Subject: RE: MPE Question

From: Tor Brekke <[email-masked]>
Date: Mon, 2 May 2005 12:25:14 +0200

Hi William, 

I think you are somewhat confused in the use of terminology here. Section 
packing is the process of having more than one (partial) IP packet in each 
MPG frame. This has nothing to do with maximum section size. All IP 
encapsulators probably support MPE Section packing. 

MPE Does additionally support fragmentation of an IP packet into multiple 
DSM-CC sections (I guess this is what you are really talking about). This 
is only useful for IP packets which do not fit into the maximum section 
size of 4096 octets. This function, while defined by the MPE standard, is 
not (normally?) supported by the IP encapsulators. I have to admit that I 
have not checked details on ever vendor here, but have not seen this in 
any of the ones I have used myself. 

Regards
Tor Brekke

"William StanisLaus" <[email-masked]> 
Sent by: [email-masked]
29.04.2005 17:56
Please respond to
[email-masked]

To
<[email-masked]>
cc

Subject
RE: MPE Question

Hi Siva and Bernhard,
DSM-CC which is a potential MPE of our present day DOES NOT support 
section
packing for normal IP data transmissions. In DSM-CC we have section length
of 12 bits, which can hold maximum of 4096 Bytes of payload data (IP in 
our
discussion). In Normal scenario we don't even use this big, since section
packing is not supported practically (theoretically YES), we use DVB 
router
one interface as Ethernet and other as DVB, on Ethernet wire we get only
1500 bytes the max, though there is a room for section
packing(theoretically) real time packet routing don't wait for another IP
packet, just push each and every ip packet received with MPE (DSM-CC) and 
to
MPEG2-TS (supports section packing, based on the timer - reason MPEG2-TS
MUST be 188 bytes, instead of wasting bytes with stuffing we have section
packing).

When we are talking about stuffing bytes, that was perfect by Bernhard, we
use for packet alignment, to be more specific, real time operating system
like PSOS, requires it be WORD aligned ( Multiples of Four) before
encryption algorithm to be applied for scrambling.

-William.

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On
> Behalf Of Bernhard Collini-Nocker
> Sent: Friday, April 29, 2005 6:55 AM
> To: [email-masked]
> Subject: Re: MPE Question
> 
> Dear Siva,
> 
> you are right in that I had understood your question different.
> 
> Generally Sections do allow for numbering that is, one can put a payload
> (for example a DSM-CC object) into a number of Sections and with
> section_number and last_section_number the reassebler knows what to do.
> MPE uses this Section mechanism, so multiple Section operations should
> be possible. Actually I have never tested whether MPE decapsulators do
> support this in real, in principle they should (again the DVB
> databroadacst standard does not say too much, if anything, about it) but
> in DSM-CC Obejct carousels is a very usual mode of operation.
> 
> Siva Veerepalli wrote:
> > Thanks for the response Bernhard, but I am a bit
> > confused about the answer. Please see my question
> > below:
> >
> > --- Bernhard Collini-Nocker <[email-masked]>
> > wrote:
> >
> >>Siva Veerepalli wrote:
> [...]
> > I understand that two MPE sections could probably
> > start in the same TS packet (I guess that is what you
> > mean by section packing).
> 
> Yes.
> 
> > My original questions was, what is the usual practice
> > with regards to fragmenting an IP datagram over
> > multiple MPE sections (irrespective of how these
> > sections are transported in TS packets)? The DVB-H
> > (data broadcast standard) allows for this, however,
> > the IPDC interim specification requires that one
> > datagram be encapsulated entirely in one mpe section
> > i.e., no datagram fragmentation over multiple MPE
> > sections.
> 
> Now the confusion starts when one introduces the wording of "over
> multiple MPE sections", because there is no such thing as a MPE section
> fragmentation.
> I will have to read the DVB-H standard again in order to find out what
> it really says. I guess the only real issues the DVB-H wrt to IP is
> addressing is the necessity of a IP datagram encapsulated in MPE is to
> support time slicing (ie a burst transmission of the resulting TS
> packets to allow for power saving) and MPE-FEC (adding redundant code to
> allow for reconstruction). In that case I woould assume that it is very
> reasonable (especially with legacy equipment) to avoid all potential
> interpretations of MPE wrt multiple section operation and section 
packing.
> 
> > thanks,
> > Siva
> [...]
> 
> Yor are very welcome,
> and I hope I got THE expected answer closer,
> Bernhard

---

From: "Anurag Sharma" <[email-masked]>
Date: Mon, 2 May 2005 16:50:42 +0530

Hi William,

DSM-CC doesn't carry any information about section packing.
The Payload Unit Start Indicator (PUSI) field in the MPEG header is used to
indicate the beginning of new DSM-CC section.
But that doesnt really specify if there is more than one section present in
the payload.
PSUI field in combination with other available information (DSM-CC headers)
can be used to check the presence of multiple sections in the payload.

Fragmentation of IP packets is supported, in case the size of the packet
exceeds a DSM-CC section size (4096 bytes)
In such cases section_number, last_section_number fields in the DSM-CC
header can be used for reassembly of the IP packets.

regards,
Anurag Sharma

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On
Behalf Of William StanisLaus
Sent: Friday, 29 April 2005 9:26 PM
To: [email-masked]
Subject: RE: MPE Question

Hi Siva and Bernhard,
DSM-CC which is a potential MPE of our present day DOES NOT support section
packing for normal IP data transmissions. In DSM-CC we have section length
of 12 bits, which can hold maximum of 4096 Bytes of payload data (IP in our
discussion). In Normal scenario we don't even use this big, since section
packing is not supported practically (theoretically YES), we use DVB router
one interface as Ethernet and other as DVB, on Ethernet wire we get only
1500 bytes the max, though there is a room for section
packing(theoretically) real time packet routing don't wait for another IP
packet, just push each and every ip packet received with MPE (DSM-CC) and to
MPEG2-TS (supports section packing, based on the timer - reason MPEG2-TS
MUST be 188 bytes, instead of wasting bytes with stuffing we have section
packing).

-William.

> interpretations of MPE wrt multiple section operation and section packing.
>
> > thanks,
> > Siva
> [...]
>
> Yor are very welcome,

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---

From: "William StanisLaus" <[email-masked]>
Date: Mon, 2 May 2005 13:01:59 +0100

Dear Tor Brekke,

Sorry if I have confused, may be I should make it more detailed :-)

In DSM-CC (MPE) we have section-length to specify the size of the payload it
carries, this can be maximum of 4096 bytes. Hence any IP packet as a
potential payload for DSM-CC can be maximum of 4096 bytes, this length
normally discovered using L2 MTU size and IP packets gets fragmented if the
packet is greater than 4096 bytes. But theoretically, DSM-CC supports
multiple segments/fragments by itself (section number and last section
number) which gives room for bigger ip packet even greater than 4096 bytes.
Does any of the vendor uses this functionally for ip data transmission is a
question !!!. I myself never come across such support for ip data
transmission. Next, if a single DSM-CC (MPE) can carry more than one IP
packet??, I don't understand if it is possible, since we don't have payload
start indicator and pointer to perform IP datagram section packing in single
DSM-CC (MPE) payload, which can be decapsulated at the other end.

Next, MPEG2-TS, for any MPEG2-TS packet it MUST be of length 188 bytes. Any
MPE (DSM-CC) packet less than 183 bytes (considering after MPEG2-TS header
and payload pointer) needs to be stuffed/padding, instead of doing so we can
do section packing, by sending next MPE packet into the same MPEG2-Transport
Stream.

Hope now it is clear

Update me if I'm wrong :-)

-William.

  _____  

From: [email-masked] [mailto:[email-masked]] On
Behalf Of Tor Brekke
Sent: Monday, May 02, 2005 11:25 AM
To: [email-masked]
Subject: RE: MPE Question

Hi William, 

MPE Does additionally support fragmentation of an IP packet into multiple
DSM-CC sections (I guess this is what you are really talking about). This is
only useful for IP packets which do not fit into the maximum section size of
4096 octets. This function, while defined by the MPE standard, is not
(normally?) supported by the IP encapsulators. I have to admit that I have
not checked details on ever vendor here, but have not seen this in any of
the ones I have used myself. 

Regards 
Tor Brekke 

29.04.2005 17:56 

Please respond to
[email-masked]

To

<[email-masked]> 

cc

Subject

RE: MPE Question

Hi Siva and Bernhard,

-William.

---

From: Tor Brekke <[email-masked]>
Date: Mon, 2 May 2005 14:23:52 +0200

Dear William, 

I was mainly objecting to your initial comment that no vendors support MPE 
Section packing, while in fact all I have come across do support it. Now 
we are saying the same thing, namely that they do not support MPE IP 
fragmentation. Hence we can probably stop this discussion now. 

--Tor

02.05.2005 14:01
Please respond to
[email-masked]

To
<[email-masked]>
cc

Subject
RE: MPE Question

Dear Tor Brekke,
 
Sorry if I have confused, may be I should make it more detailed J
 
In DSM-CC (MPE) we have section-length to specify the size of the payload 
it carries, this can be maximum of 4096 bytes. Hence any IP packet as a 
potential payload for DSM-CC can be maximum of 4096 bytes, this length 
normally discovered using L2 MTU size and IP packets gets fragmented if 
the packet is greater than 4096 bytes. But theoretically, DSM-CC supports 
multiple segments/fragments by itself (section number and last section 
number) which gives room for bigger ip packet even greater than 4096 
bytes. Does any of the vendor uses this functionally for ip data 
transmission is a question !!!. I myself never come across such support 
for ip data transmission. Next, if a single DSM-CC (MPE) can carry more 
than one IP packet??, I don’t understand if it is possible, since we don’t 
have payload start indicator and pointer to perform IP datagram section 
packing in single DSM-CC (MPE) payload, which can be decapsulated at the 
other end.
 
Next, MPEG2-TS, for any MPEG2-TS packet it MUST be of length 188 bytes. 
Any MPE (DSM-CC) packet less than 183 bytes (considering after MPEG2-TS 
header and payload pointer) needs to be stuffed/padding, instead of doing 
so we can do section packing, by sending next MPE packet into the same 
MPEG2-Transport Stream.
 
Hope now it is clear
 
Update me if I’m wrong J
 
-William.

Hi William, 

Regards 
Tor Brekke 

Please respond to
[email-masked]

To
<[email-masked]> 
cc
 
Subject
RE: MPE Question

Hi Siva and Bernhard,

-William.

packing.