

--v9Ux+11Zm5mwPlX6
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From exim@www1.ietf.org  Wed Jul 16 05:07:36 2003
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To: Tom Marshall <tmarshall@real.com>
CC: Jonathan Rosenberg <jdrosen@dynamicsoft.com>, mmusic@ietf.org
Subject: Re: [MMUSIC] RTSP & NAT discussion on wednesday and thursday.
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Hi,

I have some comments about this. I think that we should rather consider 
what we need to solve the DoS attack scenario. The main reason for 
solving this in the RTSP setting is to lift the restriction that servers 
can send media only to the IP address the TCP connection comes from. If 
one can remove this restriction one very interesting use cases becomes 
available:

- Inviting RTSP servers into SIP calls or conferences. This is not 
possible otherwise if the controlling entity is different from the 
receiving entity. This will definitely be the case if one runs 
centralized conferencing with a focal point for all traffic.

There probably are more use cases when RTSP allows the use of other 
destination addresses.

They are in fact two problems, destination validation and NAT traversal. 
However they seem to using the same protocols and are connected, so I 
think we should take the opportunity to kill two birds with one stone.

However I think that we should be careful in the design of the 
mechanism. First it shouldn't incur more than the necessary extra RTT to 
do the validation in use cases where there is no NAT. For clients behind 
NATs there will be at least one extra RTT to create the address mappings 
in the NAT. The solution of servers behind NATs will be a low priority 
and the work may only consist of keeping the door open for such 
extensions unless they come very easily which I don't think.

Best Regards

Magnus Westerlund


>  
>


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Subject: [MMUSIC] RTSP discussion today
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Hi,

There where no room available at the conference center so we will have 
to make this an ad-hoc. Please meet at 17.30 in the main foyer near the 
registration desk. We will then go down to the riverside (5 min walk) 
and have the discussion at one of the fast food places there. Based on 
yesterdays sightings there will be rather plenty of room there. We will 
continue until it is time to go to the IAB plenary.

Please don't be late, we will not wait long. Any person late can call me 
on +46 70 211 48 44 for information on where we are.

Cheers

Magnus Westerlund


A issue list for the discussions are:

RTSP discussions topics

RTSP & NAT

- Goals
- Select solution
- FW
- ALGs


RTSP Core

 - Session and control URL definitions

 - Proposal for detecting live streams via SDP 'range' attribute.  I
   think Magnus will have an updated proposal since last week?

 - Possible methods for signalling end of stream in RTP (both RTP/RTCP
   extensions and RTSP extensions are possibilities).

 - RTP extensions to make multibitrate files more cache-friendly.  The
   most important piece of information that a proxy needs is a bitrate
   field, but there are other issues as well.

 - Should REDIRECT automatically close session?
 
 - How to handle implicit redirection through session description protocol.
   Majority favors allowing it per default.

 - How to detect the updated spec? Version number change 1.1 or 2.0, or
   only use require and tag when necessary.

 - Request to Response timeout. The time a request takes until any 
response is
   received is not bound. Look at SIP solution?

RTSP MUTE/UNMUTE

- Need for it, revisit requirements advantages.


RTSP stream switching

- Requirements

- Way forward?

RTSP TLS

-into main spec if small enough!





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Subject: [MMUSIC] Slides for tomorrow
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To all presenters for tomorrow's MMUSIC session:

Please send a copy of your slides to

     csp@csperkins.org
     jo@acm.org

at least one hour prior to our meeting tomorrow, i.e.
latest at 8:00am.  We will then have them ready for your
presentations on our laptops and also put them up on the
web page.

Thanks,
Joerg


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Date: Wed, 16 Jul 2003 02:45:19 -0700 (PDT)
From: Geetha Srikantan <Geetha.Srikantan@Sun.COM>
Reply-To: Geetha Srikantan <Geetha.Srikantan@Sun.COM>
Subject: Re: [MMUSIC] RTSP discussion today
To: mmusic@ietf.org, magnus.westerlund@ericsson.com
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hi Magnus,

I have been thinking about how 'playlists' may be supported with RTSP/RTP.
Playlists are what one might use in an internet radio session for instance, 
pre-program a set of songs that are to be played out in sequence on the same
RTP session.
Would it be possible to discuss this topic at the meeting today?

From what I gather, there are multiple constraints on how playlists might work:
for instance, the RTP timescales between multiple consecutive streams on the
same RTP session cannot change, even thr the encoding rate and type can change - 
and is indicated by the Payload type of the RTP packets.

From RTSP - there are complications when PAUSE is issued.
If the RTP timestamps are allowed to advance while in a PAUSE state,
then let us look at the impact of this:

SETUP <stream a on RTP session 1>
SETUP <stream b on RTP session 1>
PLAY <stream a on RTP Session 1>
PLAY <stream b on RTP Session 1 after stream a's npt range is completed>

Now assume that a RTSP PAUSE is issued.
This PAUSE can occur at the time of playing stream a or stream b or
just at the point of switching from stream a to b. In the last case,
if timestamps are allowed to advance during PAUSE, it means all of
the packet timestamps need to be recalculated after the PAUSE point,
(as for other PAUSE cases) even though
the PLAY issued earlier would have used a different timestamp.
This seems very awkward.

I'm wondering if the decisions to allow RTP timestamps to advance during a
PAUSE is such a good idea, after all. The only motivation seemed to be that
this is the way it worked for conferencing. However the RTSP spec is relevant
to other applications too, so it would be desirable to have a spec that
defines a base-line, that is like a 'least common denominator'. After that
other specs can define what is to be done for specifc applications.
This seems to be the approach followed wrt Mute/Unmute. I would urge that
we revisit the discussion with RTP timestamps.

thanks
geetha

> Date: Wed, 16 Jul 2003 11:11:43 +0200
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> From: Magnus Westerlund <magnus.westerlund@ericsson.com>
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<mailto:mmusic-request@ietf.org?subject=subscribe>
> 
> Hi,
> 
> There where no room available at the conference center so we will have 
> to make this an ad-hoc. Please meet at 17.30 in the main foyer near the 
> registration desk. We will then go down to the riverside (5 min walk) 
> and have the discussion at one of the fast food places there. Based on 
> yesterdays sightings there will be rather plenty of room there. We will 
> continue until it is time to go to the IAB plenary.
> 
> Please don't be late, we will not wait long. Any person late can call me 
> on +46 70 211 48 44 for information on where we are.
> 
> Cheers
> 
> Magnus Westerlund
> 
> 
> A issue list for the discussions are:
> 
> RTSP discussions topics
> 
> RTSP & NAT
> 
> - Goals
> - Select solution
> - FW
> - ALGs
> 
> 
> RTSP Core
> 
>  - Session and control URL definitions
> 
>  - Proposal for detecting live streams via SDP 'range' attribute.  I
>    think Magnus will have an updated proposal since last week?
> 
>  - Possible methods for signalling end of stream in RTP (both RTP/RTCP
>    extensions and RTSP extensions are possibilities).
> 
>  - RTP extensions to make multibitrate files more cache-friendly.  The
>    most important piece of information that a proxy needs is a bitrate
>    field, but there are other issues as well.
> 
>  - Should REDIRECT automatically close session?
>  
>  - How to handle implicit redirection through session description protocol.
>    Majority favors allowing it per default.
> 
>  - How to detect the updated spec? Version number change 1.1 or 2.0, or
>    only use require and tag when necessary.
> 
>  - Request to Response timeout. The time a request takes until any 
> response is
>    received is not bound. Look at SIP solution?
> 
> RTSP MUTE/UNMUTE
> 
> - Need for it, revisit requirements advantages.
> 
> 
> RTSP stream switching
> 
> - Requirements
> 
> - Way forward?
> 
> RTSP TLS
> 
> -into main spec if small enough!
> 
> 
> 
> 
> 
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic


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Hi Geetha,

Geetha Srikantan wrote:

>hi Magnus,
>
>I have been thinking about how 'playlists' may be supported with RTSP/RTP.
>Playlists are what one might use in an internet radio session for instance, 
>pre-program a set of songs that are to be played out in sequence on the same
>RTP session.
>Would it be possible to discuss this topic at the meeting today?
>

Sure, lets see how long we can come in the discussion.

Regarding playlists, why not treat it as a live station and use HTTP to 
program the station. It does not seem suitable to perform this type of 
control in RTSP without further extensions for media resource control.

>
>From what I gather, there are multiple constraints on how playlists might work:
>for instance, the RTP timescales between multiple consecutive streams on the
>same RTP session cannot change, even thr the encoding rate and type can change - 
>and is indicated by the Payload type of the RTP packets.
>
>From RTSP - there are complications when PAUSE is issued.
>If the RTP timestamps are allowed to advance while in a PAUSE state,
>then let us look at the impact of this:
>
>SETUP <stream a on RTP session 1>
>SETUP <stream b on RTP session 1>
>PLAY <stream a on RTP Session 1>
>PLAY <stream b on RTP Session 1 after stream a's npt range is completed>
>
>Now assume that a RTSP PAUSE is issued.
>This PAUSE can occur at the time of playing stream a or stream b or
>just at the point of switching from stream a to b. In the last case,
>if timestamps are allowed to advance during PAUSE, it means all of
>the packet timestamps need to be recalculated after the PAUSE point,
>(as for other PAUSE cases) even though
>the PLAY issued earlier would have used a different timestamp.
>This seems very awkward.
>
>I'm wondering if the decisions to allow RTP timestamps to advance during a
>PAUSE is such a good idea, after all. The only motivation seemed to be that
>this is the way it worked for conferencing. However the RTSP spec is relevant
>to other applications too, so it would be desirable to have a spec that
>defines a base-line, that is like a 'least common denominator'. After that
>other specs can define what is to be done for specifc applications.
>This seems to be the approach followed wrt Mute/Unmute. I would urge that
>we revisit the discussion with RTP timestamps.
>

The REASON for having this clarification of the usage of RTP timestamps 
are RTP and RTCP itself. The RTCP based synchronization and reporting 
would be very confused if you did not have continuos timestamp space. IF 
you would go stop the RTP timestamp space during pause while RTCP keeps 
advancing it at the defined rate parts of the TS space will be reused 
and the RTCP synchronization information will be impossible to match 
against the RTSP synchronization information.

I know that people think this clarification creates some problems. 
However as having implemented this I know that it is not very many lines 
of code for the server. The client has only one significant problem 
which is to synchronize buffered data prior to pause with the data 
arriving after a pause. However this is a small practicality which have 
a solution.

Best Regards

Magnus



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Subject: RE: [MMUSIC] stream switching
To: "Gamze Seckin" <gamze@vidiator.com>
Cc: "Magnus Westerlund" <magnus.westerlund@ericsson.com>, mmusic@ietf.org
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Gamze,

Thank you for your feedback!

> I believe the draft tries to cover far too many requirements
> that are rate control related (which have been/are discussed in other wg's).

I am sorry it gives this impression.
rate control is EXPLICITELY out of the scope.
clearly rate control is dealt with using TFRC, DCCP etc

====The scope is purely media/codec control.====

I tried however to be exhaustive about the context
and of course rate control is at the hearth of it ;-)

>... since video stream switches are really not a big issue,

I am *extremely* surprised you can say this,
did you try to feed a MPEG-4 video stream into a H263 decoder recently ?
what about screen size changes?
when a video decoder tries to write into a display buffer
an image larger than the buffer the result is never pretty to see!-)

> whereas audio switches require more complicated solutions that may impact the user experience.

yes, audio is totally critical since it does not suffer any gap.

> And hence we should discuss and recommend solutions for those..

I would be horrified to limit the scope to audio!
the point on the contrary is to be able to switch streams of all types,
audio, video, text, you name it.
(streaming text is a use case that is missing in the document)

(I dont think anybody will ever need to switch text streams
for rate control reasons however) there is the case where the user wants to
switch from the italian subtitles into the german subtitles.


regards,


Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com


                                                                                                                                       
                                                                                                                                       
                                                   To:   "Magnus Westerlund" <magnus.westerlund@ericsson.com>                          
                                                    Philippe Gentric/MP4-SUR/CE/PHILIPS@EMEA1                                          
                                                   cc:   <mmusic@ietf.org>                                                             
                                                   Subject:    RE: [MMUSIC] stream switching                                           
               "Gamze Seckin"                                                                                                          
               <gamze@vidiator.com>                Classification:                                                                     
                                                                                                                                       
               Sent by:                                                                                                                
               mmusic-admin@ietf.org                                                                                                   
                                                                                                                                       
               16/07/2003 11:27                                                                                                        
                                                                                                                                       
                                                                                                                                       




hi Philippe,

I agree with Magnus's comments on differentiating content rate from transmission rate and keeping an eye on reciever buffer overflow and underflow. These are all valid and useful discussions but I believe are out of the scope of the stream switching
documents (please correct me if I am wrong).I believe the draft tries to cover far too many requirements that are rate control related (which have been/are discussed in other wg's).

I personally would expect these two drafts on stream switching to be more specific on codec change support and addressing the issues of the transport (more serious problems that need an answer).
I think section 2.5 is the core of the document, since video stream switches are really not a big issue, whereas audio switches require more complicated solutions that may impact the user experience. And hence we should discuss and recommend solutions for
those..

thanks
-gamze seckin


             -----Original Message-----
             From: Magnus Westerlund [mailto:magnus.westerlund@ericsson.com]
             Sent: Mon 7/14/2003 5:40 AM
             To: philippe.gentric@philips.com
             Cc: mmusic@ietf.org
             Subject: Re: [MMUSIC] stream switching



             Hi Phillipe,

             I hope that I can clarify anything that was unclear. I also has some
             further comments, see below.

             philippe.gentric@philips.com wrote:

             >Magnus, you wrote:
             >
             >
             >>To enable this the complete system must ensure the following things:
             >>- Congestion Control or rather adapting transmission rates to available
             >>network rate => avoiding high packet loss rates that severely effect
             >>quality.
             >>
             >>
             >
             >   yes
             >
             >
             >
             >>- Avoid that the receivers buffers either under flow (causes interrupt)
             >>or overflow (show up as packet loss).
             >>
             >>
             >>
             >
             >   yes, this is fundamental for seamless-ness
             >
             >
             >
             >>Based on this one can arrive at the conclusion that the media or content
             >>rate must be adapted, otherwise the underflow condition will be
             >>impossible to avoid. If one performs content adaptation towards lower
             >>bit-rates one must also perform adaptation towards higher rates.
             >>
             >>
             >>
             >
             >   I am not sure about this "must", could it be that your are
             >   considering differently media rate and transmission rate ?
             >
             >

             What I mean is that if the available transmission rate is less the media
             rate then you on some time scale if nothing changes you will empty your
             buffer. Therefore you "must" change the media rate to avoid this or have
             interrupts. I don't know about any other solution.

             >   because I am not considering changing the transmission rate (as a
             >   end-to-end application issue) => stream switching is only about
             >   changing the *media* rate.
             >

             I don't think you can exclude the transmission rate from the equation.
             In my opinion you need to consider transmission rate, receiver buffers,
             and the media rate all together.

             >
             >   what I want to mean is you dont *need* to increase the media rate
             >   to avoid undeflows but instead you may *want* to increase the
             >   media rate in order to improve the user experience in terms of
             >   image quality...
             >
             I am not sure what you mean, but I guess the following. In cases you are
             not transmission rate limited one is not required to increase the media
             rate, however it is commonly desired. I can agree that there are some
             need to allow the receiver to specify what is allowed in respect to
             media rate modifications.

             >
             >
             >
             >>This I think is the basic requirement and assumptions that apply to your
             >>requirements draft.
             >>
             >>Based on this any solution can be divided up into different
             >>functionality blocks:
             >>
             >>- Transmission rate control, this functionality ensures that a sender
             >>does not send more data then the network can transport without being to
             >>unfair, or overflow network buffers.
             >>
             >>
             >>
             >
             >   hum, again i prefer the term "media rate control" if you dont mind?
             >

             No, I don't think you completely understand. In a system where the
             buffer space is known you don't have to transmit the data in the same
             rate as the media rate. Due to the buffer one can during some parts of
             the session transmit data at rates that are both higher and lower than
             the media rate. However when doing this you need to ensure that you are
             not under or overflowing the receiver buffer. What you try to do is to
             simplify this system to basically say that the transmission rate is
             equal to media rate which I think prevents better performance.

             If any one does not understand this, please prod me and I will try to
             provide a better explanation of the complete system.

             >
             >
             >
             >>- Receiver buffer control, this functionality ensure that one does not
             >>overflow the client's receiver buffers.
             >>
             >>
             >>
             >
             >   yes, not sure there is much to "do" there in terms of IETF spec?
             >

             There is nothing in IETF that allows feedback or even specification
             about the receiver buffers to or by the sending side. This is analogous
             to TCP's receiver window that allow to control the flow of media.

             >
             >
             >
             >
             >>- Content rate control, functionality to ensure that the transmitted
             >>date fits the available network rate, while at the same time ensure that
             >>the receiver buffer does not underflow.
             >>
             >>
             >>
             >
             >   yes! this is stream switching principle, but again it is about
             >   "media rate", not changing the transmission rate.
             >

             This I can agree is what you describe as media rate control. By
             selecting or controlling the media rate one can meet the requirements of
             transmission rate and receiver buffers.

             >
             >
             >
             >>Based on this functionality blocks one can use one or several
             >>protocols/solutions to realize them. They do not need to be separate and
             >>can utilize information enabled by any of the other functionality
             >>blocks. However I believe that all parts must be present to have a
             >>complete solution. Also how to realize the solutions is a not fixed by
             >>this.
             >>
             >>I would suggest that one tries to group the requirements regarding which
             >>of the functionality's they address.
             >>
             >>
             >>
             >
             >   Which groups would you suggest ?
             >

             Some suggestions would be:

             Media requirements: Requirements to prevent the media from being
             corrupted or worsen quality, like limited packet losses, gap free
             switching, RAP,etc.

             Signalling requirements: Requirements that are a related to what the
             signalling mechanism needs to achieve.

             System requirements: Requirements that have more general feeling, like
             backwards compatibility, etc.


             >
             >
             >
             >
             >>When one comes to solution one must start discussing what control
             >>paradigm one desires, as it will heavily influence the solution. Three
             >>different ones are:
             >>- Server controlled: In this the server is the responsible for all
             >>decisions regarding the adaptation. The client simply reports certain
             >>measurements that the server interprets.
             >>
             >>- Client controlled: The client makes the decisions and interpretations
             >>of what it see. Then it issues commands to the server that it must
             >>follow. The server is a simple slave.
             >>
             >>
             >>
             >
             >   slave, yes, but a slave that *could* refuse to obey ;-) e.g. as
             >   discussed in my draft for rate control a server must be allowed to
             >   deny a request for a higher data rate...
             >
             >
             >
             In a true client control paradigm, this may not even be true. But the
             basic point is that the requirements may motivate the choice, but we
             should not choice a a paradigm and then write the requirements to fulfil
             them. I have a rather long list of comments to when this discussion
             needs to be started.

             >
             >
             >>- Hybrid control: In a hybrid control scenario both client and servers
             >>makes decisions and interpretations of the data.
             >>
             >>I will not try to compare these solutions this if for future
             >>discussions. If one is interested in a server controlled solution one
             >>can look at the latest proposal in 3GPP SA4:
             >>http://www.3gpp.org/ftp/tsg_sa/WG4_CODEC/TSGS4_27/Docs/S4-030501.zip
             >>Look at the buffer reporting mode variant. This proposal provides
             >>receiver buffer control and content rate control. The transmission rate
             >>control is handled through RTCP reports with enabled extended reports of
             >>packet loss vectors.
             >>
             >>
             >>
             >
             >   I have to say that using such RTCP extensions looks very much like
             >   "client control" to me ;-) but I dont really care about the
             >   terminology ;-)
             >

             Actually the mechanism in my opinion is very server controlled. The
             client provides the server side with some parameters telling it what to
             achieve. Then the client provides regular feedback to allow the server
             to run the algorithms and control the whole system.

             >
             >
             >
             >
             >>Some more direct comments on the draft:
             >>
             >>1. Introduction: The encoding could be done in real time allowing
             >>maximum flexibility in the produced content rate. However this is may
             >>not result in optimal encodings and are also very resource demanding for
             >>a server.
             >>
             >>
             >>
             >
             >
             >   yes, I did not mention this possibility because in large scale
             >   media distribution this would effectively require one "production"
             >   encoder per client, which is -even in several years from now- way
             >   beyond the cost points for this type of products.
             >
             >
             I think that spending two sentences on this is useful, just to make it
             clear that it has been considered but has significant problems.

             >
             >
             >
             >>2. Section 2.1.1 and 2.1.2: I think the behaviour in this case should
             >>really be depending on the operators policies. I would not like to have
             >>my expensively paid on demand video reduced in quality if this network
             >>is of the type you describe. However I can see that we should enable this.
             >>
             >>
             >
             >
             >   Yes, you are right, all this assumes the correct commercial
             >   agreements are in place. Our experience is however that a end user
             >   always prefers a continuous playback, even a degraded one,
             >   providing that the degradation is "resonable", all other solutions
             >   including "freezes" for rebuffereing are not acceptable for the
             >   wide public who is accustomed to TV ;-(
             >
             >From an IETF point of view (hey, just giving my own opinion ;-)
             >I think it would be a good idea that implementations *by default*
             >would "behave a la TFRC" rather than what we have today,
             >because otherwise -as sally floyd pointed out this morning-
             >we would run into rather nasty trouble.
             >

             Yes, I agree that over any best effort network you need some type of
             congestion avoidance. So default behaviour is good, however we must also
             allow for systems that has QoS agreements.

             >
             >
             >
             >
             >>3. Section 2.2: I think you need to be a bit more clear that this is one
             >>example of a service. Also the AMR rate of 5 kbps is a bit to low. The
             >>4.75 kbps mode has a quality that is not the best. However to achieve
             >>this bit-rate you must only send one AMR packet every 1.28 seconds,
             >>which means 64 amr frames per packet. This is not realistic as every
             >>packet will be required to reach the receiver to achieve acceptable
             >>quality. I would think that reasonable AMR qualities are using at least
             >>10 packet every second, meaning that a header overhead of 3 kbps.
             >>
             >>
             >>
             >
             >   right.
             >
             >
             >
             >>4. Section 2.5: I think this section assumes something that are not
             >>quite true. First the impossibility to signal this rate switch using
             >>current protocols.
             >>
             >>
             >
             >   What *is* impossible is to find a comprehensive spec for stream
             >   switching !-) and it is my intention to provide one, i would love to
             >   "use the current protocols"!
             >
             >
             >
             >>I claim it is possible but most likely not supported
             >>by any available client.
             >>
             >>
             >
             >   And that would be the point in writing that spec...
             >
             >
             >
             >>To signal the rate switch in SDP you present
             >>one different RTP payload types for each codec and configuration, most
             >>likely at least 4 maybe 5. The 40 and 50 kbps AAC stereo may be possible
             >>to encode using the same AAC configuration. The declared payload types
             >>are present in a SDP. A client shall not accept the session and setup
             >>the media stream unless it can handle all these codecs. If it has setup
             >>this media stream it has in fact accepted that any of the codec may be
             >>used in the media stream.
             >>
             >>
             >>
             >
             >   well, I completely agree that *that* may be a solution to stream
             >   switching, the point then would be to document it!-)
             >
             >

             Good, then you should rather document this deficiency rather than
             claiming that it is possible.

             >
             >
             >
             >>The server can here use different strategies when switching. The most
             >>likely one is to use a single SSRC and in the same RTP sequence number
             >>and timestamp space send the selected media quality.
             >>
             >>
             >
             >   agreed, this is a very nice possibility...that obvioulsy we would
             >   need to *seriouly* document ... because this is not the "default"
             >   thing at all from existing specs, right?
             >
             >
             >

             I have seen it as being the default behaviour, however this is nothing
             that has been thoroughly discussed in AVT and the RTP spec not be that
             clear on this point. Documenting this would be a good thing.

             >
             >
             >>When the server
             >>switched this will be indicated by the new RTP PT. This has a slight
             >>problem as RTP/RTCP does not handle switched RTP TS rate perfectly. The
             >>client may in fact lose synchronization until it receives a RTCP packet
             >>after the switch has taken place.
             >>
             >>
             >
             >   right! that is a key issue!
             >
             >
             >
             >>This happens if the packet where the
             >>RTP TS rate switches is lost. This is not a problem as long as the RTP
             >>TS rate before and after the payload type switch has the same TS rate.
             >>In other words not a problem for any video codec which all runs at
             >>90000.
             >>
             >>
             >
             >   yes, not a problem *if* (as mentioned above) you mandate the same
             >   RTPTS space for all streams ...
             >
             >
             >
             >>This is more a problem for audio codecs. I would in fact try to
             >>address this problem with audio codecs by ensuring that any audio codec
             >>is allowed to select a RTP TS rate that is a even rate multiple of its
             >>native value. This would allow audio codecs to run at a the smallest
             >>common denominator rate.
             >>
             >>
             >>
             >
             >   Is it always possible/efficient?
             >

             No, not for the currently specified RTP payload formats. It is something
             I will recommend in future payload formats to allow for this functionality.

             >
             >
             >
             >>The other strategy at points of switching would be to use different
             >>SSRCs. This would violate the semantics that a SSRC represents a certain
             >>source. This also has some problems with the synchronization of the
             >>different SSRCs. This can't be done in RTSP as RTSP due to an erroneous
             >>definition of RTP-Info did not map each synchronization information to
             >>the SSRC. This can only be fixed through a new header due to backwards
             >>compatibility problems. Otherwise RTCP could be used. By sending SR for
             >>all SSRC one could in fact ensure that the synchronization is available.
             >>It will utilize more RTCP bandwidth.
             >>
             >>
             >>
             >
             >Hum, so we should disregard this option?
             >

             I think so.

             >
             >
             >
             >>5. Section 3.1.2: I don't think you should mix congestion control with
             >>adaptation control that hard. In my opinion, how drastic a content rate
             >>change is needed and how much depends on the clients buffer status.
             >>
             >>
             >>
             >
             >sorry, I do not understand that one?
             >

             This has to do with the complete system that a sender can transmit at
             one rate, while the media rate has another rate. The discrepancy is
             handled by the receiver buffer. Therefore the control of the media rate
             can be performed more drastic or not depending on what the buffer status
             is. An almost empty receiver buffer needs to be handled quickly and
             drastically, probably be reducing the media rate significantly. If the
             buffer are rather full the handling of this can be much less drastic, a
             small discrepancy can simply be tried to waited out. Or the quality
             change can be minimal.

             >
             >
             >
             >
             >
             >>8. Section 3.7: I don't think we can deploy a solution for switching
             >>that gives full functionality and at the same time is backwards
             >>compatible. However think on how one can maintain some of the
             >>functionality and being backwards compatible may be a worth the effort.
             >>However this is rather a design evaluation criteria than a requirement.
             >>
             >>
             >>
             >
             >   do you mean it is not appropriate to have backward compatibility as
             >   a requirement?
             >
             >
             >

             It might, however I think it should be further considered. I think
             listing the level as critical is to high level.

             Cheers

             Magnus Westerlund



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--Qxx1br4bt0+wmkIi
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> >I have been thinking about how 'playlists' may be supported with RTSP/RT=
P.
> >Playlists are what one might use in an internet radio session for=20
> >instance, pre-program a set of songs that are to be played out in sequen=
ce=20
> >on the same
> >RTP session.
> >Would it be possible to discuss this topic at the meeting today?

It seems to me there are two types of playlists: those created on the server
side (pre-set) and those created on the client side (dynamic).  Which are
you interested in?  I can see ways of supporting both today without any RTSP
or RTP extensions.

> The REASON for having this clarification of the usage of RTP timestamps=
=20
> are RTP and RTCP itself. The RTCP based synchronization and reporting=20
> would be very confused if you did not have continuos timestamp space. IF=
=20
> you would go stop the RTP timestamp space during pause while RTCP keeps=
=20
> advancing it at the defined rate parts of the TS space will be reused=20
> and the RTCP synchronization information will be impossible to match=20
> against the RTSP synchronization information.

I have observed in conversations that opinions vary as to whether RTCP
should continue to be sent during the PAUSE period.  Perhaps this issue
deserves clarification?

--=20
Under any conditions, anywhere, whatever you are doing, there is some
ordinance under which you can be booked.
        -- Robert D. Sprecht, Rand Corp.

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From: Geetha Srikantan <Geetha.Srikantan@sun.com>
Reply-To: Geetha Srikantan <Geetha.Srikantan@sun.com>
Subject: Re: [MMUSIC] RTSP discussion today
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Cc: Geetha.Srikantan@sun.com, mmusic@ietf.org
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> > >I have been thinking about how 'playlists' may be supported with RTSP/RTP.
> > >Playlists are what one might use in an internet radio session for 
> > >instance, pre-program a set of songs that are to be played out in sequence 
> > >on the same
> > >RTP session.
> > >Would it be possible to discuss this topic at the meeting today?
> 
> It seems to me there are two types of playlists: those created on the server
> side (pre-set) and those created on the client side (dynamic).  Which are
> you interested in?  I can see ways of supporting both today without any RTSP
> or RTP extensions.

Server side playlists are most iteresting to me.
I'm not sure that RTSP or RTP extensions are needed, either.

> 
> > The REASON for having this clarification of the usage of RTP timestamps 
> > are RTP and RTCP itself. The RTCP based synchronization and reporting 
> > would be very confused if you did not have continuos timestamp space. IF 
> > you would go stop the RTP timestamp space during pause while RTCP keeps 
> > advancing it at the defined rate parts of the TS space will be reused 
> > and the RTCP synchronization information will be impossible to match 
> > against the RTSP synchronization information.
> 
> I have observed in conversations that opinions vary as to whether RTCP
> should continue to be sent during the PAUSE period.  Perhaps this issue
> deserves clarification?


That's definitely something to discuss as well.

geetha


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Date: Wed, 16 Jul 2003 15:57:45 +0200
From: Colin Perkins <csp@csperkins.org>
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The IESG recently review the SDPnew draft, and sent the following comments.
I'll be talking about these in MMUSIC tomorrow.

Colin


>Ned Freed:
>This document should explicitly say it obsoletes RFC 2327.
>
>This document apparently defines the application/sdp media type, replacing
>the definition in RFC 2327, but contains no media type registration form
>nor any IANA action associated with the registration. (This was also true
>of RFC 2327.)
>
>A 44 page document REALLY needs a table of contents. (I realize the RFC
>Editor is supposed to deal with this, but RFC 2327 is 42 pages and didn't
>have a TOC either.)
>
>That's it!
>
>Steve:
>k= strikes me as almost useless. It doesn't have enough information
>(such as algorithm) to really be usable. I see no protection against
>replay prevention, nor any mention of that as a requirement for secure
>transport of SDP announcements. In fact, nothing is said about channel
>requirements in this context other than "secure and trusted". Is k=
>really used? Should it be deleted in favor of a pointer to
>draft-ietf-mmusic-sdescriptions?
>
>The Security Consideration section says that automatic mechanisms
>SHOULD NOT be used to start up interactive applications without user
>knowledge. I'd prefer MUST NOT, and I'd ask for consent, not simplhy
>knowledge. See the /dev/audio part of
>http://www.cert.org/advisories/CA-1993-15.html for why this is a
>problem...
>
>Russ:
>      Section 4.3 talks about private sessions. It says:
>
>            "The details of how encryption is performed are dependent on
>            the mechanism used to convey SDP - e.g. mechanisms are defined
>            for SDP transported using SAP [RFC2974] and SIP [RFC3261]."
>
>      Why aren't S/MIME for email and TLS for WWW included here?
>
>      In section 5, the discussion of encryption keys says:
>
>            "k=clear:<encryption key>
>
>              The encryption key is included untransformed in this key
>              field. This method MUST NOT be used unless it can be
>              guaranteed that the SDP is conveyed over a secure channel.
>
>              k=base64:<encoded encryption key>
>
>              The encryption key is included in this key field but has
>              been base64 encoded because it includes characters that are
>              prohibited in SDP. This method MUST NOT be used unless it
>              can be guaranteed that the SDP is conveyed over a secure
>              channel."
>
>      These restrictions are necessary but not sufficient. You must also
>ensure that the secure channel is with the party that is authorized to
>join the session, not an intermediary. If a caching server is used, there
>ought to be a way to keep the server from accessing the key.
>
>      Also, it is generally a good idea to indicate the algorithm that a
>cryptographic key is intended to support. I suggest that the encryption
>key type be revised to specify the key as well as the algorithm that the
>key will be used with.
>
>      Finally, many security protocols require two keys, one for
>confidentiality and another for integrity. This specification does not
>support the transfer of two keys.
>
>      In section 6, the document says:
>
>            "Use of the "k=" field poses a significant security risk,
>            since it conveys session encryption keys in the clear. SDP
>            MUST NOT be used to convey key material, unless it can be
>            guaranteed that the channel over which the SDP is delivered is
>            both private and authenticated."
>
>      I agree. It would therefore be desirable for the "k=" field to
>      support
>two other alternatives. First, it would be nice to name the key without
>actually including the key. In PEM (see RFC 1040), the Recipient-ID was
>used to name key-encryption keys, and a similar scheme could be employed
>here. Second, it would be nice to encrypt the session key in a key that is
>not included in SDP. PEM also includes a mechanism for wrapped symmetric
>keys.
>
>Ted:
>In Section 5, for the description of u=<URI>
>
>          I'd suggest eliminating "as used by WWW clients." and adding a
>          citation to draft-fielding-uri-rfc2396bis (or at least rfc2396).
>          Note that this definition seems to presume that all URIs used
>          will be dereferencable, which is not true for all URIs. If this
>          is a limitation, then it should be stated.
>
>          The k=<uri> also seems to presume that the URI is
>          dereferencable. If this is a limitation of the URI, it should be
>          made explicit
>which schemes
>          are appropriate here. Frankly, it seems to mean http:; if that
>          is the case, specifying it seems like a good idea. Even for
>          dereferencable URI schemes, not all will use MIME to mark the
>          reply (think of an ftp: URI, for example). When they do, the
>          mime content-encoding specifies the encoding of the _message_,
>          so reusing the word"encoding" here seems problematic. How would
>          "For those URI schemes which use MIME, the content-encoding and
>          content-type headers of the reply may provide guidance on the
>          format of the key." work?
>
>          On that same hobby horse, the ABNF in the appendix has:
>            ; sub-rules of 'u='
>              uri = URI-reference; see RFC1630 and RFC2732
>
>          I think this should be a pointer to 2396 or the 2396bis draft.
>
>          For the a= inactive designation, we've discussed what addresses
>          to use for sessions which are being set up but for which
>          addresses are not
>	  yet known.  It was suggested apps use something like "sdp.inactive" so
>	  that the .inactive TLD could reinforce the a=inactive flag. In that
>	  instance, would the presence of that TLD be a condition under which
>	  the RTCP SHOULD is appropriately not done, and no RTCP sent? If so, is
>	  mentioning that case appropriate here?
>
>          In the IANA considerations, it looks the draft should specify
>          that the
>	  IANA must update the MIME media type registration to point to this doc
>	  instead of RFC 2327.
>
>Notes:
>
>Having Section 5 contain so much without sub-headers made it hard to
>give pointers to sections in the comments; that may be true for others
>using the spec as well.
>
>In section 5, in the section describing the first subfield of c=
>          Just as a query, has anyone considered using a specific marker
>          of private address realms for SDP? That is, using a network type
>          other than IN to indicate that the domain name or address given
>          are not globally unique/globally reachable?
>
>In the Security considerations, "Many different protocols may be used
>to distribute session description," looks like session description should
>be plural.
>
>Bill:
>In the ABNF, the definition of "m1" ends with an extra ).
>
>
>The text says that type characters are case-sensitive.
>Unfortunately, this means that ASCII values have to be
>used in the ABNF instead of strings, since ABNF strings
>are case-insensitive. e.g.
>
>            proto-version = "v=" 1*DIGIT CRLF
>
>really has to be something like
>
>            proto-version = %x76 "=" 1*DIGIT CRLF
>or
>            proto-version = %x76.3d 1*DIGIT CRLF
>
>since both "v=0" and "V=0" match the one with "v=".
>
>I realize that this latter error is copied from RFC 2327. If this is
>the only objection I'm not going to stand on it too strongly.
>
>    Bill
>
>COMMENTS:
>========
>Erik Nordmark:
>Intro/abstract doesn't say the document obsoletes RFC 2137, which
>I think is the intent.
>
>The text on internationalization says UTF-8 only applies to informational
>fields. Does this mean it isn't required to perform any normalization
>whatsoever on the UTF-8?
>Would it make sense to explicitly state that normalization isn't needed.
>
>Typo:
>                removed. It is assumed that transports of SDP specify will
>                specify this.
>s/specify//
>


-- 
Colin Perkins
csp@csperkins.org

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From: Magnus Westerlund <magnus.westerlund@ericsson.com>
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To: Tom Marshall <tmarshall@real.com>
CC: Geetha Srikantan <Geetha.Srikantan@Sun.COM>, mmusic@ietf.org
Subject: Re: [MMUSIC] RTSP discussion today
References: <20030716112905.GA27952@real.com>
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>I have observed in conversations that opinions vary as to whether RTCP
>should continue to be sent during the PAUSE period.  Perhaps this issue
>deserves clarification?
>  
>

Yes, this should be clarified in the specification. It is expected that 
RTCP is sent at all time during session from SETUP to TEARDOWN. I have 
logged a tracking bug for this.

Best Regards

Magnus


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Date: Wed, 16 Jul 2003 07:30:37 -0700
To: Colin Perkins <csp@csperkins.org>
From: Mark Baugher <mbaugher@cisco.com>
Subject: Re: [MMUSIC] IESG comments on SDPnew
Cc: mmusic@ietf.org, Russ Housley <housley@vigilsec.com>, oran@cisco.com,
        mat@cisco.com
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Colin,
   I'd like to comment on Russ's comment.  See below.

At 03:57 PM 7/16/2003 +0200, Colin Perkins wrote:
>The IESG recently review the SDPnew draft, and sent the following comments.
>I'll be talking about these in MMUSIC tomorrow.
>
>Colin
>
>
> >Ned Freed:
> >This document should explicitly say it obsoletes RFC 2327.
> >
> >This document apparently defines the application/sdp media type, replacing
> >the definition in RFC 2327, but contains no media type registration form
> >nor any IANA action associated with the registration. (This was also true
> >of RFC 2327.)
> >
> >A 44 page document REALLY needs a table of contents. (I realize the RFC
> >Editor is supposed to deal with this, but RFC 2327 is 42 pages and didn't
> >have a TOC either.)
> >
> >That's it!
> >
> >Steve:
> >k= strikes me as almost useless. It doesn't have enough information
> >(such as algorithm) to really be usable. I see no protection against
> >replay prevention, nor any mention of that as a requirement for secure
> >transport of SDP announcements. In fact, nothing is said about channel
> >requirements in this context other than "secure and trusted". Is k=
> >really used? Should it be deleted in favor of a pointer to
> >draft-ietf-mmusic-sdescriptions?
> >
> >The Security Consideration section says that automatic mechanisms
> >SHOULD NOT be used to start up interactive applications without user
> >knowledge. I'd prefer MUST NOT, and I'd ask for consent, not simplhy
> >knowledge. See the /dev/audio part of
> >http://www.cert.org/advisories/CA-1993-15.html for why this is a
> >problem...
> >
> >Russ:
> >      Section 4.3 talks about private sessions. It says:
> >
> >            "The details of how encryption is performed are dependent on
> >            the mechanism used to convey SDP - e.g. mechanisms are defined
> >            for SDP transported using SAP [RFC2974] and SIP [RFC3261]."
> >
> >      Why aren't S/MIME for email and TLS for WWW included here?
> >
> >      In section 5, the discussion of encryption keys says:
> >
> >            "k=clear:<encryption key>
> >
> >              The encryption key is included untransformed in this key
> >              field. This method MUST NOT be used unless it can be
> >              guaranteed that the SDP is conveyed over a secure channel.
> >
> >              k=base64:<encoded encryption key>
> >
> >              The encryption key is included in this key field but has
> >              been base64 encoded because it includes characters that are
> >              prohibited in SDP. This method MUST NOT be used unless it
> >              can be guaranteed that the SDP is conveyed over a secure
> >              channel."
> >
> >      These restrictions are necessary but not sufficient. You must also
> >ensure that the secure channel is with the party that is authorized to
> >join the session, not an intermediary. If a caching server is used, there
> >ought to be a way to keep the server from accessing the key.
> >
> >      Also, it is generally a good idea to indicate the algorithm that a
> >cryptographic key is intended to support. I suggest that the encryption
> >key type be revised to specify the key as well as the algorithm that the
> >key will be used with.
> >
> >      Finally, many security protocols require two keys, one for
> >confidentiality and another for integrity. This specification does not
> >support the transfer of two keys.
> >
> >      In section 6, the document says:
> >
> >            "Use of the "k=" field poses a significant security risk,
> >            since it conveys session encryption keys in the clear. SDP
> >            MUST NOT be used to convey key material, unless it can be
> >            guaranteed that the channel over which the SDP is delivered is
> >            both private and authenticated."
> >
> >      I agree. It would therefore be desirable for the "k=" field to
> >      support
> >two other alternatives. First, it would be nice to name the key without
> >actually including the key. In PEM (see RFC 1040), the Recipient-ID was
> >used to name key-encryption keys, and a similar scheme could be employed
> >here. Second, it would be nice to encrypt the session key in a key that is
> >not included in SDP. PEM also includes a mechanism for wrapped symmetric
> >keys.

I think it would be wrong to place security mechanisms inside SDP since SDP 
is used with an encapsulating protocol.  SDP needs to use the mechanisms of 
the encapsulating protocol for protecting its keys, cryptographic 
parameters, session security parameters, and other descriptions that are of 
security interest.

That being said, I agree with Russ and Steve that k= is 
under-specified.   That's what I found a year ago when I needed to use it 
for SRTP.

Mark

> >
> >Ted:
> >In Section 5, for the description of u=<URI>
> >
> >          I'd suggest eliminating "as used by WWW clients." and adding a
> >          citation to draft-fielding-uri-rfc2396bis (or at least rfc2396).
> >          Note that this definition seems to presume that all URIs used
> >          will be dereferencable, which is not true for all URIs. If this
> >          is a limitation, then it should be stated.
> >
> >          The k=<uri> also seems to presume that the URI is
> >          dereferencable. If this is a limitation of the URI, it should be
> >          made explicit
> >which schemes
> >          are appropriate here. Frankly, it seems to mean http:; if that
> >          is the case, specifying it seems like a good idea. Even for
> >          dereferencable URI schemes, not all will use MIME to mark the
> >          reply (think of an ftp: URI, for example). When they do, the
> >          mime content-encoding specifies the encoding of the _message_,
> >          so reusing the word"encoding" here seems problematic. How would
> >          "For those URI schemes which use MIME, the content-encoding and
> >          content-type headers of the reply may provide guidance on the
> >          format of the key." work?
> >
> >          On that same hobby horse, the ABNF in the appendix has:
> >            ; sub-rules of 'u='
> >              uri = URI-reference; see RFC1630 and RFC2732
> >
> >          I think this should be a pointer to 2396 or the 2396bis draft.
> >
> >          For the a= inactive designation, we've discussed what addresses
> >          to use for sessions which are being set up but for which
> >          addresses are not
> >         yet known.  It was suggested apps use something like 
> "sdp.inactive" so
> >         that the .inactive TLD could reinforce the a=inactive flag. In that
> >         instance, would the presence of that TLD be a condition under which
> >         the RTCP SHOULD is appropriately not done, and no RTCP sent? If 
> so, is
> >         mentioning that case appropriate here?
> >
> >          In the IANA considerations, it looks the draft should specify
> >          that the
> >         IANA must update the MIME media type registration to point to 
> this doc
> >         instead of RFC 2327.
> >
> >Notes:
> >
> >Having Section 5 contain so much without sub-headers made it hard to
> >give pointers to sections in the comments; that may be true for others
> >using the spec as well.
> >
> >In section 5, in the section describing the first subfield of c=
> >          Just as a query, has anyone considered using a specific marker
> >          of private address realms for SDP? That is, using a network type
> >          other than IN to indicate that the domain name or address given
> >          are not globally unique/globally reachable?
> >
> >In the Security considerations, "Many different protocols may be used
> >to distribute session description," looks like session description should
> >be plural.
> >
> >Bill:
> >In the ABNF, the definition of "m1" ends with an extra ).
> >
> >
> >The text says that type characters are case-sensitive.
> >Unfortunately, this means that ASCII values have to be
> >used in the ABNF instead of strings, since ABNF strings
> >are case-insensitive. e.g.
> >
> >            proto-version = "v=" 1*DIGIT CRLF
> >
> >really has to be something like
> >
> >            proto-version = %x76 "=" 1*DIGIT CRLF
> >or
> >            proto-version = %x76.3d 1*DIGIT CRLF
> >
> >since both "v=0" and "V=0" match the one with "v=".
> >
> >I realize that this latter error is copied from RFC 2327. If this is
> >the only objection I'm not going to stand on it too strongly.
> >
> >    Bill
> >
> >COMMENTS:
> >========
> >Erik Nordmark:
> >Intro/abstract doesn't say the document obsoletes RFC 2137, which
> >I think is the intent.
> >
> >The text on internationalization says UTF-8 only applies to informational
> >fields. Does this mean it isn't required to perform any normalization
> >whatsoever on the UTF-8?
> >Would it make sense to explicitly state that normalization isn't needed.
> >
> >Typo:
> >                removed. It is assumed that transports of SDP specify will
> >                specify this.
> >s/specify//
> >
>
>
>--
>Colin Perkins
>csp@csperkins.org
>
>_______________________________________________
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From: Hanne Moa <hanne.moa@uninett.no>
To: Colin Perkins <csp@csperkins.org>
Cc: mmusic@ietf.org
Subject: Re: [MMUSIC] IESG comments on SDPnew
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* On 2003-07-16 15:57:45 +0200 Colin Perkins wrote:
> The IESG recently review the SDPnew draft, and sent the following comments.
> I'll be talking about these in MMUSIC tomorrow.
> 
> Colin
> 
> >Steve:
> >k= strikes me as almost useless. It doesn't have enough information
> >(such as algorithm) to really be usable. I see no protection against
> >replay prevention, nor any mention of that as a requirement for secure
> >transport of SDP announcements. In fact, nothing is said about channel
> >requirements in this context other than "secure and trusted". Is k=
> >really used?

I've been monitoring SAP-packets for over a year now and never seen it.
Ditto for z= (time zone adjustments).

Furthermore, more than 90% of sdp over sap is unspecified for time,
that is: t=0 0. It is used for just about anything: on-demand, 24/7
webcams, conferences... It is so vague as to be useless.

Here's one from today:

v=0
o=- 12157 2 IN IP4 128.223.83.33
s=IETF 57 Channel-1 MPEG-4
i=IETF57 - Channel-1 MPEG-4
e=multicast@lists.uoregon.edu               <--- wow, one of the 5% valid ones!
b=AS:500
t=0 0                                       <--- a-hum
a=tool:IP/TV Content Manager 3.4.14
a=type:broadcast
a=live:capture:1
m=video 49470 RTP/AVP 31 32 96 97
c=IN IP4 224.2.195.59/127
a=x-iptv-videoheight:240
a=x-iptv-videowidth:320
a=x-iptv-svr:video 81.160.32.4 live
a=quality:8
a=framerate:30
a=fmtp:96 profile-level-id=1;config=000001B001000001B50EE04040AF0000010000000120
00845D4C285020F0A31F
a=rtpmap:96 MP4V-ES/90000
a=rtpmap:97 WBIH/90000
m=audio 19154 RTP/AVP 0 3 5 10 11 14 96 97 98 99 100 101 102 103 104 105 106
c=IN IP4 224.2.166.105/127
a=x-iptv-svr:audio 81.160.32.4 live
a=fmtp:14 layer=3; samplerate=11025; mode=stereo;
a=rtpmap:96 X-WAVE/8000
a=rtpmap:97 L8/8000/2
a=rtpmap:98 L8/8000
a=rtpmap:99 L8/22050/2
a=rtpmap:100 L8/22050
a=rtpmap:101 L8/11025/2
a=rtpmap:102 L8/11025
a=rtpmap:103 L16/22050/2
a=rtpmap:104 L16/22050
a=rtpmap:105 L16/11025/2
a=rtpmap:106 L16/11025

If t= *is* used, there's very rarely an r= (repetitions) in the same
sdp, and often an almost, but not quite identical message (+n seconds
in the second field of t= will be sent, with a slightly modified
identifier (o=) every n seconds, overlapping with another similarly
almost-clone message every n+m seconds. In these situations t=0 0
actually would have made sense!)

Oh, and e= (email-address) and p= (phone number) are used for the
strangest things. I should have saved the haiku...


HM.

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To: mmusic@ietf.org
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Cc: jo@informatik.uni-bremen.de (Joerg Ott), csp@csperkins.org,
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An updated revision of the agenda is available at

    http://www.dmn.tzi.org/ietf/mmusic/57/agenda.html

included below as text version.

Cheers,
Joerg


57th IETF: Draft MMUSIC Agenda
==============================

Thursday, 17 July 2003, 0900 - 1130, Hall IK
--------------------------------------------

0900    Agenda Bashing and Status Update               (chairs, 10)

        Recent RFCs
	- draft-ietf-mmusic-reservation-flows-01.txt	-> RFC 3524

        With RFC editor
        - draft-ietf-mmusic-sdp4nat-05.txt
        - draft-ietf-mmusic-sdpng-trans-04.txt

	With IESG
        - draft-ietf-mmusic-sdp-new-13.txt
	- draft-rajeshkumar-mmusic-gpmd-03.txt

	With AD
        - draft-ietf-mmusic-sdp-comedia-05.txt
	- draft-ietf-mmusic-srcfilter-05.txt

	WG Last Call
	- draft-ietf-mmusic-sdp-bwparam-04.txt

        Misc Updates
	- draft-camarillo-mmusic-alt-01.txt
	- draft-ietf-mmusic-kmgmt-ext-07.txt
	- draft-ietf-mmusic-sdp-implem-00.txt

0910	Revised SDP					(Perkins, 10)
        - draft-ietf-mmusic-sdp-new-13.txt

0930	SDP Security Descriptions for Media Streams	(Wing, 10)
	- draft-ietf-mmusic-sdescriptions-01.txt

0940	SDP Offer Answer Examples			(Johnston, 10)
	- draft-ietf-mmusic-offer-answer-examples-01.txt

0950	SDPng Update					(Kutscher, 20)
	- draft-ietf-mmusic-sdpng-06.txt

1010	RTP DoS Attack					(Rosenberg, 10)
	- draft-rosenberg-mmusic-rtp-denialofservice-00.txt

1020	Interactive Connectivity Establishment (ICE)	(Rosenberg, 10)
	- draft-rosenberg-sipping-ice-01.txt

1030	RTSP Update					(Westerlund, 30)
	- draft-ietf-mmusic-rfc2326bis-04.txt
	- draft-ietf-mmusic-rtsp-nat-01.txt

1100	Internet Media Guides				(Manyfolks, 30)
	- draft-nomura-mmusic-img-requirements-01.txt
	- draft-nomura-mmusic-img-framework-01.txt
	- draft-luoma-mmusic-img-muppet-02.txt
	- draft-luoma-mmusic-img-metadata-01.txt
	- draft-stallard-mmusic-dvb-thoughts-on-sds-00.txt

1130	Close



Second (formal) meeting still to be scheduled for RTSP
------------------------------------------------------
Tentatively Wednesday night over dinner

	RTSP spec editing and bug fixing		(Westerlund/Lanphier, 120)


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Date: Wed, 16 Jul 2003 10:55:32 -0700 (PDT)
From: Stephen Casner <casner@acm.org>
To: Hanne Moa <hanne.moa@uninett.no>
cc: Colin Perkins <csp@csperkins.org>, <mmusic@ietf.org>
Subject: Re: [MMUSIC] IESG comments on SDPnew
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On Wed, 16 Jul 2003, Hanne Moa wrote:

> I've been monitoring SAP-packets for over a year now and never seen it.
> Ditto for z= (time zone adjustments).
>
> Furthermore, more than 90% of sdp over sap is unspecified for time,
> that is: t=0 0. It is used for just about anything: on-demand, 24/7
> webcams, conferences... It is so vague as to be useless.

The IP/TV product, initially from Precept Software then later and still
from Cisco, uses both t= and z= but (to my recollection) not k=.

                                                        -- Steve


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To: Mark Baugher <mbaugher@cisco.com>
From: Ross Finlayson <finlayson@live.com>
Subject: Re: [MMUSIC] IESG comments on SDPnew
Cc: Colin Perkins <csp@csperkins.org>, mmusic@ietf.org,
        Russ Housley <housley@vigilsec.com>, oran@cisco.com, mat@cisco.com
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Because of the known limitations/problems with "k=", plus the fact that we 
now have a better way of describing keying information (i.e., 
"ietf-mmusic-sdescriptions"), I think that the "SDPnew" document should 
just get rid of "k=" (or, at the very least, note that it's deprecated).

         Ross.


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Date: Wed, 16 Jul 2003 18:37:04 -0400
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Sorry for the delay in responding, Magnus. Responses inline.

Magnus Westerlund wrote:

> Hi Jonathan,
> 
> I have now had time to read your draft. It summaries the problem of the 
> attack fairly well. However I think one can elaborate a bit more on some 
> use cases and in relation to NAT traversal.
> 
> First, the problem of destination addresses in combination with NATs 
> that use multiple addresses. If a NAT would assign different NAT 
> mappings to different external addresses there is a problem with the 
> limiting text that RTSP has. This also is present for a single RTP 
> session where RTP and RTCP will be separate flows. This leads to that 
> simple limitations can't be used while still NAT traversal or TURN 
> servers are in use.

Yes, I agree. That is a general RTSP issue.

> 
> Secondly the RTCP prevention that you mention in chapter 3 has more 
> flaws then you describe, but not one of them you describe I would say.

OK, well I'm glad we agree even though its for the wrong reasons...

> I 
> don't see a reason to force the sending side to have this stop and go 
> behaviour you describe. I would more work in the terms of how TFRC 
> behave, I think. If no RTCP reports are received the sending bit-rate is 
> throttled back, to almost non existing levels. This will limit the 
> severity of the attack. However with using many sessions it might still 
> be possible to achieve enough force amplification.

I'm not that familiar with TFRC. How is the initial rate set? That 
could make a big difference too.

> 
> The flaw you missed in your description of using RTCP as limiting factor 
> is first that if the attacker directs a RTCP stream to itself and only 
> the RTP stream to the target, it can simple generate false RTCP reports.

Ah - good point. I hadnt thought of that. Normally its not possible, 
but draft-ietf-mmusic-sdp4nat will allow this.

>  The senders RTCP reports contains the number of packets sent, which 
> makes it easy to increase the RTCP receiver reports extended counter. 
> The initial RTP sequence number are usually transmitted in RTSP's 
> RTP-Info header. Therefore all necessary information for faking a 
> perfect reception pattern exist, keeping any congestion control based on 
> RTCP reports happy.

Right.

> 
> Third, the solution space. As you mention an alternative to using STUN 
> in this requesting mechanism would be to develop a RTP payload format 
> and RTCP packet type to contain necessary information of granting a 
> media stream. What may be missing in STUN is the possibility to provide 
> information about the media stream that the receiver accepts.

That information is conveyed in the signaling protocol. Clearly this 
information is only useful when there is NOT an attack, so the 
recipient would be privy to the signaling.

> 
> However I don't know if such a solution would be any better. Maybe on 
> the paper it would have a clearer demultiplexing than between STUN and 
> RTP. However STUN can be used with any media protocol that can be 
> differentiated on the first byte, while a RTP/RTCP solution would be 
> limited to that protocol.

Right.

> 
> Fourth, have you looked at what solutions DCCP would provide to this 
> problem? I think that the session establishment could ensure that the 
> client accepts the media stream.

Yes, I believe it would. However, we have some time to go before that 
really becomes deployable.

> 
> Fifth, what is the current status of ICE? Can we expect any progress for 
> ICE within the IETF.

We will be discussing this today in mmusic. Yesterday, sipping 
re-affirmed its desire to move forward with ICE. We agreed that there 
are really two documents. One is the actual ICE mechanism, which is 
not sip specific at all. The other is use cases that show how ICE is 
used with SIP. THe latter will be happening in sipping, as an 
alternative to the current draft-ietf-sipping-nat-scenarios document. 
The former, however, appeared to be more of an mmusic issue. So, the 
sipping group wants mmusic to take ICE as a work item, in fact.

> 
> Sixth, doesn't one need to use STUN with authentication to prevent other 
> security attacks that based on falsifying STUN responses, even when the 
> session establisher is not an attacker?

Yes, and thats why there is authentication in stun. Mostly the 
authenticaiton is of the SERVER - the client identity is not that 
important.

Thanks,
Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
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Sorry for the delay in responding. Responses inline.

Thomas Zeng wrote:

> Jonathan:
> 
> Thanks for this timely work. I finally got a chance to review it, along with
> the email trail.
> 
> Magnus asked a good question: doesn't STUN (RFC3489) require TLS ? See
> section 9.2:
>    In order to ensure interoperability, this
>    specification describes a TLS-based mechanism.  This mechanism,
>    described in this section, MUST be implemented by clients and
>    servers.

TLS is not needed in the peer-to-peer usage. Thats because there is an 
alternate mechanism being used for obtaining the shared secret - 
namely the signaling protocol, which has its own security mechanisms.

The words above are aimed at the case where the client is contacting a 
public server. There, yes it is needed.

> 
> I suspect that some RTSP thin clients (those embedded in low-power devices)
> may not have enough resources (CPU and/or bandwidth) to run TLS... at the
> minimal, it adds more work to implementors of RTSP.

I would imagine TLS would be there for other reasons.


> 
> 
> Now, in section 5 of:
> http://www.ietf.org/internet-drafts/draft-rosenberg-mmusic-rtp-denialofservi
> ce-00.txt
> 
> You seem to imply that RTSP already follows Offer/Answer exchanges? I'd like
> to hear more on this subject...

No, clearly it doesn't. I'm being loose with my terms here. It follows 
an offer-answer like exchange in that there are two entities, and both 
tell each other IP addresses.

-Jonathan R.



-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com


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This is an automatic digest of bugs submitted and changed on the RTSP bug tracker.  To see a list of bugs, visit:

http://sf.net/projects/rtspspec

When replying, please make your Subject line more specific than "Re: Rtspspec-bugs digest"



Today's Topics:

   1. [ rtspspec-Bugs-772330 ] Clarify that RTCP shall be sent during whole session (SourceForge.net)
   2. [ rtspspec-Bugs-772330 ] Clarify that RTCP shall be sent during whole session (SourceForge.net)

--__--__--

Message: 1
To: noreply@sourceforge.net
From: "SourceForge.net" <noreply@sourceforge.net>
Date: Wed, 16 Jul 2003 07:09:52 -0700
Subject: [rtspspec-bugs] [ rtspspec-Bugs-772330 ] Clarify that RTCP shall be sent during whole session

Bugs item #772330, was opened at 2003-07-16 16:09
Message generated for change (Tracker Item Submitted) made by Item Submitter
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=377744&aid=772330&group_id=23194

Category: None
Group: Fix DS - Needs clarificiation
Status: Open
Resolution: None
Priority: 5
Submitted By: Magnus Westerlund (magwes)
Assigned to: Nobody/Anonymous (nobody)
Summary: Clarify that RTCP shall be sent during whole session

Initial Comment:
Appendix B should be clarified to point out that RTCP
is expected to be sent from succesful response of SETUP
until TEARDOWN. During PAUSE the server and client
should both continue to send RTCP as normal. 

Motivations to this behavior is:
- to avoid timing out SSRC, 
- ensure detection of packet loss at the end of stream.
- ensure that RTCP syncrhonization can work (necessary
for multiple SSRC). 
- Ensure that RTP stream work prior to PLAY if there is
some delay between them. 



----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=377744&aid=772330&group_id=23194


--__--__--

Message: 2
To: noreply@sourceforge.net
From: "SourceForge.net" <noreply@sourceforge.net>
Date: Wed, 16 Jul 2003 07:12:35 -0700
Subject: [rtspspec-bugs] [ rtspspec-Bugs-772330 ] Clarify that RTCP shall be sent during whole session

Bugs item #772330, was opened at 2003-07-16 16:09
Message generated for change (Comment added) made by magwes
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=377744&aid=772330&group_id=23194

Category: None
Group: Fix DS - Needs clarificiation
Status: Open
Resolution: None
Priority: 5
Submitted By: Magnus Westerlund (magwes)
Assigned to: Nobody/Anonymous (nobody)
Summary: Clarify that RTCP shall be sent during whole session

Initial Comment:
Appendix B should be clarified to point out that RTCP
is expected to be sent from succesful response of SETUP
until TEARDOWN. During PAUSE the server and client
should both continue to send RTCP as normal. 

Motivations to this behavior is:
- to avoid timing out SSRC, 
- ensure detection of packet loss at the end of stream.
- ensure that RTCP syncrhonization can work (necessary
for multiple SSRC). 
- Ensure that RTP stream work prior to PLAY if there is
some delay between them. 



----------------------------------------------------------------------

>Comment By: Magnus Westerlund (magwes)
Date: 2003-07-16 16:12

Message:
Logged In: YES 
user_id=302620

At the same time it should be made clear the RTCP BYE is
sent when the session is terminated, i.e. at the time of
teardown.



----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=377744&aid=772330&group_id=23194




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Date: Thu, 17 Jul 2003 08:18:59 +0200
From: Colin Perkins <csp@csperkins.org>
To: Ross Finlayson <finlayson@live.com>
Cc: mbaugher@cisco.com, mmusic@ietf.org, housley@vigilsec.com, oran@cisco.com,
        mat@cisco.com
Subject: Re: [MMUSIC] IESG comments on SDPnew
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--> Ross Finlayson <finlayson@live.com> writes:
> Because of the known limitations/problems with "k=", plus the fact that
> we now have a better way of describing keying information (i.e., 
> "ietf-mmusic-sdescriptions"), I think that the "SDPnew" document should 
> just get rid of "k=" (or, at the very least, note that it's deprecated).

Certainly we should note that it's deprecated. But, we need to determine if
there are any implementations before deciding if we can remove "k="...

-- 
Colin Perkins
csp@csperkins.org

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To: Colin Perkins <csp@csperkins.org>
Cc: dccp@ietf.org, mmusic@ietf.org, floyd@icir.org, jpanderson@sonusnet.com,
        "Phelan, Tom" <tphelan@sonusnet.com>
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Subject: [MMUSIC] Re: [dccp] stream switching (was: Using DCCP for VoIP)
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colin perkins wrote:

>Do the ideas in draft-gentric-mmusic-stream-switching-req-00.txt help any
>here?

I confirm the problems you report are the same ones the
"stream switching" proposal aims to solve, see below for details.

--> "Phelan, Tom" <tphelan@sonusnet.com> writes:
> Hi Sally,
>
> Thanks for the response.  See inline ...
>
> Tom P.
>
> [clipped]
> > >The DCCP documents talk about VoIP being one of the main
> > applications for
> > >DCCP.  I've been trying to figure out a reasonable way for a VoIP
> > >application to use DCCP.  Here's what I've come up with so
> > far.  Corrections
> > >and comments would be appreciated.
> > >

Apart from the fact that my original concern was for "media delivery"
i.e. an application where -contrary to VoIP- end to end delay is
not critical, the problems are exactly the same for *all*
media traffic, be it voice, video, text, etc

audio is a very good case for study since it
is so critical in terms of *gaps* in the stream.
however the case of *multiple* streams (A+V to start with)
must be considered (see end of the mail)!

[clipped]

> > >Now assume the network becomes congested and one (at least)
> > of my packets
> > >get dropped.  DCCP decides it must back off the transmission
> > rate, so one of
> > >my 'send's fails with EWOULDBLOCK.


This is clearly not very rich feedback, a blocking send is so very drastic!

I would love to see the DCCP stack give earlier feedback something in the spirit of:

"hey, be ready to change your rate because the connection state
seems to indicate that the available bandwidth is decreasing"

and then something like:

"hey, the available bandwidth has reduced to xxx kb/s, change your rate ASAP"

and in case of "emmergencies" (which definition would actually depend
on the congestion control that has been chosen) if the DCCP stack has
the impression that the available rate is extremely rapidly decreasing
it would send:

"hey reduce your rate to yyy kb/s NOW"

and for increases:

"hey, you can increase your rate up to zzz kb/s" (the codec
can take its time then, there is never any emmergency)

[clipped]

> > We would also like to understand better how DCCP would or would not
> > work for a VoIP flow that did not have an adaptive codec, but we
> > have not worked this through.  (E.g., under congestion, some fraction
> > of the packets from the codec would be dropped by the DCCP sender.)
> >
> > >If the codec family can support this change on the fly,
> > that's great.  But
> > >if it requires renegotiation, I'll need to wait for that.
> > If I renegotiate
> > >in band, then my change request packet will get queued until
> > DCCP decides it
> > >can transmit again.  If I renegotiate out of band, then that
> > channel might
> > >be having it's problems too.  At any rate, there will be a
> > round-trip delay
> > >or so before I can start sending packets again.
> >

stream switching is *exactly* about solving this: how to change
the rate by switching *codecs* (and/or codec config since a lot
of recent codec have wide ranges of parameters/profiles/rates etc)

deployed (streaming) products show that it is not only possible, it works fine.

the assumption is that the negociation takes time,
also the instanciation of the ressources -especially on thin client- also takes time
so it *must* take place "before". This before could be at session start,
but it could also be at anytime during the session, but then not on short notice,
(especially not with a blocking write!?-)

So -again- it is very important that the DCCP stack gives early feedback
so as to have time to "setup" (RTSP-wise) the required codecs.

> > If negotiation is required, this is about the codec, not about DCCP,
> > right?
>
> Right.  This was meant to indicate that the app probably can't
> immediately change its sending rate.
>

if the app "cannot change its rate" DCCP will be a very little use *anyway* no?


I think you must assume that either the codec rate can be changed (true for
most video codecs and a lot of recent audio codecs) and if the change of rate
goes beyond the flexibility of a given codec you must change the codec and/or its configuration.
[In the stream switching drafts the former is described as "transparent"
and the latter as "non transparent"]

Note that for coding efficiency reasons it is a *very bad idea*
to try to drive a video codec with rapid instantaneous changes of rate.

anyway the key issue is that DCCP *and* the codec(s) must have a way to
talk, be configured etc ... work together hand in hand

> > It's also not clear why you need to stay quiet until the codec change
> > request is acknowledged. DCCP has reduced its allowable send
> > rate, but not
> > to zero.

the codecs need to know the exact target rate, DCCP must give this as output
(the rate of that feedback could be configurable ?)

the "contract" between the codecs and the DCCP stack is very simple:
the chosen configuration MUST have a rate smaller (or equal) to the target.

> That is probably true, but I'm not sure how the other end would react to
> receiving old-codec packets while the new codec is half-negotiated.

It cannot (see above).

Another problem is the ability to distinguish between the packet containing data of one codec
or the other since for most decoder feeding the wrong type
of syntax can be very bad (can even lead to crashes etc)

This issue is addressed in the stream switching proposal:
typically with RTP the "old codec" uses one (dymamically attributed)
PT and the new one uses another one.

There was the possibility to use another "port",
but with DCCP this would be stupid no?

this leads me to the following question:

Can we assume that a given DCCP *connection* will be used
to transport each media e.g. "audio" (i.e. eventually with codec changes
on the fly, indicated by changes in PT of RTP packets)?

Then for audio+video there will be 2 DCCP connections right?

How is the DCCP feedback going to work then?

Indeed in stream swithing I always assumed that the target
is the *pair* A+V i.e. the target rate can be obtained
using SEVERAL combination, examples:

5 kb/s AMR audio + 245 kb/s video = 250 kb/s, basic audio
40 kb/s AAC audio + 210 kb/s video = 250 kb/s, better audio
80 kb/s AAC stereo + 170 kb/s video = 250 kb/s, good audio


******************

regards,


Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com



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To: "Phelan, Tom" <tphelan@sonusnet.com>
Cc: dccp@ietf.org, mmusic@ietf.org,
        "'Reiner Ludwig'" <Reiner.Ludwig@ericsson.com>
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Subject: [MMUSIC] RE: [dccp] Using DCCP for VoIP
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All,

IMHO this issue is related to my question in the other mail about managing audio AND video at the same time:

probably DCCP should have a way to handle "collectively" a bunch of streams, be it audio plus video or  two-way audio!


regards,

Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com


                                                                                                                                       
                                                                                                                                       
                                                   To:   "'Reiner Ludwig'" <Reiner.Ludwig@ericsson.com>                                
                                                    dccp@ietf.org                                                                      
                                                   cc:   (bcc: Philippe Gentric/MP4-SUR/CE/PHILIPS)                                    
                                                   Subject:    RE: [dccp] Using DCCP for VoIP                                          
               "Phelan, Tom"                                                                                                           
               <tphelan@sonusnet.com>              Classification:                                                                     
                                                                                                                                       
               Sent by:                                                                                                                
               dccp-admin@ietf.org                                                                                                     
                                                                                                                                       
               17/07/2003 09:17                                                                                                        
                                                                                                                                       
                                                                                                                                       




Hi Reiner,

I guess I missed this when you sent it on tsvwg, thanks for resending.  To
me it seems to say that the thought of using TRFC for two-way telephony is
fundamentally broken, so DCCP isn't usable for that until there's a new
CCID.

Tom P.

> -----Original Message-----
> From: Reiner Ludwig [mailto:Reiner.Ludwig@ericsson.com]
> Sent: Wednesday, July 16, 2003 3:06 AM
> To: dccp@ietf.org
> Subject: RE: [dccp] Using DCCP for VoIP
>
>
> I'm forwarding this mail since I believe it relates to the currrent
> discussion about DCCP for VoIP. I had sent this mail to the
> tsvwg mailing
> list a few weeks ago ...
>
> ///einer
>
>
> >X-Sender: eedrel@mailhost.eed.ericsson.se
> >X-Mailer: QUALCOMM Windows Eudora Version 5.2.0.9
> >Date: Fri, 04 Apr 2003 10:52:58 +0200
> >To: tsvwg@ietf.org
> >From: Reiner Ludwig <Reiner.Ludwig@eed.ericsson.se>
> >Subject: Re: [Tsvwg] redundant data - A TFRC Example
> >Sender: tsvwg-admin@ietf.org
> >X-BeenThere: tsvwg@ietf.org
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> >List-Unsubscribe: <https://www1.ietf.org/mailman/listinfo/tsvwg>,
> >         <mailto:tsvwg-request@ietf.org?subject=unsubscribe>
> >List-Id: Transport Area Working Group <tsvwg.ietf.org>
> >List-Post: <mailto:tsvwg@ietf.org>
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> >List-Subscribe: <https://www1.ietf.org/mailman/listinfo/tsvwg>,
> >         <mailto:tsvwg-request@ietf.org?subject=subscribe>
> >
> >I'd like to add an example for people to think about ...
> >
> >If you try to run VoIP over TFRC, you'll most likely be
> disappointed by
> >the quality. The reason is that when A talks, then (usually)
> B is silent,
> >and vice versa. I.e., a talkspurt A>B is followed by a
> talkspurt B>A is
> >followed by a talkspurt A>B, ....
> >
> >While B is silent and if the talkspurt from A is long enough
> then B's TFRC
> >send rate will decay to zero (or at least often enough below
> the required
> >coder rate). Andrei Gurtov did this experiment and told me
> how 'broken'
> >such a voice conversation becomes.
> >
> >The "easy fix" is for B to send dummy data (or even
> potentially useful
> >data like pictures, ads, calendar sync data, etc.) for the
> sole purpose of
> >maintain the TFRC rate above the required coder rate. B
> would be a good
> >Internet citizen in the sense that it is always TCP
> friendly. Still, B is
> >sending data it does't have to send necessarily.
> >
> >Should the IETF set up rules that would limit the sending of such
> >potentially useless data? Do we have hope that such rules
> would be obeyed
> >by application and protocol designers?
> >
> >I could imagine VoIP application designers that would let
> themselves be
> >convinced to move away from uncontrolled UDP to RTP/DCCP,
> but probably not
> >much further. I.e., their view could be: "We ensure that our
> flows behave
> >TCP friendly, but what we do with the available bandwidth is
> our business."
> >
> >I'm not saying that I agree to that, but I would understand
> that view.
> >
> >///Reiner
> >
> >_______________________________________________
> >tsvwg mailing list
> >tsvwg@ietf.org
> >https://www1.ietf.org/mailman/listinfo/tsvwg
>
>
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
>

_______________________________________________
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Hi,

This is a summary of the discussion during wednesday's RTSP dinner 
(2003-07-16, 17.30 - 19.30).

Participants: Magnus Westerlund, Anders Klemets, David Singer, Geetha S, 
Aravind N, Henning Schulzrinne, Thomas Zeng, Philippe Gentric, Patrik ?, 
Joerg Ott, Colin Perkins, Tom Marshall + 2 (sorry I can't remember your 
names).

Issue: Missing session level control URI in SDP. IF the session control 
URI is missing, should we allow the client to try to to aggregate these? 
If aggregated which session control URI must be used.

Discussion: This needs to be resolved. Tom Marshall did not thought that 
we should prevent the use case to aggregate unless necessary for 
interoperability. One possible resolution is to say that any media 
description missing session level control URI must be setup with 
individual RTSP session for each media stream and any synchronization 
between media be done on the receiver side. A practical resolution 
resolution could be: A client SHOULD follow the above statement but MAY 
try to aggregate. The server MAY allow this aggregation but MAY also 
refuse it using 4xx (Only non aggregated operation allowed).

Resolution?: Session declarations lacking a session level control URL, 
MUST be used in non-aggregated control.
Further discussion needed?

Issue: Need to clarify that how a=range can be interpreted to indicate 
Live signalling.

Discussion: The basic idea was that any a=range time format that are 
open ended, e.g. npt=0- or npt=now-, should be interpreted as a live 
media. However Live media is not well defined and may not be sharing the 
same properties for all use cases. For example a proxy could actually 
work as one of these TiVo boxes and record media during PAUSED live 
streams. The media stream would be unbound but not share the properties 
for a live only stream as it will be seekable in the already played 
parts. Need for a attribute specifying stream properties seem useful. 
Possible attributes are: Non-seekable, seekable backwards in time, muted.

Resolution: A open ended range format shall be interpreted as an 
infinite or unbound session. Further properties needs to define a 
separate (common) attribute to declare these things.

Issue:  Possible methods for signalling end of stream/media (not 
session) in RTP.

Discussion: Need to signal that a stream/media has ended exist mostly in 
unbound sessions. Proposal brought up to indicate this is RTCP BYE when 
the sender stops sending and has waited some time it can remove the SSRC 
of that source and send the BYE to indicate this. Another proposal was 
to send this information in RTSP methods. One could use sever to client 
TEARDOWN to indicate this session really are over, nothing more can be 
done. PAUSE can be sent when the media has been served but the client 
may rewind do other operations. The TEARDOWN idea was not liked as 
certain applications require session data to be sent from client to 
server using SET_PARAMETER. A new method should be evaluated. There 
might also exist significant synchronization problems in this.

Resolution: Propose a RTSP extension with a new method. Thomas Zeng to 
write strawman proposal for evaluation to mailing list.


Issue: Should REDIRECT automatically close session.

Discussion: This does not concern 3rr responses. As a connection related 
REDIRECT will terminate the session on the server side it is reasonable 
the same thing happens for REDIRECT request directed at the session. The 
exception to this is timed REDIRECTS that will continue exist until the 
specified time. The client should do TEARDOWN prior to this point to 
move the session to the alternative session.

Resolution: Clarify that session will be terminated by a successful 
REDIRECT, independently of its connection or session.


Issue: How to handle implicit redirection through session description 
protocol.

Discussion: Seems to be desired functionality to have an optimized way 
for saving a RTT when you perform load balance. There where also the 
issue that if a server would give a content-base or other base URL. A 
client should not reconnect unless explicitly redirected. This may 
result in different behaviour depending if the client are behind a proxy 
or not. First it was proposed that a new 200 code can be used to 
indicate that you get the SDP but are redirected. However this seem to 
have backwards problem. To optimize this in a efficient way you can use 
a new 350 code to indicate redirection but the client does receive a 
SDP. This way a old client will do the redirect as it interprets is as 
3xx code, while a new client can avoid wasting a extra describe. There 
are also a need to clarify that a server should not change the host 
address of the control in regards to the describe URI.

Resolution: Create a 350 code for this plus clarify the SHOULD NOT 
change the host address. Seems reasonable to put into the core 
specification.

Issue:  Request to Response time-out. The time a request takes until any 
response is received is not bound. Look at SIP solution?

Discussion: The time for a request to be processed is not defined. IF a 
server is taking long time to process a request it could send a 1xx 
response to indicate what it is doing. There may be soon need for this, 
especially if one uses STUN to validate connectivity. Concerns to 
backwards compatibility that a client will not expect a 1xx response 
even if this has been defined in RFC 2326. A couple to 10 seconds seem 
to be a reasonable time for a time-out. Does not seem appropriate to use 
without a feature tag. However a clarification on the issue is probably 
not a bad thing. There where also some concerns about the CSeq.

Resolution: Not resolved, Aravind to write to the list.

Issue: How to detect the updated spec? Version number change 1.1 or 2.0, 
or only use require and tag when necessary.

Discussion: Should be further discussed with through analysis of the so 
far made changes and see if they are backwards compatible. The initial 
goal has been to not be other than backwards compatible. A version 
number of 2.0 does completely change the picture for RTSP.

Resolution: Try to write up the change list properly with backwards 
analysis.


End of issues.

Reporting

Magnus Westerlund


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Date: Thu, 17 Jul 2003 20:01:18 +0200
From: Colin Perkins <csp@csperkins.org>
To: mmusic@ietf.org
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Subject: [MMUSIC] WG Last call: draft-ietf-mmusic-sdp-bwparam-04.txt
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As announced in the MMUSIC session this morning, the SDP bandwidth
parameters draft is now in working group last call. Please send any final
comments on this draft to the mailing list by 28th July. If no substantive
comments are received by that time, we propose to submit this draft to the
IESG for publication as a proposed standard RFC.

-- 
Colin Perkins
csp@csperkins.org

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Subject: [MMUSIC] Re: [dccp] blocking API (was: stream switching (was: Using DCCP for VoIP))
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Damon Lanphear wrote:

>Philippe,
>
>Can you explain the assumptions that inform your assertion that a
>blocked write attempt is "drastic" for an A/V application?  I understand
>how this may be the case for VoIP.  But for streaming A/V I have very
>sincere doubts.
>

Let me explain, then.

   My assumption is that the most efficient existing media encoders
   are all carefully optimized to operate at maximum efficiency for a
   "known in advance" target rate. In all cases best coding
   efficiency is achieved through the maintenance of a relatively
   long context (several seconds typical). Rate control -especially
   in video- is obtained thanks to computations taking into account
   as many frames as possible so as to distribute the available
   bandwidth on many frames etc...

   Specifically I am expressing the concern that driving a modern
   codec "by the frame" i.e. by giving a number of bits for each
   frame without taking any account of analysis of the media content
   is "drastically" sub-optimal.

   Preventing -without warning- an encoder from writing out an
   encoded frame for an -a priori undetermined- amount of time looks
   even worse to me in the sense that I dont know how to drive
   *efficiently* a media encoder of recent technology in a context
   where such a desesperate thing can occur. (I say recent but was
   this not by the way the whole idea of using UDP for RTP instead of
   TCP?)

   I would propose that the idea would rather be that DCCP should
   provide *the application* (which in the case of stream switching,
   encapsulates several codecs) a target rate.

   In all cases optimal results will be obtained if rate changes are
   signaled *as soon in advance* as possible.

   And the question is: why would we not do it since DCCP can provide
   such rate information very easily anyway? (TFRC does that very nicely)

>
>I am guessing that the difference between explicitly stating the rate to
>the application and socket blocking is that DCCP is providing reaction
>time to the application for whatever adaptation the app may need to do
>to fulfill DCCPs transmission requirements.
>

   Exactly !

>I submit that an application can achieve the same ends with socket
>blocking semantics.

   That you *can* do some sort of regulation, I agree, that it is
   optimal in all cases I have to disagree.

[clipped]

>I also assume that if a codec requires lead time for rate switching,
>negotiation, etc., then its the wrong codec for this type of
>application.

   Such a codec is possibly the wrong codec for telephony or
   conferencing but I would be totally frustrated to see DCCP limited
   to this type of applications!

   BTW how are we going to convince the industry to deploy a full
   new bona fide *IP protocol* for *streaming media* if it does not
   leverage the best out of *media codecs* ?

>At the very least, the codec should not require setting up
>a new decoder in response to a dynamic switch.

   Then you will be limited by the rate range: there is simply no
   standard codec of any type (speech, music, video) that covers the
   full possible range in all cases...

   Let us reverse the argument: if the bandwidth variation requires a
   different codec one could be (I am) ready to pay that price.

>Inter-key frame time for
>video should be the longest time lag over which a switch should have to
>take place.

   Allow me to translate this as:

   "the minimum forewarning time for a video codec is an Intra frame
   period"

   and then we agree!-)



regards,



Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com



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Subject: [MMUSIC] Re: [dccp] blocking API (was: stream switching (was: Using DCCP
 for VoIP))
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The relevance of this discussion to DCCP is such that there is an
expressed need for immediate/advanced notification of DCCP rate changes
to the application through the DCCP API.  There is also an expressed
need for an DCCP API that supports conventional socket blocking
semantics.  Both of these requirements, and their rationale should be
placed in the DCCP User Guide for future reference.

We can further discuss stream switching issues on the mmusic list.   

On Fri, 2003-07-18 at 06:23, philippe.gentric@philips.com wrote:
> Damon Lanphear wrote:
> 
> >Philippe,
> >
> >Can you explain the assumptions that inform your assertion that a
> >blocked write attempt is "drastic" for an A/V application?  I understand
> >how this may be the case for VoIP.  But for streaming A/V I have very
> >sincere doubts.
> >
> 
> Let me explain, then.
> 
>    My assumption is that the most efficient existing media encoders
>    are all carefully optimized to operate at maximum efficiency for a
>    "known in advance" target rate. In all cases best coding
>    efficiency is achieved through the maintenance of a relatively
>    long context (several seconds typical). Rate control -especially
>    in video- is obtained thanks to computations taking into account
>    as many frames as possible so as to distribute the available
>    bandwidth on many frames etc...
> 
>    Specifically I am expressing the concern that driving a modern
>    codec "by the frame" i.e. by giving a number of bits for each
>    frame without taking any account of analysis of the media content
>    is "drastically" sub-optimal.
> 
>    Preventing -without warning- an encoder from writing out an
>    encoded frame for an -a priori undetermined- amount of time looks
>    even worse to me in the sense that I dont know how to drive
>    *efficiently* a media encoder of recent technology in a context
>    where such a desesperate thing can occur. (I say recent but was
>    this not by the way the whole idea of using UDP for RTP instead of
>    TCP?)
> 
>    I would propose that the idea would rather be that DCCP should
>    provide *the application* (which in the case of stream switching,
>    encapsulates several codecs) a target rate.
> 
>    In all cases optimal results will be obtained if rate changes are
>    signaled *as soon in advance* as possible.
> 
>    And the question is: why would we not do it since DCCP can provide
>    such rate information very easily anyway? (TFRC does that very nicely)
> 
> >
> >I am guessing that the difference between explicitly stating the rate to
> >the application and socket blocking is that DCCP is providing reaction
> >time to the application for whatever adaptation the app may need to do
> >to fulfill DCCPs transmission requirements.
> >
> 
>    Exactly !
> 
> >I submit that an application can achieve the same ends with socket
> >blocking semantics.
> 
>    That you *can* do some sort of regulation, I agree, that it is
>    optimal in all cases I have to disagree.
> 
> [clipped]
> 
> >I also assume that if a codec requires lead time for rate switching,
> >negotiation, etc., then its the wrong codec for this type of
> >application.
> 
>    Such a codec is possibly the wrong codec for telephony or
>    conferencing but I would be totally frustrated to see DCCP limited
>    to this type of applications!
> 
>    BTW how are we going to convince the industry to deploy a full
>    new bona fide *IP protocol* for *streaming media* if it does not
>    leverage the best out of *media codecs* ?
> 
> >At the very least, the codec should not require setting up
> >a new decoder in response to a dynamic switch.
> 
>    Then you will be limited by the rate range: there is simply no
>    standard codec of any type (speech, music, video) that covers the
>    full possible range in all cases...
> 
>    Let us reverse the argument: if the bandwidth variation requires a
>    different codec one could be (I am) ready to pay that price.
> 
> >Inter-key frame time for
> >video should be the longest time lag over which a switch should have to
> >take place.
> 
>    Allow me to translate this as:
> 
>    "the minimum forewarning time for a video codec is an Intra frame
>    period"
> 
>    and then we agree!-)
> 
> 
> 
> regards,
> 
> 
> 
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
> 
-- 
Damon Lanphear <damonlan@real.com>


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Subject: [MMUSIC] SDPnew: Why not allow "s=" at the media-level?
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According to the SDP specification (currently: 
<draft-ietf-mmusic-sdp-new-13.txt>) "i=" is allowed at both the session 
level and the media level.  At the session level, it is called "session 
information"; at the media level, it is called "media title".

On the other hand, "s=" - which is called "session name" - is allowed at 
only the session level.

This seems inconsistent to me.  Why not also allow "s=" to appear at the 
media level?  And also, could we use more consistent names for these - e.g.,

At the session level:
         - call "s=" the "session name" (no change)
         - call "i=" the "session information" (no change)
At the media level:
         - call "s=" the "media name" or "media title"
         - call "i=" the "media information".

I.e., the intention here is that, at each level, "i=" - if present - would 
contain more detailed information than "s=".

         Ross.



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To: Ross Finlayson <finlayson@live.com>
From: Mark Baugher <mbaugher@cisco.com>
Subject: Re: [MMUSIC] SDPnew: Why not allow "s=" at the media-level?
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Ross
   I don't understand the requirement for a "media name" or "media 
title."  What is the need that you are addressing?

Mark
At 11:25 PM 7/18/2003 -0700, Ross Finlayson wrote:
>According to the SDP specification (currently: 
><draft-ietf-mmusic-sdp-new-13.txt>) "i=" is allowed at both the session 
>level and the media level.  At the session level, it is called "session 
>information"; at the media level, it is called "media title".
>
>On the other hand, "s=" - which is called "session name" - is allowed at 
>only the session level.
>
>This seems inconsistent to me.  Why not also allow "s=" to appear at the 
>media level?  And also, could we use more consistent names for these - e.g.,
>
>At the session level:
>         - call "s=" the "session name" (no change)
>         - call "i=" the "session information" (no change)
>At the media level:
>         - call "s=" the "media name" or "media title"
>         - call "i=" the "media information".
>
>I.e., the intention here is that, at each level, "i=" - if present - would 
>contain more detailed information than "s=".
>
>         Ross.
>
>
>
>_______________________________________________
>mmusic mailing list
>mmusic@ietf.org
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To: Mark Baugher <mbaugher@cisco.com>
From: Ross Finlayson <finlayson@live.com>
Subject: Re: [MMUSIC] SDPnew: Why not allow "s=" at the media-level?
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At 08:17 AM 7/19/03, Mark Baugher wrote:
>Ross
>   I don't understand the requirement for a "media name" or "media 
> title."  What is the need that you are addressing?

Mark,

Note that "media title" is *already* specified in SDP (as a media-level 
"i=").  Quoting from the existing specification:

       "A single "i=" field can also be used for each media definition.
       In media definitions, "i=" fields are primarily intended for
       labeling media streams.  As such, they are most likely to be
       useful when a single session has more than one distinct media
       stream of the same media type.  An example would be two different
       whiteboards, one for slides and one for feedback and questions."

All I'm proposing is that "s=" also be allowed at the media level, and that 
*this* be called "media title" (with "i=" at the media level called 
something else, e.g., "media information").

         Ross.


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From: Colin Perkins <csp@csperkins.org>
To: Ross Finlayson <finlayson@live.com>
Cc: mbaugher@cisco.com, mmusic@ietf.org
Subject: Re: [MMUSIC] SDPnew: Why not allow "s=" at the media-level?
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Ross,

The aim of SDPnew is to be backwards compatible where possible, so I'm
reluctant to do this unless there is a strong need.

Colin


--> Ross Finlayson <finlayson@live.com> writes:
> At 08:17 AM 7/19/03, Mark Baugher wrote:
> >Ross
> >   I don't understand the requirement for a "media name" or "media 
> > title."  What is the need that you are addressing?
> 
> Mark,
> 
> Note that "media title" is *already* specified in SDP (as a media-level 
> "i=").  Quoting from the existing specification:
> 
>        "A single "i=" field can also be used for each media definition.
>        In media definitions, "i=" fields are primarily intended for
>        labeling media streams.  As such, they are most likely to be
>        useful when a single session has more than one distinct media
>        stream of the same media type.  An example would be two different
>        whiteboards, one for slides and one for feedback and questions."
> 
> All I'm proposing is that "s=" also be allowed at the media level, and
> that *this* be called "media title" (with "i=" at the media level called 
> something else, e.g., "media information").
> 
>          Ross.
> 
> 
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic


-- 
Colin Perkins
csp@csperkins.org

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To: Ross Finlayson <finlayson@live.com>
From: Mark Baugher <mbaugher@cisco.com>
Subject: Re: [MMUSIC] SDPnew: Why not allow "s=" at the media-level?
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Ross
   I don't see what is gained by doing this renaming.  We would lose some 
interoperability.  It would be worse, I suppose, if we then re-purposed the i=.

Mark
At 09:53 AM 7/19/2003 -0700, Ross Finlayson wrote:
>At 08:17 AM 7/19/03, Mark Baugher wrote:
>>Ross
>>   I don't understand the requirement for a "media name" or "media 
>> title."  What is the need that you are addressing?
>
>Mark,
>
>Note that "media title" is *already* specified in SDP (as a media-level 
>"i=").  Quoting from the existing specification:
>
>       "A single "i=" field can also be used for each media definition.
>       In media definitions, "i=" fields are primarily intended for
>       labeling media streams.  As such, they are most likely to be
>       useful when a single session has more than one distinct media
>       stream of the same media type.  An example would be two different
>       whiteboards, one for slides and one for feedback and questions."
>
>All I'm proposing is that "s=" also be allowed at the media level, and 
>that *this* be called "media title" (with "i=" at the media level called 
>something else, e.g., "media information").
>
>         Ross.



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https://www1.ietf.org/mailman/listinfo/mmusic



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Date: Tue, 22 Jul 2003 08:39:28 +0200 (CEST)
To: Beau Williamson <bwilliam@cisco.com>
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        John Meylor <jmeylor@cisco.com>,
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Yes, I am very curious of how to achieve ASM at the end hosts using
SIP and sdp. Maybe some people from mmusic could give us some hints ?

Hoerdt Micka=EBl

> IMO, you'll never get a consensus on depricating ASM until all of the
> pieces are in place for SSM to accomplish the same thing.  I think that
> what you will get a consensus on is a document that identifies the missin=
g
> pieces and provides recommendations on how these pieces could be provided
> both at the protocol level, hardware level (MLDv2 Snooping??) and most
> importantly, at the application or session level to achieve the same
> many-to-many ASM behavior.
>
> Respectfully,
>
> Beau Williamson
>
>

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Philippe,

Can you explain the assumptions that inform your assertion that a
blocked write attempt is "drastic" for an A/V application?  I understand
how this may be the case for VoIP.  But for streaming A/V I have very
sincere doubts.

I am guessing that the difference between explicitly stating the rate to
the application and socket blocking is that DCCP is providing reaction
time to the application for whatever adaptation the app may need to do
to fulfill DCCPs transmission requirements. 

I submit that an application can achieve the same ends with socket
blocking semantics.  

I maintain that trigger points for codec adaptaion aka "stream
switching" should be based on the state of the post network buffer, not
changes in rate. A streaming A/V client application will have some
amount of post-network buffer. As we know, the purpose of this buffer is
to trade end-to-end delay for the ability to mitigate fluctuations in
delivery rate. If this buffer runs dry, then the media decoding stalls.
And the user experience is no longer seamless. The rate may vary a lot,
but the buffer may never drain to dangerous levels.  Decreases in codec
quality in such cases are completely avoidable.  

To illustrate how my notion of stream adaptation would work with DCCP:

In my model of an A/V application using DCCP, the application reads data
from the recipient DCCP end point at the rate required to fill its
post-network buffer.  If the rate is not fast enough to fill the buffer,
the buffer drains, if it fills all the way, it stops reading. In either
case, rate decrease due to congestion or rate decrease due to app slow
down, the DCCP rate will slow and the sending DCCP end point will
block.  At this point the transmitting DCCP will admit data either at
the rate permitted by congestion control or the rate permitted by the
read rate of the receiving application.  

The transmitting application has knowledge of the time line of the
media.  It therefore knows how the time line of the media shifts
relative to the delivery time line.  If the media time line is ahead of
the delivery timeline, then the buffer is filling, else the buffer is
draining.  We can even estimate the state of the buffer with this
information.  We therefore have enough information to determine trigger
points for media rate adaptations ("stream switching").  The DCCP never
has to signal the app with a rate, since the app knows the rate at which
it is sending AND it knows the rate it would need to achieve the
required timeline shift to maintain the state of the post network buffer
at a healthy level.  

The idea of a blocking socket need to be limited to just BSD sockets. 
The k/u shared buffer concept that the ICIR interns are driving can
provide the same semantics.  Either you have space to write into the
transmit queue or you don't.

I also assume that if a codec requires lead time for rate switching,
negotiation, etc., then its the wrong codec for this type of
application.  At the very least, the codec should not require setting up
a new decoder in response to a dynamic switch. Inter-key frame time for
video should be the longest time lag over which a switch should have to
take place.     

On Thu, 2003-07-17 at 01:33, philippe.gentric@philips.com wrote:
> colin perkins wrote:
> 
> >Do the ideas in draft-gentric-mmusic-stream-switching-req-00.txt help any
> >here?
> 
> I confirm the problems you report are the same ones the
> "stream switching" proposal aims to solve, see below for details.
> 
> --> "Phelan, Tom" <tphelan@sonusnet.com> writes:
> > Hi Sally,
> >
> > Thanks for the response.  See inline ...
> >
> > Tom P.
> >
> > [clipped]
> > > >The DCCP documents talk about VoIP being one of the main
> > > applications for
> > > >DCCP.  I've been trying to figure out a reasonable way for a VoIP
> > > >application to use DCCP.  Here's what I've come up with so
> > > far.  Corrections
> > > >and comments would be appreciated.
> > > >
> 
> Apart from the fact that my original concern was for "media delivery"
> i.e. an application where -contrary to VoIP- end to end delay is
> not critical, the problems are exactly the same for *all*
> media traffic, be it voice, video, text, etc
> 
> audio is a very good case for study since it
> is so critical in terms of *gaps* in the stream.
> however the case of *multiple* streams (A+V to start with)
> must be considered (see end of the mail)!
> 
> [clipped]
> 
> > > >Now assume the network becomes congested and one (at least)
> > > of my packets
> > > >get dropped.  DCCP decides it must back off the transmission
> > > rate, so one of
> > > >my 'send's fails with EWOULDBLOCK.
> 
> 
> This is clearly not very rich feedback, a blocking send is so very drastic!
> I would love to see the DCCP stack give earlier feedback something in the spirit of:
> 
> "hey, be ready to change your rate because the connection state
> seems to indicate that the available bandwidth is decreasing"
> 
> and then something like:
> 
> "hey, the available bandwidth has reduced to xxx kb/s, change your rate ASAP"
> 
> and in case of "emmergencies" (which definition would actually depend
> on the congestion control that has been chosen) if the DCCP stack has
> the impression that the available rate is extremely rapidly decreasing
> it would send:
> 
> "hey reduce your rate to yyy kb/s NOW"
> 
> and for increases:
> 
> "hey, you can increase your rate up to zzz kb/s" (the codec
> can take its time then, there is never any emmergency)

> 
> > > We would also like to understand better how DCCP would or would not
> > > work for a VoIP flow that did not have an adaptive codec, but we
> > > have not worked this through.  (E.g., under congestion, some fraction
> > > of the packets from the codec would be dropped by the DCCP sender.)
> > >
> > > >If the codec family can support this change on the fly,
> > > that's great.  But
> > > >if it requires renegotiation, I'll need to wait for that.
> > > If I renegotiate
> > > >in band, then my change request packet will get queued until
> > > DCCP decides it
> > > >can transmit again.  If I renegotiate out of band, then that
> > > channel might
> > > >be having it's problems too.  At any rate, there will be a
> > > round-trip delay
> > > >or so before I can start sending packets again.
> > >
> 
> stream switching is *exactly* about solving this: how to change
> the rate by switching *codecs* (and/or codec config since a lot
> of recent codec have wide ranges of parameters/profiles/rates etc)
> 
> deployed (streaming) products show that it is not only possible, it works fine.
> 
> the assumption is that the negociation takes time,
> also the instanciation of the ressources -especially on thin client- also takes time
> so it *must* take place "before". This before could be at session start,
> but it could also be at anytime during the session, but then not on short notice,
> (especially not with a blocking write!?-)
> 
> So -again- it is very important that the DCCP stack gives early feedback
> so as to have time to "setup" (RTSP-wise) the required codecs.
> 
> > > If negotiation is required, this is about the codec, not about DCCP,
> > > right?
> >
> > Right.  This was meant to indicate that the app probably can't
> > immediately change its sending rate.
> >
> 
> if the app "cannot change its rate" DCCP will be a very little use *anyway* no?
> 
> 
> I think you must assume that either the codec rate can be changed (true for
> most video codecs and a lot of recent audio codecs) and if the change of rate
> goes beyond the flexibility of a given codec you must change the codec and/or its configuration.
> [In the stream switching drafts the former is described as "transparent"
> and the latter as "non transparent"]
> 
> Note that for coding efficiency reasons it is a *very bad idea*
> to try to drive a video codec with rapid instantaneous changes of rate.
> 
> anyway the key issue is that DCCP *and* the codec(s) must have a way to
> talk, be configured etc ... work together hand in hand
> 
> > > It's also not clear why you need to stay quiet until the codec change
> > > request is acknowledged. DCCP has reduced its allowable send
> > > rate, but not
> > > to zero.
> 
> the codecs need to know the exact target rate, DCCP must give this as output
> (the rate of that feedback could be configurable ?)
> 
> the "contract" between the codecs and the DCCP stack is very simple:
> the chosen configuration MUST have a rate smaller (or equal) to the target.
> 
> > That is probably true, but I'm not sure how the other end would react to
> > receiving old-codec packets while the new codec is half-negotiated.
> 
> It cannot (see above).
> 
> Another problem is the ability to distinguish between the packet containing data of one codec
> or the other since for most decoder feeding the wrong type
> of syntax can be very bad (can even lead to crashes etc)
> 
> This issue is addressed in the stream switching proposal:
> typically with RTP the "old codec" uses one (dymamically attributed)
> PT and the new one uses another one.
> 
> There was the possibility to use another "port",
> but with DCCP this would be stupid no?
> 
> this leads me to the following question:
> 
> Can we assume that a given DCCP *connection* will be used
> to transport each media e.g. "audio" (i.e. eventually with codec changes
> on the fly, indicated by changes in PT of RTP packets)?
> 
> Then for audio+video there will be 2 DCCP connections right?
> 
> How is the DCCP feedback going to work then?
> 
> Indeed in stream swithing I always assumed that the target
> is the *pair* A+V i.e. the target rate can be obtained
> using SEVERAL combination, examples:
> 
> 5 kb/s AMR audio + 245 kb/s video = 250 kb/s, basic audio
> 40 kb/s AAC audio + 210 kb/s video = 250 kb/s, better audio
> 80 kb/s AAC stereo + 170 kb/s video = 250 kb/s, good audio
> 
> 
> ******************
> 
> regards,
> 
> 
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
> 
> 
> 
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
-- 
Damon Lanphear <damonlan@real.com>


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On Tue, 22 Jul 2003, Colin Perkins wrote:

> The question "how to achieve ASM at the end hosts" is pretty vague, given
> that the end hosts already support ASM natively.

And that ASM for IPv4 is not supported in the network at large scale
today.

>
> If you mean, how to use SSM in applications, then the SDP source filter
> extensions <draft-ietf-mmusic-sdp-srcfilter-05.txt> allow you to signal
> SSM sessions in SDP (and hence in SIP). This draft is in AD review for
> Proposed Standard.

As far as I know This is a grammar to describe SSM channel and do not
gives any protocol to announce them.

>
> If the aim is to emulate many-to-many multicast with multiple SSM channel=
s,
> then an application that knows its peers could, for example, signal a ful=
l

In my hypothesis, an application do not always knows its peers. You
signal a full mesh of SSM channels, OK but how ? which transport
protocol ? http over tcp / udp / multicast SSM/ ASM / soft state/hard
state ? how do you resolve the prob of high source dynamics ? I mean If I
only want to announce IP channels, what is the minimal protocol requirement=
 to achieve it ? If
this is SIP, I would be glad to have to pointer to documents describing
it, and it should exist as you mention it in the last mboned session.

Thanks,

Hoerdt Micka=EBl

> mesh of SSM channels using SIP. I'm not aware of any applications that do
> this, since a central server architecture is easier and scales to the siz=
es
> most people are considering, but it doesn't seem outside the realm of wha=
t
> is possible. The question is better suited for the SIPPING working group,
> though.
>
> Colin
>
>
> --> hoerdt@clarinet.u-strasbg.fr writes:
> > Yes, I am very curious of how to achieve ASM at the end hosts using
> > SIP and sdp. Maybe some people from mmusic could give us some hints ?
> >
> > Hoerdt Micka=EBl
> >
> > > IMO, you'll never get a consensus on depricating ASM until all of the
> > > pieces are in place for SSM to accomplish the same thing.  I think th=
at
> > > what you will get a consensus on is a document that identifies the
> > > missing pieces and provides recommendations on how these pieces could
> > > be provided both at the protocol level, hardware level (MLDv2
> > > Snooping??) and most importantly, at the application or session level
> > > to achieve the same many-to-many ASM behavior.
> > >
> > > Respectfully,
> > >
> > > Beau Williamson
> > >
> > >
> >
> > _______________________________________________
> > mmusic mailing list
> > mmusic@ietf.org
> > https://www1.ietf.org/mailman/listinfo/mmusic
> >
>
>
> --
> Colin Perkins
> csp@csperkins.org
>

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To: mmusic@ietf.org
Subject: [MMUSIC] MUSICNETWORK Workshop & WEDELMUSIC Conference, Leeds, UK, September 2003
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Dear MUSICNETWORK and WEDELMUSIC Friend

All the most recent innovations and hot topics related to music and multimedia
will be discussed in Leeds, UK, 15-18 September, 2003, Open to all

You are invited to attend the work of the second MUSICNETWORK
open workshop. A lot of interesting topics will be addressed:
Digital right management, music notation (XML and non), optical music recognition,
restoring, audio processing, personalisation, indexing, retrieval, 
libraries and archives, music publication, internet publication, 
cross media distribution and protection, MPEG standards, music and 
standards, etc. Innovative applications, case studies tutorials,
demonstrators, etc. 

http://www.interactivemusicnetwork.org   

for the FINAL program see:

http://www.interactivemusicnetwork.org/events/Second_OpenWorkshop_2003/programme_openworkshop_2003.html

The workshop is colocated with the WEDELMUSIC conference
innovative aspects of multimedia, DRM technologies, 

http://www.wedelmusic.org/wedelmusic2003/index.html

The final program of the WEDELMUSIC conference will be ready in
the next days. The general arrangements and schedule of 
all the events is reported in the above page. 

The registration pages are available on line for both events,
the registration for the MUSICNETWORK is free of charge. 

cheers,
Paolo Nesi
(MUSICNETWORK, Thematic Network of the European Commission)
Kia Ng
(General Chair of WEDELMUSIC2003 conference, UNIV. Leeds)



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Date: Tue, 22 Jul 2003 16:51:55 +0200
From: Colin Perkins <csp@csperkins.org>
To: hoerdt@clarinet.u-strasbg.fr
Cc: bwilliam@cisco.com, lenny@juniper.net, dmm@1-4-5.net, jmeylor@cisco.com,
        brian@innovationslab.net, mboned@network-services.uoregon.edu,
        fenner@research.att.com, mjh@icir.org, randy@psg.com, mmusic@ietf.org
Subject: Re: [MMUSIC] Re: [MBONED] WG action for 
 draft-savola-mboned-mcast-rpaddr-03.txt
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--> hoerdt@clarinet.u-strasbg.fr writes:
> > If you mean, how to use SSM in applications, then the SDP source filter
> > extensions <draft-ietf-mmusic-sdp-srcfilter-05.txt> allow you to signal
> > SSM sessions in SDP (and hence in SIP). This draft is in AD review for
> > Proposed Standard.
> 
> As far as I know This is a grammar to describe SSM channel and do not
> gives any protocol to announce them.

Correct. SDP is used by other protocols, such as RTSP, SIP or SAP, which
do the actual setup.

> > If the aim is to emulate many-to-many multicast with multiple SSM
> > channels, then an application that knows its peers could, for example,
> > signal a full
> 
> In my hypothesis, an application do not always knows its peers. You
> signal a full mesh of SSM channels, OK but how ? which transport
> protocol ? http over tcp / udp / multicast SSM/ ASM / soft state/hard
> state ? how do you resolve the prob of high source dynamics ? I mean If I
> only want to announce IP channels, what is the minimal protocol
> requirement to achieve it ? If this is SIP, I would be glad to have to
> pointer to documents describing it, and it should exist as you mention it
> in the last mboned session.

If you know the peers, I would expect standard SIP signalling to work with
minimal - if any - extensions. This would let you build a conferencing app
above a mesh of SSM channels, for example. The SIPPING working group would
be the correct place to discuss this. 

I suspect, however, that you wish to fully emulate an ASM service over SSM,
including the rendezvous and discovery aspects of ASM, rather than building
an application that uses the SSM service in a novel way to provide many-to-
many multicast. I question what problem you are trying to solve by doing
this.

-- 
Colin Perkins
csp@csperkins.org

_______________________________________________
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Subject: Re: [MMUSIC] Re: [MBONED] WG action for  draft-savola-mboned-mcast-rpaddr-03.txt
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<snip>
=2E..
</snip>

> including the rendezvous and discovery aspects of ASM, rather than buildi=
ng
> an application that uses the SSM service in a novel way to provide many-t=
o-
> many multicast. I question what problem you are trying to solve by doing
> this.

You didn't answered my question but you answered your own: to
fully emulated an ASM service over SSM. Many applications do not know the
peers before the application start and may require a lightweight mechanism
to do source discovery and Group managment at IP level instead of have
the full machinery of SIP. Is there a working group for that ?

Read : I don't want to do an HTTP GET on some overloaded web server only
to know that there are no new sources in my highly dynamic session. I
prefer to open an SSM control channel on my Host, and to manage my Group
on with my application requirement at IP level. If some higher session
level requirement are required by the application, then I will use
SIP/RTSCP/RTP etc...

Then you may ask : why emulate ASM over SSM as we already have ASM ?
Answer : At this moment, ASM for IPv4 is not scalable in interdomain but
SSM is, and if you want to have something else than TV on
the large-scale Internet it would be good to have some IP level mechanism
to still have an ASM behaviour at the interdomain scale.

Hoerdt Micka=EBl





>
> --
> Colin Perkins
> csp@csperkins.org
>
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic
>

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From: Colin Perkins <csp@csperkins.org>
To: hoerdt@clarinet.u-strasbg.fr
Cc: bwilliam@cisco.com, lenny@juniper.net, dmm@1-4-5.net, jmeylor@cisco.com,
        brian@innovationslab.net, mboned@network-services.uoregon.edu,
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Subject: Re: [MMUSIC] Re: [MBONED] WG action for 
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The question "how to achieve ASM at the end hosts" is pretty vague, given
that the end hosts already support ASM natively.=20

If you mean, how to use SSM in applications, then the SDP source filter
extensions <draft-ietf-mmusic-sdp-srcfilter-05.txt> allow you to signal
SSM sessions in SDP (and hence in SIP). This draft is in AD review for
Proposed Standard.

If the aim is to emulate many-to-many multicast with multiple SSM channels,
then an application that knows its peers could, for example, signal a full
mesh of SSM channels using SIP. I'm not aware of any applications that do
this, since a central server architecture is easier and scales to the sizes
most people are considering, but it doesn't seem outside the realm of what
is possible. The question is better suited for the SIPPING working group,
though.

Colin


--> hoerdt@clarinet.u-strasbg.fr writes:
> Yes, I am very curious of how to achieve ASM at the end hosts using
> SIP and sdp. Maybe some people from mmusic could give us some hints ?
>=20
> Hoerdt Micka=EBl
>=20
> > IMO, you'll never get a consensus on depricating ASM until all of the
> > pieces are in place for SSM to accomplish the same thing.  I think that
> > what you will get a consensus on is a document that identifies the
> > missing pieces and provides recommendations on how these pieces could
> > be provided both at the protocol level, hardware level (MLDv2
> > Snooping??) and most importantly, at the application or session level
> > to achieve the same many-to-many ASM behavior.
> >
> > Respectfully,
> >
> > Beau Williamson
> >
> >
>=20
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic
>=20


--=20
Colin Perkins
csp@csperkins.org

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Subject: [MMUSIC] Re: [dccp] stream switching (was: Using DCCP for VoIP)
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Hi Damon and Philippe,

I agree with you Damon that there shouldn't be a large problem for a 
streaming server to use a blocking socket as long some time-out of 
fairly short time (100-500 ms) is available. Then a streaming server can 
maintain its relation to the expected transmission schedule. When 
falling to much behind the server can simply switch to a lower bit-rate 
version and see if that enables it to catch up with the transmission 
schedule. However to make such a mechanism to provide decent performance 
some limitations are needed, like client buffer sizes, initial buffering.

I think that as long as you have some receiver buffer to enable the 
sender side to have time to decide on what the appropriate response is 
to a blocking operation this can work. However in applications that does 
not have this behaviour, like VoIP as you mention, that only have a 
receiver buffer to remove network jitter and which desire a end-to-end 
delay below 400 ms.

However for the control model that I think Philippe is having in mind 
the blocking socket does not work very well. My understanding of the 
model Philippe is using in his proposal for stream switching control for 
RTSP is that the server will basically send according to transmission 
schedule for the current rate. Then when the client detects that the 
network buffers builds up for that rate and that media is not delivered 
fast enough the client will signal the server to drop to lower rate. The 
new rate will then allow the network buffers to drain and the client 
buffer to refill in time sense. That way the server has no need to 
maintain close control over the receiver buffers as this is monitored 
and controlled by the client.

I think that one major issue around the stream switching is what control 
models one envision to use. The second question is then how this relates 
to any congestion control mechanism in use. It seams to me that having a 
client controlled stream switching model may not work that well with the 
suggested congestion control models provided by DCCP.


Further comments to your reply.

Damon Lanphear wrote:

> Philippe,
> 
> Can you explain the assumptions that inform your assertion that a
> blocked write attempt is "drastic" for an A/V application?  I understand
> how this may be the case for VoIP.  But for streaming A/V I have very
> sincere doubts.
> 
> I am guessing that the difference between explicitly stating the rate to
> the application and socket blocking is that DCCP is providing reaction
> time to the application for whatever adaptation the app may need to do
> to fulfill DCCPs transmission requirements. 
> 
> I submit that an application can achieve the same ends with socket
> blocking semantics.  
> 
> I maintain that trigger points for codec adaptaion aka "stream
> switching" should be based on the state of the post network buffer, not
> changes in rate. A streaming A/V client application will have some
> amount of post-network buffer. As we know, the purpose of this buffer is
> to trade end-to-end delay for the ability to mitigate fluctuations in
> delivery rate. If this buffer runs dry, then the media decoding stalls.
> And the user experience is no longer seamless. The rate may vary a lot,
> but the buffer may never drain to dangerous levels.  Decreases in codec
> quality in such cases are completely avoidable.  
> 
> To illustrate how my notion of stream adaptation would work with DCCP:
> 
> In my model of an A/V application using DCCP, the application reads data
> from the recipient DCCP end point at the rate required to fill its
> post-network buffer.  If the rate is not fast enough to fill the buffer,
> the buffer drains, if it fills all the way, it stops reading. In either
> case, rate decrease due to congestion or rate decrease due to app slow
> down, the DCCP rate will slow and the sending DCCP end point will
> block.  At this point the transmitting DCCP will admit data either at
> the rate permitted by congestion control or the rate permitted by the
> read rate of the receiving application.  

I don't think using app slow signalling is appropriate for a streaming 
session, I think that a bit more flow control is actually required to 
prevent wasting bandwidth on packets that get dropped on the receiver 
side due to overflowing buffers. However this can be accomplished at 
application layer for those application that needs this.

> 
> The transmitting application has knowledge of the time line of the
> media.  It therefore knows how the time line of the media shifts
> relative to the delivery time line.  If the media time line is ahead of
> the delivery timeline, then the buffer is filling, else the buffer is
> draining.  We can even estimate the state of the buffer with this
> information.  We therefore have enough information to determine trigger
> points for media rate adaptations ("stream switching").  The DCCP never
> has to signal the app with a rate, since the app knows the rate at which
> it is sending AND it knows the rate it would need to achieve the
> required timeline shift to maintain the state of the post network buffer
> at a healthy level.  
> 
> The idea of a blocking socket need to be limited to just BSD sockets. 
> The k/u shared buffer concept that the ICIR interns are driving can
> provide the same semantics.  Either you have space to write into the
> transmit queue or you don't.
> 
> I also assume that if a codec requires lead time for rate switching,
> negotiation, etc., then its the wrong codec for this type of
> application.  At the very least, the codec should not require setting up
> a new decoder in response to a dynamic switch. Inter-key frame time for
> video should be the longest time lag over which a switch should have to
> take place. 

Due to how media codecs work there are switching points that will result 
in optimal quality and there are other points that will result in worse 
quality. However to my understanding switching down in rate can normally 
be achieved with very little degradation due to the simple fact that we 
are switching from a fuller codec state to a less complete state. For 
upswitches in rate there is usually more need for finding the optimal 
switch point or quality will suffer severely. However there is no time 
pressure when switching up so one can wait for these points in the 
presentation.

Cheers


Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com


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Thread-Topic: RTSP and mobility
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From: "Enrico Balatti" <balatti@cefriel.it>
To: <mmusic@ietf.org>
Subject: [MMUSIC] RTSP and mobility
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Dear All,
=20
I've a question regarding to RTSP protocol an Mobility.
=20
Let say we have a Mobile Host (MH) that starts an RTSP session.
Now, the MH moves into a new "network domain" and it wants to continue
with its RTSP session.
My question is:
what is the best way that it can use to continue with the session?
It could do the following:
- teardown the session in the old domain
- restart the session in the new domain (from the exact "streaming =
point" it was in the old domain)
=20
Can it teardown the session in the new domain?(my doubt is that in the =
new domain it is reachable
via a different IPaddress...for example with MobileIP via a new =
CareOfAddress).
=20
Best Regards,
=20

Ing. Enrico M. Balatti          =20
Tel. 02-23954327

Fax. +39 02 23954527

 < mailto:balatti@cefriel.it>=20

CEFRIEL -Network Systems Area=20
Via Fucini, 2=20
20133 Milano - Italy=20


<  <http://www.cefriel.it/> http://www.cefriel.it/>=20

=20

=20

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META HTTP-EQUIV=3D"Content-Type" CONTENT=3D"text/html; =
charset=3Diso-8859-1">


<META content=3D"MSHTML 5.50.4926.2500" name=3DGENERATOR></HEAD>
<BODY>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D066215715-22072003>Dear=20
All,</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D066215715-22072003></SPAN></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D066215715-22072003>I've a =
question=20
regarding to RTSP protocol an Mobility.</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D066215715-22072003></SPAN></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D066215715-22072003>Let =
say we have a=20
Mobile Host (MH)&nbsp;that starts an RTSP session.</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D066215715-22072003>Now, =
the=20
MH&nbsp;moves into a new "network domain"&nbsp;and it wants to=20
continue</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D066215715-22072003>with =
its RTSP=20
session.</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D066215715-22072003>My =
question=20
is:</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D066215715-22072003>what =
is the best way=20
that it can use to continue with the session?</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D066215715-22072003>It =
could do the=20
following:</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D066215715-22072003>- =
teardown the=20
session in the old domain</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D066215715-22072003>- =
restart the=20
session in the new domain (from the exact "streaming point" it was in =
the old=20
domain)</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D066215715-22072003></SPAN></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D066215715-22072003>Can it =
teardown the=20
session in the new domain?(my doubt is that in the new domain it is=20
reachable</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D066215715-22072003>via a =
different=20
IPaddress...for example with MobileIP via a new=20
CareOfAddress).</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2><SPAN=20
class=3D066215715-22072003></SPAN></FONT>&nbsp;</DIV>
<DIV><FONT face=3DArial size=3D2><SPAN class=3D066215715-22072003>Best=20
Regards,</SPAN></FONT></DIV>
<DIV><FONT face=3DArial size=3D2></FONT>&nbsp;</DIV>
<DIV>
<P style=3D"MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px"><FONT face=3DVerdana=20
size=3D2><EM>Ing. Enrico M. =
Balatti&nbsp;&nbsp;&nbsp;&nbsp;</EM></FONT><FONT=20
size=3D2><FONT face=3DVerdana><EM>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
<BR>Tel.=20
02-23954327</EM></FONT></FONT></P>
<P style=3D"MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px"><FONT face=3DVerdana=20
size=3D2><EM>Fax. +39 02 23954527</EM></FONT></P>
<P style=3D"MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px"><U><FONT size=3D2><FONT =

face=3DVerdana><EM>&nbsp;<FONT color=3D#0000ff>&lt;<A=20
href=3D"mailto:balatti@cefriel.it">mailto:balatti@cefriel.it</A>&gt;</FON=
T></EM></FONT></FONT></U>=20
</P></DIV>
<P style=3D"MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px"><EM><FONT =
face=3DVerdana=20
size=3D2>CEFRIEL</FONT> -</EM><EM><FONT face=3DVerdana size=3D2>Network =
Systems Area=20
<BR>Via Fucini, 2 <BR>20133 Milano - Italy <BR></FONT><FONT =
face=3D"Courier New"=20
size=3D2></FONT><FONT face=3DArial size=3D2></FONT></EM></P><FONT =
face=3DArial>
<P style=3D"MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px"><FONT =
size=3D2></FONT></P>
<P style=3D"MARGIN-TOP: 0px; MARGIN-BOTTOM: 0px"><U><FONT face=3DVerdana =

color=3D#0000ff size=3D2><EM>&lt;</EM></FONT><A target=3D_blank=20
href=3D"http://www.cefriel.it/"><FONT face=3DVerdana=20
size=3D2><EM>http://www.cefriel.it/</EM></FONT></A><FONT face=3DVerdana=20
color=3D#0000ff size=3D2><EM>&gt;</EM></FONT></U><FONT face=3DVerdana =
color=3D#0000ff=20
size=3D2><EM> </EM></FONT></P></FONT>
<P><FONT size=3D2></FONT>&nbsp;</P>
<DIV>&nbsp;</DIV></BODY></HTML>

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I agree, and this type of statements could be supported by history
(I will be short):

1984 : First IP stack.
1985 : Deering start his thesis (Internet size about 2000 hosts)
December  1985 : RFC 966 "Host groups : a multicast extension to the
Internet Protocol"

September 1986 : start of implementation.
May 1988 : First IP multicast ROUTING based on 4.3+ networking code
(Internet size, about 30000 hosts).

In the old times, when ASM over IP has been invented, Ethernet was pretty
successfull and supported broadcast/multicast. So a natural way
to do multicast over IP, was to deploy Broadcast and prune mechanisms,
which works pretty well for small topologies (dvmrp, pim-dense).

1991 : Deering has finished his thesis, Holbrook start to work on Multicast
1992 : the First internet Audiocast at the IETF : what a wonderful new
techno, but will it scale ? (Internet size : about 800 000 hosts).
Broadcast && Prune is no more considered as a doable solution .

1993-94 : Receiver Initiated multicast protocol time. Achieves very
good scalability but how do we achieve source discovery now ? The
Internet start to become very complex, and now it can be fully
considered as a complex system. Anyway, due to RFC1112 there must
be some "broadcast and prune mechanism" somewhere due to the logical
nature of an IP group (an class D IP multicast address is a Name, and do
not gives any topological information on the group): MSDP.

1994-95 : Web explosion (about 6*10^6 hosts at the end of 1995). Hoolbrook
may then still working on his thesis, looking at what is happening to the
Internet (growing growing growing...) and asking himself : why putting
source discovery in the network ?

2001 : (S,G) channel mode is out. it get rid of Source discovery and many
multicast complex problems only by pushing complexity in the end hosts. No
more multicast address allocation/collision, no more RP discovery, no more
MSDP. It simply obey to a simple rule in any complex system : Core pieces
must but simple, any other mechanisms should be considered at the ends
hosts first, as changing these core pieces may take down the entire
system.

Well, this is just short history, and I am sure that we could write a
pretty interesting document about "IP multicast history 1984-2003" and
what I conclude from history is that :

-Broadcast is OK for LANs

-Broadcast and prune is OK for small domains.

- Receiver driven only mechanisms is OK for big
  size topologies like the Internet that we have TODAY : it scale.

  It is ok too if we consider large domains (but small compared to
  the Internet size) with a few Rendez-vous point, for source discovery,
  if the number of RP becomes to high, we fall in the Broadcast and prune.

- ASM model is not compatible with Receiver driven only technology because
 "Sources just send, and the group is open" - RFC1112.

- SSM model is fully compatible with Receiver driven technology

- To achieve ASM model in the interdomain we'll always need source
  discovery AND some broadcast (at least to the RP). Do not have
  source discovery or broadcast means having one RP per group, or
  having the RP serving a well known set of group : this is the case
  in the Embedded Rp solution, and this is the case with SSM over IP.



Hoerdt Micka=EBl



On Tue, 22 Jul 2003, David Meyer wrote:

>
> =09Folks,
>
> =09Here's something that would be productive: Let's talk
> =09about facts, and stay away from statements such as
>
> ... ASM for IPv4 is not scalable in interdomain but SSM is ...
>
> =09We need to support this type of statement, otherwise it
> =09is just marketing for SSM (maybe that is appropriate
> =09somewhere, but not on the MBONED list).
>
> =09Let's stay away from marketing and speculating about what
> =09might happen (or for that matter, what might have
> =09happened), and spend our resources on multicast
> =09deployment, which is the charter of MBONED.
>
> =09Thanks,
>
> =09Dave
>
>

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To: "Enrico Balatti" <balatti@cefriel.it>
cc: mmusic@ietf.org
Subject: Re: [MMUSIC] RTSP and mobility 
In-reply-to: Your message of "Tue, 22 Jul 2003 18:09:47 +0200."
             <6F5FB8313FE82C4EA10DA4DA40B90949B0610D@swing.cefriel.it> 
Date: Tue, 22 Jul 2003 12:48:46 -0400
From: Ashutosh Dutta <adutta@research.telcordia.com>
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Enrico,
       please see the paper
       
       http://www.cs.columbia.edu/~hgs/papers/Schu0007_Application.pdf,
       it talks about some issues related to RTSP and mobility when IP
       address  changes on the  mobile because  of subnet  movement or
       domain movement.

Thanks
Ashutosh

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From: Tom Taylor <taylor@nortelnetworks.com>
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Subject: [MMUSIC] SDP Syntax vs. RFC 3108
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I took the action last week to compare RFC 3108 syntax against sdp-new, to see if 
any action was necessary to realign them.

RFC 3108 documents the SDP conventions for ATM.  It defines a lot of attributes, 
which should not be a problem for syntax.  However, it also modifies the c= and m= 
lines.  The c= line is not a problem; the m= line has a different grammar from SDP-new.


m= line:
========

SDP-new syntax:
media-field =         "m=" media SP port ["/" integer]
                             SP proto 1*(SP fmt) CRLF

       media =               token

       port =                1*DIGIT

       proto  =              token "/" token
                             / token

       fmt =                 token



RFC 3108 syntax (most complicated form):

m=<media> <virtualConnectionId> <transport#1> <format list#1>
          <transport#2> <format list#2> ... <transport#M> <format list#M>

media presents no problems -- same as in basic SDP.

virtualConnectionId can have several forms, matching the patterns
          token
          token "/" token
          token "/" token "/" token
          token "/" token "/" token "/" token

        To fit this, you would need to substitute
          token *("/" token))
        for the existing sub-rule
          port ["/" integer]

transport always matches
          token "/" token

        <format list> matches 1*(SP fmt)

The problem lies in the repetition.  You would need to change
          SP proto 1*(SP fmt)
to
        1*(SP proto 1*(SP fmt))

So the complete m= line to accommodate RFC 3108 becomes

  media-field =         "m=" media SP token *("/" token))
                             1*(SP proto 1*(SP fmt)) CRLF

Tom Taylor









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Subject: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream switching)
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Magnus,Damon,

let us forget a minute about the exact application,
(because my point is *not* specific to stream switching)
let us instead concentrate on the following problem:

you write:

"the server can simply switch to a lower bit-rate"

This is an indication we are on agreement on one thing:
DCCP is about rate-driven applications.

This is why my concern has been from the very start:
how is the sending application (what ever it is)
going to know what rate it must use?

The answers you gave so far seem to indicate you are confident
the application can "compute" such a rate based on the behavior of a blocking API...

(ok, allow me now to *also* put aside my humble opinion that  trying to achieve that is not a good idea)

I advocate that it would be a shame **because the information is already available**!

Allow me to quote Section 3 of RFC 3448:

"   Generally speaking, TFRC's congestion control mechanism works as
   follows:

   o  The receiver measures the loss event rate and feeds this
      information back to the sender.

   o  The sender also uses these feedback messages to measure the
      round-trip time (RTT).

   o  The loss event rate and RTT are then fed into TFRC's throughput
      equation, giving the acceptable transmit rate.

   o  The sender then adjusts its transmit rate to match the calculated
      rate.
"

This seems to imply that a "natural" sender-side API for DCCP would explicitely
inform the application ("sender") about this "acceptable transmit rate".

It also happens to be the *best thing* that can be provided to
an application designed to perform network adaptation.


regards,

Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com



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From: "Phelan, Tom" <tphelan@sonusnet.com>
To: "'philippe.gentric@philips.com'" <philippe.gentric@philips.com>,
        Magnus Westerlund <magnus.westerlund@ericsson.com>
Cc: Damon Lanphear <damonlan@real.com>, dccp@ietf.org, mmusic@ietf.org,
        "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
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Subject: [MMUSIC] RE: [dccp] natural DCCP sender-side API: (was stream switching)
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Hi Phillipe,

In thinking about your draft on stream rate switching and this discussion on
APIs I've come to the conclusion that there are actually three different
applications being discussed, with three different sets of requirements.
One of these applications can be reasonably satisfied with a blocking API
(although there could be some efficiencies with other capabilities).  For
the other two I'm not sure yet what would work.

Excuse me if I'm re-inventing something here, but the three applications I
have in mind are:
 o	One-way pre-recorded media
 o	One-way live media
 o	Two-way interactive media

The relevant difference, as far as this discussion goes, between recorded
and live media is that recorded media can be transmitted from the sender as
fast as the network allows (assuming buffering at the receiver).  Live media
can only be transmitted at the rate that it's generated.

The difference between one-way (live) and two-way is the size of the playout
buffer.  In one-way media you can use a playout buffer that's hundreds of
times larger than the round trip time.  In two-way media the playout buffer
is on the same order of magnitude as the round trip time.

So, it seems to me that one-way pre-recorded media can be reasonably served
by DCCP with TFRC and a sockets-like (blocking) API.  For example, assume
that the sender has a media stream in two bit rates, high and low.  Also
assume that the sender is able to estimate the depth of the receiver's
playout buffer (either via feedback from the receiver or some other means).
Now set three thresholds in the playout buffer, a low threshold, a playback
start threshold and a high threshold, in order of increasing depth.

To start the connection, the sender begins transmitting data from the high
bit rate stream as fast as TFRC allows (blocking the transmit thread for
rate control).  Since TFRC is in slow-start, this is probably too slow
initially, but eventually the rate might increase to fast enough and past.
The receiver buffers data until the playback start threshold is reached, and
then begins playback.

If the TFRC rate never gets fast enough, or a packet loss makes TFRC drop
the rate, the receiver will drain the playout buffer faster than it's being
filled.  If the playout buffer drops below the low threshold, the sender
switches to the low bit rate stream.  Assuming that the network has a little
bit more capacity than the low bit rate stream requires, the playout buffer
will begin filling again.

When the buffer crosses the high threshold the sender switches to the high
bit rate stream.  Assuming that the network still doesn't have enough
capacity for the high bit rate stream, the playout buffer will drain.  When
it reaches the low threshold the sender switches back to the low bit rate.
The sender will oscillate back and forth like this until the connection is
terminated.

So, in this scheme, the sender doesn't need to know the rate that TFRC has
determined, it simply always sends as fast as TFRC allows.  TFRC shapes the
stream to the network's requirements, and the feedback about the playout
buffer allows the sender to shape the stream to the application's
requirements.

I haven't been able to work out acceptable scenarios for the other two
applications yet.  It seems almost certain to me that TFRC and a blocking
API is not at all suitable for two-way media.  It might be suitable for
one-way live media, but I haven't figured out how it could be yet.  If
anyone has ideas here I'd like to hear them :-).

Tom P.


> -----Original Message-----
> From: philippe.gentric@philips.com 
> [mailto:philippe.gentric@philips.com]
> Sent: Wednesday, July 23, 2003 7:59 AM
> To: Magnus Westerlund
> Cc: Damon Lanphear; dccp@ietf.org; mmusic@ietf.org
> Subject: Re: [dccp] natural DCCP sender-side API: (was stream 
> switching)
> 
> 
> 
> Magnus,Damon,
> 
> let us forget a minute about the exact application,
> (because my point is *not* specific to stream switching)
> let us instead concentrate on the following problem:
> 
> you write:
> 
> "the server can simply switch to a lower bit-rate"
> 
> This is an indication we are on agreement on one thing:
> DCCP is about rate-driven applications.
> 
> This is why my concern has been from the very start:
> how is the sending application (what ever it is)
> going to know what rate it must use?
> 
> The answers you gave so far seem to indicate you are confident
> the application can "compute" such a rate based on the 
> behavior of a blocking API...
> 
> (ok, allow me now to *also* put aside my humble opinion that  
> trying to achieve that is not a good idea)
> 
> I advocate that it would be a shame **because the information 
> is already available**!
> 
> Allow me to quote Section 3 of RFC 3448:
> 
> "   Generally speaking, TFRC's congestion control mechanism works as
>    follows:
> 
>    o  The receiver measures the loss event rate and feeds this
>       information back to the sender.
> 
>    o  The sender also uses these feedback messages to measure the
>       round-trip time (RTT).
> 
>    o  The loss event rate and RTT are then fed into TFRC's throughput
>       equation, giving the acceptable transmit rate.
> 
>    o  The sender then adjusts its transmit rate to match the 
> calculated
>       rate.
> "
> 
> This seems to imply that a "natural" sender-side API for DCCP 
> would explicitely
> inform the application ("sender") about this "acceptable 
> transmit rate".
> 
> It also happens to be the *best thing* that can be provided to
> an application designed to perform network adaptation.
> 
> 
> regards,
> 
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
> 
> 
> 
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
> 

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From: Damon Lanphear <damonlan@real.com>
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Subject: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream switching)
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Philippe,

No one is really taking the position that a DCCP API should not make the
transmission rate available to the application.  This is quite a
straightforward issue. DCCP can easily expose this key piece of
information.  

I am more concerned with how an application meets DCCPs transmission
limits (i.e. transmits at the required rate).  

Let's put the issue of adaptation aside for a moment and just concern
ourselves with how an application paces data to the network. My view is
that DCCP offers the application both congestion control AND the ability
to manage the transmission schedule.  I assume that DCCP will pace data
to the lower layers at the rate required of the associated CCID spec.
For the application to do this pacing as well would be redundant work.

What I don't quite understand about your position is the role played by
the application in pacing data.  Do you maintain that the application
should pace data, or DCCP or both? That is, is the use of the transmit
rate to the application purely informative of a rate adaptation process,
or of the transmit process as a whole?

On Wed, 2003-07-23 at 04:59, philippe.gentric@philips.com wrote:
> Magnus,Damon,
> 
> let us forget a minute about the exact application,
> (because my point is *not* specific to stream switching)
> let us instead concentrate on the following problem:
> 
> you write:
> 
> "the server can simply switch to a lower bit-rate"
> 
> This is an indication we are on agreement on one thing:
> DCCP is about rate-driven applications.
> 
> This is why my concern has been from the very start:
> how is the sending application (what ever it is)
> going to know what rate it must use?
> 
> The answers you gave so far seem to indicate you are confident
> the application can "compute" such a rate based on the behavior of a blocking API...
> 
> (ok, allow me now to *also* put aside my humble opinion that  trying to achieve that is not a good idea)
> 
> I advocate that it would be a shame **because the information is already available**!
> 
> Allow me to quote Section 3 of RFC 3448:
> 
> "   Generally speaking, TFRC's congestion control mechanism works as
>    follows:
> 
>    o  The receiver measures the loss event rate and feeds this
>       information back to the sender.
> 
>    o  The sender also uses these feedback messages to measure the
>       round-trip time (RTT).
> 
>    o  The loss event rate and RTT are then fed into TFRC's throughput
>       equation, giving the acceptable transmit rate.
> 
>    o  The sender then adjusts its transmit rate to match the calculated
>       rate.
> "
> 
> This seems to imply that a "natural" sender-side API for DCCP would explicitely
> inform the application ("sender") about this "acceptable transmit rate".
> 
> It also happens to be the *best thing* that can be provided to
> an application designed to perform network adaptation.
> 
> 
> regards,
> 
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
> 
-- 
Damon Lanphear <damonlan@real.com>


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Hi Tom,

you write:

>The relevant difference, as far as this discussion goes, between recorded
>and live media is that recorded media can be transmitted from the sender as
>fast as the network allows (assuming buffering at the receiver).

and then latter (still about recorded media):

>So, in this scheme, the sender doesn't need to know the rate that TFRC has
>determined, it simply always sends as fast as TFRC allows.

1) I am sorry but *from a network point of view*
I dont see a difference between this and "download"?

Except that to my knowledge all the products doing that use HTTP
since it solves a rather large number of other problems at the same time!

2) Now *from a user point of view*

"download" has a flavor usually called "progressive download"
whereby the downloaded media file has a structure enabling
to start playback before download is finished.

In this mode usually the slide bar that the player
uses to display the media time has 2 colors,
one displaying the current time in the media,
the other the *received* time in the media,
if this second mark stays ahead of the first mark playback is un-interrupted,
otherwise the player stops and displays a message such as "please wait, rebufferring".

So I dont see either, from a user point of view,
how different a behavior the case you describe would have?

****************

I conclude about this use case of the DCCP blocking API you described,
that it is not very attractive at all.

Surely DCCP has better assets to lure implementers?-)...
I think an API providing a target rate would be a good starting point;-)

regards,

Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com



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From: Damon Lanphear <damonlan@real.com>
To: "Phelan, Tom" <tphelan@sonusnet.com>
Cc: "'philippe.gentric@philips.com'" <philippe.gentric@philips.com>,
        Magnus Westerlund <magnus.westerlund@ericsson.com>, dccp@ietf.org,
        mmusic@ietf.org, "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
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Subject: [MMUSIC] RE: [dccp] natural DCCP sender-side API: (was stream switching)
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Tom,

Thank you for providing better structure to our discussion.  This is
precisely what we needed to speak more precisely on these matters!

I haven't been able to work out acceptable scenarios for the other two
> applications yet.  It seems almost certain to me that TFRC and a blocking
> API is not at all suitable for two-way media.  It might be suitable for
> one-way live media, but I haven't figured out how it could be yet.  If
> anyone has ideas here I'd like to hear them :-).

I'd like to understand the alternative to a blocking API for two-way
media.  I assume that in this case the application is responsible for
managing the transmission rate.  I guess I get confused when I consider
that some agent in the pipeline will have to block transmission when the
transmission attempt oversteps the congestion control rate.  What does
it matter if this agent is DCCP or the application, particularly if we
have access to the transmit queue in DCCP, as is the case in the ICIR
implementation ? 

As regards unidirectional live,  its differs from unidirectional
on-demand in that there's no data sitting on disk with which to fill a
post-network buffer to a point where an up shift seems appropriate. 
Downshifts are straightforward, however, since under sending can just as
well happen with live streams.  So we need a metric for up shifts that
does not rely on buffer state.  Perhaps some measure of the stability of
the available congestion controlled throughput over time?

On Wed, 2003-07-23 at 07:43, Phelan, Tom wrote:
> Hi Phillipe,
> 
> In thinking about your draft on stream rate switching and this discussion on
> APIs I've come to the conclusion that there are actually three different
> applications being discussed, with three different sets of requirements.
> One of these applications can be reasonably satisfied with a blocking API
> (although there could be some efficiencies with other capabilities).  For
> the other two I'm not sure yet what would work.
> 
> Excuse me if I'm re-inventing something here, but the three applications I
> have in mind are:
>  o	One-way pre-recorded media
>  o	One-way live media
>  o	Two-way interactive media
> 
> The relevant difference, as far as this discussion goes, between recorded
> and live media is that recorded media can be transmitted from the sender as
> fast as the network allows (assuming buffering at the receiver).  Live media
> can only be transmitted at the rate that it's generated.
> 
> The difference between one-way (live) and two-way is the size of the playout
> buffer.  In one-way media you can use a playout buffer that's hundreds of
> times larger than the round trip time.  In two-way media the playout buffer
> is on the same order of magnitude as the round trip time.
> 
> So, it seems to me that one-way pre-recorded media can be reasonably served
> by DCCP with TFRC and a sockets-like (blocking) API.  For example, assume
> that the sender has a media stream in two bit rates, high and low.  Also
> assume that the sender is able to estimate the depth of the receiver's
> playout buffer (either via feedback from the receiver or some other means).
> Now set three thresholds in the playout buffer, a low threshold, a playback
> start threshold and a high threshold, in order of increasing depth.
> 
> To start the connection, the sender begins transmitting data from the high
> bit rate stream as fast as TFRC allows (blocking the transmit thread for
> rate control).  Since TFRC is in slow-start, this is probably too slow
> initially, but eventually the rate might increase to fast enough and past.
> The receiver buffers data until the playback start threshold is reached, and
> then begins playback.
> 
> If the TFRC rate never gets fast enough, or a packet loss makes TFRC drop
> the rate, the receiver will drain the playout buffer faster than it's being
> filled.  If the playout buffer drops below the low threshold, the sender
> switches to the low bit rate stream.  Assuming that the network has a little
> bit more capacity than the low bit rate stream requires, the playout buffer
> will begin filling again.
> 
> When the buffer crosses the high threshold the sender switches to the high
> bit rate stream.  Assuming that the network still doesn't have enough
> capacity for the high bit rate stream, the playout buffer will drain.  When
> it reaches the low threshold the sender switches back to the low bit rate.
> The sender will oscillate back and forth like this until the connection is
> terminated.
> 
> So, in this scheme, the sender doesn't need to know the rate that TFRC has
> determined, it simply always sends as fast as TFRC allows.  TFRC shapes the
> stream to the network's requirements, and the feedback about the playout
> buffer allows the sender to shape the stream to the application's
> requirements.
> 

> 
> Tom P.
> 
> 
> > -----Original Message-----
> > From: philippe.gentric@philips.com 
> > [mailto:philippe.gentric@philips.com]
> > Sent: Wednesday, July 23, 2003 7:59 AM
> > To: Magnus Westerlund
> > Cc: Damon Lanphear; dccp@ietf.org; mmusic@ietf.org
> > Subject: Re: [dccp] natural DCCP sender-side API: (was stream 
> > switching)
> > 
> > 
> > 
> > Magnus,Damon,
> > 
> > let us forget a minute about the exact application,
> > (because my point is *not* specific to stream switching)
> > let us instead concentrate on the following problem:
> > 
> > you write:
> > 
> > "the server can simply switch to a lower bit-rate"
> > 
> > This is an indication we are on agreement on one thing:
> > DCCP is about rate-driven applications.
> > 
> > This is why my concern has been from the very start:
> > how is the sending application (what ever it is)
> > going to know what rate it must use?
> > 
> > The answers you gave so far seem to indicate you are confident
> > the application can "compute" such a rate based on the 
> > behavior of a blocking API...
> > 
> > (ok, allow me now to *also* put aside my humble opinion that  
> > trying to achieve that is not a good idea)
> > 
> > I advocate that it would be a shame **because the information 
> > is already available**!
> > 
> > Allow me to quote Section 3 of RFC 3448:
> > 
> > "   Generally speaking, TFRC's congestion control mechanism works as
> >    follows:
> > 
> >    o  The receiver measures the loss event rate and feeds this
> >       information back to the sender.
> > 
> >    o  The sender also uses these feedback messages to measure the
> >       round-trip time (RTT).
> > 
> >    o  The loss event rate and RTT are then fed into TFRC's throughput
> >       equation, giving the acceptable transmit rate.
> > 
> >    o  The sender then adjusts its transmit rate to match the 
> > calculated
> >       rate.
> > "
> > 
> > This seems to imply that a "natural" sender-side API for DCCP 
> > would explicitely
> > inform the application ("sender") about this "acceptable 
> > transmit rate".
> > 
> > It also happens to be the *best thing* that can be provided to
> > an application designed to perform network adaptation.
> > 
> > 
> > regards,
> > 
> > Philippe Gentric
> > Software Architect
> > Philips MP4Net
> > philippe.gentric@philips.com
> > http://www.platform4.philips.com
> > 
> > 
> > 
> > _______________________________________________
> > dccp IETF mailing list: dccp@ietf.org
> > list info:  https://www1.ietf.org/mailman/listinfo/dccp
> > wg charter: http://www.ietf.org/html.charters/dccp-charter.html
> > 
-- 
Damon Lanphear <damonlan@real.com>


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To: Damon Lanphear <damonlan@real.com>
Cc: dccp@ietf.org, Magnus Westerlund <magnus.westerlund@ericsson.com>,
        mmusic@ietf.org
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Subject: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream switching)
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Damon, you write:

>I assume that DCCP will pace data
>to the lower layers at the rate required of the associated CCID spec.
>For the application to do this pacing as well would be redundant work.

I am assuming it is a *different job*, they live on different planets,
the DCCP stack cares about "real seconds",
the application cares about "media seconds".

>What I don't quite understand about your position is the role played by
>the application in pacing data.  Do you maintain that the application
>should pace data, or DCCP or both?

Both, but differently?

Streaming means that 1 second of content MUST be sent for
every elapsed "real time" second (at least on the average).
So the application cannot "pace seconds"...
but I am assuming the application job contract
does not say how many bytes one second of media is.

In short I am assuming that the sending application
can change the media data rate in order to
*follow* the network data rate.

For conferencing -the media being encoded in real time-
I assume that the DCCP stack will be used to pilot
the encoder (tell it which rate to produce).

For pre-recorded media delivery the solution is stream switching
(or download! see the other mail)

For live "TV" (very large number of receivers) changing
the rate is either not relevant (e.g. end to end SSM)
or it uses a relay server which folds the issue as being
like pre-recorded media playback -each receiver maintaining
a private server connection- then one should use stream switching,
each stream "flavor" being simultaneously produced by a different encoder.

regards,

Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com


                                                                                                                                       
                                                                                                                                       
                                                   To:   Philippe Gentric/MP4-SUR/CE/PHILIPS@EMEA1                                     
                                                   cc:   Magnus Westerlund <magnus.westerlund@ericsson.com>                            
                                                    dccp@ietf.org                                                                      
                                                    mmusic@ietf.org                                                                    
               Damon Lanphear                      Subject:    Re: [dccp] natural DCCP sender-side API: (was stream switching)         
               <damonlan@real.com>                                                                                                     
                                                   Classification:                                                                     
               23/07/2003 19:42                                                                                                        
                                                                                                                                       
                                                                                                                                       




Philippe,

No one is really taking the position that a DCCP API should not make the
transmission rate available to the application.  This is quite a
straightforward issue. DCCP can easily expose this key piece of
information.

I am more concerned with how an application meets DCCPs transmission
limits (i.e. transmits at the required rate).

Let's put the issue of adaptation aside for a moment and just concern
ourselves with how an application paces data to the network. My view is
that DCCP offers the application both congestion control AND the ability
to manage the transmission schedule.  I assume that DCCP will pace data
to the lower layers at the rate required of the associated CCID spec.
For the application to do this pacing as well would be redundant work.

What I don't quite understand about your position is the role played by
the application in pacing data.  Do you maintain that the application
should pace data, or DCCP or both? That is, is the use of the transmit
rate to the application purely informative of a rate adaptation process,
or of the transmit process as a whole?

On Wed, 2003-07-23 at 04:59, philippe.gentric@philips.com wrote:
> Magnus,Damon,
>
> let us forget a minute about the exact application,
> (because my point is *not* specific to stream switching)
> let us instead concentrate on the following problem:
>
> you write:
>
> "the server can simply switch to a lower bit-rate"
>
> This is an indication we are on agreement on one thing:
> DCCP is about rate-driven applications.
>
> This is why my concern has been from the very start:
> how is the sending application (what ever it is)
> going to know what rate it must use?
>
> The answers you gave so far seem to indicate you are confident
> the application can "compute" such a rate based on the behavior of a blocking API...
>
> (ok, allow me now to *also* put aside my humble opinion that  trying to achieve that is not a good idea)
>
> I advocate that it would be a shame **because the information is already available**!
>
> Allow me to quote Section 3 of RFC 3448:
>
> "   Generally speaking, TFRC's congestion control mechanism works as
>    follows:
>
>    o  The receiver measures the loss event rate and feeds this
>       information back to the sender.
>
>    o  The sender also uses these feedback messages to measure the
>       round-trip time (RTT).
>
>    o  The loss event rate and RTT are then fed into TFRC's throughput
>       equation, giving the acceptable transmit rate.
>
>    o  The sender then adjusts its transmit rate to match the calculated
>       rate.
> "
>
> This seems to imply that a "natural" sender-side API for DCCP would explicitely
> inform the application ("sender") about this "acceptable transmit rate".
>
> It also happens to be the *best thing* that can be provided to
> an application designed to perform network adaptation.
>
>
> regards,
>
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
>
--
Damon Lanphear <damonlan@real.com>







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To: Damon Lanphear <damonlan@real.com>, philippe.gentric@philips.com
From: Kamlesh Talreja <kamlesh@real.com>
Subject: Re: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was
  stream switching)
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        mmusic@ietf.org
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Without discounting the need to convey the transmission rate available to 
the application, we also need to
point out the immediacy of a socket block, as opposed to an intermittent 
reading of the transmission rate.
Since the transmission rate would be changing at a much finer granularity, 
and the congestion control
mechanism would make sure the application does not exceed. If the 
application intends to exactly track
the transmission rate changes, it would end up spending too much time as 
part of an out-of-band
notification process. A blocking API allows the application to pace its 
delivery in an integrated manner
without the overhead of asynchronous callbacks or other mechanisms to 
notify it continuously of
transmission rate changes.
However, to prevent the kind of oscillatory behavior that Tom talked about, 
the application could read the
available transmission rate at a much less frequency to make sure that the 
media rate does not exceed the available
throughput over a longer period of time.
Kamlesh


At 10:42 AM 7/23/2003 -0700, Damon Lanphear wrote:
>Philippe,
>
>No one is really taking the position that a DCCP API should not make the
>transmission rate available to the application.  This is quite a
>straightforward issue. DCCP can easily expose this key piece of
>information.
>
>I am more concerned with how an application meets DCCPs transmission
>limits (i.e. transmits at the required rate).
>
>Let's put the issue of adaptation aside for a moment and just concern
>ourselves with how an application paces data to the network. My view is
>that DCCP offers the application both congestion control AND the ability
>to manage the transmission schedule.  I assume that DCCP will pace data
>to the lower layers at the rate required of the associated CCID spec.
>For the application to do this pacing as well would be redundant work.
>
>What I don't quite understand about your position is the role played by
>the application in pacing data.  Do you maintain that the application
>should pace data, or DCCP or both? That is, is the use of the transmit
>rate to the application purely informative of a rate adaptation process,
>or of the transmit process as a whole?
>
>On Wed, 2003-07-23 at 04:59, philippe.gentric@philips.com wrote:
> > Magnus,Damon,
> >
> > let us forget a minute about the exact application,
> > (because my point is *not* specific to stream switching)
> > let us instead concentrate on the following problem:
> >
> > you write:
> >
> > "the server can simply switch to a lower bit-rate"
> >
> > This is an indication we are on agreement on one thing:
> > DCCP is about rate-driven applications.
> >
> > This is why my concern has been from the very start:
> > how is the sending application (what ever it is)
> > going to know what rate it must use?
> >
> > The answers you gave so far seem to indicate you are confident
> > the application can "compute" such a rate based on the behavior of a 
> blocking API...
> >
> > (ok, allow me now to *also* put aside my humble opinion that  trying to 
> achieve that is not a good idea)
> >
> > I advocate that it would be a shame **because the information is 
> already available**!
> >
> > Allow me to quote Section 3 of RFC 3448:
> >
> > "   Generally speaking, TFRC's congestion control mechanism works as
> >    follows:
> >
> >    o  The receiver measures the loss event rate and feeds this
> >       information back to the sender.
> >
> >    o  The sender also uses these feedback messages to measure the
> >       round-trip time (RTT).
> >
> >    o  The loss event rate and RTT are then fed into TFRC's throughput
> >       equation, giving the acceptable transmit rate.
> >
> >    o  The sender then adjusts its transmit rate to match the calculated
> >       rate.
> > "
> >
> > This seems to imply that a "natural" sender-side API for DCCP would 
> explicitely
> > inform the application ("sender") about this "acceptable transmit rate".
> >
> > It also happens to be the *best thing* that can be provided to
> > an application designed to perform network adaptation.
> >
> >
> > regards,
> >
> > Philippe Gentric
> > Software Architect
> > Philips MP4Net
> > philippe.gentric@philips.com
> > http://www.platform4.philips.com
> >
>--
>Damon Lanphear <damonlan@real.com>
>
>
>_______________________________________________
>mmusic mailing list
>mmusic@ietf.org
>https://www1.ietf.org/mailman/listinfo/mmusic

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  Kamlesh T. Talreja                     E-mail: kamlesh@real.com
  Software Development Engineer          Phone:  206-892-6193
  HelixServer Product Development
  RealNetworks, Inc.                     http://www.real.com/


_______________________________________________
mmusic mailing list
mmusic@ietf.org
https://www1.ietf.org/mailman/listinfo/mmusic



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Subject: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream switching)
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On Wed, 2003-07-23 at 11:12, philippe.gentric@philips.com wrote:
> Damon, you write:
> 
> >I assume that DCCP will pace data
> >to the lower layers at the rate required of the associated CCID spec.
> >For the application to do this pacing as well would be redundant work.
> 
> I am assuming it is a *different job*, they live on different planets,
> the DCCP stack cares about "real seconds",
> the application cares about "media seconds".

I don't share that assumption.  Probably because the domain in which I
work is on-demand and unidirectional live media delivery.  I view the
delivery time line in terms of a rate. That rate is determined by the
attributes of the session: the state of the network, and the state of
the client side buffer. The media time line may shift relative to the
transmission time line.  So my application cares about "media seconds"
only to the extent that it needs that information to know when and how
to adapt. 

> >What I don't quite understand about your position is the role played by
> >the application in pacing data.  Do you maintain that the application
> >should pace data, or DCCP or both?
> 
> Both, but differently?
> 
> Streaming means that 1 second of content MUST be sent for
> every elapsed "real time" second (at least on the average).

I don't agree with the MUST.  It MAY if the congestion control will
allow it.  Or it may send more if the congestion control, session type
(i.e. on-demand), and buffer state allows. Or it may send less if there
is too much buffer stored up at the client. The application should be
constantly adapting its transmission pattern to meet a broad set of
requirements, that include congestion control.

> So the application cannot "pace seconds"...
> but I am assuming the application job contract
> does not say how many bytes one second of media is.
> 
> In short I am assuming that the sending application
> can change the media data rate in order to
> *follow* the network data rate.

I agree.  But how closely you want to follow the network rate  is
determined by the application type, and the state of the client buffer.
Oscillating the transmission pattern with congestion control
fluctuations can be a really bad thing for the user.

> 
> For conferencing -the media being encoded in real time-
> I assume that the DCCP stack will be used to pilot
> the encoder (tell it which rate to produce).

> For pre-recorded media delivery the solution is stream switching
> (or download! see the other mail)

> For live "TV" (very large number of receivers) changing
> the rate is either not relevant (e.g. end to end SSM)
> or it uses a relay server which folds the issue as being
> like pre-recorded media playback -each receiver maintaining
> a private server connection- then one should use stream switching,
> each stream "flavor" being simultaneously produced by a different encoder.
> 
> regards,
> 
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
> 
> 
>                                                                                                                                        
>                                                                                                                                        
>                                                    To:   Philippe Gentric/MP4-SUR/CE/PHILIPS@EMEA1                                     
>                                                    cc:   Magnus Westerlund <magnus.westerlund@ericsson.com>                            
>                                                     dccp@ietf.org                                                                      
>                                                     mmusic@ietf.org                                                                    
>                Damon Lanphear                      Subject:    Re: [dccp] natural DCCP sender-side API: (was stream switching)         
>                <damonlan@real.com>                                                                                                     
>                                                    Classification:                                                                     
>                23/07/2003 19:42                                                                                                        
>                                                                                                                                        
>                                                                                                                                        
> 
> 
> 
> 
> Philippe,
> 
> No one is really taking the position that a DCCP API should not make the
> transmission rate available to the application.  This is quite a
> straightforward issue. DCCP can easily expose this key piece of
> information.
> 
> I am more concerned with how an application meets DCCPs transmission
> limits (i.e. transmits at the required rate).
> 
> Let's put the issue of adaptation aside for a moment and just concern
> ourselves with how an application paces data to the network. My view is
> that DCCP offers the application both congestion control AND the ability
> to manage the transmission schedule.  I assume that DCCP will pace data
> to the lower layers at the rate required of the associated CCID spec.
> For the application to do this pacing as well would be redundant work.
> 
> What I don't quite understand about your position is the role played by
> the application in pacing data.  Do you maintain that the application
> should pace data, or DCCP or both? That is, is the use of the transmit
> rate to the application purely informative of a rate adaptation process,
> or of the transmit process as a whole?
> 
> On Wed, 2003-07-23 at 04:59, philippe.gentric@philips.com wrote:
> > Magnus,Damon,
> >
> > let us forget a minute about the exact application,
> > (because my point is *not* specific to stream switching)
> > let us instead concentrate on the following problem:
> >
> > you write:
> >
> > "the server can simply switch to a lower bit-rate"
> >
> > This is an indication we are on agreement on one thing:
> > DCCP is about rate-driven applications.
> >
> > This is why my concern has been from the very start:
> > how is the sending application (what ever it is)
> > going to know what rate it must use?
> >
> > The answers you gave so far seem to indicate you are confident
> > the application can "compute" such a rate based on the behavior of a blocking API...
> >
> > (ok, allow me now to *also* put aside my humble opinion that  trying to achieve that is not a good idea)
> >
> > I advocate that it would be a shame **because the information is already available**!
> >
> > Allow me to quote Section 3 of RFC 3448:
> >
> > "   Generally speaking, TFRC's congestion control mechanism works as
> >    follows:
> >
> >    o  The receiver measures the loss event rate and feeds this
> >       information back to the sender.
> >
> >    o  The sender also uses these feedback messages to measure the
> >       round-trip time (RTT).
> >
> >    o  The loss event rate and RTT are then fed into TFRC's throughput
> >       equation, giving the acceptable transmit rate.
> >
> >    o  The sender then adjusts its transmit rate to match the calculated
> >       rate.
> > "
> >
> > This seems to imply that a "natural" sender-side API for DCCP would explicitely
> > inform the application ("sender") about this "acceptable transmit rate".
> >
> > It also happens to be the *best thing* that can be provided to
> > an application designed to perform network adaptation.
> >
> >
> > regards,
> >
> > Philippe Gentric
> > Software Architect
> > Philips MP4Net
> > philippe.gentric@philips.com
> > http://www.platform4.philips.com
> >
> --
> Damon Lanphear <damonlan@real.com>
> 
> 
> 
> 
> 
-- 
Damon Lanphear <damonlan@real.com>


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On Wed, 2003-07-23 at 10:43, philippe.gentric@philips.com wrote:
> Hi Tom,
> 
> you write:
> 
> >The relevant difference, as far as this discussion goes, between recorded
> >and live media is that recorded media can be transmitted from the sender as
> >fast as the network allows (assuming buffering at the receiver).
> 
> and then latter (still about recorded media):
> 
> >So, in this scheme, the sender doesn't need to know the rate that TFRC has
> >determined, it simply always sends as fast as TFRC allows.
> 
> 1) I am sorry but *from a network point of view*
> I dont see a difference between this and "download"?

The only substantive difference is that the transmitted data may not be
stored statically on the device in the case of streaming.  So if you
have a small embedded device, with limited storage, you can experience
media from the network without having the cache the whole thing on the
device. The problem then becomes one of balancing the use of device
storage (i.e. client buffer management) and congestion control.

> 
> Except that to my knowledge all the products doing that use HTTP
> since it solves a rather large number of other problems at the same time!
> 
> 2) Now *from a user point of view*
> 
> "download" has a flavor usually called "progressive download"
> whereby the downloaded media file has a structure enabling
> to start playback before download is finished.
> 
> In this mode usually the slide bar that the player
> uses to display the media time has 2 colors,
> one displaying the current time in the media,
> the other the *received* time in the media,
> if this second mark stays ahead of the first mark playback is un-interrupted,
> otherwise the player stops and displays a message such as "please wait, rebufferring".
> 
> So I dont see either, from a user point of view,
> how different a behavior the case you describe would have?
> 
> ****************
> 
> I conclude about this use case of the DCCP blocking API you described,
> that it is not very attractive at all.
> 
> Surely DCCP has better assets to lure implementers?-)...
> I think an API providing a target rate would be a good starting point;-)
> 
> regards,
> 
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
> 
> 
> 
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
-- 
Damon Lanphear <damonlan@real.com>


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From: "Sean Robinson" <srobinson@real.com>
To: "Damon Lanphear" <damonlan@real.com>, "Phelan, Tom" <tphelan@sonusnet.com>
Cc: philippe.gentric@philips.com,
        "Magnus Westerlund" <magnus.westerlund@ericsson.com>, dccp@ietf.org,
        mmusic@ietf.org, "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
Subject: RE: [MMUSIC] RE: [dccp] natural DCCP sender-side API: (was stream switching)
Date: Wed, 23 Jul 2003 16:22:32 -0700
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I agree that Tom's contribution has provided a good basis for this
discussion.  The decision is further complicated by the inclusion of media
composition.  Consider we following media availablity constraints (which can
be applied to each of the named media application, On demand, live and
2-way)

- A single fixed rate media source
- multiple discrete media encodings
- a fully scalable media encoding (such as MPEG-4 FGS)

Now, given that in the second case we could add as many rates as we desire
and that the third case doesn't really exist (no codec is infitely
scalable), we can treat these as the same for the purposes of this
discussion.  We can view this from the application level as a series of
decision points in which the application concludes the best media data to
send at a given moment given the current network conditions.  The design of
the media is obviously a critical factor in the succcess of the application
as some media may work better in some application than others.  It is
assumed that low latency applicaiton will require more frequent decision
points where an on-demand application may require fewer.  We can think of
the media transmitted between these decision points as a media unit.

Here I would like to bring up a point that I feel has been neglected in the
discussion to this point.  That is the perspective of resource efficiency in
the interaction between a user level media application and a kernel level
protocol.  From this perspective the frequency of interaction between the
two sides should be minimized.  Also we would further hope that the need for
user level packet scheduling would also be minimized.

If the 2 above points are agreed to, we can then conclude that in the ideal
case we would want the interaction with the protocol to match as closely as
possible with those media decision points.  In other words, the application
should only have to interact with the dataflow when there is some meaningful
action to be taken.  This seems to me to be the best method for evaluation
of an API semantic.

First, let's take the simple blocking semantic.  The first question we
should ask (which is not specified in the DCCP user manual) is what triggers
that the block has cleared?  If we take the naive assumption that the file
descriptor is cleared for writing after the transmission of each datagram,
then our interaction with the protocol will also be on every datagram (if we
are instantly responsive to the signal).  This is likely more than we would
like in all but the very most scalable solutions.  Keep in mind, however,
that flow control through file descriptors is a well supported concept
throughout different OSes and this is very attractive in the design of a
protocol. Further, if we define parameters for when the desriptor is marked
for writing we can get greater control over its scalability.  It should also
be noted that this mechanism is not really optional, since the prtocol must
support blocking when the pre-netwqork buffer is full.

Now the rate-signalling approach has also been proposed, but it implies a
network-driven scheduling model over a media-driven model.  TFRC will
generate a new throughput claculation once per round trip time and if this
is the frequency at which the rate would be signalled, then we could either
find this to be too frequent or too sparse depending on the underlying
network.  Certainly an agrument could be made, media decision points should
be syncronized with network condition and if this is possible, this is a
more attractive solution.  It is important to note, however, that at a fine
grained level over delivery rate is not that relevant to the delivery
characteristcs, but rather the data size of individual media units.  So, if
TFRC reports 20kbs at a given window, it doesn't necesicearily mean that the
application should choose the 20kbs stream, but should evaluate the data to
be transmitted for available streams at that decision point.

Another option outside of direct feedback would be a polling approach,
whereby the application set interupt timers to evaluate the dataflow at
appropriate points in the application.  This method could work well in
stuations in which the throughput has a low degree of variance, since the
evaluation interval could be tailored to the desired media.  As the variance
increases, the effectiveness of this approach decreases since the data in
the pre-network queue may be delivered faster or slower than expected,
causing an increased number of "wasted" check in which no action is taken.

Another approach could be to tag specific datagrams for signalling on
transmission.  Then DCCP would signal (using some means) when a given
datagram is transmitted.  If one datagram per media unit, then we could get
a notification at every media unit, which is what we want.  The semantics of
defining this within an API could be quite complex, however.

Which brings me to a final important point.  As mentioned in several points,
we must consider the method in which the information is signalled.  Some
OSes have more advanced signalling mechanism than others and the more
digression from standard mechanisms, the less integrated into the OS the
protocol becomes.  This is an extremely imprrtant factor in this discussion
and should not be treated likely.

S
> -----Original Message-----
> From: mmusic-admin@ietf.org [mailto:mmusic-admin@ietf.org]On Behalf Of
> Damon Lanphear
> Sent: Wednesday, July 23, 2003 10:52 AM
> To: Phelan, Tom
> Cc: 'philippe.gentric@philips.com'; Magnus Westerlund; dccp@ietf.org;
> mmusic@ietf.org; Pasco Anderson, Jay
> Subject: [MMUSIC] RE: [dccp] natural DCCP sender-side API: (was stream
> switching)
>
>
> Tom,
>
> Thank you for providing better structure to our discussion.  This is
> precisely what we needed to speak more precisely on these matters!
>
> I haven't been able to work out acceptable scenarios for the other two
> > applications yet.  It seems almost certain to me that TFRC and
> a blocking
> > API is not at all suitable for two-way media.  It might be suitable for
> > one-way live media, but I haven't figured out how it could be yet.  If
> > anyone has ideas here I'd like to hear them :-).
>
> I'd like to understand the alternative to a blocking API for two-way
> media.  I assume that in this case the application is responsible for
> managing the transmission rate.  I guess I get confused when I consider
> that some agent in the pipeline will have to block transmission when the
> transmission attempt oversteps the congestion control rate.  What does
> it matter if this agent is DCCP or the application, particularly if we
> have access to the transmit queue in DCCP, as is the case in the ICIR
> implementation ?
>
> As regards unidirectional live,  its differs from unidirectional
> on-demand in that there's no data sitting on disk with which to fill a
> post-network buffer to a point where an up shift seems appropriate.
> Downshifts are straightforward, however, since under sending can just as
> well happen with live streams.  So we need a metric for up shifts that
> does not rely on buffer state.  Perhaps some measure of the stability of
> the available congestion controlled throughput over time?
>
> On Wed, 2003-07-23 at 07:43, Phelan, Tom wrote:
> > Hi Phillipe,
> >
> > In thinking about your draft on stream rate switching and this
> discussion on
> > APIs I've come to the conclusion that there are actually three different
> > applications being discussed, with three different sets of requirements.
> > One of these applications can be reasonably satisfied with a
> blocking API
> > (although there could be some efficiencies with other
> capabilities).  For
> > the other two I'm not sure yet what would work.
> >
> > Excuse me if I'm re-inventing something here, but the three
> applications I
> > have in mind are:
> >  o	One-way pre-recorded media
> >  o	One-way live media
> >  o	Two-way interactive media
> >
> > The relevant difference, as far as this discussion goes,
> between recorded
> > and live media is that recorded media can be transmitted from
> the sender as
> > fast as the network allows (assuming buffering at the
> receiver).  Live media
> > can only be transmitted at the rate that it's generated.
> >
> > The difference between one-way (live) and two-way is the size
> of the playout
> > buffer.  In one-way media you can use a playout buffer that's
> hundreds of
> > times larger than the round trip time.  In two-way media the
> playout buffer
> > is on the same order of magnitude as the round trip time.
> >
> > So, it seems to me that one-way pre-recorded media can be
> reasonably served
> > by DCCP with TFRC and a sockets-like (blocking) API.  For
> example, assume
> > that the sender has a media stream in two bit rates, high and low.  Also
> > assume that the sender is able to estimate the depth of the receiver's
> > playout buffer (either via feedback from the receiver or some
> other means).
> > Now set three thresholds in the playout buffer, a low
> threshold, a playback
> > start threshold and a high threshold, in order of increasing depth.
> >
> > To start the connection, the sender begins transmitting data
> from the high
> > bit rate stream as fast as TFRC allows (blocking the transmit thread for
> > rate control).  Since TFRC is in slow-start, this is probably too slow
> > initially, but eventually the rate might increase to fast
> enough and past.
> > The receiver buffers data until the playback start threshold is
> reached, and
> > then begins playback.
> >
> > If the TFRC rate never gets fast enough, or a packet loss makes
> TFRC drop
> > the rate, the receiver will drain the playout buffer faster
> than it's being
> > filled.  If the playout buffer drops below the low threshold, the sender
> > switches to the low bit rate stream.  Assuming that the network
> has a little
> > bit more capacity than the low bit rate stream requires, the
> playout buffer
> > will begin filling again.
> >
> > When the buffer crosses the high threshold the sender switches
> to the high
> > bit rate stream.  Assuming that the network still doesn't have enough
> > capacity for the high bit rate stream, the playout buffer will
> drain.  When
> > it reaches the low threshold the sender switches back to the
> low bit rate.
> > The sender will oscillate back and forth like this until the
> connection is
> > terminated.
> >
> > So, in this scheme, the sender doesn't need to know the rate
> that TFRC has
> > determined, it simply always sends as fast as TFRC allows.
> TFRC shapes the
> > stream to the network's requirements, and the feedback about the playout
> > buffer allows the sender to shape the stream to the application's
> > requirements.
> >
>
> >
> > Tom P.
> >
> >
> > > -----Original Message-----
> > > From: philippe.gentric@philips.com
> > > [mailto:philippe.gentric@philips.com]
> > > Sent: Wednesday, July 23, 2003 7:59 AM
> > > To: Magnus Westerlund
> > > Cc: Damon Lanphear; dccp@ietf.org; mmusic@ietf.org
> > > Subject: Re: [dccp] natural DCCP sender-side API: (was stream
> > > switching)
> > >
> > >
> > >
> > > Magnus,Damon,
> > >
> > > let us forget a minute about the exact application,
> > > (because my point is *not* specific to stream switching)
> > > let us instead concentrate on the following problem:
> > >
> > > you write:
> > >
> > > "the server can simply switch to a lower bit-rate"
> > >
> > > This is an indication we are on agreement on one thing:
> > > DCCP is about rate-driven applications.
> > >
> > > This is why my concern has been from the very start:
> > > how is the sending application (what ever it is)
> > > going to know what rate it must use?
> > >
> > > The answers you gave so far seem to indicate you are confident
> > > the application can "compute" such a rate based on the
> > > behavior of a blocking API...
> > >
> > > (ok, allow me now to *also* put aside my humble opinion that
> > > trying to achieve that is not a good idea)
> > >
> > > I advocate that it would be a shame **because the information
> > > is already available**!
> > >
> > > Allow me to quote Section 3 of RFC 3448:
> > >
> > > "   Generally speaking, TFRC's congestion control mechanism works as
> > >    follows:
> > >
> > >    o  The receiver measures the loss event rate and feeds this
> > >       information back to the sender.
> > >
> > >    o  The sender also uses these feedback messages to measure the
> > >       round-trip time (RTT).
> > >
> > >    o  The loss event rate and RTT are then fed into TFRC's throughput
> > >       equation, giving the acceptable transmit rate.
> > >
> > >    o  The sender then adjusts its transmit rate to match the
> > > calculated
> > >       rate.
> > > "
> > >
> > > This seems to imply that a "natural" sender-side API for DCCP
> > > would explicitely
> > > inform the application ("sender") about this "acceptable
> > > transmit rate".
> > >
> > > It also happens to be the *best thing* that can be provided to
> > > an application designed to perform network adaptation.
> > >
> > >
> > > regards,
> > >
> > > Philippe Gentric
> > > Software Architect
> > > Philips MP4Net
> > > philippe.gentric@philips.com
> > > http://www.platform4.philips.com
> > >
> > >
> > >
> > > _______________________________________________
> > > dccp IETF mailing list: dccp@ietf.org
> > > list info:  https://www1.ietf.org/mailman/listinfo/dccp
> > > wg charter: http://www.ietf.org/html.charters/dccp-charter.html
> > >
> --
> Damon Lanphear <damonlan@real.com>
>
>
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic


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From: "Phelan, Tom" <tphelan@sonusnet.com>
To: "'Damon Lanphear'" <damonlan@real.com>,
        "Phelan, Tom"
	 <tphelan@sonusnet.com>
Cc: "'philippe.gentric@philips.com'" <philippe.gentric@philips.com>,
        Magnus Westerlund <magnus.westerlund@ericsson.com>, dccp@ietf.org,
        mmusic@ietf.org, "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
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Subject: [MMUSIC] RE: [dccp] natural DCCP sender-side API: (was stream switching)
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Hi Damon,

See inline ...

Tom P.

> -----Original Message-----
> From: Damon Lanphear [mailto:damonlan@real.com]
> Sent: Wednesday, July 23, 2003 1:52 PM
> To: Phelan, Tom
> Cc: 'philippe.gentric@philips.com'; Magnus Westerlund; dccp@ietf.org;
> mmusic@ietf.org; Pasco Anderson, Jay
> Subject: RE: [dccp] natural DCCP sender-side API: (was stream 
> switching)
> 
> 
> Tom,
> 
> Thank you for providing better structure to our discussion.  This is
> precisely what we needed to speak more precisely on these matters!

Thanks :-).

> 
> I haven't been able to work out acceptable scenarios for the other two
> > applications yet.  It seems almost certain to me that TFRC 
> and a blocking
> > API is not at all suitable for two-way media.  It might be 
> suitable for
> > one-way live media, but I haven't figured out how it could 
> be yet.  If
> > anyone has ideas here I'd like to hear them :-).
> 
> I'd like to understand the alternative to a blocking API for two-way
> media.  I assume that in this case the application is responsible for
> managing the transmission rate.  I guess I get confused when 
> I consider
> that some agent in the pipeline will have to block 
> transmission when the
> transmission attempt oversteps the congestion control rate.  What does
> it matter if this agent is DCCP or the application, particularly if we
> have access to the transmit queue in DCCP, as is the case in the ICIR
> implementation ? 

Actually, my big worry here is TFRC, not the API.  I'm baffled about how to
map slow start plus mostly smooth changes but occasional abrupt changes and
a small playout buffer into something workable.

Another thing that concerns me (touched on in the paragraph above) is the
disconnect between a transport protocol making rate decisions and an
application making rate decisions.  It seems to me that these particular
applications are much better equipped to make the rate decisions - they know
about what is possible.  It also seems that the application can make at
least as good a decision about what constitutes network congestion.  The app
will need feedback about the playout buffer state, and this is largely
redundant with the DCCP acks.  If the app is making rate decisions and
detecting network congestion, what do we need DCCP for?

> 
> As regards unidirectional live,  its differs from unidirectional
> on-demand in that there's no data sitting on disk with which to fill a
> post-network buffer to a point where an up shift seems appropriate. 
> Downshifts are straightforward, however, since under sending 
> can just as
> well happen with live streams.  So we need a metric for up shifts that
> does not rely on buffer state.  Perhaps some measure of the 
> stability of
> the available congestion controlled throughput over time?

Yes, this is a problem - downshifts are straightforward, but under what
conditions do you upshift?  If your playout buffer is being depleted you can
downshift at some threshold and stop the depletion.  The problem is that
your playout buffer will never get re-filled, and you're now stuck at the
lower level.  If you upshift and things go bad again, the playout buffer
will go to an even lower level.  Enough of these shifts and the playout
buffer will run out - even if you could have maintained things at the lower
bit rate.

> 
> On Wed, 2003-07-23 at 07:43, Phelan, Tom wrote:
> > Hi Phillipe,
> > 
> > In thinking about your draft on stream rate switching and 
> this discussion on
> > APIs I've come to the conclusion that there are actually 
> three different
> > applications being discussed, with three different sets of 
> requirements.
> > One of these applications can be reasonably satisfied with 
> a blocking API
> > (although there could be some efficiencies with other 
> capabilities).  For
> > the other two I'm not sure yet what would work.
> > 
> > Excuse me if I'm re-inventing something here, but the three 
> applications I
> > have in mind are:
> >  o	One-way pre-recorded media
> >  o	One-way live media
> >  o	Two-way interactive media
> > 
> > The relevant difference, as far as this discussion goes, 
> between recorded
> > and live media is that recorded media can be transmitted 
> from the sender as
> > fast as the network allows (assuming buffering at the 
> receiver).  Live media
> > can only be transmitted at the rate that it's generated.
> > 
> > The difference between one-way (live) and two-way is the 
> size of the playout
> > buffer.  In one-way media you can use a playout buffer 
> that's hundreds of
> > times larger than the round trip time.  In two-way media 
> the playout buffer
> > is on the same order of magnitude as the round trip time.
> > 
> > So, it seems to me that one-way pre-recorded media can be 
> reasonably served
> > by DCCP with TFRC and a sockets-like (blocking) API.  For 
> example, assume
> > that the sender has a media stream in two bit rates, high 
> and low.  Also
> > assume that the sender is able to estimate the depth of the 
> receiver's
> > playout buffer (either via feedback from the receiver or 
> some other means).
> > Now set three thresholds in the playout buffer, a low 
> threshold, a playback
> > start threshold and a high threshold, in order of increasing depth.
> > 
> > To start the connection, the sender begins transmitting 
> data from the high
> > bit rate stream as fast as TFRC allows (blocking the 
> transmit thread for
> > rate control).  Since TFRC is in slow-start, this is 
> probably too slow
> > initially, but eventually the rate might increase to fast 
> enough and past.
> > The receiver buffers data until the playback start 
> threshold is reached, and
> > then begins playback.
> > 
> > If the TFRC rate never gets fast enough, or a packet loss 
> makes TFRC drop
> > the rate, the receiver will drain the playout buffer faster 
> than it's being
> > filled.  If the playout buffer drops below the low 
> threshold, the sender
> > switches to the low bit rate stream.  Assuming that the 
> network has a little
> > bit more capacity than the low bit rate stream requires, 
> the playout buffer
> > will begin filling again.
> > 
> > When the buffer crosses the high threshold the sender 
> switches to the high
> > bit rate stream.  Assuming that the network still doesn't 
> have enough
> > capacity for the high bit rate stream, the playout buffer 
> will drain.  When
> > it reaches the low threshold the sender switches back to 
> the low bit rate.
> > The sender will oscillate back and forth like this until 
> the connection is
> > terminated.
> > 
> > So, in this scheme, the sender doesn't need to know the 
> rate that TFRC has
> > determined, it simply always sends as fast as TFRC allows.  
> TFRC shapes the
> > stream to the network's requirements, and the feedback 
> about the playout
> > buffer allows the sender to shape the stream to the application's
> > requirements.
> > 
> 
> > 
> > Tom P.
> > 
> > 
> > > -----Original Message-----
> > > From: philippe.gentric@philips.com 
> > > [mailto:philippe.gentric@philips.com]
> > > Sent: Wednesday, July 23, 2003 7:59 AM
> > > To: Magnus Westerlund
> > > Cc: Damon Lanphear; dccp@ietf.org; mmusic@ietf.org
> > > Subject: Re: [dccp] natural DCCP sender-side API: (was stream 
> > > switching)
> > > 
> > > 
> > > 
> > > Magnus,Damon,
> > > 
> > > let us forget a minute about the exact application,
> > > (because my point is *not* specific to stream switching)
> > > let us instead concentrate on the following problem:
> > > 
> > > you write:
> > > 
> > > "the server can simply switch to a lower bit-rate"
> > > 
> > > This is an indication we are on agreement on one thing:
> > > DCCP is about rate-driven applications.
> > > 
> > > This is why my concern has been from the very start:
> > > how is the sending application (what ever it is)
> > > going to know what rate it must use?
> > > 
> > > The answers you gave so far seem to indicate you are confident
> > > the application can "compute" such a rate based on the 
> > > behavior of a blocking API...
> > > 
> > > (ok, allow me now to *also* put aside my humble opinion that  
> > > trying to achieve that is not a good idea)
> > > 
> > > I advocate that it would be a shame **because the information 
> > > is already available**!
> > > 
> > > Allow me to quote Section 3 of RFC 3448:
> > > 
> > > "   Generally speaking, TFRC's congestion control 
> mechanism works as
> > >    follows:
> > > 
> > >    o  The receiver measures the loss event rate and feeds this
> > >       information back to the sender.
> > > 
> > >    o  The sender also uses these feedback messages to measure the
> > >       round-trip time (RTT).
> > > 
> > >    o  The loss event rate and RTT are then fed into 
> TFRC's throughput
> > >       equation, giving the acceptable transmit rate.
> > > 
> > >    o  The sender then adjusts its transmit rate to match the 
> > > calculated
> > >       rate.
> > > "
> > > 
> > > This seems to imply that a "natural" sender-side API for DCCP 
> > > would explicitely
> > > inform the application ("sender") about this "acceptable 
> > > transmit rate".
> > > 
> > > It also happens to be the *best thing* that can be provided to
> > > an application designed to perform network adaptation.
> > > 
> > > 
> > > regards,
> > > 
> > > Philippe Gentric
> > > Software Architect
> > > Philips MP4Net
> > > philippe.gentric@philips.com
> > > http://www.platform4.philips.com
> > > 
> > > 
> > > 
> > > _______________________________________________
> > > dccp IETF mailing list: dccp@ietf.org
> > > list info:  https://www1.ietf.org/mailman/listinfo/dccp
> > > wg charter: http://www.ietf.org/html.charters/dccp-charter.html
> > > 
> -- 
> Damon Lanphear <damonlan@real.com>
> 

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From: "Phelan, Tom" <tphelan@sonusnet.com>
To: "'philippe.gentric@philips.com'" <philippe.gentric@philips.com>,
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Hi Phillipe,

From your point below - I don't see much difference between this (one-way
pre-recorded media) and file download either.  Just that in "normal" file
download it wouldn't be reasonable to consider changing the encoding scheme
in mid-transfer in order to keep up with some real-time considerations.

Note that to simplify things, my discussion assumed that the receiver could
buffer the entire program if it needed to.  I think it would be pretty easy
to extend the scheme to handle receivers that couldn't buffer the whole
program.  Something like a fourth buffer threshold that if hit causes the
sender to pause for a short time ...

Tom P.

> -----Original Message-----
> From: philippe.gentric@philips.com 
> [mailto:philippe.gentric@philips.com]
> Sent: Wednesday, July 23, 2003 1:43 PM
> To: Phelan, Tom
> Cc: dccp@ietf.org; mmusic@ietf.org
> Subject: RE: [dccp] natural DCCP sender-side API: (was stream 
> switching)
> 
> 
> Hi Tom,
> 
> you write:
> 
> >The relevant difference, as far as this discussion goes, 
> between recorded
> >and live media is that recorded media can be transmitted 
> from the sender as
> >fast as the network allows (assuming buffering at the receiver).
> 
> and then latter (still about recorded media):
> 
> >So, in this scheme, the sender doesn't need to know the rate 
> that TFRC has
> >determined, it simply always sends as fast as TFRC allows.
> 
> 1) I am sorry but *from a network point of view*
> I dont see a difference between this and "download"?
> 
> Except that to my knowledge all the products doing that use HTTP
> since it solves a rather large number of other problems at 
> the same time!
> 
> 2) Now *from a user point of view*
> 
> "download" has a flavor usually called "progressive download"
> whereby the downloaded media file has a structure enabling
> to start playback before download is finished.
> 
> In this mode usually the slide bar that the player
> uses to display the media time has 2 colors,
> one displaying the current time in the media,
> the other the *received* time in the media,
> if this second mark stays ahead of the first mark playback is 
> un-interrupted,
> otherwise the player stops and displays a message such as 
> "please wait, rebufferring".
> 
> So I dont see either, from a user point of view,
> how different a behavior the case you describe would have?
> 
> ****************
> 
> I conclude about this use case of the DCCP blocking API you described,
> that it is not very attractive at all.
> 
> Surely DCCP has better assets to lure implementers?-)...
> I think an API providing a target rate would be a good 
> starting point;-)
> 
> regards,
> 
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
> 
> 

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Hi Damon,

you write:

>I view the
>delivery time line in terms of a rate. That rate is determined by the
>attributes of the session: the state of the network, and the state of
>the client side buffer.

Why do you want to monitor the receiver buffers?

I though there was only 3 possibilities corresponding to the 3 protocols:

A) you dont care about "streaming" i.e. about "sending media in real time"
and then you should use HTTP progressive download (TCP)
and monitor the buffer because it may run dry.
or
B) You stream "old fashion" i.e. push data into the network
irrespective of the network status (UDP)
and monitor the buffer because it may run dry.
or
C) you use DCCP and then your application should simply follow the rate indicated by DCCP
because *if* the sender follows the rate indicated by DCCP
then it *does not need* to monitor the client side buffers
since the data will arrive on time thanks to DCCP
and therefore the client buffers will always contain the same
amount of media time... and playback will always be smooth.

is not this what DCCP is all about?

>The media time line may shift relative to the transmission time line

you mean on purpose or jitter?


regards

Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com


                                                                                                                                       
                                                                                                                                       
                                                   To:   Philippe Gentric/MP4-SUR/CE/PHILIPS@EMEA1                                     
                                                   cc:   dccp@ietf.org                                                                 
                                                    Magnus Westerlund <magnus.westerlund@ericsson.com>                                 
                                                    mmusic@ietf.org                                                                    
               Damon Lanphear                      Subject:    Re: [dccp] natural DCCP sender-side API: (was stream switching)         
               <damonlan@real.com>                                                                                                     
                                                   Classification:                                                                     
               Sent by:                                                                                                                
               dccp-admin@ietf.org                                                                                                     
                                                                                                                                       
               23/07/2003 21:38                                                                                                        
                                                                                                                                       
                                                                                                                                       




On Wed, 2003-07-23 at 11:12, philippe.gentric@philips.com wrote:
> Damon, you write:
>
> >I assume that DCCP will pace data
> >to the lower layers at the rate required of the associated CCID spec.
> >For the application to do this pacing as well would be redundant work.
>
> I am assuming it is a *different job*, they live on different planets,
> the DCCP stack cares about "real seconds",
> the application cares about "media seconds".

I don't share that assumption.  Probably because the domain in which I
work is on-demand and unidirectional live media delivery.  I view the
delivery time line in terms of a rate. That rate is determined by the
attributes of the session: the state of the network, and the state of
the client side buffer. The media time line may shift relative to the
transmission time line.  So my application cares about "media seconds"
only to the extent that it needs that information to know when and how
to adapt.

> >What I don't quite understand about your position is the role played by
> >the application in pacing data.  Do you maintain that the application
> >should pace data, or DCCP or both?
>
> Both, but differently?
>
> Streaming means that 1 second of content MUST be sent for
> every elapsed "real time" second (at least on the average).

I don't agree with the MUST.  It MAY if the congestion control will
allow it.  Or it may send more if the congestion control, session type
(i.e. on-demand), and buffer state allows. Or it may send less if there
is too much buffer stored up at the client. The application should be
constantly adapting its transmission pattern to meet a broad set of
requirements, that include congestion control.

> So the application cannot "pace seconds"...
> but I am assuming the application job contract
> does not say how many bytes one second of media is.
>
> In short I am assuming that the sending application
> can change the media data rate in order to
> *follow* the network data rate.

I agree.  But how closely you want to follow the network rate  is
determined by the application type, and the state of the client buffer.
Oscillating the transmission pattern with congestion control
fluctuations can be a really bad thing for the user.

>
> For conferencing -the media being encoded in real time-
> I assume that the DCCP stack will be used to pilot
> the encoder (tell it which rate to produce).

> For pre-recorded media delivery the solution is stream switching
> (or download! see the other mail)

> For live "TV" (very large number of receivers) changing
> the rate is either not relevant (e.g. end to end SSM)
> or it uses a relay server which folds the issue as being
> like pre-recorded media playback -each receiver maintaining
> a private server connection- then one should use stream switching,
> each stream "flavor" being simultaneously produced by a different encoder.
>
> regards,
>
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
>
>
>
>
>                                                    To:   Philippe Gentric/MP4-SUR/CE/PHILIPS@EMEA1
>                                                    cc:   Magnus Westerlund <magnus.westerlund@ericsson.com>
>                                                     dccp@ietf.org
>                                                     mmusic@ietf.org
>                Damon Lanphear                      Subject:    Re: [dccp] natural DCCP sender-side API: (was stream switching)
>                <damonlan@real.com>
>                                                    Classification:
>                23/07/2003 19:42
>
>
>
>
>
>
> Philippe,
>
> No one is really taking the position that a DCCP API should not make the
> transmission rate available to the application.  This is quite a
> straightforward issue. DCCP can easily expose this key piece of
> information.
>
> I am more concerned with how an application meets DCCPs transmission
> limits (i.e. transmits at the required rate).
>
> Let's put the issue of adaptation aside for a moment and just concern
> ourselves with how an application paces data to the network. My view is
> that DCCP offers the application both congestion control AND the ability
> to manage the transmission schedule.  I assume that DCCP will pace data
> to the lower layers at the rate required of the associated CCID spec.
> For the application to do this pacing as well would be redundant work.
>
> What I don't quite understand about your position is the role played by
> the application in pacing data.  Do you maintain that the application
> should pace data, or DCCP or both? That is, is the use of the transmit
> rate to the application purely informative of a rate adaptation process,
> or of the transmit process as a whole?
>
> On Wed, 2003-07-23 at 04:59, philippe.gentric@philips.com wrote:
> > Magnus,Damon,
> >
> > let us forget a minute about the exact application,
> > (because my point is *not* specific to stream switching)
> > let us instead concentrate on the following problem:
> >
> > you write:
> >
> > "the server can simply switch to a lower bit-rate"
> >
> > This is an indication we are on agreement on one thing:
> > DCCP is about rate-driven applications.
> >
> > This is why my concern has been from the very start:
> > how is the sending application (what ever it is)
> > going to know what rate it must use?
> >
> > The answers you gave so far seem to indicate you are confident
> > the application can "compute" such a rate based on the behavior of a blocking API...
> >
> > (ok, allow me now to *also* put aside my humble opinion that  trying to achieve that is not a good idea)
> >
> > I advocate that it would be a shame **because the information is already available**!
> >
> > Allow me to quote Section 3 of RFC 3448:
> >
> > "   Generally speaking, TFRC's congestion control mechanism works as
> >    follows:
> >
> >    o  The receiver measures the loss event rate and feeds this
> >       information back to the sender.
> >
> >    o  The sender also uses these feedback messages to measure the
> >       round-trip time (RTT).
> >
> >    o  The loss event rate and RTT are then fed into TFRC's throughput
> >       equation, giving the acceptable transmit rate.
> >
> >    o  The sender then adjusts its transmit rate to match the calculated
> >       rate.
> > "
> >
> > This seems to imply that a "natural" sender-side API for DCCP would explicitely
> > inform the application ("sender") about this "acceptable transmit rate".
> >
> > It also happens to be the *best thing* that can be provided to
> > an application designed to perform network adaptation.
> >
> >
> > regards,
> >
> > Philippe Gentric
> > Software Architect
> > Philips MP4Net
> > philippe.gentric@philips.com
> > http://www.platform4.philips.com
> >
> --
> Damon Lanphear <damonlan@real.com>
>
>
>
>
>
--
Damon Lanphear <damonlan@real.com>


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Subject: Re: [MMUSIC] RE: [dccp] natural DCCP sender-side API: (was stream switching)
To: Damon Lanphear <damonlan@real.com>
Cc: dccp@ietf.org, mmusic@ietf.org
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Hi Damon,

>> >So, in this scheme, the sender doesn't need to know the rate that TFRC has
>> >determined, it simply always sends as fast as TFRC allows.
>>
>> 1) I am sorry but *from a network point of view*
>> I dont see a difference between this and "download"?
>
>The only substantive difference is that the transmitted data may not be
>stored statically on the device in the case of streaming.  So if you
>have a small embedded device, with limited storage, you can experience
>media from the network without having the cache the whole thing on the
>device.

with progressive download  if you have no room for storage
you can garbage media  as soon as it is decoded as well ...
and slow down the sender if needed too ...

regards,

Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com


                                                                                                                                       
                                                                                                                                       
                                                   To:   Philippe Gentric/MP4-SUR/CE/PHILIPS@EMEA1                                     
                                                   cc:   "Phelan, Tom" <tphelan@sonusnet.com>                                          
                                                    dccp@ietf.org                                                                      
                                                    mmusic@ietf.org                                                                    
               Damon Lanphear                      Subject:    [MMUSIC] RE: [dccp] natural DCCP sender-side API: (was stream           
               <damonlan@real.com>                  switching)                                                                         
                                                                                                                                       
               Sent by:                            Classification:                                                                     
               mmusic-admin@ietf.org                                                                                                   
                                                                                                                                       
               23/07/2003 21:42                                                                                                        
                                                                                                                                       
                                                                                                                                       




On Wed, 2003-07-23 at 10:43, philippe.gentric@philips.com wrote:
> Hi Tom,
>
> you write:
>
> >The relevant difference, as far as this discussion goes, between recorded
> >and live media is that recorded media can be transmitted from the sender as
> >fast as the network allows (assuming buffering at the receiver).
>
> and then latter (still about recorded media):
>
> >So, in this scheme, the sender doesn't need to know the rate that TFRC has
> >determined, it simply always sends as fast as TFRC allows.
>
> 1) I am sorry but *from a network point of view*
> I dont see a difference between this and "download"?

The only substantive difference is that the transmitted data may not be
stored statically on the device in the case of streaming.  So if you
have a small embedded device, with limited storage, you can experience
media from the network without having the cache the whole thing on the
device. The problem then becomes one of balancing the use of device
storage (i.e. client buffer management) and congestion control.

>
> Except that to my knowledge all the products doing that use HTTP
> since it solves a rather large number of other problems at the same time!
>
> 2) Now *from a user point of view*
>
> "download" has a flavor usually called "progressive download"
> whereby the downloaded media file has a structure enabling
> to start playback before download is finished.
>
> In this mode usually the slide bar that the player
> uses to display the media time has 2 colors,
> one displaying the current time in the media,
> the other the *received* time in the media,
> if this second mark stays ahead of the first mark playback is un-interrupted,
> otherwise the player stops and displays a message such as "please wait, rebufferring".
>
> So I dont see either, from a user point of view,
> how different a behavior the case you describe would have?
>
> ****************
>
> I conclude about this use case of the DCCP blocking API you described,
> that it is not very attractive at all.
>
> Surely DCCP has better assets to lure implementers?-)...
> I think an API providing a target rate would be a good starting point;-)
>
> regards,
>
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
>
>
>
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
--
Damon Lanphear <damonlan@real.com>


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From: "Rosen, Brian" <Brian.Rosen@marconi.com>
To: "'Mark Handley'" <M.Handley@cs.ucl.ac.uk>,
        "Phelan, Tom"
	 <tphelan@sonusnet.com>
Cc: "'Damon Lanphear'" <damonlan@real.com>,
        "'philippe.gentric@philips.com'"
	 <philippe.gentric@philips.com>,
        Magnus Westerlund
	 <magnus.westerlund@ericsson.com>, dccp@ietf.org,
        mmusic@ietf.org, "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
Date: Thu, 24 Jul 2003 11:35:05 -0400
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Subject: [MMUSIC] RE: [dccp] natural DCCP sender-side API: (was stream switching)
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As someone who is presently making such a videophone, let me add just
a couple of details, as I think Mark's observations are very close
to what we need.

Most video codecs cannot quickly change their encoding rates, and they
often encounter a glitch when they do.  Many are based on hardware
implementations in the encoder which force you to stop the encoder, change
a bunch of settings, and restart it.  It's possible, and we'll do it,
but not very often, please.

Second, we have found that delay is not just a problem, it is a cliff.
If you go over 150 ms or so, you fall off the cliff.  The difference 
between, say 250 ms and 500 ms is about 2 orders of magnitude less
that the difference between 150 ms and 200 ms (there is in fact some
variation, because it's a human response thing, 150 ms is something like
a 95% point for detecting delay).  These are one way delays, and,
as an aside, are actually a limit for the audio, but are determined
by the video, because you need the audio to match the video (lip sync)
the video delay is harder to control (codec complexity), but the
limit is your ability to hear delay.  So, generally, we have NO
buffering (like less than 1ms) for any network related things.
On the other hand, to make it work, we, unlike many, have relatively
constant data rates out of the encoder without using buffering to
accomplish it.

So, we can tolerate a reasonable bound on TRFC rate variation, we'll
always send at that rate, or less.   In practice, you tend to
quantize transmit rates, so we will have to send at the next lowest
rate for a given TRFC limit.   Some other codecs can be forced to
an exact data rate by buffering peaks, and again, you often see
quantization of rates.

A small problem that arises is that the signalling (SIP) typically
includes a negotiation of rates.  There isn't a way to signal a 
dynamically changing rate.  This is straightforward to address by 
us sip guys.  If it changes slowly enough, we can just signal
the change using the mechanisms we have.

In VoIP, things are a little more complex.  There are a variety of
algorithms, and a few of them are defined to work on more than one
data rate.  In general, like the hardware encoder, you can't switch
algorithms without a noticeable glitch.  Some implementations of
multirate codecs can switch reasonably smoothly, others can't.
It's presently uncommon to find a VoIP phone with a variable data
rate codec, but it is common to find VoIP phones with more than
one algorithm, each algorithm having a different data rate.  Switching
algorithms is definitely a signalling problem.  On the other hand, 
nearly all voice codecs are constant bit rate inherently.

Brian


> -----Original Message-----
> From: Mark Handley [mailto:M.Handley@cs.ucl.ac.uk]
> Sent: Thursday, July 24, 2003 10:46 AM
> To: Phelan, Tom
> Cc: 'Damon Lanphear'; 'philippe.gentric@philips.com'; Magnus 
> Westerlund;
> dccp@ietf.org; mmusic@ietf.org; Pasco Anderson, Jay
> Subject: Re: [dccp] natural DCCP sender-side API: (was stream 
> switching)
> 
> 
> 
> 
> >Actually, my big worry here is TFRC, not the API.  I'm 
> baffled about how to
> >map slow start plus mostly smooth changes but occasional 
> abrupt changes and
> >a small playout buffer into something workable.
> >
> >Another thing that concerns me (touched on in the paragraph 
> above) is the
> >disconnect between a transport protocol making rate decisions and an
> >application making rate decisions.  It seems to me that 
> these particular
> >applications are much better equipped to make the rate 
> decisions - they know
> >about what is possible.  It also seems that the application 
> can make at
> >least as good a decision about what constitutes network 
> congestion.  The app
> >will need feedback about the playout buffer state, and this 
> is largely
> >redundant with the DCCP acks.  If the app is making rate 
> decisions and
> >detecting network congestion, what do we need DCCP for?
> 
> [I'm just dropping back into a discussion I haven't been following, so
> forgive me if this duplicates previous discussion]
> 
> There seem to be two obvious sorts of apps that might use TFRC:
> 
>  - streaming media
>  - videotelephony
> 
> That isn't to say that there are different apps, but these two typify
> two classes of apps.  Both are fine with variable packet rates.  But
> streaming media has significantly more playout buffer available.
> 
> Streaming media apps can run the codec (or choice of pre-encoded
> stream) at approximately constant bitrate, and send at variable
> bitrate, using the playout buffer to deal with the temporary
> mismatches.  
> 
> Videotelephony apps don't have sufficient delay budget to fix things
> at the receiver, but they do have the luxury of encoding live, so they
> can change the compression parameters on the fly.  They usually don't
> have luxury of re-encoding twice though, so if their choice of
> quantization parameters gives a rate that is different from what is
> expected (because the video content was unpredictable), then they
> might be in trouble.  Also, if the TFRC bandwidth envelope changes
> unexpectedly, you can be in trouble.
> 
> 
> So, why do I say all this?
> 
> 
> My assumption is that streaming media apps will normally send at the
> TFRC rate.  What they need is sufficient advance warning that the
> playout buffer is running low so that they can switch down to a lower
> rate.  And if the playout buffer is starting to get rather large, then
> they can switch up to a higher rate.  Assuming rate switching is not a
> trivial operation, and that the rate can only be switched at certain
> re-sync points, then there is some danger that if congestion suddently
> gets really bad, then the playout buffer will be exhausted before the
> codec can be switched.  My assumption here is that a really good API
> would allow the sender to send above the TFRC rate for a period of
> time, so long as the rate mismatch isn't too bad.  A factor of two
> might be reasonable as an upper bound on the oversending rate.
> 
> 
> Videotelephony apps probably can't send at precisely the TFRC rate
> without sacrificing delay to an undesirable extent.  This means two
> things. First, the app needs to be allowed to send at rates above the
> TFRC rate for a period of time (again, bounded to avoid extreme
> unfairness).  Second, if the app sends under the TFRC rate for a short
> period, it shouldn't lose it's ability to send faster later, so long
> as it didn't undersend by too much.  For such apps, the TFRC rate is a
> guide rate - the app should be capable of varying around the guide
> rate, so long as it stays within reasonable bounds, and so long as the
> long-term average is close to the TFRC rate.
> 
> 
> Anyway, in both cases, if the kernel strictly enforces the TFRC rate,
> app designers will either not use DCCP, or they'll pad their signal
> with redundant data so they can operate within a more predictable
> codec envelope.  Both are undesirable.
> 
> 
> I'm not sure how we best design an API to satisfy this, but I think
> it's really important that we do think about how this can be achieved.
> 
> 
> The general philosophy that the TFRC rate is a guide-rate to be
> followed loosely will probably also apply with TFRC-PS and VoIP, but
> we know a lot less about this space.
> 
> Cheers,
> 	Mark
> 
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
> 

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To: Mark Handley <M.Handley@cs.ucl.ac.uk>
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Subject: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream switching)
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Hi Mark,


>My assumption is that streaming media apps will normally send at the
>TFRC rate.

Could it be "at a rate equal or inferior to the TFRC rate"?

What will happen if an application "does not use" the
bandwidth indicated by TFRC?

Often there will be no other choice,
for example if my application can do 200 kb/s and 400 kb/s
and TFRC indicates 380 kb/s then I must still use the media
at 200 kb/s and SEND it at 200 kb/s because if I try
to send my 200 kb/s media at 380 kb/s I will simply explode
the player buffers very rapidly?

>What they need is sufficient advance warning that the
>playout buffer is running low so that they can switch down to a lower
>rate.

yes on advance warning about the TFRC rate,
but I see the need for the sender to monitor
the playout buffer as unnecessary complexity:

I think that if the application *generates* (and sends) data at
(or below) the TFRC rate then data will arrive on time
and the playout buffer will always remain stable?

>And if the playout buffer is starting to get rather large, then
>they can switch up to a higher rate.

you are assuming that the application sends data
at a data rate larger than the media data rate...

then yes! if you play with this fire you will
need to monitor the player side buffers very carefully!

The only advantage I can see with that trick
is that *if you are lucky* during the first minutes of streaming
you can play this trick to build up your player-side buffer
using the positive gaps between the TFRC rate and the highest available
media rate smaller than the TFRC rate; which means that playback can be started
with minimal lead time i.e. it shortens the time the user waits between the streaming
request and movie starts to play...unfortunately if you are unlucky
you will underflow...

do you seen any other advantage?

anyway it is a more complicated solution.

I would simply stream at the first available
media rate smaller than the TFRC rate.


>Assuming rate switching is not a
>trivial operation, and that the rate can only be switched at certain
>re-sync points, then there is some danger that if congestion suddently
>gets really bad, then the playout buffer will be exhausted before the
>codec can be switched.

Let us compare:

if you switch "in a hurry" it maybe that the result
for the end user does not look very good,
however the alternative (keep on sending at the same rate)
is not very attractive either for the end user,
since the player will drain its buffers anyway.

the difference is that it is worse for the network!

>My assumption here is that a really good API
>would allow the sender to send above the TFRC rate for a period of
>time, so long as the rate mismatch isn't too bad.  A factor of two
>might be reasonable as an upper bound on the oversending rate.

I though if you wanted to do that you would declare it as a new
rate control policy (since it is one, no?) i.e. give it another CCID ?

What would be the point of defining TFRC and then "cheat on it" ?

How would you define "TFRC conformance" then?

>Anyway, in both cases, if the kernel strictly enforces the TFRC rate,
>app designers will either not use DCCP, or they'll pad their signal
>with redundant data so they can operate within a more predictable
>codec envelope.

Do you mean send garbage?
what kind of gain would that bring ?
what is a predictable codec envelope?


regards,


Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com


                                                                                                                                       
                                                                                                                                       
                                                   To:   "Phelan, Tom" <tphelan@sonusnet.com>                                          
                                                   cc:   "'Damon Lanphear'" <damonlan@real.com>                                        
                                                    Philippe Gentric/MP4-SUR/CE/PHILIPS@EMEA1                                          
                                                    Magnus Westerlund <magnus.westerlund@ericsson.com>                                 
               Mark Handley                         dccp@ietf.org                                                                      
               <M.Handley@cs.ucl.ac.uk>             mmusic@ietf.org                                                                    
                                                    "Pasco Anderson, Jay" <jpanderson@sonusnet.com>                                    
               Sent by:                            Subject:    Re: [dccp] natural DCCP sender-side API: (was stream switching)         
               mjh@cs.ucl.ac.uk                                                                                                        
                                                   Classification:                                                                     
               24/07/2003 16:46                                                                                                        
                                                                                                                                       
                                                                                                                                       





>Actually, my big worry here is TFRC, not the API.  I'm baffled about how to
>map slow start plus mostly smooth changes but occasional abrupt changes and
>a small playout buffer into something workable.
>
>Another thing that concerns me (touched on in the paragraph above) is the
>disconnect between a transport protocol making rate decisions and an
>application making rate decisions.  It seems to me that these particular
>applications are much better equipped to make the rate decisions - they know
>about what is possible.  It also seems that the application can make at
>least as good a decision about what constitutes network congestion.  The app
>will need feedback about the playout buffer state, and this is largely
>redundant with the DCCP acks.  If the app is making rate decisions and
>detecting network congestion, what do we need DCCP for?

[I'm just dropping back into a discussion I haven't been following, so
forgive me if this duplicates previous discussion]

There seem to be two obvious sorts of apps that might use TFRC:

 - streaming media
 - videotelephony

That isn't to say that there are different apps, but these two typify
two classes of apps.  Both are fine with variable packet rates.  But
streaming media has significantly more playout buffer available.

Streaming media apps can run the codec (or choice of pre-encoded
stream) at approximately constant bitrate, and send at variable
bitrate, using the playout buffer to deal with the temporary
mismatches.

Videotelephony apps don't have sufficient delay budget to fix things
at the receiver, but they do have the luxury of encoding live, so they
can change the compression parameters on the fly.  They usually don't
have luxury of re-encoding twice though, so if their choice of
quantization parameters gives a rate that is different from what is
expected (because the video content was unpredictable), then they
might be in trouble.  Also, if the TFRC bandwidth envelope changes
unexpectedly, you can be in trouble.


So, why do I say all this?


My assumption is that streaming media apps will normally send at the
TFRC rate.  What they need is sufficient advance warning that the
playout buffer is running low so that they can switch down to a lower
rate.  And if the playout buffer is starting to get rather large, then
they can switch up to a higher rate.  Assuming rate switching is not a
trivial operation, and that the rate can only be switched at certain
re-sync points, then there is some danger that if congestion suddently
gets really bad, then the playout buffer will be exhausted before the
codec can be switched.  My assumption here is that a really good API
would allow the sender to send above the TFRC rate for a period of
time, so long as the rate mismatch isn't too bad.  A factor of two
might be reasonable as an upper bound on the oversending rate.


Videotelephony apps probably can't send at precisely the TFRC rate
without sacrificing delay to an undesirable extent.  This means two
things. First, the app needs to be allowed to send at rates above the
TFRC rate for a period of time (again, bounded to avoid extreme
unfairness).  Second, if the app sends under the TFRC rate for a short
period, it shouldn't lose it's ability to send faster later, so long
as it didn't undersend by too much.  For such apps, the TFRC rate is a
guide rate - the app should be capable of varying around the guide
rate, so long as it stays within reasonable bounds, and so long as the
long-term average is close to the TFRC rate.


Anyway, in both cases, if the kernel strictly enforces the TFRC rate,
app designers will either not use DCCP, or they'll pad their signal
with redundant data so they can operate within a more predictable
codec envelope.  Both are undesirable.


I'm not sure how we best design an API to satisfy this, but I think
it's really important that we do think about how this can be achieved.


The general philosophy that the TFRC rate is a guide-rate to be
followed loosely will probably also apply with TFRC-PS and VoIP, but
we know a lot less about this space.

Cheers,
             Mark






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To: "Rosen, Brian" <Brian.Rosen@marconi.com>
Cc: dccp@ietf.org, mmusic@ietf.org
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Hi Brian,

>we'll always send at that [TFRC] rate, or less.   In practice, you tend to
>quantize transmit rates, so we will have to send at the next lowest
>rate for a given TRFC limit.

I am glad to see that we reach exactly the same conclusion ...

it is funny that it seems to be for reasons that look so different !

regards,


Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com


                                                                                                                                       
                                                                                                                                       
                                                   To:   "'Mark Handley'" <M.Handley@cs.ucl.ac.uk>                                     
                                                    "Phelan, Tom" <tphelan@sonusnet.com>                                               
                                                   cc:   "'Damon Lanphear'" <damonlan@real.com>                                        
                                                    Philippe Gentric/MP4-SUR/CE/PHILIPS@EMEA1                                          
               "Rosen, Brian"                       Magnus Westerlund <magnus.westerlund@ericsson.com>                                 
               <Brian.Rosen@marconi.com             dccp@ietf.org                                                                      
               >                                    mmusic@ietf.org                                                                    
                                                    "Pasco Anderson, Jay" <jpanderson@sonusnet.com>                                    
               Sent by:                            Subject:    RE: [dccp] natural DCCP sender-side API: (was stream switching)         
               dccp-admin@ietf.org                                                                                                     
                                                   Classification:                                                                     
               24/07/2003 17:35                                                                                                        
                                                                                                                                       
                                                                                                                                       




As someone who is presently making such a videophone, let me add just
a couple of details, as I think Mark's observations are very close
to what we need.

Most video codecs cannot quickly change their encoding rates, and they
often encounter a glitch when they do.  Many are based on hardware
implementations in the encoder which force you to stop the encoder, change
a bunch of settings, and restart it.  It's possible, and we'll do it,
but not very often, please.

Second, we have found that delay is not just a problem, it is a cliff.
If you go over 150 ms or so, you fall off the cliff.  The difference
between, say 250 ms and 500 ms is about 2 orders of magnitude less
that the difference between 150 ms and 200 ms (there is in fact some
variation, because it's a human response thing, 150 ms is something like
a 95% point for detecting delay).  These are one way delays, and,
as an aside, are actually a limit for the audio, but are determined
by the video, because you need the audio to match the video (lip sync)
the video delay is harder to control (codec complexity), but the
limit is your ability to hear delay.  So, generally, we have NO
buffering (like less than 1ms) for any network related things.
On the other hand, to make it work, we, unlike many, have relatively
constant data rates out of the encoder without using buffering to
accomplish it.

So, we can tolerate a reasonable bound on TRFC rate variation, we'll
always send at that rate, or less.   In practice, you tend to
quantize transmit rates, so we will have to send at the next lowest
rate for a given TRFC limit.   Some other codecs can be forced to
an exact data rate by buffering peaks, and again, you often see
quantization of rates.

A small problem that arises is that the signalling (SIP) typically
includes a negotiation of rates.  There isn't a way to signal a
dynamically changing rate.  This is straightforward to address by
us sip guys.  If it changes slowly enough, we can just signal
the change using the mechanisms we have.

In VoIP, things are a little more complex.  There are a variety of
algorithms, and a few of them are defined to work on more than one
data rate.  In general, like the hardware encoder, you can't switch
algorithms without a noticeable glitch.  Some implementations of
multirate codecs can switch reasonably smoothly, others can't.
It's presently uncommon to find a VoIP phone with a variable data
rate codec, but it is common to find VoIP phones with more than
one algorithm, each algorithm having a different data rate.  Switching
algorithms is definitely a signalling problem.  On the other hand,
nearly all voice codecs are constant bit rate inherently.

Brian


> -----Original Message-----
> From: Mark Handley [mailto:M.Handley@cs.ucl.ac.uk]
> Sent: Thursday, July 24, 2003 10:46 AM
> To: Phelan, Tom
> Cc: 'Damon Lanphear'; 'philippe.gentric@philips.com'; Magnus
> Westerlund;
> dccp@ietf.org; mmusic@ietf.org; Pasco Anderson, Jay
> Subject: Re: [dccp] natural DCCP sender-side API: (was stream
> switching)
>
>
>
>
> >Actually, my big worry here is TFRC, not the API.  I'm
> baffled about how to
> >map slow start plus mostly smooth changes but occasional
> abrupt changes and
> >a small playout buffer into something workable.
> >
> >Another thing that concerns me (touched on in the paragraph
> above) is the
> >disconnect between a transport protocol making rate decisions and an
> >application making rate decisions.  It seems to me that
> these particular
> >applications are much better equipped to make the rate
> decisions - they know
> >about what is possible.  It also seems that the application
> can make at
> >least as good a decision about what constitutes network
> congestion.  The app
> >will need feedback about the playout buffer state, and this
> is largely
> >redundant with the DCCP acks.  If the app is making rate
> decisions and
> >detecting network congestion, what do we need DCCP for?
>
> [I'm just dropping back into a discussion I haven't been following, so
> forgive me if this duplicates previous discussion]
>
> There seem to be two obvious sorts of apps that might use TFRC:
>
>  - streaming media
>  - videotelephony
>
> That isn't to say that there are different apps, but these two typify
> two classes of apps.  Both are fine with variable packet rates.  But
> streaming media has significantly more playout buffer available.
>
> Streaming media apps can run the codec (or choice of pre-encoded
> stream) at approximately constant bitrate, and send at variable
> bitrate, using the playout buffer to deal with the temporary
> mismatches.
>
> Videotelephony apps don't have sufficient delay budget to fix things
> at the receiver, but they do have the luxury of encoding live, so they
> can change the compression parameters on the fly.  They usually don't
> have luxury of re-encoding twice though, so if their choice of
> quantization parameters gives a rate that is different from what is
> expected (because the video content was unpredictable), then they
> might be in trouble.  Also, if the TFRC bandwidth envelope changes
> unexpectedly, you can be in trouble.
>
>
> So, why do I say all this?
>
>
> My assumption is that streaming media apps will normally send at the
> TFRC rate.  What they need is sufficient advance warning that the
> playout buffer is running low so that they can switch down to a lower
> rate.  And if the playout buffer is starting to get rather large, then
> they can switch up to a higher rate.  Assuming rate switching is not a
> trivial operation, and that the rate can only be switched at certain
> re-sync points, then there is some danger that if congestion suddently
> gets really bad, then the playout buffer will be exhausted before the
> codec can be switched.  My assumption here is that a really good API
> would allow the sender to send above the TFRC rate for a period of
> time, so long as the rate mismatch isn't too bad.  A factor of two
> might be reasonable as an upper bound on the oversending rate.
>
>
> Videotelephony apps probably can't send at precisely the TFRC rate
> without sacrificing delay to an undesirable extent.  This means two
> things. First, the app needs to be allowed to send at rates above the
> TFRC rate for a period of time (again, bounded to avoid extreme
> unfairness).  Second, if the app sends under the TFRC rate for a short
> period, it shouldn't lose it's ability to send faster later, so long
> as it didn't undersend by too much.  For such apps, the TFRC rate is a
> guide rate - the app should be capable of varying around the guide
> rate, so long as it stays within reasonable bounds, and so long as the
> long-term average is close to the TFRC rate.
>
>
> Anyway, in both cases, if the kernel strictly enforces the TFRC rate,
> app designers will either not use DCCP, or they'll pad their signal
> with redundant data so they can operate within a more predictable
> codec envelope.  Both are undesirable.
>
>
> I'm not sure how we best design an API to satisfy this, but I think
> it's really important that we do think about how this can be achieved.
>
>
> The general philosophy that the TFRC rate is a guide-rate to be
> followed loosely will probably also apply with TFRC-PS and VoIP, but
> we know a lot less about this space.
>
> Cheers,
>            Mark
>
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
>

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From: Damon Lanphear <damonlan@real.com>
To: philippe.gentric@philips.com
Cc: dccp@ietf.org, mmusic@ietf.org
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On Thu, 2003-07-24 at 07:52, philippe.gentric@philips.com wrote:
> Hi Damon,
> 
> you write:
> 
> >I view the
> >delivery time line in terms of a rate. That rate is determined by the
> >attributes of the session: the state of the network, and the state of
> >the client side buffer.
> 
> Why do you want to monitor the receiver buffers?

Because the buffer state is the best indicator of the continuity of the
presentation.  

> I though there was only 3 possibilities corresponding to the 3 protocols:
> 
> A) you dont care about "streaming" i.e. about "sending media in real time"
> and then you should use HTTP progressive download (TCP)
> and monitor the buffer because it may run dry.
> or

I don't think of streaming as "sending media in real time", I think of
streaming as sending data while adhering to real time constraints.  This
is not the same as progressive download. 

I also happen to think that TCP _streaming_ is the correct solution for
certain application deployments.   

> B) You stream "old fashion" i.e. push data into the network
> irrespective of the network status (UDP)
> and monitor the buffer because it may run dry.
> or
> C) you use DCCP and then your application should simply follow the rate indicated by DCCP
> because *if* the sender follows the rate indicated by DCCP
> then it *does not need* to monitor the client side buffers
> since the data will arrive on time thanks to DCCP

?!? How does DCCP guarantee on time delivery?  

DCCP's transmission rate may vary over time.  I understand that you
assume the sender will follow the rate indicated by DCCP as closely as
possible.  But as you point out, this requires that DCCP tell the app
"in advance" of rate changes.  I submit that there can be no such thing
as advanced rate change warnings.  DCCP changes it rate in response to
stimuli that it receives in the immediate moment.  We can not expect
DCCP to predict the amount of loss or change in RTT in the next N window
durations.

> and therefore the client buffers will always contain the same
> amount of media time... and playback will always be smooth.

Perhaps that will be the case in a perfect world where there is no such
thing as transient congestion or our codecs provide use with infinite
granularity of scalability. 

> is not this what DCCP is all about?

DCCP is about providing congestion control to applications that wouldn't
otherwise use congestion control.  The benefit of DCCP to such
applications is the offloading of congestion response to a robust and
correct solution, rather than having to re-invent the wheel. 

> >The media time line may shift relative to the transmission time line
> 
> you mean on purpose or jitter?

I mean on purpose, and due to congestion events.

> 
> 
> regards
> 
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
> 
> 
>                                                                                                                                        
>                                                                                                                                        
>                                                    To:   Philippe Gentric/MP4-SUR/CE/PHILIPS@EMEA1                                     
>                                                    cc:   dccp@ietf.org                                                                 
>                                                     Magnus Westerlund <magnus.westerlund@ericsson.com>                                 
>                                                     mmusic@ietf.org                                                                    
>                Damon Lanphear                      Subject:    Re: [dccp] natural DCCP sender-side API: (was stream switching)         
>                <damonlan@real.com>                                                                                                     
>                                                    Classification:                                                                     
>                Sent by:                                                                                                                
>                dccp-admin@ietf.org                                                                                                     
>                                                                                                                                        
>                23/07/2003 21:38                                                                                                        
>                                                                                                                                        
>                                                                                                                                        
> 
> 
> 
> 
> On Wed, 2003-07-23 at 11:12, philippe.gentric@philips.com wrote:
> > Damon, you write:
> >
> > >I assume that DCCP will pace data
> > >to the lower layers at the rate required of the associated CCID spec.
> > >For the application to do this pacing as well would be redundant work.
> >
> > I am assuming it is a *different job*, they live on different planets,
> > the DCCP stack cares about "real seconds",
> > the application cares about "media seconds".
> 
> I don't share that assumption.  Probably because the domain in which I
> work is on-demand and unidirectional live media delivery.  I view the
> delivery time line in terms of a rate. That rate is determined by the
> attributes of the session: the state of the network, and the state of
> the client side buffer. The media time line may shift relative to the
> transmission time line.  So my application cares about "media seconds"
> only to the extent that it needs that information to know when and how
> to adapt.
> 
> > >What I don't quite understand about your position is the role played by
> > >the application in pacing data.  Do you maintain that the application
> > >should pace data, or DCCP or both?
> >
> > Both, but differently?
> >
> > Streaming means that 1 second of content MUST be sent for
> > every elapsed "real time" second (at least on the average).
> 
> I don't agree with the MUST.  It MAY if the congestion control will
> allow it.  Or it may send more if the congestion control, session type
> (i.e. on-demand), and buffer state allows. Or it may send less if there
> is too much buffer stored up at the client. The application should be
> constantly adapting its transmission pattern to meet a broad set of
> requirements, that include congestion control.
> 
> > So the application cannot "pace seconds"...
> > but I am assuming the application job contract
> > does not say how many bytes one second of media is.
> >
> > In short I am assuming that the sending application
> > can change the media data rate in order to
> > *follow* the network data rate.
> 
> I agree.  But how closely you want to follow the network rate  is
> determined by the application type, and the state of the client buffer.
> Oscillating the transmission pattern with congestion control
> fluctuations can be a really bad thing for the user.
> 
> >
> > For conferencing -the media being encoded in real time-
> > I assume that the DCCP stack will be used to pilot
> > the encoder (tell it which rate to produce).
> 
> > For pre-recorded media delivery the solution is stream switching
> > (or download! see the other mail)
> 
> > For live "TV" (very large number of receivers) changing
> > the rate is either not relevant (e.g. end to end SSM)
> > or it uses a relay server which folds the issue as being
> > like pre-recorded media playback -each receiver maintaining
> > a private server connection- then one should use stream switching,
> > each stream "flavor" being simultaneously produced by a different encoder.
> >
> > regards,
> >
> > Philippe Gentric
> > Software Architect
> > Philips MP4Net
> > philippe.gentric@philips.com
> > http://www.platform4.philips.com
> >
> >
> >
> >
> >                                                    To:   Philippe Gentric/MP4-SUR/CE/PHILIPS@EMEA1
> >                                                    cc:   Magnus Westerlund <magnus.westerlund@ericsson.com>
> >                                                     dccp@ietf.org
> >                                                     mmusic@ietf.org
> >                Damon Lanphear                      Subject:    Re: [dccp] natural DCCP sender-side API: (was stream switching)
> >                <damonlan@real.com>
> >                                                    Classification:
> >                23/07/2003 19:42
> >
> >
> >
> >
> >
> >
> > Philippe,
> >
> > No one is really taking the position that a DCCP API should not make the
> > transmission rate available to the application.  This is quite a
> > straightforward issue. DCCP can easily expose this key piece of
> > information.
> >
> > I am more concerned with how an application meets DCCPs transmission
> > limits (i.e. transmits at the required rate).
> >
> > Let's put the issue of adaptation aside for a moment and just concern
> > ourselves with how an application paces data to the network. My view is
> > that DCCP offers the application both congestion control AND the ability
> > to manage the transmission schedule.  I assume that DCCP will pace data
> > to the lower layers at the rate required of the associated CCID spec.
> > For the application to do this pacing as well would be redundant work.
> >
> > What I don't quite understand about your position is the role played by
> > the application in pacing data.  Do you maintain that the application
> > should pace data, or DCCP or both? That is, is the use of the transmit
> > rate to the application purely informative of a rate adaptation process,
> > or of the transmit process as a whole?
> >
> > On Wed, 2003-07-23 at 04:59, philippe.gentric@philips.com wrote:
> > > Magnus,Damon,
> > >
> > > let us forget a minute about the exact application,
> > > (because my point is *not* specific to stream switching)
> > > let us instead concentrate on the following problem:
> > >
> > > you write:
> > >
> > > "the server can simply switch to a lower bit-rate"
> > >
> > > This is an indication we are on agreement on one thing:
> > > DCCP is about rate-driven applications.
> > >
> > > This is why my concern has been from the very start:
> > > how is the sending application (what ever it is)
> > > going to know what rate it must use?
> > >
> > > The answers you gave so far seem to indicate you are confident
> > > the application can "compute" such a rate based on the behavior of a blocking API...
> > >
> > > (ok, allow me now to *also* put aside my humble opinion that  trying to achieve that is not a good idea)
> > >
> > > I advocate that it would be a shame **because the information is already available**!
> > >
> > > Allow me to quote Section 3 of RFC 3448:
> > >
> > > "   Generally speaking, TFRC's congestion control mechanism works as
> > >    follows:
> > >
> > >    o  The receiver measures the loss event rate and feeds this
> > >       information back to the sender.
> > >
> > >    o  The sender also uses these feedback messages to measure the
> > >       round-trip time (RTT).
> > >
> > >    o  The loss event rate and RTT are then fed into TFRC's throughput
> > >       equation, giving the acceptable transmit rate.
> > >
> > >    o  The sender then adjusts its transmit rate to match the calculated
> > >       rate.
> > > "
> > >
> > > This seems to imply that a "natural" sender-side API for DCCP would explicitely
> > > inform the application ("sender") about this "acceptable transmit rate".
> > >
> > > It also happens to be the *best thing* that can be provided to
> > > an application designed to perform network adaptation.
> > >
> > >
> > > regards,
> > >
> > > Philippe Gentric
> > > Software Architect
> > > Philips MP4Net
> > > philippe.gentric@philips.com
> > > http://www.platform4.philips.com
> > >
> > --
> > Damon Lanphear <damonlan@real.com>
> >
> >
> >
> >
> >
> --
> Damon Lanphear <damonlan@real.com>
> 
> 
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
> 
> 
> 
> 
> 
> 
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
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-- 
Damon Lanphear <damonlan@real.com>


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On Thu, 2003-07-24 at 07:58, philippe.gentric@philips.com wrote:
> Hi Damon,
> 
> >> >So, in this scheme, the sender doesn't need to know the rate that TFRC has
> >> >determined, it simply always sends as fast as TFRC allows.
> >>
> >> 1) I am sorry but *from a network point of view*
> >> I dont see a difference between this and "download"?
> >
> >The only substantive difference is that the transmitted data may not be
> >stored statically on the device in the case of streaming.  So if you
> >have a small embedded device, with limited storage, you can experience
> >media from the network without having the cache the whole thing on the
> >device.
> 
> with progressive download  if you have no room for storage
> you can garbage media  as soon as it is decoded as well ...
> and slow down the sender if needed too ...

At this point, then why bother creating a differentiation between
progressive download and streaming?  If you are tossing data you just
received from the network and decoded, you haven't actually downloaded
anything in the traditional sense of the word.




> 
> regards,
> 
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
> 
> 
>                                                                                                                                        
>                                                                                                                                        
>                                                    To:   Philippe Gentric/MP4-SUR/CE/PHILIPS@EMEA1                                     
>                                                    cc:   "Phelan, Tom" <tphelan@sonusnet.com>                                          
>                                                     dccp@ietf.org                                                                      
>                                                     mmusic@ietf.org                                                                    
>                Damon Lanphear                      Subject:    [MMUSIC] RE: [dccp] natural DCCP sender-side API: (was stream           
>                <damonlan@real.com>                  switching)                                                                         
>                                                                                                                                        
>                Sent by:                            Classification:                                                                     
>                mmusic-admin@ietf.org                                                                                                   
>                                                                                                                                        
>                23/07/2003 21:42                                                                                                        
>                                                                                                                                        
>                                                                                                                                        
> 
> 
> 
> 
> On Wed, 2003-07-23 at 10:43, philippe.gentric@philips.com wrote:
> > Hi Tom,
> >
> > you write:
> >
> > >The relevant difference, as far as this discussion goes, between recorded
> > >and live media is that recorded media can be transmitted from the sender as
> > >fast as the network allows (assuming buffering at the receiver).
> >
> > and then latter (still about recorded media):
> >
> > >So, in this scheme, the sender doesn't need to know the rate that TFRC has
> > >determined, it simply always sends as fast as TFRC allows.
> >
> > 1) I am sorry but *from a network point of view*
> > I dont see a difference between this and "download"?
> 
> The only substantive difference is that the transmitted data may not be
> stored statically on the device in the case of streaming.  So if you
> have a small embedded device, with limited storage, you can experience
> media from the network without having the cache the whole thing on the
> device. The problem then becomes one of balancing the use of device
> storage (i.e. client buffer management) and congestion control.
> 
> >
> > Except that to my knowledge all the products doing that use HTTP
> > since it solves a rather large number of other problems at the same time!
> >
> > 2) Now *from a user point of view*
> >
> > "download" has a flavor usually called "progressive download"
> > whereby the downloaded media file has a structure enabling
> > to start playback before download is finished.
> >
> > In this mode usually the slide bar that the player
> > uses to display the media time has 2 colors,
> > one displaying the current time in the media,
> > the other the *received* time in the media,
> > if this second mark stays ahead of the first mark playback is un-interrupted,
> > otherwise the player stops and displays a message such as "please wait, rebufferring".
> >
> > So I dont see either, from a user point of view,
> > how different a behavior the case you describe would have?
> >
> > ****************
> >
> > I conclude about this use case of the DCCP blocking API you described,
> > that it is not very attractive at all.
> >
> > Surely DCCP has better assets to lure implementers?-)...
> > I think an API providing a target rate would be a good starting point;-)
> >
> > regards,
> >
> > Philippe Gentric
> > Software Architect
> > Philips MP4Net
> > philippe.gentric@philips.com
> > http://www.platform4.philips.com
> >
> >
> >
> > _______________________________________________
> > dccp IETF mailing list: dccp@ietf.org
> > list info:  https://www1.ietf.org/mailman/listinfo/dccp
> > wg charter: http://www.ietf.org/html.charters/dccp-charter.html
> --
> Damon Lanphear <damonlan@real.com>
> 
> 
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic
> 
> 
> 
> 
> 
> 
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
-- 
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Subject: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream switching)
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On Thu, 2003-07-24 at 11:03, philippe.gentric@philips.com wrote:
> Hi Mark,
> 
> 
> >My assumption is that streaming media apps will normally send at the
> >TFRC rate.
> 
> Could it be "at a rate equal or inferior to the TFRC rate"?
> 
> What will happen if an application "does not use" the
> bandwidth indicated by TFRC?
> 
> Often there will be no other choice,
> for example if my application can do 200 kb/s and 400 kb/s
> and TFRC indicates 380 kb/s then I must still use the media
> at 200 kb/s and SEND it at 200 kb/s because if I try
> to send my 200 kb/s media at 380 kb/s I will simply explode
> the player buffers very rapidly?
> 
> >What they need is sufficient advance warning that the
> >playout buffer is running low so that they can switch down to a lower
> >rate.
> 
> yes on advance warning about the TFRC rate,

How can you ever get an advance warning about TFRC rate changes.  These
changes are response to immediate stimuli, to my knowledge that are not
predicted by the current suite of algorithms.

> but I see the need for the sender to monitor
> the playout buffer as unnecessary complexity:
> 
> I think that if the application *generates* (and sends) data at
> (or below) the TFRC rate then data will arrive on time
> and the playout buffer will always remain stable?

so you are assuming that the application is generating the data on the
fly.  This is a very different scenario that certain other streaming
media applications.  So, again, the streaming model that one applies is
tied directly to the sort of application. 

You need to monitor the playout buffer in some way for applications that
can not adapt closely to the congestion controlled rate. Since there may
be other, more coarse grained, adaptations you can make to maintain the
continuity of playout.


> 
> >And if the playout buffer is starting to get rather large, then
> >they can switch up to a higher rate.
> 
> you are assuming that the application sends data
> at a data rate larger than the media data rate...
> 
> then yes! if you play with this fire you will
> need to monitor the player side buffers very carefully!
> 
> The only advantage I can see with that trick
> is that *if you are lucky* during the first minutes of streaming
> you can play this trick to build up your player-side buffer
> using the positive gaps between the TFRC rate and the highest available
> media rate smaller than the TFRC rate; which means that playback can be started
> with minimal lead time i.e. it shortens the time the user waits between the streaming
> request and movie starts to play...unfortunately if you are unlucky
> you will underflow...
> 
> do you seen any other advantage?
> 
> anyway it is a more complicated solution.
> 
> I would simply stream at the first available
> media rate smaller than the TFRC rate.
> 
> 
> >Assuming rate switching is not a
> >trivial operation, and that the rate can only be switched at certain
> >re-sync points, then there is some danger that if congestion suddently
> >gets really bad, then the playout buffer will be exhausted before the
> >codec can be switched.
> 
> Let us compare:
> 
> if you switch "in a hurry" it maybe that the result
> for the end user does not look very good,
> however the alternative (keep on sending at the same rate)
> is not very attractive either for the end user,
> since the player will drain its buffers anyway.
> 
> the difference is that it is worse for the network!
> 
> >My assumption here is that a really good API
> >would allow the sender to send above the TFRC rate for a period of
> >time, so long as the rate mismatch isn't too bad.  A factor of two
> >might be reasonable as an upper bound on the oversending rate.
> 
> I though if you wanted to do that you would declare it as a new
> rate control policy (since it is one, no?) i.e. give it another CCID ?
> 
> What would be the point of defining TFRC and then "cheat on it" ?
> 
> How would you define "TFRC conformance" then?
> 
> >Anyway, in both cases, if the kernel strictly enforces the TFRC rate,
> >app designers will either not use DCCP, or they'll pad their signal
> >with redundant data so they can operate within a more predictable
> >codec envelope.
> 
> Do you mean send garbage?
> what kind of gain would that bring ?
> what is a predictable codec envelope?
> 
> 
> regards,
> 
> 
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
> 
> 
>                                                                                                                                        
>                                                                                                                                        
>                                                    To:   "Phelan, Tom" <tphelan@sonusnet.com>                                          
>                                                    cc:   "'Damon Lanphear'" <damonlan@real.com>                                        
>                                                     Philippe Gentric/MP4-SUR/CE/PHILIPS@EMEA1                                          
>                                                     Magnus Westerlund <magnus.westerlund@ericsson.com>                                 
>                Mark Handley                         dccp@ietf.org                                                                      
>                <M.Handley@cs.ucl.ac.uk>             mmusic@ietf.org                                                                    
>                                                     "Pasco Anderson, Jay" <jpanderson@sonusnet.com>                                    
>                Sent by:                            Subject:    Re: [dccp] natural DCCP sender-side API: (was stream switching)         
>                mjh@cs.ucl.ac.uk                                                                                                        
>                                                    Classification:                                                                     
>                24/07/2003 16:46                                                                                                        
>                                                                                                                                        
>                                                                                                                                        
> 
> 
> 
> 
> 
> >Actually, my big worry here is TFRC, not the API.  I'm baffled about how to
> >map slow start plus mostly smooth changes but occasional abrupt changes and
> >a small playout buffer into something workable.
> >
> >Another thing that concerns me (touched on in the paragraph above) is the
> >disconnect between a transport protocol making rate decisions and an
> >application making rate decisions.  It seems to me that these particular
> >applications are much better equipped to make the rate decisions - they know
> >about what is possible.  It also seems that the application can make at
> >least as good a decision about what constitutes network congestion.  The app
> >will need feedback about the playout buffer state, and this is largely
> >redundant with the DCCP acks.  If the app is making rate decisions and
> >detecting network congestion, what do we need DCCP for?
> 
> [I'm just dropping back into a discussion I haven't been following, so
> forgive me if this duplicates previous discussion]
> 
> There seem to be two obvious sorts of apps that might use TFRC:
> 
>  - streaming media
>  - videotelephony
> 
> That isn't to say that there are different apps, but these two typify
> two classes of apps.  Both are fine with variable packet rates.  But
> streaming media has significantly more playout buffer available.
> 
> Streaming media apps can run the codec (or choice of pre-encoded
> stream) at approximately constant bitrate, and send at variable
> bitrate, using the playout buffer to deal with the temporary
> mismatches.
> 
> Videotelephony apps don't have sufficient delay budget to fix things
> at the receiver, but they do have the luxury of encoding live, so they
> can change the compression parameters on the fly.  They usually don't
> have luxury of re-encoding twice though, so if their choice of
> quantization parameters gives a rate that is different from what is
> expected (because the video content was unpredictable), then they
> might be in trouble.  Also, if the TFRC bandwidth envelope changes
> unexpectedly, you can be in trouble.
> 
> 
> So, why do I say all this?
> 
> 
> My assumption is that streaming media apps will normally send at the
> TFRC rate.  What they need is sufficient advance warning that the
> playout buffer is running low so that they can switch down to a lower
> rate.  And if the playout buffer is starting to get rather large, then
> they can switch up to a higher rate.  Assuming rate switching is not a
> trivial operation, and that the rate can only be switched at certain
> re-sync points, then there is some danger that if congestion suddently
> gets really bad, then the playout buffer will be exhausted before the
> codec can be switched.  My assumption here is that a really good API
> would allow the sender to send above the TFRC rate for a period of
> time, so long as the rate mismatch isn't too bad.  A factor of two
> might be reasonable as an upper bound on the oversending rate.
> 
> 
> Videotelephony apps probably can't send at precisely the TFRC rate
> without sacrificing delay to an undesirable extent.  This means two
> things. First, the app needs to be allowed to send at rates above the
> TFRC rate for a period of time (again, bounded to avoid extreme
> unfairness).  Second, if the app sends under the TFRC rate for a short
> period, it shouldn't lose it's ability to send faster later, so long
> as it didn't undersend by too much.  For such apps, the TFRC rate is a
> guide rate - the app should be capable of varying around the guide
> rate, so long as it stays within reasonable bounds, and so long as the
> long-term average is close to the TFRC rate.
> 
> 
> Anyway, in both cases, if the kernel strictly enforces the TFRC rate,
> app designers will either not use DCCP, or they'll pad their signal
> with redundant data so they can operate within a more predictable
> codec envelope.  Both are undesirable.
> 
> 
> I'm not sure how we best design an API to satisfy this, but I think
> it's really important that we do think about how this can be achieved.
> 
> 
> The general philosophy that the TFRC rate is a guide-rate to be
> followed loosely will probably also apply with TFRC-PS and VoIP, but
> we know a lot less about this space.
> 
> Cheers,
>              Mark
> 
> 
> 
> 
> 
> 
> _______________________________________________
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> list info:  https://www1.ietf.org/mailman/listinfo/dccp
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Subject: [MMUSIC] One-way live media with DCCP/TFRC
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Hi,

I've been continuing to think about the one-way live media case and have
come up with the following scheme for using DCCP with TFRC.  Recall that
one-way live differs from one-way pre-recorded media by having a max
possible sending rate equal to the encoding rate (except for very short
bursts, perhaps), and differs from two-way interactive media by being
tolerant of delay.

So, for this scheme we have a playout buffer at the receiver and transmit
buffer at the sender.  Note that these buffers contain media streams, not
packets, and their lengths are measured in seconds, not bytes or packets.

The transmit buffer is filled at the encoding rate and drained at the TFRC
transmit rate.  The playout buffer is filled at the network arrival rate and
drained at the decoding rate.  The playout buffer has a playback start
threshold and the transmit buffer has a "switch encoding" threshold.  These
thresholds are on the order of a few to several seconds and switch encoding
is less than playback start.

Assume that the encoder can encode at two rates, a high rate and a low rate.
At the start of a connection, the sender places data into the transmit
buffer at the high encoding rate.  The buffer is drained at the TFRC rate,
which at this point is in slow-start and is probably slower than the
required rate.  This will cause a backup in the transmit buffer.  Eventually
TFRC will slow-start to a rate slightly above the rate necessary to sustain
the encoding rate.  When this happens the transmit buffer will drain and
we'll reach a steady-state condition where the transmit buffer is empty and
we're transmitting at a rate that is probably below the maximum allowed by
TFRC.  Note that, by my interpretation of TFRC at least, we won't be
penalized for transmitting less than we could.  You're only penalized when
you transmit nothing for some number of roundtrip times.

Meanwhile at the receiver, the playout buffer is filling, and when it
reaches the playback start threshold playback will start.  After TFRC
slow-start and the transmit buffer is drained, this buffer will reach a
steady state where packets are arriving from the network at the encoding
rate (ignoring jitter) and being drained from the buffer at the (equal)
decoding rate.  The depth of the buffer will be the playback start threshold
plus the maximum depth of the transmit buffer during slow start.

Now assume that network congestion forces TFRC to drop its rate to below
that needed by the high rate encoding.  The transmit buffer will begin to
fill and the playout buffer will begin to drain.  When the transmit buffer
reaches the switch encoding threshold, the sender switches to the low rate
encoding, and converts all of the data in the transmit buffer to low rate
encoding.  I'll ignore issues of how to do this efficiently, but it's
important not to discard this data, and to convert it.

Assuming that the network can support the new, lower, rate (and a little
more) the transmit buffer will begin to drain and the playout buffer will
begin to fill.  Eventually the transmit buffer will empty, the playout
buffer will be back to its steady-state level, and we'll be transmitting
data at the new, lower, encoding rate.

At this point (perhaps after a slight delay) the sender can switch back to
the higher rate.  If the new rate can't be sustained the transmit buffer
will fill again (and the playout buffer will drain).  When the switch
encoding threshold is reached the sender goes back to the lower encoding
rate.  This oscillation continues until the stream ends or the network is
able to support the high rate for the long term.

It might be useful for DCCP to tell the application about rate changes.  For
instance, when DCCP/TFRC has decided on a rate too low for the high rate
encoding the application could make the change to the low rate immediately.
This would work, but it might lead to unnecessary switches to the lower
rate.  In particular, when DCCP decides on a new rate, it has no way of
knowing whether this is a transient or a long-term change.  If it's
transient the transmit buffer might be able to absorb the problem, and a
change to the lower rate might unnecessarily reduce the quality seen by the
user.  If we wait for the switch encoding threshold we can be more sure that
the rate change is long-term.  Also, if we rely on rate indications for the
downshift, we need to ignore it during slow-start.

It might be more useful to know when DCCP has raised the rate sufficiently
to switch to the high rate (after the transmit buffer has been drained).

Note that this scheme is also suitable for one-way pre-recorded media, as
long as the transmit buffer is only filled at the encoding rate, not at the
disk read rate.  Overall I'd say that this is better than the previous
scheme (for one-way pre-recorded media), and I think that some of the
commenters on the previous message must have had something like this in
mind.

I still don't know how to do the two-way interactive media.

Tom P.

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From: "Sean Robinson" <srobinson@real.com>
To: "Damon Lanphear" <damonlan@real.com>, "Phelan, Tom" <tphelan@sonusnet.com>
Cc: philippe.gentric@philips.com,
        "Magnus Westerlund" <magnus.westerlund@ericsson.com>, dccp@ietf.org,
        mmusic@ietf.org, "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
Subject: RE: [MMUSIC] RE: [dccp] natural DCCP sender-side API: (was stream switching)
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I agree that Tom's contribution has provided a good basis for this
discussion.  The decision is further complicated by the inclusion of media
composition.  Consider we following media availablity constraints (which can
be applied to each of the named media application, On demand, live and
2-way)

- A single fixed rate media source
- multiple discrete media encodings
- a fully scalable media encoding (such as MPEG-4 FGS)

Now, given that in the second case we could add as many rates as we desire
and that the third case doesn't really exist (no codec is infitely
scalable), we can treat these as the same for the purposes of this
discussion.  We can view this from the application level as a series of
decision points in which the application concludes the best media data to
send at a given moment given the current network conditions.  The design of
the media is obviously a critical factor in the succcess of the application
as some media may work better in some application than others.  It is
assumed that low latency applicaiton will require more frequent decision
points where an on-demand application may require fewer.  We can think of
the media transmitted between these decision points as a media unit.

Here I would like to bring up a point that I feel has been neglected in the
discussion to this point.  That is the perspective of resource efficiency in
the interaction between a user level media application and a kernel level
protocol.  From this perspective the frequency of interaction between the
two sides should be minimized.  Also we would further hope that the need for
user level packet scheduling would also be minimized.

If the 2 above points are agreed to, we can then conclude that in the ideal
case we would want the interaction with the protocol to match as closely as
possible with those media decision points.  In other words, the application
should only have to interact with the dataflow when there is some meaningful
action to be taken.  This seems to me to be the best method for evaluation
of an API semantic.

First, let's take the simple blocking semantic.  The first question we
should ask (which is not specified in the DCCP user manual) is what triggers
that the block has cleared?  If we take the naive assumption that the file
descriptor is cleared for writing after the transmission of each datagram,
then our interaction with the protocol will also be on every datagram (if we
are instantly responsive to the signal).  This is likely more than we would
like in all but the very most scalable solutions.  Keep in mind, however,
that flow control through file descriptors is a well supported concept
throughout different OSes and this is very attractive in the design of a
protocol. Further, if we define parameters for when the desriptor is marked
for writing we can get greater control over its scalability.  It should also
be noted that this mechanism is not really optional, since the prtocol must
support blocking when the pre-netwqork buffer is full.

Now the rate-signalling approach has also been proposed, but it implies a
network-driven scheduling model over a media-driven model.  TFRC will
generate a new throughput claculation once per round trip time and if this
is the frequency at which the rate would be signalled, then we could either
find this to be too frequent or too sparse depending on the underlying
network.  Certainly an agrument could be made, media decision points should
be syncronized with network condition and if this is possible, this is a
more attractive solution.  It is important to note, however, that at a fine
grained level over delivery rate is not that relevant to the delivery
characteristcs, but rather the data size of individual media units.  So, if
TFRC reports 20kbs at a given window, it doesn't necesicearily mean that the
application should choose the 20kbs stream, but should evaluate the data to
be transmitted for available streams at that decision point.

Another option outside of direct feedback would be a polling approach,
whereby the application set interupt timers to evaluate the dataflow at
appropriate points in the application.  This method could work well in
stuations in which the throughput has a low degree of variance, since the
evaluation interval could be tailored to the desired media.  As the variance
increases, the effectiveness of this approach decreases since the data in
the pre-network queue may be delivered faster or slower than expected,
causing an increased number of "wasted" check in which no action is taken.

Another approach could be to tag specific datagrams for signalling on
transmission.  Then DCCP would signal (using some means) when a given
datagram is transmitted.  If one datagram per media unit, then we could get
a notification at every media unit, which is what we want.  The semantics of
defining this within an API could be quite complex, however.

Which brings me to a final important point.  As mentioned in several points,
we must consider the method in which the information is signalled.  Some
OSes have more advanced signalling mechanism than others and the more
digression from standard mechanisms, the less integrated into the OS the
protocol becomes.  This is an extremely imprrtant factor in this discussion
and should not be treated likely.

S
> -----Original Message-----
> From: mmusic-admin@ietf.org [mailto:mmusic-admin@ietf.org]On Behalf Of
> Damon Lanphear
> Sent: Wednesday, July 23, 2003 10:52 AM
> To: Phelan, Tom
> Cc: 'philippe.gentric@philips.com'; Magnus Westerlund; dccp@ietf.org;
> mmusic@ietf.org; Pasco Anderson, Jay
> Subject: [MMUSIC] RE: [dccp] natural DCCP sender-side API: (was stream
> switching)
>
>
> Tom,
>
> Thank you for providing better structure to our discussion.  This is
> precisely what we needed to speak more precisely on these matters!
>
> I haven't been able to work out acceptable scenarios for the other two
> > applications yet.  It seems almost certain to me that TFRC and
> a blocking
> > API is not at all suitable for two-way media.  It might be suitable for
> > one-way live media, but I haven't figured out how it could be yet.  If
> > anyone has ideas here I'd like to hear them :-).
>
> I'd like to understand the alternative to a blocking API for two-way
> media.  I assume that in this case the application is responsible for
> managing the transmission rate.  I guess I get confused when I consider
> that some agent in the pipeline will have to block transmission when the
> transmission attempt oversteps the congestion control rate.  What does
> it matter if this agent is DCCP or the application, particularly if we
> have access to the transmit queue in DCCP, as is the case in the ICIR
> implementation ?
>
> As regards unidirectional live,  its differs from unidirectional
> on-demand in that there's no data sitting on disk with which to fill a
> post-network buffer to a point where an up shift seems appropriate.
> Downshifts are straightforward, however, since under sending can just as
> well happen with live streams.  So we need a metric for up shifts that
> does not rely on buffer state.  Perhaps some measure of the stability of
> the available congestion controlled throughput over time?
>
> On Wed, 2003-07-23 at 07:43, Phelan, Tom wrote:
> > Hi Phillipe,
> >
> > In thinking about your draft on stream rate switching and this
> discussion on
> > APIs I've come to the conclusion that there are actually three different
> > applications being discussed, with three different sets of requirements.
> > One of these applications can be reasonably satisfied with a
> blocking API
> > (although there could be some efficiencies with other
> capabilities).  For
> > the other two I'm not sure yet what would work.
> >
> > Excuse me if I'm re-inventing something here, but the three
> applications I
> > have in mind are:
> >  o	One-way pre-recorded media
> >  o	One-way live media
> >  o	Two-way interactive media
> >
> > The relevant difference, as far as this discussion goes,
> between recorded
> > and live media is that recorded media can be transmitted from
> the sender as
> > fast as the network allows (assuming buffering at the
> receiver).  Live media
> > can only be transmitted at the rate that it's generated.
> >
> > The difference between one-way (live) and two-way is the size
> of the playout
> > buffer.  In one-way media you can use a playout buffer that's
> hundreds of
> > times larger than the round trip time.  In two-way media the
> playout buffer
> > is on the same order of magnitude as the round trip time.
> >
> > So, it seems to me that one-way pre-recorded media can be
> reasonably served
> > by DCCP with TFRC and a sockets-like (blocking) API.  For
> example, assume
> > that the sender has a media stream in two bit rates, high and low.  Also
> > assume that the sender is able to estimate the depth of the receiver's
> > playout buffer (either via feedback from the receiver or some
> other means).
> > Now set three thresholds in the playout buffer, a low
> threshold, a playback
> > start threshold and a high threshold, in order of increasing depth.
> >
> > To start the connection, the sender begins transmitting data
> from the high
> > bit rate stream as fast as TFRC allows (blocking the transmit thread for
> > rate control).  Since TFRC is in slow-start, this is probably too slow
> > initially, but eventually the rate might increase to fast
> enough and past.
> > The receiver buffers data until the playback start threshold is
> reached, and
> > then begins playback.
> >
> > If the TFRC rate never gets fast enough, or a packet loss makes
> TFRC drop
> > the rate, the receiver will drain the playout buffer faster
> than it's being
> > filled.  If the playout buffer drops below the low threshold, the sender
> > switches to the low bit rate stream.  Assuming that the network
> has a little
> > bit more capacity than the low bit rate stream requires, the
> playout buffer
> > will begin filling again.
> >
> > When the buffer crosses the high threshold the sender switches
> to the high
> > bit rate stream.  Assuming that the network still doesn't have enough
> > capacity for the high bit rate stream, the playout buffer will
> drain.  When
> > it reaches the low threshold the sender switches back to the
> low bit rate.
> > The sender will oscillate back and forth like this until the
> connection is
> > terminated.
> >
> > So, in this scheme, the sender doesn't need to know the rate
> that TFRC has
> > determined, it simply always sends as fast as TFRC allows.
> TFRC shapes the
> > stream to the network's requirements, and the feedback about the playout
> > buffer allows the sender to shape the stream to the application's
> > requirements.
> >
>
> >
> > Tom P.
> >
> >
> > > -----Original Message-----
> > > From: philippe.gentric@philips.com
> > > [mailto:philippe.gentric@philips.com]
> > > Sent: Wednesday, July 23, 2003 7:59 AM
> > > To: Magnus Westerlund
> > > Cc: Damon Lanphear; dccp@ietf.org; mmusic@ietf.org
> > > Subject: Re: [dccp] natural DCCP sender-side API: (was stream
> > > switching)
> > >
> > >
> > >
> > > Magnus,Damon,
> > >
> > > let us forget a minute about the exact application,
> > > (because my point is *not* specific to stream switching)
> > > let us instead concentrate on the following problem:
> > >
> > > you write:
> > >
> > > "the server can simply switch to a lower bit-rate"
> > >
> > > This is an indication we are on agreement on one thing:
> > > DCCP is about rate-driven applications.
> > >
> > > This is why my concern has been from the very start:
> > > how is the sending application (what ever it is)
> > > going to know what rate it must use?
> > >
> > > The answers you gave so far seem to indicate you are confident
> > > the application can "compute" such a rate based on the
> > > behavior of a blocking API...
> > >
> > > (ok, allow me now to *also* put aside my humble opinion that
> > > trying to achieve that is not a good idea)
> > >
> > > I advocate that it would be a shame **because the information
> > > is already available**!
> > >
> > > Allow me to quote Section 3 of RFC 3448:
> > >
> > > "   Generally speaking, TFRC's congestion control mechanism works as
> > >    follows:
> > >
> > >    o  The receiver measures the loss event rate and feeds this
> > >       information back to the sender.
> > >
> > >    o  The sender also uses these feedback messages to measure the
> > >       round-trip time (RTT).
> > >
> > >    o  The loss event rate and RTT are then fed into TFRC's throughput
> > >       equation, giving the acceptable transmit rate.
> > >
> > >    o  The sender then adjusts its transmit rate to match the
> > > calculated
> > >       rate.
> > > "
> > >
> > > This seems to imply that a "natural" sender-side API for DCCP
> > > would explicitely
> > > inform the application ("sender") about this "acceptable
> > > transmit rate".
> > >
> > > It also happens to be the *best thing* that can be provided to
> > > an application designed to perform network adaptation.
> > >
> > >
> > > regards,
> > >
> > > Philippe Gentric
> > > Software Architect
> > > Philips MP4Net
> > > philippe.gentric@philips.com
> > > http://www.platform4.philips.com
> > >
> > >
> > >
> > > _______________________________________________
> > > dccp IETF mailing list: dccp@ietf.org
> > > list info:  https://www1.ietf.org/mailman/listinfo/dccp
> > > wg charter: http://www.ietf.org/html.charters/dccp-charter.html
> > >
> --
> Damon Lanphear <damonlan@real.com>
>
>
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic


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Not really.  If you are going to have a problem, you would
rather have the video go before the audio, and thus you
would prefer to keep the congestion control separate.

I'd rather they be entirely separate.

Brian

> -----Original Message-----
> From: Eddie Kohler [mailto:kohler@icir.org]
> Sent: Thursday, July 24, 2003 4:21 PM
> To: philippe.gentric@philips.com
> Cc: Phelan, Tom; dccp@ietf.org; mmusic@ietf.org; 'Reiner Ludwig'
> Subject: Re: [dccp] Using DCCP for VoIP 
> 
> 
> Hi all,
> 
> On this issue:
> 
> > IMHO this issue is related to my question in the other mail about
> > managing audio AND video at the same time: probably DCCP 
> should have a
> > way to handle "collectively" a bunch of streams, be it 
> audio plus video
> > or two-way audio!
> 
> Our thought was that, given DCCP's unreliability, it is 
> trivial to layer
> multiple streams on top. The first byte of packet data could indicate
> stream number to the application. This works as long as both 
> streams want
> to share the same congestion control state + CC mechanism -- 
> is this the
> case?
> 
> Eddie
> 
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
> 

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Date: Thu, 24 Jul 2003 14:58:46 -0700
From: Eddie Kohler <kohler@icir.org>
Subject: [MMUSIC] What's wrong with TFRC for VoIP and other apps?
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Hi all,

I just wanted to try to summarize the issues people have brought up, in
other threads, about why TFRC and/or DCCP will be inappropriate for VoIP
and other apps. I agree with Tom Phelan's comment that the biggest issues
have to do with TFRC, not the API. I've left off the solutions people have
proposed to these problems.

1. Rate slows down during idle periods

   The TFRC allowed sending rate will drop down to something very small
   (2-4 packets/RTT) when the sender is idle. This may cause problems
   particualrly with VoIP conversations, which are naturally idle-one-way
   then idle-the-other-way. The rampup from the small rate to the fair rate
   may take several to many RTTs, ouch.

2. Rate will not increase during app-limited period

   This is essentially the same problem as above. Say the application is
   sending at rate R. The allowed rate will not increase much beyond R
   (say, more than 2R) until the app transmits at a faster rate. 

3. Apps with fixed sets of rates

   An app might have a discrete set of sending rates. Must it send at the
   highest app rate <= the TFRC allowed rate? Would be very nice to allow
   some flexibility, so that it could send at, say, the highest rate <=
   1.8*TFRC_allowed_rate.

4. Rate changes/oscillations

   There are application costs, possibly significant ones, associated with
   changing rates. If the app has to change its rate frequently, because of
   CC, that's a problem.

Have I missed anything?

Eddie

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From: Eddie Kohler <kohler@icir.org>
Subject: [MMUSIC] Re: [dccp] Using DCCP for VoIP
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> Not really.  If you are going to have a problem, you would
> rather have the video go before the audio, and thus you
> would prefer to keep the congestion control separate.
> 
> I'd rather they be entirely separate.

This may be a good reason to keep the data *together*, on one connection,
actually. The sender can react to congestion feedback by throwing out the
video first. If you have two separate connections, both of their rates will
decrease.

Eddie

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   of "Thu, 24 Jul 2003 15:26:27 EDT." <4CF48720B6E9D4118D040060CF2074E9082BB486@sonusdc3.sonusnet.com> 
Date: Thu, 24 Jul 2003 15:09:48 -0700
From: Eddie Kohler <kohler@icir.org>
Subject: [MMUSIC] Re: [dccp] One-way live media with DCCP/TFRC
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> Note that, by my interpretation of TFRC at least, we won't be
> penalized for transmitting less than we could.  You're only penalized when
> you transmit nothing for some number of roundtrip times.

My understanding is, you are not penalized -- you still get to send at your
(allowed) rate -- but your maximum allowed transmit rate doesn't continue
to increase. THe maximum allowed transmit rate is bounded above by some
multiple of the current transmit rate. This is essentially the same as in
the idle case.

> It might be useful for DCCP to tell the application about rate changes.  

We absolutely want the API to take care of this.

Eddie

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Date: Thu, 24 Jul 2003 15:20:38 -0700
From: Eddie Kohler <kohler@icir.org>
Subject: [MMUSIC] Packet drop API / what happens with packet drops now?
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What happens in currently-deployed codecs when packets are dropped?

Clearly codecs, and VoIP in particular, can handle loss. Possibly even high
loss rates. One way to think about DCCP's allowed sending rate is that it
moves drops that *would* have happened in the network *anyway*, into the
sending host. (Although DCCP will generally drop more than the network
would have, to ensure fairness, and because of congestion-control
infelicities that we want to fix.) So how disastrous are these drops?

Another way to put this: A DCCP API might never block -- or it might block
for at most T seconds. Instead, writing a packet into a full send buffer
would drop that packet; or it might drop an older packet---a drop-from-head
send buffer; or it might drop the oldest packet with lowest priority
annotation.

Now the app simply sees a loss rate, which DCCP will happily report. For
codec switching, you can simply switch when the loss rate is intolerably
high -- which you would have had to do anyway.

How horrible would this be?

Eddie

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From: "Phelan, Tom" <tphelan@sonusnet.com>
To: "'Eddie Kohler'" <kohler@icir.org>, "Phelan, Tom" <tphelan@sonusnet.com>
Cc: "'Damon Lanphear'" <damonlan@real.com>,
        "'philippe.gentric@philips.com'"
	 <philippe.gentric@philips.com>,
        Magnus Westerlund
	 <magnus.westerlund@ericsson.com>, dccp@ietf.org,
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Subject: [MMUSIC] RE: [dccp] natural DCCP sender-side API: (was stream switching)
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Hi Eddie,

If DCCP conflicts with an application's requirements, then the application
won't use it, whether DCCP is network friendly or not.  Note that I think
that network-friendly reaction to congestion is absolutely one of my
application's requirements (my app is two-way voice).  I hope that I can use
DCCP to get that, but I'm having difficulties making it work.  Not that I've
given up hope, mind you.  I think I've managed to work out reasonable ways
to use DCCP for similar, but not quite identical apps.  And I intend to keep
trying for my app.

I think it's very important for DCCP to know whether it's really useful for
two-way voice or not.  All of the DCCP documents mention it as a primary
target application.  Some people on this list might already know how to make
it work, but I don't yet, and I haven't seen anyone give a credible scheme
for it yet, so I'll keep trying.

Tom P.

> -----Original Message-----
> From: Eddie Kohler [mailto:kohler@icir.org]
> Sent: Thursday, July 24, 2003 5:27 PM
> To: Phelan, Tom
> Cc: 'Damon Lanphear'; 'philippe.gentric@philips.com'; Magnus 
> Westerlund;
> dccp@ietf.org; mmusic@ietf.org; Pasco Anderson, Jay
> Subject: Re: [dccp] natural DCCP sender-side API: (was stream 
> switching)
> 
> 
> 
> > Another thing that concerns me (touched on in the paragraph 
> above) is the
> > disconnect between a transport protocol making rate decisions and an
> > application making rate decisions.  It seems to me that 
> these particular
> > applications are much better equipped to make the rate 
> decisions - they know
> > about what is possible.  It also seems that the application 
> can make at
> > least as good a decision about what constitutes network 
> congestion.  The app
> > will need feedback about the playout buffer state, and this 
> is largely
> > redundant with the DCCP acks.  If the app is making rate 
> decisions and
> > detecting network congestion, what do we need DCCP for?
> 
> My take:
> 
> Your paragraph was written from the application's point of 
> view, not that
> of the network. DCCP is about implementing congestion control that is
> appropriate for the network: in other words, currently, 
> TCP-friendly CC.
> This may conflict with application "requirements".
> 
> 
> For example:
> 
> > It seems to me that these particular
> > applications are much better equipped to make the rate 
> decisions - they know
> > about what is possible. 
> 
> What is possible for the application may not be TCP-friendly 
> or appropriate
> for the network (if the app has a minimum rate, for example).
> 
> > It also seems that the application can make at
> > least as good a decision about what constitutes network congestion. 
> 
> The app should make a decision that is TCP-friendly -- in 
> which case you've
> got DCCP all over again. You need acks, probably ECN Nonces, ....
> 
> 
> We have a congestion control problem, for which we need a congestion
> control solution. Avoiding DCCP doesn't avoid the problem.
> 
> So we should solve the problem! And I think we can solve it!
> 
> 
> Now, it may end up that DCCP is not appropriate, once the congestion
> control problem is solved. I'm not against UDP with application-level
> congestion control. But CC is a hard problem, which we are 
> trying to solve
> for you.
> 
> 
> Also:
> 
> > The app will need feedback about the playout buffer state, 
> and this is
> > largely redundant with the DCCP acks.
> 
> The app should be able to extract this information from the 
> DCCP API, so no
> app-level acks are necessary.
> 
> 
> Eddie
> 

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From: "Phelan, Tom" <tphelan@sonusnet.com>
To: "'Eddie Kohler'" <kohler@icir.org>, dccp@ietf.org, mmusic@ietf.org
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Subject: [MMUSIC] RE: What's wrong with TFRC for VoIP and other apps?
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Hi Eddie,

One more problem I see for two-way voice is slow-start.  This is somewhat
related to "rate slows down during idle periods", but you're stuck with it
even if you don't do silence suppression.

I don't have a "TCP-friendly" solution for this yet.

Tom P.

> -----Original Message-----
> From: Eddie Kohler [mailto:kohler@icir.org]
> Sent: Thursday, July 24, 2003 5:59 PM
> To: dccp@ietf.org; mmusic@ietf.org
> Cc: tphelan@sonusnet.com
> Subject: What's wrong with TFRC for VoIP and other apps?
> 
> 
> Hi all,
> 
> I just wanted to try to summarize the issues people have 
> brought up, in
> other threads, about why TFRC and/or DCCP will be 
> inappropriate for VoIP
> and other apps. I agree with Tom Phelan's comment that the 
> biggest issues
> have to do with TFRC, not the API. I've left off the 
> solutions people have
> proposed to these problems.
> 
> 1. Rate slows down during idle periods
> 
>    The TFRC allowed sending rate will drop down to something 
> very small
>    (2-4 packets/RTT) when the sender is idle. This may cause problems
>    particualrly with VoIP conversations, which are naturally 
> idle-one-way
>    then idle-the-other-way. The rampup from the small rate to 
> the fair rate
>    may take several to many RTTs, ouch.
> 
> 2. Rate will not increase during app-limited period
> 
>    This is essentially the same problem as above. Say the 
> application is
>    sending at rate R. The allowed rate will not increase much beyond R
>    (say, more than 2R) until the app transmits at a faster rate. 
> 
> 3. Apps with fixed sets of rates
> 
>    An app might have a discrete set of sending rates. Must it 
> send at the
>    highest app rate <= the TFRC allowed rate? Would be very 
> nice to allow
>    some flexibility, so that it could send at, say, the 
> highest rate <=
>    1.8*TFRC_allowed_rate.
> 
> 4. Rate changes/oscillations
> 
>    There are application costs, possibly significant ones, 
> associated with
>    changing rates. If the app has to change its rate 
> frequently, because of
>    CC, that's a problem.
> 
> Have I missed anything?
> 
> Eddie
> 

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From: "Phelan, Tom" <tphelan@sonusnet.com>
To: "'Eddie Kohler'" <kohler@icir.org>, "Phelan, Tom" <tphelan@sonusnet.com>
Cc: "'dccp@ietf.org'" <dccp@ietf.org>, "'mmusic@ietf.org'"
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Hi Eddie,

See inline ...

Tom P.

> -----Original Message-----
> From: Eddie Kohler [mailto:kohler@icir.org]
> Sent: Thursday, July 24, 2003 6:10 PM
> To: Phelan, Tom
> Cc: 'dccp@ietf.org'; 'mmusic@ietf.org'; Pasco Anderson, Jay
> Subject: Re: [dccp] One-way live media with DCCP/TFRC 
> 
> 
> > Note that, by my interpretation of TFRC at least, we won't be
> > penalized for transmitting less than we could.  You're only 
> penalized when
> > you transmit nothing for some number of roundtrip times.
> 
> My understanding is, you are not penalized -- you still get 
> to send at your
> (allowed) rate -- but your maximum allowed transmit rate 
> doesn't continue
> to increase. THe maximum allowed transmit rate is bounded 
> above by some
> multiple of the current transmit rate. This is essentially 
> the same as in
> the idle case.

Oh, I missed this.  So if the high rate is more than twice or so the low
rate you'll have to slow-start up to it when you upshift, regardless of how
low the RTT has become.  I think that the scheme I described still works,
though.  You just have some transmit buffer buildup as the rate ramps up,
like in slow-start at the beginning of the connection.

> 
> > It might be useful for DCCP to tell the application about 
> rate changes.  
> 
> We absolutely want the API to take care of this.
> 
> Eddie
> 

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From: "Phelan, Tom" <tphelan@sonusnet.com>
To: "'Eddie Kohler'" <kohler@icir.org>, dccp@ietf.org, mmusic@ietf.org
Cc: "Phelan, Tom" <tphelan@sonusnet.com>
Date: Thu, 24 Jul 2003 21:40:27 -0400
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Subject: [MMUSIC] RE: Packet drop API / what happens with packet drops now?
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Hi Eddie,

I actually think that there's a big advantage to throwing packets away at
the sender, rather than having the network choose the packets to throw away,
even if you end up discarding more packets that way.  When the sender
chooses the packets to discard, it can ensure that important packets (like
frame markers, etc.) are preserved.  The network simply makes random
decisions.

Tom P.

> -----Original Message-----
> From: Eddie Kohler [mailto:kohler@icir.org]
> Sent: Thursday, July 24, 2003 6:21 PM
> To: dccp@ietf.org; mmusic@ietf.org
> Cc: tphelan@sonusnet.com
> Subject: Packet drop API / what happens with packet drops now?
> 
> 
> What happens in currently-deployed codecs when packets are dropped?
> 
> Clearly codecs, and VoIP in particular, can handle loss. 
> Possibly even high
> loss rates. One way to think about DCCP's allowed sending 
> rate is that it
> moves drops that *would* have happened in the network 
> *anyway*, into the
> sending host. (Although DCCP will generally drop more than the network
> would have, to ensure fairness, and because of congestion-control
> infelicities that we want to fix.) So how disastrous are these drops?
> 
> Another way to put this: A DCCP API might never block -- or 
> it might block
> for at most T seconds. Instead, writing a packet into a full 
> send buffer
> would drop that packet; or it might drop an older packet---a 
> drop-from-head
> send buffer; or it might drop the oldest packet with lowest priority
> annotation.
> 
> Now the app simply sees a loss rate, which DCCP will happily 
> report. For
> codec switching, you can simply switch when the loss rate is 
> intolerably
> high -- which you would have had to do anyway.
> 
> How horrible would this be?
> 
> Eddie
> 

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Date: Thu, 24 Jul 2003 23:49:34 -0700
From: Eddie Kohler <kohler@icir.org>
Subject: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream switching)
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Hi Tom,

> If DCCP conflicts with an application's requirements, then the application
> won't use it, whether DCCP is network friendly or not. 

Totally agree. And totally agree that we must figure out whether DCCP is
really useful for two-way voice. But, for example, an application with a
requirement "must achieve a minimum bandwidth" would not be appropriate for
DCCP, because it requires non-TCP-friendly congestion control.

Nothing that you have discussed is that far out, but some of it is getting
far out enough that I wanted to make the concern explicit. (For instance,
we've been talking about apps that can transmit only at a discrete set of
rates---unless 0pps was one of those rates, such an app would have a
minimum bandwidth requirement.)

> Note that I think
> that network-friendly reaction to congestion is absolutely one of my
> application's requirements (my app is two-way voice).  I hope that I can use
> DCCP to get that, but I'm having difficulties making it work.  Not that I've
> given up hope, mind you.  I think I've managed to work out reasonable ways
> to use DCCP for similar, but not quite identical apps.  And I intend to keep
> trying for my app.
> 
> I think it's very important for DCCP to know whether it's really useful for
> two-way voice or not.  All of the DCCP documents mention it as a primary
> target application.  Some people on this list might already know how to make
> it work, but I don't yet, and I haven't seen anyone give a credible scheme
> for it yet, so I'll keep trying.

FYI I really appreciate this discussion!!!

Eddie

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Subject: [MMUSIC] Re: [dccp] what is DCCP for? (was: natural DCCP sender-side API)
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Damon,

you write:

> ?!? How does DCCP guarantee on time delivery?

(let me first check something, I define "on time delivery" as:
the amount of time its takes for data to transit
from sender to receiver is constant. do you agree?)

My understanding of DCCP is that it would tell the sender at which max rate to send.

Then I assume that *if the sender does its part of the job*,
(which is to abide by the max rate indicated by DCCP)
then the system (application + DCCP) will run "in the best possible way"
...
which is: *avoid congestion*
(if DCCP does not do that, please change the name!-)
...
which means on time delivery of data!

so I conclude that DCCP "allows" on time delivery, right?

**

the reason one could go from "allow" to "guarantee" would be (king of ad absurdum):

I have been assuming (this is the "contract" I would wish DCCP to operate under)
that when DCCP gives the sending rate indication it does so based on
the *best possible knowledge about the network*.

Therefore I would like to be able to assume that if the network "behavior"
is such that even DCCP cannot fulfill the "contract" then *nothing* would do the job.

In other words I am assuming that if an application strictly doing its job
(strictly respecting the MAX send rate indicated by DCCP)
does not get on time delivery ... then the application would "fail" in any case.
(my definition of "fail" for streaming is: playback is interrupted)

Am I putting irrealistic hopes in DCCP?

but then what would it be good for?

regards,



Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com



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Subject: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream switching)
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Damon,

>> yes on advance warning about the TFRC rate,
>
>How can you ever get an advance warning about TFRC rate changes.  These
>changes are response to immediate stimuli, to my knowledge that are not
>predicted by the current suite of algorithms.

Yes.

TFRC can update the rate computation everytime it receives feedback from the receiver.

What I would like is that the sender application gets this information as soon as it is updated.
this is the meaning of "advance warning" for me.

I can use it to drive my media source (RT encoder or stream switch).

It contrast sharply with a "blocking write" which is "too late" for me:
once my source has produced a frame what I am supposed to do
if DCCP blocks it ? garbage it ? wait? but how long should I wait?
wait for what? for a timeout ? but what will happen after the timeout ?
will I write this frame or not ? If I have to change the rate how am
going to know which rate to choose ? etc ...

on the other hand I would expect that DCCP never blocks a write
if the source always follows the DCCP indicated rate ....

regards,

Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com



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From: "Phelan, Tom" <tphelan@sonusnet.com>
To: "'Eddie Kohler'" <kohler@icir.org>, "Phelan, Tom" <tphelan@sonusnet.com>
Cc: "'Damon Lanphear'" <damonlan@real.com>,
        "'philippe.gentric@philips.com'"
	 <philippe.gentric@philips.com>,
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	 <magnus.westerlund@ericsson.com>, dccp@ietf.org,
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Hi Eddie,

See inline ...

Tom P.

> -----Original Message-----
> From: Eddie Kohler [mailto:kohler@icir.org]
> Sent: Friday, July 25, 2003 2:50 AM
> To: Phelan, Tom
> Cc: 'Damon Lanphear'; 'philippe.gentric@philips.com'; Magnus 
> Westerlund;
> dccp@ietf.org; mmusic@ietf.org; Pasco Anderson, Jay
> Subject: Re: [dccp] natural DCCP sender-side API: (was stream 
> switching)
> 
> 
> 
> Hi Tom,
> 
> > If DCCP conflicts with an application's requirements, then 
> the application
> > won't use it, whether DCCP is network friendly or not. 
> 
> Totally agree. And totally agree that we must figure out 
> whether DCCP is
> really useful for two-way voice. But, for example, an 
> application with a
> requirement "must achieve a minimum bandwidth" would not be 
> appropriate for
> DCCP, because it requires non-TCP-friendly congestion control.

I think I'd rephrase that as "must achieve a minimum bandwidth and everyone
else be damned would not be appropriate".

> Nothing that you have discussed is that far out, but some of 
> it is getting
> far out enough that I wanted to make the concern explicit. 
> (For instance,
> we've been talking about apps that can transmit only at a 
> discrete set of
> rates---unless 0pps was one of those rates, such an app would have a
> minimum bandwidth requirement.)

I haven't mentioned this in my e-mails so far because they were long enough
without it, but I assume that when the TFRC rate falls below the minimum
coding rate we throw away packets to shape the flow to the TFRC rate.  As I
said before, it seems better to me that the sender makes intelligent
decisions about packet discard, rather than the network makes random
decisions.  Eventually you could get to the point that the media stream is
completely unintelligible, and maybe you should disconnect.  I certainly
don't feel that you should keep blasting away at some minimum acceptable
rate regardless of what happens to those packets in the network.

> 
> > Note that I think
> > that network-friendly reaction to congestion is absolutely one of my
> > application's requirements (my app is two-way voice).  I 
> hope that I can use
> > DCCP to get that, but I'm having difficulties making it 
> work.  Not that I've
> > given up hope, mind you.  I think I've managed to work out 
> reasonable ways
> > to use DCCP for similar, but not quite identical apps.  And 
> I intend to keep
> > trying for my app.
> > 
> > I think it's very important for DCCP to know whether it's 
> really useful for
> > two-way voice or not.  All of the DCCP documents mention it 
> as a primary
> > target application.  Some people on this list might already 
> know how to make
> > it work, but I don't yet, and I haven't seen anyone give a 
> credible scheme
> > for it yet, so I'll keep trying.
> 
> FYI I really appreciate this discussion!!!
> 
> Eddie
> 

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From: "Rosen, Brian" <Brian.Rosen@marconi.com>
To: "'Eddie Kohler'" <kohler@icir.org>, "Phelan, Tom" <tphelan@sonusnet.com>
Cc: "'Damon Lanphear'" <damonlan@real.com>,
        "'philippe.gentric@philips.com'"
	 <philippe.gentric@philips.com>,
        Magnus Westerlund
	 <magnus.westerlund@ericsson.com>, dccp@ietf.org,
        mmusic@ietf.org, "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
Subject: RE: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream
	 switching)
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The requirement is pretty easy to state:

For two way voice, the data rate is quantized, and constant.  You can
tolerate some packet loss, which is in the percent or so range without
problems, and some packets are more important than others.  It takes
some time to change rates.  Delay is one of the most important parameters.
Add any significant delay, and we can't use it.

For video, the data rate can be less constant (ours is only slightly
variable), there are more reasons to do sender marking of packets to
be discarded, and delay is even more important.

A nice characteristic you can use is that voice and video has the
possibility of admission control.  You can say that a transport
protocol can't really directly deal with that, but at least at the
moment, that's how you get a rate change, so the same mechanism
can get you admission control.  In the end, you either get an
acceptable rate that you can send constant bit rates at, or you
stop sending at all.  

I'm more sanguine about complexity.  I'll tolerate some level of code
complexity if I get something out of it.  Let's face it, TCP-friendly
isn't something that matters to me.  Better experience for our
users is.  If TCP-friendly ultimately results in a better user
experience, good.  If it doesn't ....

Brian

> -----Original Message-----
> From: Eddie Kohler [mailto:kohler@icir.org]
> Sent: Friday, July 25, 2003 2:50 AM
> To: Phelan, Tom
> Cc: 'Damon Lanphear'; 'philippe.gentric@philips.com'; Magnus 
> Westerlund;
> dccp@ietf.org; mmusic@ietf.org; Pasco Anderson, Jay
> Subject: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream
> switching)
> 
> 
> Hi Tom,
> 
> > If DCCP conflicts with an application's requirements, then 
> the application
> > won't use it, whether DCCP is network friendly or not. 
> 
> Totally agree. And totally agree that we must figure out 
> whether DCCP is
> really useful for two-way voice. But, for example, an 
> application with a
> requirement "must achieve a minimum bandwidth" would not be 
> appropriate for
> DCCP, because it requires non-TCP-friendly congestion control.
> 
> Nothing that you have discussed is that far out, but some of 
> it is getting
> far out enough that I wanted to make the concern explicit. 
> (For instance,
> we've been talking about apps that can transmit only at a 
> discrete set of
> rates---unless 0pps was one of those rates, such an app would have a
> minimum bandwidth requirement.)
> 
> > Note that I think
> > that network-friendly reaction to congestion is absolutely one of my
> > application's requirements (my app is two-way voice).  I 
> hope that I can use
> > DCCP to get that, but I'm having difficulties making it 
> work.  Not that I've
> > given up hope, mind you.  I think I've managed to work out 
> reasonable ways
> > to use DCCP for similar, but not quite identical apps.  And 
> I intend to keep
> > trying for my app.
> > 
> > I think it's very important for DCCP to know whether it's 
> really useful for
> > two-way voice or not.  All of the DCCP documents mention it 
> as a primary
> > target application.  Some people on this list might already 
> know how to make
> > it work, but I don't yet, and I haven't seen anyone give a 
> credible scheme
> > for it yet, so I'll keep trying.
> 
> FYI I really appreciate this discussion!!!
> 
> Eddie
> 
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic
> 

_______________________________________________
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https://www1.ietf.org/mailman/listinfo/mmusic



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To: "Phelan, Tom" <tphelan@sonusnet.com>
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Subject: [MMUSIC] Re: [dccp] One-way live media with DCCP/TFRC
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Tom,

first thank you for this detailed and clear description of how a typical system would work!

I agree it  is useful to insist that streaming is about "seconds" rather than "bytes";-)

I share your belief  that the same scheme applies to one-way pre-recorded media.

I also share your hope hat an application transmitting data *below* the TFRC rate is not penalized,
because, as you demonstrate, this is what a streaming application will *have* to do.
By the way can someone give a confirmation about that ?

*****
one remark:

you write:

> ... when DCCP/TFRC has decided on a rate too low for the high rate
>encoding the application could make the change to the low rate immediately.
>This would work, but it might lead to unnecessary switches to the lower
>rate.

Let me give my interpretation of what  "unnecessary switches to the lower rate" are.

For me the "risk" (of reduced quality seen by the user) is the direct result of the congestion control policy.

TFRC is already designed to give you a rate that changes in a "less drastic" manner than  TCP divide-by-two,
and in general to give "smoother" rate variations etc...

In other words, if I dont like the risk associated with using a given congestion control
(say TRFC) the right thing to do should be to design another one, no?


regards,

Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com



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From: "Phelan, Tom" <tphelan@sonusnet.com>
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        "Phelan, Tom" <tphelan@sonusnet.com>
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Subject: [MMUSIC] RE: [dccp] One-way live media with DCCP/TFRC
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Hi Philippe,

From an e-mail from Eddie it appears that I wasn't totally correct that
there's no penalty for sending below the maximum rate, but I don't think it
changes my scheme.

From what Eddie said, and from looking at the TFRC RFC again, I think that
while you're sending below the TFRC max rate the max rate doesn't grow (even
if it could).  So if you want to now increase your sending rate, the maximum
you can send in the next RTT is twice what you just sent, regardless of how
low the RTT is.  You need to slow-start up to the rate that you could have
been sending if you were greedy.

Tom P.

> -----Original Message-----
> From: philippe.gentric@philips.com 
> [mailto:philippe.gentric@philips.com]
> Sent: Friday, July 25, 2003 10:10 AM
> To: Phelan, Tom
> Cc: 'dccp@ietf.org'; 'mmusic@ietf.org'
> Subject: Re: [dccp] One-way live media with DCCP/TFRC
> 
> 
> Tom,
> 
> first thank you for this detailed and clear description of 
> how a typical system would work!
> 
> I agree it  is useful to insist that streaming is about 
> "seconds" rather than "bytes";-)
> 
> I share your belief  that the same scheme applies to one-way 
> pre-recorded media.
> 
> I also share your hope hat an application transmitting data 
> *below* the TFRC rate is not penalized,
> because, as you demonstrate, this is what a streaming 
> application will *have* to do.
> By the way can someone give a confirmation about that ?
> 
> *****
> one remark:
> 
> you write:
> 
> > ... when DCCP/TFRC has decided on a rate too low for the high rate
> >encoding the application could make the change to the low 
> rate immediately.
> >This would work, but it might lead to unnecessary switches 
> to the lower
> >rate.
> 
> Let me give my interpretation of what  "unnecessary switches 
> to the lower rate" are.
> 
> For me the "risk" (of reduced quality seen by the user) is 
> the direct result of the congestion control policy.
> 
> TFRC is already designed to give you a rate that changes in a 
> "less drastic" manner than  TCP divide-by-two,
> and in general to give "smoother" rate variations etc...
> 
> In other words, if I dont like the risk associated with using 
> a given congestion control
> (say TRFC) the right thing to do should be to design another one, no?
> 
> 
> regards,
> 
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
> 
> 

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>Hi all,
>
>On this issue:
>
>> IMHO this issue is related to my question in the other mail about
>> managing audio AND video at the same time: probably DCCP should have a
>> way to handle "collectively" a bunch of streams, be it audio plus video
>> or two-way audio!
>
>Our thought was that, given DCCP's unreliability, it is trivial to layer
>multiple streams on top. The first byte of packet data could indicate
>stream number to the application. This works as long as both streams want
>to share the same congestion control state + CC mechanism -- is this the
>case?

a multiplex? (that would clash rather badly with the idea that RTP can be mapped
trivially using the port numbers !-)

One thing is sure, I have questions about how it would work with multiple DCCP "sessions":

If DCCP is running 2 sessions from host A to host B,
and at a given time DCCP tells *each* session "you have 200 kb/s"
=> does it mean the available bandwidth is 400 kb/s ?
but then the application could prefer to allocate +50 kb/s to audio
and +350 kb/s to video ...
=> or does it mean the total is 200 kb/s? but then DCCP would
have to assume that the 2 sessions are correctly managed (linked/grouped) so that
they dont "fight" for it, right? otherwise what a mess!

So the need is rather for a "grouping", like the API would enable
the application to tell DCCP: "these are 2 (or more) streams,
but it is a single CC "session", i.e. give me a single rate for the group
I will do the repartition". (same spirit as RTSP aggregate control)


regards

Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com



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Hi,

Here is my comments on this draft.

1. As a WG draft you should have the short copyright statement and not 
only the long one at the end of the draft.

2. In section 1 I would like that you clarify that RFC 2828 contains 
security terminology.

3. Section 3.1. This section needs to be improved. As I understand it 
the a=crypto attribute can be used with any transport and media. 
Therefore the section should not start with defining that this defines 
the value for RTP/SAVP. The actual crypto suits will be required to be 
registered and defined for each individual transport. There might in 
fact be even further restrictions that apply to future crypto suits.

4. Section 3.4, I think the session parameters are actually specific to 
the crypto suit, primarily. Secondarily it can be dependent on more things.

5. Section 3 and 4. In general I think the basic definition of the 
a=crypto attribute can be more cleanly separated from the specific 
application for SRTP.

6. Section 4.1, Is usage of multiple a=crypto lines allowed. IF yes this 
section contradict this.

7. Section 4.1.4, last sentence: How can one add a new name that is 
identical and still carry any difference. Please reword.

8. Section 4.2, I think there is a large shortcoming regarding the uri: 
parameter. I think one must clearly define the format one retrieves the 
keys when using the URI. Of course this format can be crypto suit 
dependent.

9. Section 4.3.1, second and third paragraph. I think the definition of 
the SSRC, ROC, SEQ, could be better done. As I understand it any of the 
three is sufficient, why not express it that way. Then one MAY have the 
parameter anyway.

10. Section 5.4, second paragraph: I think the limitation you would like 
to declare here needs some discussion. First you forbid the usage of 
multiple m= lines on the same port, after last weeks discussion I don't 
know if this is acceptable, at least not without further motivation. I 
would also write some recommendations/considerations regarding grouping 
  of media lines here.

11. Section 5.7, I am not certain that session parameters can't be 
restrained from being changed. For example the SRC (ROC) parameter seems 
one that might need to be included and changed in an offer for rekeying. 
  Are there any synchronization problem that can arise when doing 
rekeying? There seems to be need to define from what seq the new key are 
valid.

12. When it comes to SRTPs protection mechanism it seems necessary to be 
able to define the window size using the a=crypto parameter. There are a 
lot of difference between a uncompressed video stream running at a 
couple of hundreds of Mbyte/s using 100 000 packets each second. This 
will require a much larger window then a 64 kbit stream that sends 15 
packets every second.

13. Section 6.1 First paragraph, last sentence. The attack is only 
avoided if there is one master key per SSRC, not media stream. I think 
that there is some ambiguity in the use of media stream, which needs to 
be clarified to avoid misunderstanding.

14. Section 6.2, second paragraph, first sentence: The attribute is 
crypto not SRTP as it says in the text.

15. Section 7.: The ABNF does not define the extension space. For 
example the crypto-suite definition should have an extra alternative 
crypto-suit-extension which is VCHAR. I think the whole ABNF needs to be 
thought through to be more complete in the extension sense.

16. Section 7. Why have the 2^ optional value if it does not matter. 
Please simplify this.

17. Section 7, The absolute URI should not rely only on RFC 2396, there 
is an extension to that document, please see RFC 2732.

18. Last page, has not the normal number of lines.


Best Regards


Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
----------------------------------------------------------------------
Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com



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To: philippe.gentric@philips.com
cc: Damon Lanphear <damonlan@real.com>, dccp@ietf.org, mmusic@ietf.org
In-Reply-To: Message from philippe.gentric@philips.com 
   of "Fri, 25 Jul 2003 14:43:56 +0200." <OF3F80C11E.6CBE73AB-ONC1256D6E.004269D4-C1256D6E.0046C1CA@diamond.philips.com> 
Date: Fri, 25 Jul 2003 08:09:04 -0700
From: Eddie Kohler <kohler@icir.org>
Subject: [MMUSIC] Re: [dccp] what is DCCP for? (was: natural DCCP sender-side API)
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Phillipe

> Then I assume that *if the sender does its part of the job*,
> (which is to abide by the max rate indicated by DCCP)
> then the system (application + DCCP) will run "in the best possible way"
> ...
> which is: *avoid congestion*
> (if DCCP does not do that, please change the name!-)
> ...
> which means on time delivery of data!

DCCP traffic is still best effort traffic. Best effort traffic must expect
loss. That's the only way the network can signal congestion currently.
(DCCP will then avoid congestion *collapse* by backing off its send rate.)
Furthermore, there may be variable delay, depending on the network. There
is no magic "do not drop or delay my packets" button in the Internet today.

Except that when ECN is deployed in routers, DCCP packets will get marked
when UDP packets would get dropped.

> Am I putting irrealistic hopes in DCCP?

Yes. DCCP cannot predict congestion in the network. It sounds like you want
intserv (a guaranteed bandwidth reservation).

You can get some of what you want, in that DCCP will tell the app the best
rate it is currently allowing, and if that's not good enough, your app can
quit.

Eddie

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Mark,

>>What will happen if an application "does not use" the
>>bandwidth indicated by TFRC?
>
>OK, my assumption here was that streaming media was coming from disk.
>Thus you can always send faster then the receiver is consuming.

I am not sure about what you mean by "always" but what I am sure is that it cannot be "all the time":
specifically you can do that up to the moment when your client side buffer is full,
because a media decoder is not regulated on a *data* rate but on *media time*...
so if you send data faster than the media rate you fill up the client buffer ...

(which brings back the previous conclusion that pre-recorded media is not that much different than one-way "live")

regards,


Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com



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Subject: RE: [MMUSIC] RTSP and mobility 
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Dear Ashutosh,

thank you for you quickly reply.

I tried to implement what the paper says about RTSP mobility.
The Client now send the SETUP after the handoff, but the RTSP
server (Darwin Streaming Server) doesn't respond with any message.

Looking the Server source code I think that the Server doesn't
accept the incoming SETUP message because it doesn't belong to
any opend RTSP session (it is like there is a relation between=20
the session and the transport socket and the session accepts packet
from its client socket). Therefore if the packet arrive with a source=20
address different (due to mobility), the packet is rejected.

I don't know if this mean that the Server is not RTSP standard =
compliant.

Do you know where the RTSP specification=20
talks about the RTSP application-mobility?

Thanks,
Enrico


-----Original Message-----
From: Ashutosh Dutta [mailto:adutta@research.telcordia.com]
Sent: marted=EC 22 luglio 2003 18.49
To: Enrico Balatti
Cc: mmusic@ietf.org
Subject: Re: [MMUSIC] RTSP and mobility=20



Enrico,
       please see the paper
      =20
       http://www.cs.columbia.edu/~hgs/papers/Schu0007_Application.pdf,
       it talks about some issues related to RTSP and mobility when IP
       address  changes on the  mobile because  of subnet  movement or
       domain movement.

Thanks
Ashutosh

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Subject: [MMUSIC] RE: [dccp] rapid rate change codecs (was ... something else!)
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Hi, Tom, Eddie,

(just sending to the lists now, getting too many duplicates!)

>Hi Philippe,
>
>From an e-mail from Eddie it appears that I wasn't totally correct that
>there's no penalty for sending below the maximum rate, but I don't think it
>changes my scheme.
>
>From what Eddie said, and from looking at the TFRC RFC again, I think that
>while you're sending below the TFRC max rate the max rate doesn't grow (even
>if it could).  So if you want to now increase your sending rate, the maximum
>you can send in the next RTT is twice what you just sent, regardless of how
>low the RTT is.  You need to slow-start up to the rate that you could have
>been sending if you were greedy.
>
>Tom P.

Yes,  it means that the application will have to "probe" by sending data at the TFRC rate,
which in turn means oscillating  between
* sending a "low" media rate too fast (which will fill up the player buffers)
* sending a "high" media rate too slow (which will deplete the player buffers)
to keep a constant buffer at the receiver.

(Damon: you were right, DCCP is not any progress here,
we will still need to monitor the receiver buffers as we do now !-)

for media delivery (large buffers) this is ok (assuming you have the capability to switch etc ..;-)

Unfortunately for very small buffers (i.e. small delay, VoIP) that means switching *VERY often*!

I think it leads to the conclusion that DCCP for VoIP is useful with codecs
for which the rate can be changed very often with no penalty ?

This would be OK for voice (with AMR, EVRC etc) but maybe not so much for video?

<from other mail>

>> Am I putting irrealistic hopes in DCCP?
>
>Yes. DCCP cannot predict congestion in the network.

Actually that part is ok: DCCP will tell the sender to reduce the rate,
give it a new target, this is good.

>
>You can get some of what you want, in that DCCP will tell the app the best
>rate it is currently allowing ...

Ah, but finally the irrealistic hope I was putting in DCCP is discovered:
DCCP can not tell the application when to increase its rate unless
the application "probes" the network first by ... increasing its rate.

But one who has the right codecs can live with that ;-)

regards,


Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com



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From: Damon Lanphear <damonlan@real.com>
To: "Phelan, Tom" <tphelan@sonusnet.com>
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Subject: [MMUSIC] Re: [dccp] RE: Packet drop API / what happens with packet drops
 now?
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I agree with Tom.  I think that rather than dropping packets on write in
the sending DCCP, you'd want to block and let the app decide whether the
blocked packet should be queued in the app or dropped.  One of the
things we can do for live unidirectional media, as an example, is prune
an app layer queue to smoothly degrade perceptual distortion based on a
prioritization scheme.

On Thu, 2003-07-24 at 18:40, Phelan, Tom wrote:
> Hi Eddie,
> 
> I actually think that there's a big advantage to throwing packets away at
> the sender, rather than having the network choose the packets to throw away,
> even if you end up discarding more packets that way.  When the sender
> chooses the packets to discard, it can ensure that important packets (like
> frame markers, etc.) are preserved.  The network simply makes random
> decisions.
> 
> Tom P.
> 
> > -----Original Message-----
> > From: Eddie Kohler [mailto:kohler@icir.org]
> > Sent: Thursday, July 24, 2003 6:21 PM
> > To: dccp@ietf.org; mmusic@ietf.org
> > Cc: tphelan@sonusnet.com
> > Subject: Packet drop API / what happens with packet drops now?
> > 
> > 
> > What happens in currently-deployed codecs when packets are dropped?
> > 
> > Clearly codecs, and VoIP in particular, can handle loss. 
> > Possibly even high
> > loss rates. One way to think about DCCP's allowed sending 
> > rate is that it
> > moves drops that *would* have happened in the network 
> > *anyway*, into the
> > sending host. (Although DCCP will generally drop more than the network
> > would have, to ensure fairness, and because of congestion-control
> > infelicities that we want to fix.) So how disastrous are these drops?
> > 
> > Another way to put this: A DCCP API might never block -- or 
> > it might block
> > for at most T seconds. Instead, writing a packet into a full 
> > send buffer
> > would drop that packet; or it might drop an older packet---a 
> > drop-from-head
> > send buffer; or it might drop the oldest packet with lowest priority
> > annotation.
> > 
> > Now the app simply sees a loss rate, which DCCP will happily 
> > report. For
> > codec switching, you can simply switch when the loss rate is 
> > intolerably
> > high -- which you would have had to do anyway.
> > 
> > How horrible would this be?
> > 
> > Eddie
> > 
> 
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
-- 
Damon Lanphear <damonlan@real.com>


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Subject: [MMUSIC] Re: [dccp] What's wrong with TFRC for VoIP and other apps?
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Eddie,

I would add that when ECN is not available loss becomes a considerable
factor that bounds the TFRC rate.  The TFRC algorithm periodically
touches the upper bounds of the link capacity, at which point loss is
induced, and the algorithm decreases the rate.  The result is periodic
distortion. 

This distortion can be mitigated through a resend mechanism.  But when
you combine a resend mechanism with adherence to the TFRC rate, you get
a more complicated solution. You have to define a trade off between
delay for satisfying resends and minimizing distortion. 

Of course, congestion induced loss is a fact of life in the best effort
internet.  But we can at least define a way by which TFRC can further
minimize periodic loss.  I understand that TFRC as it is currently
defined has been designed to significantly dampen periodic oscillations.
I think, however, that we may want to go a step further and say that
TFRC can optionally limit itself to some maximum rate, that may vary
over the duration of the session, but is defined by the application.  

The intent in doing so is to obviate the requirement that TFRC
constantly push against an unknown upper bounds.  So unless congestion
causes the upper bound to be close to the defined maximal rate, periodic
loss will be eliminated.  If the maximal rate is close to the link rate
(due to congestion, or otherwise) then we are no better off than
before.  But at least there is an opportunity to specifically provision
sessions for known media rates.

On Thu, 2003-07-24 at 14:58, Eddie Kohler wrote:
> Hi all,
> 
> I just wanted to try to summarize the issues people have brought up, in
> other threads, about why TFRC and/or DCCP will be inappropriate for VoIP
> and other apps. I agree with Tom Phelan's comment that the biggest issues
> have to do with TFRC, not the API. I've left off the solutions people have
> proposed to these problems.
> 
> 1. Rate slows down during idle periods
> 
>    The TFRC allowed sending rate will drop down to something very small
>    (2-4 packets/RTT) when the sender is idle. This may cause problems
>    particualrly with VoIP conversations, which are naturally idle-one-way
>    then idle-the-other-way. The rampup from the small rate to the fair rate
>    may take several to many RTTs, ouch.
> 
> 2. Rate will not increase during app-limited period
> 
>    This is essentially the same problem as above. Say the application is
>    sending at rate R. The allowed rate will not increase much beyond R
>    (say, more than 2R) until the app transmits at a faster rate. 
> 
> 3. Apps with fixed sets of rates
> 
>    An app might have a discrete set of sending rates. Must it send at the
>    highest app rate <= the TFRC allowed rate? Would be very nice to allow
>    some flexibility, so that it could send at, say, the highest rate <=
>    1.8*TFRC_allowed_rate.
> 
> 4. Rate changes/oscillations
> 
>    There are application costs, possibly significant ones, associated with
>    changing rates. If the app has to change its rate frequently, because of
>    CC, that's a problem.
> 
> Have I missed anything?
> 
> Eddie
> 
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
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Tom,

Great way to frame this problem.  I like this approach.  I have one
apprehension:

On Thu, 2003-07-24 at 12:26, Phelan, Tom wrote:
At this point (perhaps after a slight delay) the sender can switch back
to
> the higher rate.  If the new rate can't be sustained the transmit buffer
> will fill again (and the playout buffer will drain).  When the switch
> encoding threshold is reached the sender goes back to the lower encoding
> rate.  This oscillation continues until the stream ends or the network is
> able to support the high rate for the long term.

I think we'd like to avoid the oscillation you describe.  Or at least
extend the period over which it can occur.  But that all comes down to
understand the impact of the oscillation on the subjective experience of
the user.  If we're delivering video, and there is a perceivable
difference in the distortion of the high and low rates, then switching
back and forth over even 20s intervals could be truly annoying. 

I think of this oscillation problem as being kind of like that which we
encounter with congestion control algorithms.  Where there is some
unknown upper bounds against which we have to test periodically at a
cost.  I'm not sure what a good solution is.  I think whatever solution
is put forward will have to be dependent on the attributes of the media,
and perhaps tie upshift attempts to a combination of buffer state and
some measure of stability of the upper bounds rate. 



On Thu, 2003-07-24 at 12:26, Phelan, Tom wrote:
> Hi,
> 
> I've been continuing to think about the one-way live media case and have
> come up with the following scheme for using DCCP with TFRC.  Recall that
> one-way live differs from one-way pre-recorded media by having a max
> possible sending rate equal to the encoding rate (except for very short
> bursts, perhaps), and differs from two-way interactive media by being
> tolerant of delay.
> 
> So, for this scheme we have a playout buffer at the receiver and transmit
> buffer at the sender.  Note that these buffers contain media streams, not
> packets, and their lengths are measured in seconds, not bytes or packets.
> 
> The transmit buffer is filled at the encoding rate and drained at the TFRC
> transmit rate.  The playout buffer is filled at the network arrival rate and
> drained at the decoding rate.  The playout buffer has a playback start
> threshold and the transmit buffer has a "switch encoding" threshold.  These
> thresholds are on the order of a few to several seconds and switch encoding
> is less than playback start.
> 
> Assume that the encoder can encode at two rates, a high rate and a low rate.
> At the start of a connection, the sender places data into the transmit
> buffer at the high encoding rate.  The buffer is drained at the TFRC rate,
> which at this point is in slow-start and is probably slower than the
> required rate.  This will cause a backup in the transmit buffer.  Eventually
> TFRC will slow-start to a rate slightly above the rate necessary to sustain
> the encoding rate.  When this happens the transmit buffer will drain and
> we'll reach a steady-state condition where the transmit buffer is empty and
> we're transmitting at a rate that is probably below the maximum allowed by
> TFRC.  Note that, by my interpretation of TFRC at least, we won't be
> penalized for transmitting less than we could.  You're only penalized when
> you transmit nothing for some number of roundtrip times.
> 
> Meanwhile at the receiver, the playout buffer is filling, and when it
> reaches the playback start threshold playback will start.  After TFRC
> slow-start and the transmit buffer is drained, this buffer will reach a
> steady state where packets are arriving from the network at the encoding
> rate (ignoring jitter) and being drained from the buffer at the (equal)
> decoding rate.  The depth of the buffer will be the playback start threshold
> plus the maximum depth of the transmit buffer during slow start.
> 
> Now assume that network congestion forces TFRC to drop its rate to below
> that needed by the high rate encoding.  The transmit buffer will begin to
> fill and the playout buffer will begin to drain.  When the transmit buffer
> reaches the switch encoding threshold, the sender switches to the low rate
> encoding, and converts all of the data in the transmit buffer to low rate
> encoding.  I'll ignore issues of how to do this efficiently, but it's
> important not to discard this data, and to convert it.
> 
> Assuming that the network can support the new, lower, rate (and a little
> more) the transmit buffer will begin to drain and the playout buffer will
> begin to fill.  Eventually the transmit buffer will empty, the playout
> buffer will be back to its steady-state level, and we'll be transmitting
> data at the new, lower, encoding rate.
> 
> At this point (perhaps after a slight delay) the sender can switch back to
> the higher rate.  If the new rate can't be sustained the transmit buffer
> will fill again (and the playout buffer will drain).  When the switch
> encoding threshold is reached the sender goes back to the lower encoding
> rate.  This oscillation continues until the stream ends or the network is
> able to support the high rate for the long term.
> 
> It might be useful for DCCP to tell the application about rate changes.  For
> instance, when DCCP/TFRC has decided on a rate too low for the high rate
> encoding the application could make the change to the low rate immediately.
> This would work, but it might lead to unnecessary switches to the lower
> rate.  In particular, when DCCP decides on a new rate, it has no way of
> knowing whether this is a transient or a long-term change.  If it's
> transient the transmit buffer might be able to absorb the problem, and a
> change to the lower rate might unnecessarily reduce the quality seen by the
> user.  If we wait for the switch encoding threshold we can be more sure that
> the rate change is long-term.  Also, if we rely on rate indications for the
> downshift, we need to ignore it during slow-start.
> 
> It might be more useful to know when DCCP has raised the rate sufficiently
> to switch to the high rate (after the transmit buffer has been drained).
> 
> Note that this scheme is also suitable for one-way pre-recorded media, as
> long as the transmit buffer is only filled at the encoding rate, not at the
> disk read rate.  Overall I'd say that this is better than the previous
> scheme (for one-way pre-recorded media), and I think that some of the
> commenters on the previous message must have had something like this in
> mind.
> 
> I still don't know how to do the two-way interactive media.
> 
> Tom P.
> 
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
-- 
Damon Lanphear <damonlan@real.com>


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Subject: Re: [MMUSIC] RE: [dccp] rapid rate change codecs (was ...
	something else!)
From: Damon Lanphear <damonlan@real.com>
To: philippe.gentric@philips.com
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inline:

On Fri, 2003-07-25 at 09:10, philippe.gentric@philips.com wrote:
> Hi, Tom, Eddie,
> 
> (just sending to the lists now, getting too many duplicates!)
> 
> >Hi Philippe,
> >
> >From an e-mail from Eddie it appears that I wasn't totally correct that
> >there's no penalty for sending below the maximum rate, but I don't think it
> >changes my scheme.
> >
> >From what Eddie said, and from looking at the TFRC RFC again, I think that
> >while you're sending below the TFRC max rate the max rate doesn't grow (even
> >if it could).  So if you want to now increase your sending rate, the maximum
> >you can send in the next RTT is twice what you just sent, regardless of how
> >low the RTT is.  You need to slow-start up to the rate that you could have
> >been sending if you were greedy.
> >
> >Tom P.
> 
> Yes,  it means that the application will have to "probe" by sending data at the TFRC rate,
> which in turn means oscillating  between
> * sending a "low" media rate too fast (which will fill up the player buffers)
> * sending a "high" media rate too slow (which will deplete the player buffers)
> to keep a constant buffer at the receiver.
> 
> (Damon: you were right, DCCP is not any progress here,
> we will still need to monitor the receiver buffers as we do now !-)
> 
> for media delivery (large buffers) this is ok (assuming you have the capability to switch etc ..;-)
> 
> Unfortunately for very small buffers (i.e. small delay, VoIP) that means switching *VERY often*!
> 
> I think it leads to the conclusion that DCCP for VoIP is useful with codecs
> for which the rate can be changed very often with no penalty ?
> 
> This would be OK for voice (with AMR, EVRC etc) but maybe not so much for video?

Yes.  Video quality oscillation is going to be a big bad problem. 
Unless we have truly wonderful codecs with very fine grained scalability
(which I understand are very expensive in terms of rate efficiency), we
have to live with potentially annoying oscillations over relatively
short timescales.  So any robust video solution that uses TFRC and media
adaptation will have provide a way to exchange potential for
oscillation/maximization of quality vs. stability/lowest common
denominator quality.

> 
> <from other mail>
> 
> >> Am I putting irrealistic hopes in DCCP?
> >
> >Yes. DCCP cannot predict congestion in the network.
> 
> Actually that part is ok: DCCP will tell the sender to reduce the rate,
> give it a new target, this is good.
> 
> >
> >You can get some of what you want, in that DCCP will tell the app the best
> >rate it is currently allowing ...
> 
> Ah, but finally the irrealistic hope I was putting in DCCP is discovered:
> DCCP can not tell the application when to increase its rate unless
> the application "probes" the network first by ... increasing its rate.
> 
> But one who has the right codecs can live with that ;-)
> 
> regards,
> 
> 
> Philippe Gentric
> Software Architect
> Philips MP4Net
> philippe.gentric@philips.com
> http://www.platform4.philips.com
> 
> 
> 
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic
-- 
Damon Lanphear <damonlan@real.com>


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Subject: Re: [MMUSIC] delay API (was: Packet drop API / what happens with packet
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Eddie,

>What happens in currently-deployed codecs when packets are dropped?
>

all recent codecs can handle substancial amounts of loss
(that is: well implemented decoders can ;-) but mimizing
losses should remain the highest priority because
the perceived quality for (X-loss) is always
smaller than if the codec had produced (X-loss)bits
in the first place.


>Clearly codecs, and VoIP in particular, can handle loss. Possibly even high
>loss rates. One way to think about DCCP's allowed sending rate is that it
>moves drops that *would* have happened in the network *anyway*, into the
>sending host. (Although DCCP will generally drop more than the network
>would have, to ensure fairness, and because of congestion-control
>infelicities that we want to fix.) So how disastrous are these drops?

What is desirable is that DCCP tells the sender "dont send that much!"
and as Tom expressed it:

>"it seems better to me that the sender makes intelligent
>decisions about packet discard, rather than the network makes random
>decisions

which also apply to the DCCP stack (sender side):
it is not in a good position to make the best decision.


>Another way to put this: A DCCP API might never block -- or it might block
>for at most T seconds. Instead, writing a packet into a full send buffer
>would drop that packet; or it might drop an older packet---a drop-from-head
>send buffer; or it might drop the oldest packet with lowest priority
>annotation.
>
>Now the app simply sees a loss rate, which DCCP will happily report. For
>codec switching, you can simply switch when the loss rate is intolerably
>high -- which you would have had to do anyway.
>
>How horrible would this be?

You make it sound like the DCCP sender API would be some mysterious black hole?-)

I vote for "extremely horrible"?-)

What about a *delay* API:

When the rate changes the application is notified
(e.g. a call back would be nice, at startup an application
would be able to pass a rate callback pointer function)

If the application complies i.e. waits the right amount of time
between each packet and/or send packets with the right size
so that its rate is below the indicated rate, then all is good.

If the application does not comply (sends a packet too soon and/or too big) the API replys:

"This packet will be sent, but with a delay of xxx ms"
(and *sends* it, the delay being computed to match the current CC max rate)

obviously such a message implies that the sender is sending with a rate too high...
(at that stage an application which passed "null" at startup
for the rate callback pointer function can use an explicit call
to get the rate...)

If the application sends *really* too much
the API returns with *increasing delays* until a
more severe error occurs: "packet not accepted, buffer is full".

In short, the (int) returned by "send" would not be
the amount of data sent but the amount of *delay*
the packet will suffer before flying out.
Zero meaning the application rate is below the max (TFRC) rate.


regards,


Philippe Gentric
Software Architect
Philips MP4Net
philippe.gentric@philips.com
http://www.platform4.philips.com



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From: "Rosen, Brian" <Brian.Rosen@marconi.com>
To: "'Damon Lanphear'" <damonlan@real.com>, Eddie Kohler <kohler@icir.org>
Cc: dccp@ietf.org, mmusic@ietf.org
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Subject: [MMUSIC] RE: [dccp] What's wrong with TFRC for VoIP and other apps?
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In VoIP (audio and video) you NEVER resend.  You drop
and move on. So, the resend mechanism is baggage for us.
It's one of the reasons UDP is used.

Having an agreed upon max rate would be good.
It would be nice to have some kind of negotiation:
	I want to send at 64K
	You can only send at max 40K
	Okay, the max I can use then is 32K
	Fine, 32K it is

Brian

> -----Original Message-----
> From: Damon Lanphear [mailto:damonlan@real.com]
> Sent: Friday, July 25, 2003 12:37 PM
> To: Eddie Kohler
> Cc: dccp@ietf.org; mmusic@ietf.org
> Subject: Re: [dccp] What's wrong with TFRC for VoIP and other apps?
> 
> 
> Eddie,
> 
> I would add that when ECN is not available loss becomes a considerable
> factor that bounds the TFRC rate.  The TFRC algorithm periodically
> touches the upper bounds of the link capacity, at which point loss is
> induced, and the algorithm decreases the rate.  The result is periodic
> distortion. 
> 
> This distortion can be mitigated through a resend mechanism.  But when
> you combine a resend mechanism with adherence to the TFRC 
> rate, you get
> a more complicated solution. You have to define a trade off between
> delay for satisfying resends and minimizing distortion. 
> 
> Of course, congestion induced loss is a fact of life in the 
> best effort
> internet.  But we can at least define a way by which TFRC can further
> minimize periodic loss.  I understand that TFRC as it is currently
> defined has been designed to significantly dampen periodic 
> oscillations.
> I think, however, that we may want to go a step further and say that
> TFRC can optionally limit itself to some maximum rate, that may vary
> over the duration of the session, but is defined by the application.  
> 
> The intent in doing so is to obviate the requirement that TFRC
> constantly push against an unknown upper bounds.  So unless congestion
> causes the upper bound to be close to the defined maximal 
> rate, periodic
> loss will be eliminated.  If the maximal rate is close to the 
> link rate
> (due to congestion, or otherwise) then we are no better off than
> before.  But at least there is an opportunity to specifically 
> provision
> sessions for known media rates.
> 
> On Thu, 2003-07-24 at 14:58, Eddie Kohler wrote:
> > Hi all,
> > 
> > I just wanted to try to summarize the issues people have 
> brought up, in
> > other threads, about why TFRC and/or DCCP will be 
> inappropriate for VoIP
> > and other apps. I agree with Tom Phelan's comment that the 
> biggest issues
> > have to do with TFRC, not the API. I've left off the 
> solutions people have
> > proposed to these problems.
> > 
> > 1. Rate slows down during idle periods
> > 
> >    The TFRC allowed sending rate will drop down to 
> something very small
> >    (2-4 packets/RTT) when the sender is idle. This may 
> cause problems
> >    particualrly with VoIP conversations, which are 
> naturally idle-one-way
> >    then idle-the-other-way. The rampup from the small rate 
> to the fair rate
> >    may take several to many RTTs, ouch.
> > 
> > 2. Rate will not increase during app-limited period
> > 
> >    This is essentially the same problem as above. Say the 
> application is
> >    sending at rate R. The allowed rate will not increase 
> much beyond R
> >    (say, more than 2R) until the app transmits at a faster rate. 
> > 
> > 3. Apps with fixed sets of rates
> > 
> >    An app might have a discrete set of sending rates. Must 
> it send at the
> >    highest app rate <= the TFRC allowed rate? Would be very 
> nice to allow
> >    some flexibility, so that it could send at, say, the 
> highest rate <=
> >    1.8*TFRC_allowed_rate.
> > 
> > 4. Rate changes/oscillations
> > 
> >    There are application costs, possibly significant ones, 
> associated with
> >    changing rates. If the app has to change its rate 
> frequently, because of
> >    CC, that's a problem.
> > 
> > Have I missed anything?
> > 
> > Eddie
> > 
> > _______________________________________________
> > dccp IETF mailing list: dccp@ietf.org
> > list info:  https://www1.ietf.org/mailman/listinfo/dccp
> > wg charter: http://www.ietf.org/html.charters/dccp-charter.html
> -- 
> Damon Lanphear <damonlan@real.com>
> 
> 
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
> 

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From: "Phelan, Tom" <tphelan@sonusnet.com>
To: "'Damon Lanphear'" <damonlan@real.com>
Cc: "'dccp@ietf.org'" <dccp@ietf.org>, "'mmusic@ietf.org'"
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Subject: [MMUSIC] RE: [dccp] One-way live media with DCCP/TFRC
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Hi Damon,

Yes, the application can pick its "upshift probe" period based on its
knowledge of the user perception of rate shifts (the one up to probe and the
possible one down if the probe fails).  I suspect many apps might choose to
never probe up.

Tom P.

> -----Original Message-----
> From: Damon Lanphear [mailto:damonlan@real.com]
> Sent: Friday, July 25, 2003 12:54 PM
> To: Phelan, Tom
> Cc: 'dccp@ietf.org'; 'mmusic@ietf.org'; Pasco Anderson, Jay
> Subject: Re: [dccp] One-way live media with DCCP/TFRC
> 
> 
> Tom,
> 
> Great way to frame this problem.  I like this approach.  I have one
> apprehension:
> 
> On Thu, 2003-07-24 at 12:26, Phelan, Tom wrote:
> At this point (perhaps after a slight delay) the sender can 
> switch back
> to
> > the higher rate.  If the new rate can't be sustained the 
> transmit buffer
> > will fill again (and the playout buffer will drain).  When 
> the switch
> > encoding threshold is reached the sender goes back to the 
> lower encoding
> > rate.  This oscillation continues until the stream ends or 
> the network is
> > able to support the high rate for the long term.
> 
> I think we'd like to avoid the oscillation you describe.  Or at least
> extend the period over which it can occur.  But that all comes down to
> understand the impact of the oscillation on the subjective 
> experience of
> the user.  If we're delivering video, and there is a perceivable
> difference in the distortion of the high and low rates, then switching
> back and forth over even 20s intervals could be truly annoying. 
> 
> I think of this oscillation problem as being kind of like 
> that which we
> encounter with congestion control algorithms.  Where there is some
> unknown upper bounds against which we have to test periodically at a
> cost.  I'm not sure what a good solution is.  I think 
> whatever solution
> is put forward will have to be dependent on the attributes of 
> the media,
> and perhaps tie upshift attempts to a combination of buffer state and
> some measure of stability of the upper bounds rate. 
> 
> 
> 
> On Thu, 2003-07-24 at 12:26, Phelan, Tom wrote:
> > Hi,
> > 
> > I've been continuing to think about the one-way live media 
> case and have
> > come up with the following scheme for using DCCP with TFRC. 
>  Recall that
> > one-way live differs from one-way pre-recorded media by having a max
> > possible sending rate equal to the encoding rate (except 
> for very short
> > bursts, perhaps), and differs from two-way interactive 
> media by being
> > tolerant of delay.
> > 
> > So, for this scheme we have a playout buffer at the 
> receiver and transmit
> > buffer at the sender.  Note that these buffers contain 
> media streams, not
> > packets, and their lengths are measured in seconds, not 
> bytes or packets.
> > 
> > The transmit buffer is filled at the encoding rate and 
> drained at the TFRC
> > transmit rate.  The playout buffer is filled at the network 
> arrival rate and
> > drained at the decoding rate.  The playout buffer has a 
> playback start
> > threshold and the transmit buffer has a "switch encoding" 
> threshold.  These
> > thresholds are on the order of a few to several seconds and 
> switch encoding
> > is less than playback start.
> > 
> > Assume that the encoder can encode at two rates, a high 
> rate and a low rate.
> > At the start of a connection, the sender places data into 
> the transmit
> > buffer at the high encoding rate.  The buffer is drained at 
> the TFRC rate,
> > which at this point is in slow-start and is probably slower than the
> > required rate.  This will cause a backup in the transmit 
> buffer.  Eventually
> > TFRC will slow-start to a rate slightly above the rate 
> necessary to sustain
> > the encoding rate.  When this happens the transmit buffer 
> will drain and
> > we'll reach a steady-state condition where the transmit 
> buffer is empty and
> > we're transmitting at a rate that is probably below the 
> maximum allowed by
> > TFRC.  Note that, by my interpretation of TFRC at least, we won't be
> > penalized for transmitting less than we could.  You're only 
> penalized when
> > you transmit nothing for some number of roundtrip times.
> > 
> > Meanwhile at the receiver, the playout buffer is filling, 
> and when it
> > reaches the playback start threshold playback will start.  
> After TFRC
> > slow-start and the transmit buffer is drained, this buffer 
> will reach a
> > steady state where packets are arriving from the network at 
> the encoding
> > rate (ignoring jitter) and being drained from the buffer at 
> the (equal)
> > decoding rate.  The depth of the buffer will be the 
> playback start threshold
> > plus the maximum depth of the transmit buffer during slow start.
> > 
> > Now assume that network congestion forces TFRC to drop its 
> rate to below
> > that needed by the high rate encoding.  The transmit buffer 
> will begin to
> > fill and the playout buffer will begin to drain.  When the 
> transmit buffer
> > reaches the switch encoding threshold, the sender switches 
> to the low rate
> > encoding, and converts all of the data in the transmit 
> buffer to low rate
> > encoding.  I'll ignore issues of how to do this 
> efficiently, but it's
> > important not to discard this data, and to convert it.
> > 
> > Assuming that the network can support the new, lower, rate 
> (and a little
> > more) the transmit buffer will begin to drain and the 
> playout buffer will
> > begin to fill.  Eventually the transmit buffer will empty, 
> the playout
> > buffer will be back to its steady-state level, and we'll be 
> transmitting
> > data at the new, lower, encoding rate.
> > 
> > At this point (perhaps after a slight delay) the sender can 
> switch back to
> > the higher rate.  If the new rate can't be sustained the 
> transmit buffer
> > will fill again (and the playout buffer will drain).  When 
> the switch
> > encoding threshold is reached the sender goes back to the 
> lower encoding
> > rate.  This oscillation continues until the stream ends or 
> the network is
> > able to support the high rate for the long term.
> > 
> > It might be useful for DCCP to tell the application about 
> rate changes.  For
> > instance, when DCCP/TFRC has decided on a rate too low for 
> the high rate
> > encoding the application could make the change to the low 
> rate immediately.
> > This would work, but it might lead to unnecessary switches 
> to the lower
> > rate.  In particular, when DCCP decides on a new rate, it 
> has no way of
> > knowing whether this is a transient or a long-term change.  If it's
> > transient the transmit buffer might be able to absorb the 
> problem, and a
> > change to the lower rate might unnecessarily reduce the 
> quality seen by the
> > user.  If we wait for the switch encoding threshold we can 
> be more sure that
> > the rate change is long-term.  Also, if we rely on rate 
> indications for the
> > downshift, we need to ignore it during slow-start.
> > 
> > It might be more useful to know when DCCP has raised the 
> rate sufficiently
> > to switch to the high rate (after the transmit buffer has 
> been drained).
> > 
> > Note that this scheme is also suitable for one-way 
> pre-recorded media, as
> > long as the transmit buffer is only filled at the encoding 
> rate, not at the
> > disk read rate.  Overall I'd say that this is better than 
> the previous
> > scheme (for one-way pre-recorded media), and I think that 
> some of the
> > commenters on the previous message must have had something 
> like this in
> > mind.
> > 
> > I still don't know how to do the two-way interactive media.
> > 
> > Tom P.
> > 
> > _______________________________________________
> > dccp IETF mailing list: dccp@ietf.org
> > list info:  https://www1.ietf.org/mailman/listinfo/dccp
> > wg charter: http://www.ietf.org/html.charters/dccp-charter.html
> -- 
> Damon Lanphear <damonlan@real.com>
> 

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To: "Phelan, Tom" <tphelan@sonusnet.com>
cc: "'Damon Lanphear'" <damonlan@real.com>,
        "'philippe.gentric@philips.com'" <philippe.gentric@philips.com>,
        Magnus Westerlund <magnus.westerlund@ericsson.com>, dccp@ietf.org,
        mmusic@ietf.org, "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
In-Reply-To: Message from "Phelan, Tom" <tphelan@sonusnet.com> 
   of "Thu, 24 Jul 2003 10:02:01 EDT." <4CF48720B6E9D4118D040060CF2074E9082BB481@sonusdc3.sonusnet.com> 
Date: Thu, 24 Jul 2003 14:26:34 -0700
From: Eddie Kohler <kohler@icir.org>
Subject: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream switching)
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> Another thing that concerns me (touched on in the paragraph above) is the
> disconnect between a transport protocol making rate decisions and an
> application making rate decisions.  It seems to me that these particular
> applications are much better equipped to make the rate decisions - they know
> about what is possible.  It also seems that the application can make at
> least as good a decision about what constitutes network congestion.  The app
> will need feedback about the playout buffer state, and this is largely
> redundant with the DCCP acks.  If the app is making rate decisions and
> detecting network congestion, what do we need DCCP for?

My take:

Your paragraph was written from the application's point of view, not that
of the network. DCCP is about implementing congestion control that is
appropriate for the network: in other words, currently, TCP-friendly CC.
This may conflict with application "requirements".


For example:

> It seems to me that these particular
> applications are much better equipped to make the rate decisions - they know
> about what is possible. 

What is possible for the application may not be TCP-friendly or appropriate
for the network (if the app has a minimum rate, for example).

> It also seems that the application can make at
> least as good a decision about what constitutes network congestion. 

The app should make a decision that is TCP-friendly -- in which case you've
got DCCP all over again. You need acks, probably ECN Nonces, ....


We have a congestion control problem, for which we need a congestion
control solution. Avoiding DCCP doesn't avoid the problem.

So we should solve the problem! And I think we can solve it!


Now, it may end up that DCCP is not appropriate, once the congestion
control problem is solved. I'm not against UDP with application-level
congestion control. But CC is a hard problem, which we are trying to solve
for you.


Also:

> The app will need feedback about the playout buffer state, and this is
> largely redundant with the DCCP acks.

The app should be able to extract this information from the DCCP API, so no
app-level acks are necessary.


Eddie

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Date: Tue, 22 Jul 2003 08:25:16 -0700
From: David Meyer <dmm@1-4-5.net>
To: mboned@network-services.uoregon.edu
Cc: mmusic@ietf.org
Subject: Re: [MMUSIC] Re: [MBONED] WG action for  draft-savola-mboned-mcast-rpaddr-03.txt
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	Folks,

	Here's something that would be productive: Let's talk
	about facts, and stay away from statements such as 

... ASM for IPv4 is not scalable in interdomain but SSM is ...

	We need to support this type of statement, otherwise it
	is just marketing for SSM (maybe that is appropriate
	somewhere, but not on the MBONED list). 

	Let's stay away from marketing and speculating about what
	might happen (or for that matter, what might have
	happened), and spend our resources on multicast
	deployment, which is the charter of MBONED. 

	Thanks,

	Dave


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From: Mark Handley <M.Handley@cs.ucl.ac.uk>
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To: "Phelan, Tom" <tphelan@sonusnet.com>
cc: "'Damon Lanphear'" <damonlan@real.com>,
        "'philippe.gentric@philips.com'" <philippe.gentric@philips.com>,
        Magnus Westerlund <magnus.westerlund@ericsson.com>, dccp@ietf.org,
        mmusic@ietf.org, "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
In-reply-to: Your message of "Thu, 24 Jul 2003 10:02:01 EDT."
             <4CF48720B6E9D4118D040060CF2074E9082BB481@sonusdc3.sonusnet.com> 
Date: Thu, 24 Jul 2003 15:46:18 +0100
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Subject: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream switching)
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>Actually, my big worry here is TFRC, not the API.  I'm baffled about how to
>map slow start plus mostly smooth changes but occasional abrupt changes and
>a small playout buffer into something workable.
>
>Another thing that concerns me (touched on in the paragraph above) is the
>disconnect between a transport protocol making rate decisions and an
>application making rate decisions.  It seems to me that these particular
>applications are much better equipped to make the rate decisions - they know
>about what is possible.  It also seems that the application can make at
>least as good a decision about what constitutes network congestion.  The app
>will need feedback about the playout buffer state, and this is largely
>redundant with the DCCP acks.  If the app is making rate decisions and
>detecting network congestion, what do we need DCCP for?

[I'm just dropping back into a discussion I haven't been following, so
forgive me if this duplicates previous discussion]

There seem to be two obvious sorts of apps that might use TFRC:

 - streaming media
 - videotelephony

That isn't to say that there are different apps, but these two typify
two classes of apps.  Both are fine with variable packet rates.  But
streaming media has significantly more playout buffer available.

Streaming media apps can run the codec (or choice of pre-encoded
stream) at approximately constant bitrate, and send at variable
bitrate, using the playout buffer to deal with the temporary
mismatches.  

Videotelephony apps don't have sufficient delay budget to fix things
at the receiver, but they do have the luxury of encoding live, so they
can change the compression parameters on the fly.  They usually don't
have luxury of re-encoding twice though, so if their choice of
quantization parameters gives a rate that is different from what is
expected (because the video content was unpredictable), then they
might be in trouble.  Also, if the TFRC bandwidth envelope changes
unexpectedly, you can be in trouble.


So, why do I say all this?


My assumption is that streaming media apps will normally send at the
TFRC rate.  What they need is sufficient advance warning that the
playout buffer is running low so that they can switch down to a lower
rate.  And if the playout buffer is starting to get rather large, then
they can switch up to a higher rate.  Assuming rate switching is not a
trivial operation, and that the rate can only be switched at certain
re-sync points, then there is some danger that if congestion suddently
gets really bad, then the playout buffer will be exhausted before the
codec can be switched.  My assumption here is that a really good API
would allow the sender to send above the TFRC rate for a period of
time, so long as the rate mismatch isn't too bad.  A factor of two
might be reasonable as an upper bound on the oversending rate.


Videotelephony apps probably can't send at precisely the TFRC rate
without sacrificing delay to an undesirable extent.  This means two
things. First, the app needs to be allowed to send at rates above the
TFRC rate for a period of time (again, bounded to avoid extreme
unfairness).  Second, if the app sends under the TFRC rate for a short
period, it shouldn't lose it's ability to send faster later, so long
as it didn't undersend by too much.  For such apps, the TFRC rate is a
guide rate - the app should be capable of varying around the guide
rate, so long as it stays within reasonable bounds, and so long as the
long-term average is close to the TFRC rate.


Anyway, in both cases, if the kernel strictly enforces the TFRC rate,
app designers will either not use DCCP, or they'll pad their signal
with redundant data so they can operate within a more predictable
codec envelope.  Both are undesirable.


I'm not sure how we best design an API to satisfy this, but I think
it's really important that we do think about how this can be achieved.


The general philosophy that the TFRC rate is a guide-rate to be
followed loosely will probably also apply with TFRC-PS and VoIP, but
we know a lot less about this space.

Cheers,
	Mark

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In-Reply-To: Message from philippe.gentric@philips.com 
   of "Wed, 23 Jul 2003 19:43:04 +0200." <OFDF9890E5.9F3EA45B-ONC1256D6C.005D4D0A-C1256D6C.00622E55@diamond.philips.com> 
Date: Thu, 24 Jul 2003 14:08:28 -0700
From: Eddie Kohler <kohler@icir.org>
Subject: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream switching)
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> Surely DCCP has better assets to lure implementers?-)...
> I think an API providing a target rate would be a good starting point;-)

It's been mentioned a couple times deep in emails, but just to make it
explicit:

We absolutely expect APIs to provide the current congestion control state
to applications. This includes, but is not limited to, the maximum allowed
rate.

Eddie

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In-Reply-To: Message from philippe.gentric@philips.com 
   of "Thu, 17 Jul 2003 10:37:47 +0200." <OF7F5F1A27.2B4F0A45-ONC1256D66.002EE356-C1256D66.0030515D@diamond.philips.com> 
Date: Thu, 24 Jul 2003 13:21:19 -0700
From: Eddie Kohler <kohler@icir.org>
Subject: [MMUSIC] Re: [dccp] Using DCCP for VoIP
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Hi all,

On this issue:

> IMHO this issue is related to my question in the other mail about
> managing audio AND video at the same time: probably DCCP should have a
> way to handle "collectively" a bunch of streams, be it audio plus video
> or two-way audio!

Our thought was that, given DCCP's unreliability, it is trivial to layer
multiple streams on top. The first byte of packet data could indicate
stream number to the application. This works as long as both streams want
to share the same congestion control state + CC mechanism -- is this the
case?

Eddie

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Subject: [MMUSIC] Re: [dccp] natural DCCP sender-side API: (was stream switching)
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>>My assumption is that streaming media apps will normally send at the
>>TFRC rate.
>
>Could it be "at a rate equal or inferior to the TFRC rate"?
>
>What will happen if an application "does not use" the
>bandwidth indicated by TFRC?

OK, my assumption here was that streaming media was coming from disk.
Thus you can always send faster then the receiver is consuming.  This
isn't always true - live broadcast fits in the spectrum between
streaming media and teleconferencing.  But you can do your own
extrapolation - my high level point that the for many apps the TFRC
rate should be treated as a reference rate rather than an absolute
mandate is still the case.

>What would be the point of defining TFRC and then "cheat on it" ?

You have to understand that TFRC is only an approximation.  It
"cheats" on TCP on short timescales.  And at high loss rates, even
different TCP implementations aren't very fair to each other. If the
apps "cheat" on TFRC on shortish timescales, but in such a way that it
generally averages out in the end, then this is very similar to what
TFCR is doing anyway relative to TCP.  Our goals for TFRC were that it
was within a factor of two of TCP's average rate on medium timescales.
Thus it doesn't make sense to argue about an app being (say) 10% over
the TFRC rate on short timescales - the app's constraints are more
important than a small factor of fairness in rate.  What matters is
that no-one loses badly (from a fairness point of view) and that the
goodput through the bottleneck is close to 100% (so we don't want to
encourage unnecessary padding to keep the app's rate up to the TFRC
rate).

Cheers,
	Mark

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Hi - two quick comments from the meeting slides -

On the bandwidth parameter giving the total (all users) bandwidth for =
RTP multiparty conferences: in this case there is some sense, but the =
layering issue is somewhat orthogonal (i.e. is does solve for layering). =
The notion of layered codecs (one or more sources) has some commonality =
to RMT-ALC which enables layering (e.g. over a number of SSM channels). =
So actually describing the layered session (media/content/whatever) =
could be done once for both cases (or many layered cases) and the change =
proposed does not deal with this. With layered deliver, it's important =
that devices understand what is available and their capabilities (e.g. =
for data rates over communications links and for decoding) so the =
minimum bandwidth is more important than "total bandwidth". In any case, =
is it really part of the main SDP spec to include laying descriptors or =
a child spec.? (draft-ietf-mmusic-sdp-bwparam-04.txt)

I think the meeting established SHOULD NOT -> MUST NOT for automatically =
opening interactive sessions (without in-sequence user intervention) is =
not so great unless there is a disclaimer that with pre-authorization =
you may do automatic. I agree, and just one to add that the "no human =
user present" case is also valid and can be served by stating you can do =
automatic with pre-authorization (remote monitoring and auto-answering =
to teleconferences are the obvious use cases I've seen).

Cheers, Rod.

  =
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
    Rod Walsh
    Nokia Research Center
    Tampere, Finland
    +358 50 483 5632
    rod.walsh@nokia.com
  =
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
=20

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From: "Phelan, Tom" <tphelan@sonusnet.com>
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Subject: [MMUSIC] Two-way media with DCCP and TFRC
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Hi,

I've come up with the following scheme for using DCCP/TFRC with two-way
interactive media.  As a reminder, two-way media differs from one-way live
in being very intolerant of delay.  One-way live differs from one-way
pre-recorded in having a maximum transmit rate equal to the encoding rate
(rather than the disk read rate).

The procedure here is a significant departure from current practice.  I
haven't been able to fully digest the system implications of this scheme
yet, but some of them, especially with regard to congestion and call
admission control seem pretty exciting.

Assume that each end of the connection is capable of using a number of
codecs with increasing bandwidth needs, where each step up is less than
twice the rate of the previous step, and that the sender can switch between
them at "low cost" (perhaps a big assumption).  Assume also that DCCP
provides immediate feedback to the application when it changes the computed
sending rate.

To start, the calling part sends an INVITE (loosely using SIP terminology)
indicating the IP address and DCCP port to use for media at its end.
Without informing the called user, the called system responds to the INVITE
by connecting to the media port.  Both end systems then begin exchanging
test data, at the (slowly increasing) rate allowed by TFRC.  The purpose of
this test data is to see what rate the connection can be ramped up to.  If
that rate is less than a minimum acceptable rate, the call is cleared
(conceptually, the calling user hears "fast busy" and the called user is
never informed of the incoming call).  Note that once the rate has ramped up
sufficiently for the highest rate codec there's no need to go further.

If an acceptable rate can be achieved, the called user is informed of the
incoming call.  The test data is continued during this period.  Once the
called user accepts the call, the test data is replaced by real data at the
same rate.

If congestion is encountered during the call, TFRC will reduce its allowed
sending rate.  When that rate falls below the codec currently is use, the
sender switches to a lower rate codec.  If the rate continues to fall the
sender will eventually get to its lowest rate codec.  If the TFRC rate
continues to fall past the lowest rate codec, the sender must discard
packets to conform to that rate.

If the network capacity is sufficient to support one of the lower rate
codecs, eventually the congestion will clear and TFRC will slowly increase
the allowed transmit rate.  Since the application will continue to transmit
at its codec rate, TFRC will limit this increase to at most twice the
current sending rate (my interpretation of the TFRC paper here, I could be
wrong :-)).  This is the reason that the sender must use a codec suite with
rates in steps of less that two times the previous rate.  If the TFRC rate
increases sufficiently for the next codec step, the sender may switch to the
higher rate step.  If the network can't support the new rate, eventually
congestion will reappear and the sender will fall back to the lower rate.
Over time the sender will oscillate between the lower and higher rate with a
period equal to the time it takes TFRC to probe between the two rates.

This procedure doesn't work when silence suppression is in use.  I need to
think about that some more.

Tom P.

_______________________________________________
mmusic mailing list
mmusic@ietf.org
https://www1.ietf.org/mailman/listinfo/mmusic



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Date: Mon, 28 Jul 2003 10:32:24 -0400
From: Henning Schulzrinne <hgs@cs.columbia.edu>
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        "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
Subject: Re: [MMUSIC] Two-way media with DCCP and TFRC
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Like all measurement-based admissions control mechanism (and dozens have 
been proposed...), this one may well introduce unacceptable call setup 
delays. Once the other side has accepted a call, the last thing you want 
is "dead air", even for a few milliseconds (since the 'Hello' will get 
lost, which messes up the human two-way handshake pretty badly).

You have a bit more room prior to ringing, but acceptable post-dial 
delay is probably no more than a second or two for landline phones. If 
you consider that the call may well be an emergency call, you really 
don't want to go probing the network for a few seconds before you 
connect to the PSAP...

I'm not arguing against measurement-based admission control, but 
existing published experience has not been very encouraging, from what I 
can tell.

Henning

Phelan, Tom wrote:

> Hi,
> 
> I've come up with the following scheme for using DCCP/TFRC with two-way
> interactive media.  As a reminder, two-way media differs from one-way live
> in being very intolerant of delay.  One-way live differs from one-way
> pre-recorded in having a maximum transmit rate equal to the encoding rate
> (rather than the disk read rate).
> 
> The procedure here is a significant departure from current practice.  I
> haven't been able to fully digest the system implications of this scheme
> yet, but some of them, especially with regard to congestion and call
> admission control seem pretty exciting.
> 
> Assume that each end of the connection is capable of using a number of
> codecs with increasing bandwidth needs, where each step up is less than
> twice the rate of the previous step, and that the sender can switch between
> them at "low cost" (perhaps a big assumption).  Assume also that DCCP
> provides immediate feedback to the application when it changes the computed
> sending rate.
> 
> To start, the calling part sends an INVITE (loosely using SIP terminology)
> indicating the IP address and DCCP port to use for media at its end.
> Without informing the called user, the called system responds to the INVITE
> by connecting to the media port.  Both end systems then begin exchanging
> test data, at the (slowly increasing) rate allowed by TFRC.  The purpose of
> this test data is to see what rate the connection can be ramped up to.  If
> that rate is less than a minimum acceptable rate, the call is cleared
> (conceptually, the calling user hears "fast busy" and the called user is
> never informed of the incoming call).  Note that once the rate has ramped up
> sufficiently for the highest rate codec there's no need to go further.
> 
> If an acceptable rate can be achieved, the called user is informed of the
> incoming call.  The test data is continued during this period.  Once the
> called user accepts the call, the test data is replaced by real data at the
> same rate.
> 
> If congestion is encountered during the call, TFRC will reduce its allowed
> sending rate.  When that rate falls below the codec currently is use, the
> sender switches to a lower rate codec.  If the rate continues to fall the
> sender will eventually get to its lowest rate codec.  If the TFRC rate
> continues to fall past the lowest rate codec, the sender must discard
> packets to conform to that rate.
> 
> If the network capacity is sufficient to support one of the lower rate
> codecs, eventually the congestion will clear and TFRC will slowly increase
> the allowed transmit rate.  Since the application will continue to transmit
> at its codec rate, TFRC will limit this increase to at most twice the
> current sending rate (my interpretation of the TFRC paper here, I could be
> wrong :-)).  This is the reason that the sender must use a codec suite with
> rates in steps of less that two times the previous rate.  If the TFRC rate
> increases sufficiently for the next codec step, the sender may switch to the
> higher rate step.  If the network can't support the new rate, eventually
> congestion will reappear and the sender will fall back to the lower rate.
> Over time the sender will oscillate between the lower and higher rate with a
> period equal to the time it takes TFRC to probe between the two rates.
> 
> This procedure doesn't work when silence suppression is in use.  I need to
> think about that some more.
> 
> Tom P.
> 
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic


_______________________________________________
mmusic mailing list
mmusic@ietf.org
https://www1.ietf.org/mailman/listinfo/mmusic



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From: "Phelan, Tom" <tphelan@sonusnet.com>
To: "'Henning Schulzrinne'" <hgs@cs.columbia.edu>,
        "Phelan, Tom"
	 <tphelan@sonusnet.com>
Cc: "'dccp@ietf.org'" <dccp@ietf.org>, "'mmusic@ietf.org'"
	 <mmusic@ietf.org>,
        "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
Subject: RE: [MMUSIC] Two-way media with DCCP and TFRC
Date: Mon, 28 Jul 2003 10:40:26 -0400
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Hi Henning,

Yes, I recognize that the post-dial delay problem is a big one.  The big
problem I faced with trying to map two-may media onto DCCP and TFRC was the
TFRC slow-start.  This probing mechanism actually turns it (slow-start) from
a bug to get around into a feature to use.  My understanding of TFRC is
insufficient to tell how long the ramp up will take, but for the bandwidth
needed by voice, it seems like it could be less than a second.

Tom P.

> -----Original Message-----
> From: Henning Schulzrinne [mailto:hgs@cs.columbia.edu]
> Sent: Monday, July 28, 2003 10:32 AM
> To: Phelan, Tom
> Cc: 'dccp@ietf.org'; 'mmusic@ietf.org'; Pasco Anderson, Jay
> Subject: Re: [MMUSIC] Two-way media with DCCP and TFRC
> 
> 
> Like all measurement-based admissions control mechanism (and 
> dozens have 
> been proposed...), this one may well introduce unacceptable 
> call setup 
> delays. Once the other side has accepted a call, the last 
> thing you want 
> is "dead air", even for a few milliseconds (since the 'Hello' 
> will get 
> lost, which messes up the human two-way handshake pretty badly).
> 
> You have a bit more room prior to ringing, but acceptable post-dial 
> delay is probably no more than a second or two for landline 
> phones. If 
> you consider that the call may well be an emergency call, you really 
> don't want to go probing the network for a few seconds before you 
> connect to the PSAP...
> 
> I'm not arguing against measurement-based admission control, but 
> existing published experience has not been very encouraging, 
> from what I 
> can tell.
> 
> Henning
> 
> Phelan, Tom wrote:
> 
> > Hi,
> > 
> > I've come up with the following scheme for using DCCP/TFRC 
> with two-way
> > interactive media.  As a reminder, two-way media differs 
> from one-way live
> > in being very intolerant of delay.  One-way live differs 
> from one-way
> > pre-recorded in having a maximum transmit rate equal to the 
> encoding rate
> > (rather than the disk read rate).
> > 
> > The procedure here is a significant departure from current 
> practice.  I
> > haven't been able to fully digest the system implications 
> of this scheme
> > yet, but some of them, especially with regard to congestion and call
> > admission control seem pretty exciting.
> > 
> > Assume that each end of the connection is capable of using 
> a number of
> > codecs with increasing bandwidth needs, where each step up 
> is less than
> > twice the rate of the previous step, and that the sender 
> can switch between
> > them at "low cost" (perhaps a big assumption).  Assume also 
> that DCCP
> > provides immediate feedback to the application when it 
> changes the computed
> > sending rate.
> > 
> > To start, the calling part sends an INVITE (loosely using 
> SIP terminology)
> > indicating the IP address and DCCP port to use for media at its end.
> > Without informing the called user, the called system 
> responds to the INVITE
> > by connecting to the media port.  Both end systems then 
> begin exchanging
> > test data, at the (slowly increasing) rate allowed by TFRC. 
>  The purpose of
> > this test data is to see what rate the connection can be 
> ramped up to.  If
> > that rate is less than a minimum acceptable rate, the call 
> is cleared
> > (conceptually, the calling user hears "fast busy" and the 
> called user is
> > never informed of the incoming call).  Note that once the 
> rate has ramped up
> > sufficiently for the highest rate codec there's no need to 
> go further.
> > 
> > If an acceptable rate can be achieved, the called user is 
> informed of the
> > incoming call.  The test data is continued during this 
> period.  Once the
> > called user accepts the call, the test data is replaced by 
> real data at the
> > same rate.
> > 
> > If congestion is encountered during the call, TFRC will 
> reduce its allowed
> > sending rate.  When that rate falls below the codec 
> currently is use, the
> > sender switches to a lower rate codec.  If the rate 
> continues to fall the
> > sender will eventually get to its lowest rate codec.  If 
> the TFRC rate
> > continues to fall past the lowest rate codec, the sender 
> must discard
> > packets to conform to that rate.
> > 
> > If the network capacity is sufficient to support one of the 
> lower rate
> > codecs, eventually the congestion will clear and TFRC will 
> slowly increase
> > the allowed transmit rate.  Since the application will 
> continue to transmit
> > at its codec rate, TFRC will limit this increase to at most 
> twice the
> > current sending rate (my interpretation of the TFRC paper 
> here, I could be
> > wrong :-)).  This is the reason that the sender must use a 
> codec suite with
> > rates in steps of less that two times the previous rate.  
> If the TFRC rate
> > increases sufficiently for the next codec step, the sender 
> may switch to the
> > higher rate step.  If the network can't support the new 
> rate, eventually
> > congestion will reappear and the sender will fall back to 
> the lower rate.
> > Over time the sender will oscillate between the lower and 
> higher rate with a
> > period equal to the time it takes TFRC to probe between the 
> two rates.
> > 
> > This procedure doesn't work when silence suppression is in 
> use.  I need to
> > think about that some more.
> > 
> > Tom P.
> > 
> > _______________________________________________
> > mmusic mailing list
> > mmusic@ietf.org
> > https://www1.ietf.org/mailman/listinfo/mmusic
> 

_______________________________________________
mmusic mailing list
mmusic@ietf.org
https://www1.ietf.org/mailman/listinfo/mmusic



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From: "Phelan, Tom" <tphelan@sonusnet.com>
To: "'Henning Schulzrinne'" <hgs@cs.columbia.edu>
Cc: "'dccp@ietf.org'" <dccp@ietf.org>, "'mmusic@ietf.org'"
	 <mmusic@ietf.org>,
        "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
Subject: RE: [dccp] Re: [MMUSIC] Two-way media with DCCP and TFRC
Date: Mon, 28 Jul 2003 16:17:43 -0400
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Hi,

Henning has pointed out a basic problem with the two-way media over DCCP
procedure - the "probe" time must be small enough to meet user expectations
of connect time, probably on the order of magnitude of one second.  Note
that this seems to me to be a fundamental problem with any congestion
control that uses slow-start, not just TFRC.  Whether this can be achieved
with TFRC depends on the details of TFRC slow-start.

As I understand it, TFRC basically starts with an initial rate, and then
doubles it every round-trip time until congestion is encountered.  RFC3448
says that the initial rate is 1 packet/second.  Now I have to admit that one
packet per round-trip time sounds more like TCP's behavior to me, but I'll
go with what the RFC says.  Note that the difference is *very* significant
for two-way voice.  I'd appreciate it if someone had some authoritative
info.

Let's assume that a voice call has a minimum acceptable codec of G.711 with
40ms packetization interval.  That translates to 25 packets/second.  The
TFRC rate will be 1 pkt/sec in the first RTT, 2 in the second, 4 in the
third and so on, reaching 32 pkt/sec in the sixth RTT.  Add two more RTTs
for the initial DCCP connection handshake, and you have 8 RTTs.  If the RTT
is 100ms (on the hairy edge of usable for voice) then you have held up the
connection progress for 800ms.  If the RTT is 20ms the ramp up time is 160ms
- hardly noticeable.

If the minimum codec has a 20ms packetization interval, that doubles the
needed rate, but only adds one round-trip time to the ramp up.

So, the questions are:  Does this analysis hold water?  If it does, are
these connection setup delays acceptable?

Tom P.

> -----Original Message-----
> From: Henning Schulzrinne [mailto:hgs@cs.columbia.edu]
> Sent: Monday, July 28, 2003 10:32 AM
> To: Phelan, Tom
> Cc: 'dccp@ietf.org'; 'mmusic@ietf.org'; Pasco Anderson, Jay
> Subject: [dccp] Re: [MMUSIC] Two-way media with DCCP and TFRC
> 
> 
> Like all measurement-based admissions control mechanism (and 
> dozens have 
> been proposed...), this one may well introduce unacceptable 
> call setup 
> delays. Once the other side has accepted a call, the last 
> thing you want 
> is "dead air", even for a few milliseconds (since the 'Hello' 
> will get 
> lost, which messes up the human two-way handshake pretty badly).
> 
> You have a bit more room prior to ringing, but acceptable post-dial 
> delay is probably no more than a second or two for landline 
> phones. If 
> you consider that the call may well be an emergency call, you really 
> don't want to go probing the network for a few seconds before you 
> connect to the PSAP...
> 
> I'm not arguing against measurement-based admission control, but 
> existing published experience has not been very encouraging, 
> from what I 
> can tell.
> 
> Henning
> 
> Phelan, Tom wrote:
> 
> > Hi,
> > 
> > I've come up with the following scheme for using DCCP/TFRC 
> with two-way
> > interactive media.  As a reminder, two-way media differs 
> from one-way live
> > in being very intolerant of delay.  One-way live differs 
> from one-way
> > pre-recorded in having a maximum transmit rate equal to the 
> encoding rate
> > (rather than the disk read rate).
> > 
> > The procedure here is a significant departure from current 
> practice.  I
> > haven't been able to fully digest the system implications 
> of this scheme
> > yet, but some of them, especially with regard to congestion and call
> > admission control seem pretty exciting.
> > 
> > Assume that each end of the connection is capable of using 
> a number of
> > codecs with increasing bandwidth needs, where each step up 
> is less than
> > twice the rate of the previous step, and that the sender 
> can switch between
> > them at "low cost" (perhaps a big assumption).  Assume also 
> that DCCP
> > provides immediate feedback to the application when it 
> changes the computed
> > sending rate.
> > 
> > To start, the calling part sends an INVITE (loosely using 
> SIP terminology)
> > indicating the IP address and DCCP port to use for media at its end.
> > Without informing the called user, the called system 
> responds to the INVITE
> > by connecting to the media port.  Both end systems then 
> begin exchanging
> > test data, at the (slowly increasing) rate allowed by TFRC. 
>  The purpose of
> > this test data is to see what rate the connection can be 
> ramped up to.  If
> > that rate is less than a minimum acceptable rate, the call 
> is cleared
> > (conceptually, the calling user hears "fast busy" and the 
> called user is
> > never informed of the incoming call).  Note that once the 
> rate has ramped up
> > sufficiently for the highest rate codec there's no need to 
> go further.
> > 
> > If an acceptable rate can be achieved, the called user is 
> informed of the
> > incoming call.  The test data is continued during this 
> period.  Once the
> > called user accepts the call, the test data is replaced by 
> real data at the
> > same rate.
> > 
> > If congestion is encountered during the call, TFRC will 
> reduce its allowed
> > sending rate.  When that rate falls below the codec 
> currently is use, the
> > sender switches to a lower rate codec.  If the rate 
> continues to fall the
> > sender will eventually get to its lowest rate codec.  If 
> the TFRC rate
> > continues to fall past the lowest rate codec, the sender 
> must discard
> > packets to conform to that rate.
> > 
> > If the network capacity is sufficient to support one of the 
> lower rate
> > codecs, eventually the congestion will clear and TFRC will 
> slowly increase
> > the allowed transmit rate.  Since the application will 
> continue to transmit
> > at its codec rate, TFRC will limit this increase to at most 
> twice the
> > current sending rate (my interpretation of the TFRC paper 
> here, I could be
> > wrong :-)).  This is the reason that the sender must use a 
> codec suite with
> > rates in steps of less that two times the previous rate.  
> If the TFRC rate
> > increases sufficiently for the next codec step, the sender 
> may switch to the
> > higher rate step.  If the network can't support the new 
> rate, eventually
> > congestion will reappear and the sender will fall back to 
> the lower rate.
> > Over time the sender will oscillate between the lower and 
> higher rate with a
> > period equal to the time it takes TFRC to probe between the 
> two rates.
> > 
> > This procedure doesn't work when silence suppression is in 
> use.  I need to
> > think about that some more.
> > 
> > Tom P.
> > 
> > _______________________________________________
> > mmusic mailing list
> > mmusic@ietf.org
> > https://www1.ietf.org/mailman/listinfo/mmusic
> 
> 
> _______________________________________________
> dccp IETF mailing list: dccp@ietf.org
> list info:  https://www1.ietf.org/mailman/listinfo/dccp
> wg charter: http://www.ietf.org/html.charters/dccp-charter.html
> 

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Date: Mon, 28 Jul 2003 16:23:53 -0400
From: Henning Schulzrinne <hgs@cs.columbia.edu>
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        "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
Subject: Re: [dccp] Re: [MMUSIC] Two-way media with DCCP and TFRC
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Phelan, Tom wrote:
What happens if only one of these packets gets lost?


> Hi,
> 
> Henning has pointed out a basic problem with the two-way media over DCCP
> procedure - the "probe" time must be small enough to meet user expectations
> of connect time, probably on the order of magnitude of one second.  Note
> that this seems to me to be a fundamental problem with any congestion
> control that uses slow-start, not just TFRC.  Whether this can be achieved
> with TFRC depends on the details of TFRC slow-start.
> 
> As I understand it, TFRC basically starts with an initial rate, and then
> doubles it every round-trip time until congestion is encountered.  RFC3448
> says that the initial rate is 1 packet/second.  Now I have to admit that one
> packet per round-trip time sounds more like TCP's behavior to me, but I'll
> go with what the RFC says.  Note that the difference is *very* significant
> for two-way voice.  I'd appreciate it if someone had some authoritative
> info.
> 
> Let's assume that a voice call has a minimum acceptable codec of G.711 with
> 40ms packetization interval.  That translates to 25 packets/second.  The
> TFRC rate will be 1 pkt/sec in the first RTT, 2 in the second, 4 in the
> third and so on, reaching 32 pkt/sec in the sixth RTT.  Add two more RTTs
> for the initial DCCP connection handshake, and you have 8 RTTs.  If the RTT
> is 100ms (on the hairy edge of usable for voice) then you have held up the
> connection progress for 800ms.  If the RTT is 20ms the ramp up time is 160ms
> - hardly noticeable.
> 
> If the minimum codec has a 20ms packetization interval, that doubles the
> needed rate, but only adds one round-trip time to the ramp up.
> 
> So, the questions are:  Does this analysis hold water?  If it does, are
> these connection setup delays acceptable?



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Cc: "'dccp@ietf.org'" <dccp@ietf.org>, "'mmusic@ietf.org'"
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Subject: RE: [dccp] Re: [MMUSIC] Two-way media with DCCP and TFRC
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Hi Henning,

> What happens if only one of these packets gets lost?

Slow-start stops and the next rate is half of the current rate (if any
packets are lost).

Tom P.

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Subject: Re: [MMUSIC] Two-way media with DCCP and TFRC
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This kind of scheme might work for video. I have seen interactive 
video applications which tell the user that the video is being 
prepared, after call setup. It is OK if that takes a few seconds to 
do. However, VoIP is quite different, and there are some further 
issues there.

Firstly, as Brian has pointed out, rate adaptive codecs for VoIP are 
very rare. Practically speaking, nearly all commercial VoIP phones use 
single rate codecs. Many can support multiple codecs. However, 
frequently, once a codec is selected, it cannot be changed easily 
during the call. This is commonly the case for hardware phones, where 
I believe the codecs are stored in flash and downloaded into RAM once 
a codec is selected in the call. We have had a lot of folks ask how, 
in SIP, to signal that the called party has to pick one of the N 
offered codecs, and then stick to it. RFC 3264 describes means for 
doing that.

Such a phone would not permit rate adaptivity by switching codecs as 
you describe below. Thus, it would be all or nothing in terms of 
sending rate.

Even assuming there was rate adaptivity for voice, there are 
perceptual issues when the encoding is frequently changed. It is 
apparently more annoying for users to oscillate between high and low 
rate codecs, than to stay constant with a medium rate codec. I seem to 
recall some studies along these lines in the late 90s by Jean Bolot 
and his students, though I cannot find the specific reference.

-Jonathan R.

Phelan, Tom wrote:

> Hi,
> 
> I've come up with the following scheme for using DCCP/TFRC with two-way
> interactive media.  As a reminder, two-way media differs from one-way live
> in being very intolerant of delay.  One-way live differs from one-way
> pre-recorded in having a maximum transmit rate equal to the encoding rate
> (rather than the disk read rate).
> 
> The procedure here is a significant departure from current practice.  I
> haven't been able to fully digest the system implications of this scheme
> yet, but some of them, especially with regard to congestion and call
> admission control seem pretty exciting.
> 
> Assume that each end of the connection is capable of using a number of
> codecs with increasing bandwidth needs, where each step up is less than
> twice the rate of the previous step, and that the sender can switch between
> them at "low cost" (perhaps a big assumption).  Assume also that DCCP
> provides immediate feedback to the application when it changes the computed
> sending rate.
> 
> To start, the calling part sends an INVITE (loosely using SIP terminology)
> indicating the IP address and DCCP port to use for media at its end.
> Without informing the called user, the called system responds to the INVITE
> by connecting to the media port.  Both end systems then begin exchanging
> test data, at the (slowly increasing) rate allowed by TFRC.  The purpose of
> this test data is to see what rate the connection can be ramped up to.  If
> that rate is less than a minimum acceptable rate, the call is cleared
> (conceptually, the calling user hears "fast busy" and the called user is
> never informed of the incoming call).  Note that once the rate has ramped up
> sufficiently for the highest rate codec there's no need to go further.
> 
> If an acceptable rate can be achieved, the called user is informed of the
> incoming call.  The test data is continued during this period.  Once the
> called user accepts the call, the test data is replaced by real data at the
> same rate.
> 
> If congestion is encountered during the call, TFRC will reduce its allowed
> sending rate.  When that rate falls below the codec currently is use, the
> sender switches to a lower rate codec.  If the rate continues to fall the
> sender will eventually get to its lowest rate codec.  If the TFRC rate
> continues to fall past the lowest rate codec, the sender must discard
> packets to conform to that rate.
> 
> If the network capacity is sufficient to support one of the lower rate
> codecs, eventually the congestion will clear and TFRC will slowly increase
> the allowed transmit rate.  Since the application will continue to transmit
> at its codec rate, TFRC will limit this increase to at most twice the
> current sending rate (my interpretation of the TFRC paper here, I could be
> wrong :-)).  This is the reason that the sender must use a codec suite with
> rates in steps of less that two times the previous rate.  If the TFRC rate
> increases sufficiently for the next codec step, the sender may switch to the
> higher rate step.  If the network can't support the new rate, eventually
> congestion will reappear and the sender will fall back to the lower rate.
> Over time the sender will oscillate between the lower and higher rate with a
> period equal to the time it takes TFRC to probe between the two rates.
> 
> This procedure doesn't work when silence suppression is in use.  I need to
> think about that some more.
> 
> Tom P.
> 
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic
> 

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com


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To: Eddie Kohler <kohler@icir.org>
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Subject: Re: [MMUSIC] Packet drop API / what happens with packet drops now?
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Eddie,

It is really quite a bit worse to through away the packet at the 
sender, as opposed to informing the application and having it respond 
by ceasing transmission or lowering its rate. The difference has to do 
with error propagation that result from compression algorithms. The 
loss of a single packet causes reconstruction errors in the decoder, 
which propagate into subsequent audio frames or video macroblocks. The 
lower the rate, the longer these artifacts persist. If the sender 
knows that it cannot send, it is much better to back off in a way that 
does not result in a desynchronization of encoder and decoder state.

Indeed, I performed some studies to look at this phenomenon as part of 
my dissertation work. For G.729 (an 8kbps audio codec), I found that 
it was much more useful to keep the the state of the encoder and 
decoder synchronized than it was to faithfully reconstruct the speech 
content of a lost frame, due to this error propagation. The results, 
if you are interested, are described in:

http://www.jdrosen.net/e6880/index.html

-Jonathan R.

Eddie Kohler wrote:

> What happens in currently-deployed codecs when packets are dropped?
> 
> Clearly codecs, and VoIP in particular, can handle loss. Possibly even high
> loss rates. One way to think about DCCP's allowed sending rate is that it
> moves drops that *would* have happened in the network *anyway*, into the
> sending host. (Although DCCP will generally drop more than the network
> would have, to ensure fairness, and because of congestion-control
> infelicities that we want to fix.) So how disastrous are these drops?
> 
> Another way to put this: A DCCP API might never block -- or it might block
> for at most T seconds. Instead, writing a packet into a full send buffer
> would drop that packet; or it might drop an older packet---a drop-from-head
> send buffer; or it might drop the oldest packet with lowest priority
> annotation.
> 
> Now the app simply sees a loss rate, which DCCP will happily report. For
> codec switching, you can simply switch when the loss rate is intolerably
> high -- which you would have had to do anyway.
> 
> How horrible would this be?
> 
> Eddie
> 
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic
> 

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
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Hi Magnus

-bwparam-04 is an excellent document - thanks for doing the hard work!

The ID allows TIAS to be less than the sum of the total bandwidth as =
media bandwdith may vary diferently (makes sense). Also, this feature =
can be useful for when an application specifically expects/requires that =
all the media will not be used. Such as in a "internationalised TV =
program" - e.g. a single video stream and 2 audio streams of different =
languages to end-receivers required to decode only 1 video and 1 audio =
stream. In my eyes, this works without any changes at all to the ID =
(there's no need to explicitly mention this use case). However, I'd be =
interested to know if you see that there are any problems in this usage?

I also spotted one trivial typo - first word, last paragraph, section =
6.3 - missing "

I don't think either of these should have an effect last call since the =
ID is already so mature.

Cheers, Rod.


> -----Original Message-----
> From: ext Colin Perkins [mailto:csp@csperkins.org]
> Sent: Thursday, July 17, 2003 9:01 PM
> To: mmusic@ietf.org
> Cc: jo@tzi.uni-bremen.de
> Subject: [MMUSIC] WG Last call: draft-ietf-mmusic-sdp-bwparam-04.txt
>=20
>=20
> As announced in the MMUSIC session this morning, the SDP bandwidth
> parameters draft is now in working group last call. Please=20
> send any final
> comments on this draft to the mailing list by 28th July. If=20
> no substantive
> comments are received by that time, we propose to submit this=20
> draft to the
> IESG for publication as a proposed standard RFC.
>=20
> --=20
> Colin Perkins
> csp@csperkins.org
>=20
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic
>=20

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From: "Phelan, Tom" <tphelan@sonusnet.com>
To: "'Jonathan Rosenberg'" <jdrosen@dynamicsoft.com>
Cc: "'dccp@ietf.org'" <dccp@ietf.org>, "'mmusic@ietf.org'"
	 <mmusic@ietf.org>,
        "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
Subject: RE: [MMUSIC] Two-way media with DCCP and TFRC
Date: Wed, 30 Jul 2003 08:32:18 -0400
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Hi Jonathon,

I agree that the assumption of multiple codecs for a single session is an
enormous leap of faith.  Given the difficulties you talk about, it would
appear that you think end-to-end congestion control like what's described in
draft-iab-congestion-00.txt isn't practical.  Do you have any other comments
on that draft?

Tom P.

> -----Original Message-----
> From: Jonathan Rosenberg [mailto:jdrosen@dynamicsoft.com]
> Sent: Tuesday, July 29, 2003 1:38 AM
> To: Phelan, Tom
> Cc: 'dccp@ietf.org'; 'mmusic@ietf.org'; Pasco Anderson, Jay
> Subject: Re: [MMUSIC] Two-way media with DCCP and TFRC
> 
> 
> This kind of scheme might work for video. I have seen interactive 
> video applications which tell the user that the video is being 
> prepared, after call setup. It is OK if that takes a few seconds to 
> do. However, VoIP is quite different, and there are some further 
> issues there.
> 
> Firstly, as Brian has pointed out, rate adaptive codecs for VoIP are 
> very rare. Practically speaking, nearly all commercial VoIP 
> phones use 
> single rate codecs. Many can support multiple codecs. However, 
> frequently, once a codec is selected, it cannot be changed easily 
> during the call. This is commonly the case for hardware phones, where 
> I believe the codecs are stored in flash and downloaded into RAM once 
> a codec is selected in the call. We have had a lot of folks ask how, 
> in SIP, to signal that the called party has to pick one of the N 
> offered codecs, and then stick to it. RFC 3264 describes means for 
> doing that.
> 
> Such a phone would not permit rate adaptivity by switching codecs as 
> you describe below. Thus, it would be all or nothing in terms of 
> sending rate.
> 
> Even assuming there was rate adaptivity for voice, there are 
> perceptual issues when the encoding is frequently changed. It is 
> apparently more annoying for users to oscillate between high and low 
> rate codecs, than to stay constant with a medium rate codec. 
> I seem to 
> recall some studies along these lines in the late 90s by Jean Bolot 
> and his students, though I cannot find the specific reference.
> 
> -Jonathan R.
> 
> Phelan, Tom wrote:
> 
> > Hi,
> > 
> > I've come up with the following scheme for using DCCP/TFRC 
> with two-way
> > interactive media.  As a reminder, two-way media differs 
> from one-way live
> > in being very intolerant of delay.  One-way live differs 
> from one-way
> > pre-recorded in having a maximum transmit rate equal to the 
> encoding rate
> > (rather than the disk read rate).
> > 
> > The procedure here is a significant departure from current 
> practice.  I
> > haven't been able to fully digest the system implications 
> of this scheme
> > yet, but some of them, especially with regard to congestion and call
> > admission control seem pretty exciting.
> > 
> > Assume that each end of the connection is capable of using 
> a number of
> > codecs with increasing bandwidth needs, where each step up 
> is less than
> > twice the rate of the previous step, and that the sender 
> can switch between
> > them at "low cost" (perhaps a big assumption).  Assume also 
> that DCCP
> > provides immediate feedback to the application when it 
> changes the computed
> > sending rate.
> > 
> > To start, the calling part sends an INVITE (loosely using 
> SIP terminology)
> > indicating the IP address and DCCP port to use for media at its end.
> > Without informing the called user, the called system 
> responds to the INVITE
> > by connecting to the media port.  Both end systems then 
> begin exchanging
> > test data, at the (slowly increasing) rate allowed by TFRC. 
>  The purpose of
> > this test data is to see what rate the connection can be 
> ramped up to.  If
> > that rate is less than a minimum acceptable rate, the call 
> is cleared
> > (conceptually, the calling user hears "fast busy" and the 
> called user is
> > never informed of the incoming call).  Note that once the 
> rate has ramped up
> > sufficiently for the highest rate codec there's no need to 
> go further.
> > 
> > If an acceptable rate can be achieved, the called user is 
> informed of the
> > incoming call.  The test data is continued during this 
> period.  Once the
> > called user accepts the call, the test data is replaced by 
> real data at the
> > same rate.
> > 
> > If congestion is encountered during the call, TFRC will 
> reduce its allowed
> > sending rate.  When that rate falls below the codec 
> currently is use, the
> > sender switches to a lower rate codec.  If the rate 
> continues to fall the
> > sender will eventually get to its lowest rate codec.  If 
> the TFRC rate
> > continues to fall past the lowest rate codec, the sender 
> must discard
> > packets to conform to that rate.
> > 
> > If the network capacity is sufficient to support one of the 
> lower rate
> > codecs, eventually the congestion will clear and TFRC will 
> slowly increase
> > the allowed transmit rate.  Since the application will 
> continue to transmit
> > at its codec rate, TFRC will limit this increase to at most 
> twice the
> > current sending rate (my interpretation of the TFRC paper 
> here, I could be
> > wrong :-)).  This is the reason that the sender must use a 
> codec suite with
> > rates in steps of less that two times the previous rate.  
> If the TFRC rate
> > increases sufficiently for the next codec step, the sender 
> may switch to the
> > higher rate step.  If the network can't support the new 
> rate, eventually
> > congestion will reappear and the sender will fall back to 
> the lower rate.
> > Over time the sender will oscillate between the lower and 
> higher rate with a
> > period equal to the time it takes TFRC to probe between the 
> two rates.
> > 
> > This procedure doesn't work when silence suppression is in 
> use.  I need to
> > think about that some more.
> > 
> > Tom P.
> > 
> > _______________________________________________
> > mmusic mailing list
> > mmusic@ietf.org
> > https://www1.ietf.org/mailman/listinfo/mmusic
> > 
> 
> -- 
> Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
> Chief Technology Officer                    Parsippany, NJ 07054-2711
> dynamicsoft
> jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
> http://www.jdrosen.net                      PHONE: (973) 952-5000
> http://www.dynamicsoft.com
> 

_______________________________________________
mmusic mailing list
mmusic@ietf.org
https://www1.ietf.org/mailman/listinfo/mmusic



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Date: Wed, 30 Jul 2003 11:39:43 -0400
From: Jonathan Rosenberg <jdrosen@dynamicsoft.com>
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        "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
Subject: Re: [MMUSIC] Two-way media with DCCP and TFRC
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My take on draft-iab-congestion is that, for voip, what the draft 
effectively implies is that you will send at your specific 
codec-defined rate, and then when congestion hits the defined 
percentage, stop. That is, there will be a binary choice of either 
sending or not, as opposed to a continuum of rates.

I dont think that this is a bad thing, but does mean that the 
threshold loss rate is incredibly important. The current draft talks 
about relatively high loss rates, ones where the voice quality is 
probably already unacceptable. However, it is my understanding that 
these rates are very sensitive to the assumed TCP parameters, and that 
they could be quite a bit lower if computed differently.

-Jonathan R.

Phelan, Tom wrote:

> Hi Jonathon,
> 
> I agree that the assumption of multiple codecs for a single session is an
> enormous leap of faith.  Given the difficulties you talk about, it would
> appear that you think end-to-end congestion control like what's described in
> draft-iab-congestion-00.txt isn't practical.  Do you have any other comments
> on that draft?
> 
> Tom P.
> 
> 
>>-----Original Message-----
>>From: Jonathan Rosenberg [mailto:jdrosen@dynamicsoft.com]
>>Sent: Tuesday, July 29, 2003 1:38 AM
>>To: Phelan, Tom
>>Cc: 'dccp@ietf.org'; 'mmusic@ietf.org'; Pasco Anderson, Jay
>>Subject: Re: [MMUSIC] Two-way media with DCCP and TFRC
>>
>>
>>This kind of scheme might work for video. I have seen interactive 
>>video applications which tell the user that the video is being 
>>prepared, after call setup. It is OK if that takes a few seconds to 
>>do. However, VoIP is quite different, and there are some further 
>>issues there.
>>
>>Firstly, as Brian has pointed out, rate adaptive codecs for VoIP are 
>>very rare. Practically speaking, nearly all commercial VoIP 
>>phones use 
>>single rate codecs. Many can support multiple codecs. However, 
>>frequently, once a codec is selected, it cannot be changed easily 
>>during the call. This is commonly the case for hardware phones, where 
>>I believe the codecs are stored in flash and downloaded into RAM once 
>>a codec is selected in the call. We have had a lot of folks ask how, 
>>in SIP, to signal that the called party has to pick one of the N 
>>offered codecs, and then stick to it. RFC 3264 describes means for 
>>doing that.
>>
>>Such a phone would not permit rate adaptivity by switching codecs as 
>>you describe below. Thus, it would be all or nothing in terms of 
>>sending rate.
>>
>>Even assuming there was rate adaptivity for voice, there are 
>>perceptual issues when the encoding is frequently changed. It is 
>>apparently more annoying for users to oscillate between high and low 
>>rate codecs, than to stay constant with a medium rate codec. 
>>I seem to 
>>recall some studies along these lines in the late 90s by Jean Bolot 
>>and his students, though I cannot find the specific reference.
>>
>>-Jonathan R.
>>
>>Phelan, Tom wrote:
>>
>>
>>>Hi,
>>>
>>>I've come up with the following scheme for using DCCP/TFRC 
>>
>>with two-way
>>
>>>interactive media.  As a reminder, two-way media differs 
>>
>>from one-way live
>>
>>>in being very intolerant of delay.  One-way live differs 
>>
>>from one-way
>>
>>>pre-recorded in having a maximum transmit rate equal to the 
>>
>>encoding rate
>>
>>>(rather than the disk read rate).
>>>
>>>The procedure here is a significant departure from current 
>>
>>practice.  I
>>
>>>haven't been able to fully digest the system implications 
>>
>>of this scheme
>>
>>>yet, but some of them, especially with regard to congestion and call
>>>admission control seem pretty exciting.
>>>
>>>Assume that each end of the connection is capable of using 
>>
>>a number of
>>
>>>codecs with increasing bandwidth needs, where each step up 
>>
>>is less than
>>
>>>twice the rate of the previous step, and that the sender 
>>
>>can switch between
>>
>>>them at "low cost" (perhaps a big assumption).  Assume also 
>>
>>that DCCP
>>
>>>provides immediate feedback to the application when it 
>>
>>changes the computed
>>
>>>sending rate.
>>>
>>>To start, the calling part sends an INVITE (loosely using 
>>
>>SIP terminology)
>>
>>>indicating the IP address and DCCP port to use for media at its end.
>>>Without informing the called user, the called system 
>>
>>responds to the INVITE
>>
>>>by connecting to the media port.  Both end systems then 
>>
>>begin exchanging
>>
>>>test data, at the (slowly increasing) rate allowed by TFRC. 
>>
>> The purpose of
>>
>>>this test data is to see what rate the connection can be 
>>
>>ramped up to.  If
>>
>>>that rate is less than a minimum acceptable rate, the call 
>>
>>is cleared
>>
>>>(conceptually, the calling user hears "fast busy" and the 
>>
>>called user is
>>
>>>never informed of the incoming call).  Note that once the 
>>
>>rate has ramped up
>>
>>>sufficiently for the highest rate codec there's no need to 
>>
>>go further.
>>
>>>If an acceptable rate can be achieved, the called user is 
>>
>>informed of the
>>
>>>incoming call.  The test data is continued during this 
>>
>>period.  Once the
>>
>>>called user accepts the call, the test data is replaced by 
>>
>>real data at the
>>
>>>same rate.
>>>
>>>If congestion is encountered during the call, TFRC will 
>>
>>reduce its allowed
>>
>>>sending rate.  When that rate falls below the codec 
>>
>>currently is use, the
>>
>>>sender switches to a lower rate codec.  If the rate 
>>
>>continues to fall the
>>
>>>sender will eventually get to its lowest rate codec.  If 
>>
>>the TFRC rate
>>
>>>continues to fall past the lowest rate codec, the sender 
>>
>>must discard
>>
>>>packets to conform to that rate.
>>>
>>>If the network capacity is sufficient to support one of the 
>>
>>lower rate
>>
>>>codecs, eventually the congestion will clear and TFRC will 
>>
>>slowly increase
>>
>>>the allowed transmit rate.  Since the application will 
>>
>>continue to transmit
>>
>>>at its codec rate, TFRC will limit this increase to at most 
>>
>>twice the
>>
>>>current sending rate (my interpretation of the TFRC paper 
>>
>>here, I could be
>>
>>>wrong :-)).  This is the reason that the sender must use a 
>>
>>codec suite with
>>
>>>rates in steps of less that two times the previous rate.  
>>
>>If the TFRC rate
>>
>>>increases sufficiently for the next codec step, the sender 
>>
>>may switch to the
>>
>>>higher rate step.  If the network can't support the new 
>>
>>rate, eventually
>>
>>>congestion will reappear and the sender will fall back to 
>>
>>the lower rate.
>>
>>>Over time the sender will oscillate between the lower and 
>>
>>higher rate with a
>>
>>>period equal to the time it takes TFRC to probe between the 
>>
>>two rates.
>>
>>>This procedure doesn't work when silence suppression is in 
>>
>>use.  I need to
>>
>>>think about that some more.
>>>
>>>Tom P.
>>>
>>>_______________________________________________
>>>mmusic mailing list
>>>mmusic@ietf.org
>>>https://www1.ietf.org/mailman/listinfo/mmusic
>>>
>>
>>-- 
>>Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
>>Chief Technology Officer                    Parsippany, NJ 07054-2711
>>dynamicsoft
>>jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
>>http://www.jdrosen.net                      PHONE: (973) 952-5000
>>http://www.dynamicsoft.com
>>
> 
> 

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com


_______________________________________________
mmusic mailing list
mmusic@ietf.org
https://www1.ietf.org/mailman/listinfo/mmusic



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From: "Phelan, Tom" <tphelan@sonusnet.com>
To: "'Jonathan Rosenberg'" <jdrosen@dynamicsoft.com>,
        "Phelan, Tom"
	 <tphelan@sonusnet.com>
Cc: "'dccp@ietf.org'" <dccp@ietf.org>, "'mmusic@ietf.org'"
	 <mmusic@ietf.org>,
        "Pasco Anderson, Jay" <jpanderson@sonusnet.com>
Subject: RE: [MMUSIC] Two-way media with DCCP and TFRC
Date: Wed, 30 Jul 2003 13:40:28 -0400
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Hi Jonathan,

Yes, that seems reasonable.  If we can forget the slow-start issues with the
procedure I proposed, it can help in the high-loss situation Sally
describes.  As the procedure says, once the TFRC rate drops below the
minimum acceptable rate (which will be your only rate), you discard packets
at the sender to conform to the TFRC rate.  If you're discarding at sender
to conform to the TFRC rate, as opposed to discarding in the network, I
think you can continue to send and be fair to TCP, regardless of the local
and network loss rates.

It also seems to me that if you aren't pumping way to many packets into a
congested situation, you might actually be able to get more packets through.

Tom P.

> -----Original Message-----
> From: Jonathan Rosenberg [mailto:jdrosen@dynamicsoft.com]
> Sent: Wednesday, July 30, 2003 11:40 AM
> To: Phelan, Tom
> Cc: 'dccp@ietf.org'; 'mmusic@ietf.org'; Pasco Anderson, Jay
> Subject: Re: [MMUSIC] Two-way media with DCCP and TFRC
> 
> 
> My take on draft-iab-congestion is that, for voip, what the draft 
> effectively implies is that you will send at your specific 
> codec-defined rate, and then when congestion hits the defined 
> percentage, stop. That is, there will be a binary choice of either 
> sending or not, as opposed to a continuum of rates.
> 
> I dont think that this is a bad thing, but does mean that the 
> threshold loss rate is incredibly important. The current draft talks 
> about relatively high loss rates, ones where the voice quality is 
> probably already unacceptable. However, it is my understanding that 
> these rates are very sensitive to the assumed TCP parameters, 
> and that 
> they could be quite a bit lower if computed differently.
> 
> -Jonathan R.
> 
> Phelan, Tom wrote:
> 
> > Hi Jonathon,
> > 
> > I agree that the assumption of multiple codecs for a single 
> session is an
> > enormous leap of faith.  Given the difficulties you talk 
> about, it would
> > appear that you think end-to-end congestion control like 
> what's described in
> > draft-iab-congestion-00.txt isn't practical.  Do you have 
> any other comments
> > on that draft?
> > 
> > Tom P.
> > 
> > 
> >>-----Original Message-----
> >>From: Jonathan Rosenberg [mailto:jdrosen@dynamicsoft.com]
> >>Sent: Tuesday, July 29, 2003 1:38 AM
> >>To: Phelan, Tom
> >>Cc: 'dccp@ietf.org'; 'mmusic@ietf.org'; Pasco Anderson, Jay
> >>Subject: Re: [MMUSIC] Two-way media with DCCP and TFRC
> >>
> >>
> >>This kind of scheme might work for video. I have seen interactive 
> >>video applications which tell the user that the video is being 
> >>prepared, after call setup. It is OK if that takes a few seconds to 
> >>do. However, VoIP is quite different, and there are some further 
> >>issues there.
> >>
> >>Firstly, as Brian has pointed out, rate adaptive codecs for 
> VoIP are 
> >>very rare. Practically speaking, nearly all commercial VoIP 
> >>phones use 
> >>single rate codecs. Many can support multiple codecs. However, 
> >>frequently, once a codec is selected, it cannot be changed easily 
> >>during the call. This is commonly the case for hardware 
> phones, where 
> >>I believe the codecs are stored in flash and downloaded 
> into RAM once 
> >>a codec is selected in the call. We have had a lot of folks 
> ask how, 
> >>in SIP, to signal that the called party has to pick one of the N 
> >>offered codecs, and then stick to it. RFC 3264 describes means for 
> >>doing that.
> >>
> >>Such a phone would not permit rate adaptivity by switching 
> codecs as 
> >>you describe below. Thus, it would be all or nothing in terms of 
> >>sending rate.
> >>
> >>Even assuming there was rate adaptivity for voice, there are 
> >>perceptual issues when the encoding is frequently changed. It is 
> >>apparently more annoying for users to oscillate between 
> high and low 
> >>rate codecs, than to stay constant with a medium rate codec. 
> >>I seem to 
> >>recall some studies along these lines in the late 90s by Jean Bolot 
> >>and his students, though I cannot find the specific reference.
> >>
> >>-Jonathan R.
> >>
> >>Phelan, Tom wrote:
> >>
> >>
> >>>Hi,
> >>>
> >>>I've come up with the following scheme for using DCCP/TFRC 
> >>
> >>with two-way
> >>
> >>>interactive media.  As a reminder, two-way media differs 
> >>
> >>from one-way live
> >>
> >>>in being very intolerant of delay.  One-way live differs 
> >>
> >>from one-way
> >>
> >>>pre-recorded in having a maximum transmit rate equal to the 
> >>
> >>encoding rate
> >>
> >>>(rather than the disk read rate).
> >>>
> >>>The procedure here is a significant departure from current 
> >>
> >>practice.  I
> >>
> >>>haven't been able to fully digest the system implications 
> >>
> >>of this scheme
> >>
> >>>yet, but some of them, especially with regard to 
> congestion and call
> >>>admission control seem pretty exciting.
> >>>
> >>>Assume that each end of the connection is capable of using 
> >>
> >>a number of
> >>
> >>>codecs with increasing bandwidth needs, where each step up 
> >>
> >>is less than
> >>
> >>>twice the rate of the previous step, and that the sender 
> >>
> >>can switch between
> >>
> >>>them at "low cost" (perhaps a big assumption).  Assume also 
> >>
> >>that DCCP
> >>
> >>>provides immediate feedback to the application when it 
> >>
> >>changes the computed
> >>
> >>>sending rate.
> >>>
> >>>To start, the calling part sends an INVITE (loosely using 
> >>
> >>SIP terminology)
> >>
> >>>indicating the IP address and DCCP port to use for media 
> at its end.
> >>>Without informing the called user, the called system 
> >>
> >>responds to the INVITE
> >>
> >>>by connecting to the media port.  Both end systems then 
> >>
> >>begin exchanging
> >>
> >>>test data, at the (slowly increasing) rate allowed by TFRC. 
> >>
> >> The purpose of
> >>
> >>>this test data is to see what rate the connection can be 
> >>
> >>ramped up to.  If
> >>
> >>>that rate is less than a minimum acceptable rate, the call 
> >>
> >>is cleared
> >>
> >>>(conceptually, the calling user hears "fast busy" and the 
> >>
> >>called user is
> >>
> >>>never informed of the incoming call).  Note that once the 
> >>
> >>rate has ramped up
> >>
> >>>sufficiently for the highest rate codec there's no need to 
> >>
> >>go further.
> >>
> >>>If an acceptable rate can be achieved, the called user is 
> >>
> >>informed of the
> >>
> >>>incoming call.  The test data is continued during this 
> >>
> >>period.  Once the
> >>
> >>>called user accepts the call, the test data is replaced by 
> >>
> >>real data at the
> >>
> >>>same rate.
> >>>
> >>>If congestion is encountered during the call, TFRC will 
> >>
> >>reduce its allowed
> >>
> >>>sending rate.  When that rate falls below the codec 
> >>
> >>currently is use, the
> >>
> >>>sender switches to a lower rate codec.  If the rate 
> >>
> >>continues to fall the
> >>
> >>>sender will eventually get to its lowest rate codec.  If 
> >>
> >>the TFRC rate
> >>
> >>>continues to fall past the lowest rate codec, the sender 
> >>
> >>must discard
> >>
> >>>packets to conform to that rate.
> >>>
> >>>If the network capacity is sufficient to support one of the 
> >>
> >>lower rate
> >>
> >>>codecs, eventually the congestion will clear and TFRC will 
> >>
> >>slowly increase
> >>
> >>>the allowed transmit rate.  Since the application will 
> >>
> >>continue to transmit
> >>
> >>>at its codec rate, TFRC will limit this increase to at most 
> >>
> >>twice the
> >>
> >>>current sending rate (my interpretation of the TFRC paper 
> >>
> >>here, I could be
> >>
> >>>wrong :-)).  This is the reason that the sender must use a 
> >>
> >>codec suite with
> >>
> >>>rates in steps of less that two times the previous rate.  
> >>
> >>If the TFRC rate
> >>
> >>>increases sufficiently for the next codec step, the sender 
> >>
> >>may switch to the
> >>
> >>>higher rate step.  If the network can't support the new 
> >>
> >>rate, eventually
> >>
> >>>congestion will reappear and the sender will fall back to 
> >>
> >>the lower rate.
> >>
> >>>Over time the sender will oscillate between the lower and 
> >>
> >>higher rate with a
> >>
> >>>period equal to the time it takes TFRC to probe between the 
> >>
> >>two rates.
> >>
> >>>This procedure doesn't work when silence suppression is in 
> >>
> >>use.  I need to
> >>
> >>>think about that some more.
> >>>
> >>>Tom P.
> >>>
> >>>_______________________________________________
> >>>mmusic mailing list
> >>>mmusic@ietf.org
> >>>https://www1.ietf.org/mailman/listinfo/mmusic
> >>>
> >>
> >>-- 
> >>Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
> >>Chief Technology Officer                    Parsippany, NJ 
> 07054-2711
> >>dynamicsoft
> >>jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
> >>http://www.jdrosen.net                      PHONE: (973) 952-5000
> >>http://www.dynamicsoft.com
> >>
> > 
> > 
> 
> -- 
> Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
> Chief Technology Officer                    Parsippany, NJ 07054-2711
> dynamicsoft
> jdrosen@dynamicsoft.com                     FAX:   (973) 952-5050
> http://www.jdrosen.net                      PHONE: (973) 952-5000
> http://www.dynamicsoft.com
> 

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https://www1.ietf.org/mailman/listinfo/mmusic



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> Here is my comments on this draft.

Thanks for your comments.  Sorry for the delay, I have been out of
the office.

> 1. As a WG draft you should have the short copyright statement and not
> only the long one at the end of the draft.

Yes, sorry we didn't correct this, I see you commented on this same
issue when you reviewed -00.

> 2. In section 1 I would like that you clarify that RFC 2828 contains
> security terminology.

Okay.

> 3. Section 3.1. This section needs to be improved. As I understand it
> the a=crypto attribute can be used with any transport and media.
> Therefore the section should not start with defining that this defines
> the value for RTP/SAVP. The actual crypto suits will be required to be
> registered and defined for each individual transport. There might in
> fact be even further restrictions that apply to future crypto suits.

-sdescriptions- is only trying to describe a=crypto for the RTP/SAVP
(SRTP) transport.

> 4. Section 3.4, I think the session parameters are actually specific to
> the crypto suit, primarily.

But "encrypted_srtcp" can be specified for any and all crypto suites.  Are
there session parameters that are specific to a cryptographic suite?

> Secondarily it can be dependent on more things.

Could you explain?

> 5. Section 3 and 4. In general I think the basic definition of the
> a=crypto attribute can be more cleanly separated from the specific
> application for SRTP.

You mean, for example, to allow -sdescriptions- to define the keys
used by some non-SRTP application (whiteboarding, perhaps)?  We're
trying to only define usage with SRTP (RTP/SAVP).

> 6. Section 4.1, Is usage of multiple a=crypto lines allowed. IF yes this
> section contradict this.

I agree some different wording would clarify this section.  Will work
on it.

> 7. Section 4.1.4, last sentence: How can one add a new name that is
> identical and still carry any difference. Please reword.

Okay.

> 8. Section 4.2, I think there is a large shortcoming regarding the uri:
> parameter. I think one must clearly define the format one retrieves the
> keys when using the URI. Of course this format can be crypto suit
> dependent.

We're strongly considering dropping the URI parameter.  If anyone
feels strongly about keeping it, speak up.

> 9. Section 4.3.1, second and third paragraph. I think the definition of
> the SSRC, ROC, SEQ, could be better done. As I understand it any of the
> three is sufficient, why not express it that way. Then one MAY have the
> parameter anyway.

We'll tighten up that wording, thanks.

> 10. Section 5.4, second paragraph: I think the limitation you would like
> to declare here needs some discussion. First you forbid the usage of
> multiple m= lines on the same port, after last weeks discussion I don't
> know if this is acceptable, at least not without further motivation. I
> would also write some recommendations/considerations regarding grouping
>   of media lines here.

In this I-D, we will be removing all references to multiple media lines
with the same port.  A completely separate, unrelated, Internet Draft
needs to be written -- with consensus from the WG -- describing how multiple
media lines with the same UDP port are supposed to be interpreted.

(As an aside, the behavior for multiple media lines with the same port
hasn't been specified elsewhere, so it is ambiguous.  I personally feel we
need to create an unambigiuos method to express the desired behavior when
an Offer contains multiple media lines with the same port.)

> 11. Section 5.7, I am not certain that session parameters can't be
> restrained from being changed. For example the SRC (ROC) parameter seems
> one that might need to be included and changed in an offer for rekeying.

Good point.  We haven't put enough thought into rekeying yet as it's
unnecessary with voice applications and the maximum key lifetimes of
the crypto suites defined in SRTP.

>   Are there any synchronization problem that can arise when doing
> rekeying? There seems to be need to define from what seq the new key are
> valid.

That seems to be more a problem with SRTP than -sdescriiptions-.

To resolve the synchronization problem you have to use a per-packet MKI
(which adds a few bytes to each SRTP packet) or the "from,to" mechanism
(which doesn't add bytes to each SRTP packet); both MKI and "from,to"
are described in SRTP itself.

Do you feel putting like the above paragraph might be useful in
-sdescriptions-?

> 12. When it comes to SRTPs protection mechanism it seems necessary to be
> able to define the window size using the a=crypto parameter. There are a
> lot of difference between a uncompressed video stream running at a
> couple of hundreds of Mbyte/s using 100 000 packets each second. This
> will require a much larger window then a 64 kbit stream that sends 15
> packets every second.

SRTP (draft-ietf-avt-09.txt) says that the SRTP-WINDOW-SIZE is a
receiver-side, implementation-dependent parameter.  If it is signaled
in a unicast SDP, SRTP-WINDOW-SIZE would become a sender-side parameter.

Is that your intent of having the SRTP-WINDOW-SIZE indicated in the
a=crypto line?

> 13. Section 6.1 First paragraph, last sentence. The attack is only
> avoided if there is one master key per SSRC, not media stream. I think
> that there is some ambiguity in the use of media stream, which needs to
> be clarified to avoid misunderstanding.

Okay, we'll examine that.  Thanks.

> 14. Section 6.2, second paragraph, first sentence: The attribute is
> crypto not SRTP as it says in the text.

Okay.

> 15. Section 7.: The ABNF does not define the extension space. For
> example the crypto-suite definition should have an extra alternative
> crypto-suit-extension which is VCHAR. I think the whole ABNF needs to be
> thought through to be more complete in the extension sense.

Yes, it does.

In Vienna it was also pointed out that we need IANA registration of
all of the stuff in -sdescriptions-, as well.  We'll be adding that
to the next I-D.

> 16. Section 7. Why have the 2^ optional value if it does not matter.
> Please simplify this.

At an earlier review, Mark was asked to have a method to specify
power-of-two key lifetimes.  This seemed the easiest way to allow
specifying power-of-two key lifetimes.

But rereading the draft, I see we never added text explaining the
purpose of "2^"!  We'll add that at the next revision.  Thanks.

> 17. Section 7, The absolute URI should not rely only on RFC 2396, there
> is an extension to that document, please see RFC 2732.

Thanks.

> 18. Last page, has not the normal number of lines.

Again, thanks for your review.

-d

> Best Regards
>
>
> Magnus Westerlund
>
> Multimedia Technologies, Ericsson Research EAB/TVA/A
> ----------------------------------------------------------------------
> Ericsson AB                | Phone +46 8 4048287
> Torshamsgatan 23           | Fax   +46 8 7575550
> S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com
>
>
>
> _______________________________________________
> mmusic mailing list
> mmusic@ietf.org
> https://www1.ietf.org/mailman/listinfo/mmusic


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