Subject: Re: [SCTP]Congestion Control Parameters

From: Andrea Senatore <[email-masked]>
Date: Mon, 28 Oct 2002 20:05:21 +0100

Tuexen Michael wrote:

>Hi Andrea,
Hi Michael,

>
>
>this would mean that you have m * n path if one peer has
>n the other m IP addresses. Using the current terminology
>has only n + m. This was considered less complexity.
>
You could use fixed paths associating every node of interface to one 
destination.
So you has only min(n,m) paths...

>
>
>The other reason is that normally the IP layer selects the
>source address of the packet according to its forwarding table.
>Selecting the source address at the SCTP layer (called source
>selection) is not very easy and even if you select an IP-address
>as a source address the IP layer may send it out on an interface
>which has not bound that address. In the bakeoff some implementations
>showed up with using source address selection and it came out
>that it is a difficult task to get that stuff right.
>
Sorry I did not know these issues...but I think that a good congestion 
control mechanism
should keep congestion parameters for each used path.

>
>
>In general, the forwarding in an IP network is mostly based on
>the destination address, not on the source address.
>
>These are some of the reasons why this notion was choosen.
>
....... :-/

>
>
>I know of some people working on the path notion which is defined
>as a pair of source and destination addresses and it is not a trivial
>part. 
>
>Best regards
>Michael
>
>Michael Tuexen   Tel.:   +49 89 722 47210
>Siemens AG       Fax:    +49 89 722 48212
>ICN WN CC SE 7   e-mail: [email-masked]
>
>>-----Original Message-----
>>From: Andrea Senatore [mailto:[email-masked]]
>>Sent: Monday, October 28, 2002 5:05 PM
>>To: Tuexen Michael
>>Subject: Re: [SCTP]Congestion Control Parameters
>>
>>
>>Tuexen Michael wrote:
>>
>>>Hi Andrea,
>>>
>>>it is a definition, so it is not correct or incorrect. That
>>>is the term used.
>>>
>>>What 'behaviour' of SCTP are you thinking to be not correct?
>>>
>>IMHO  "congestion control parameters"  would be kept for each 
>>source-destination pair  (i.e. sender interface <----------> receiver 
>>interface) and not for
>>each destination as written in RFC.
>>These parameters depends on destination only when the sender has a 
>>single interface.
>>Best Regards,
>>
>>-- Andrea
>>========================================================
>>Andrea Senatore,     
>>Mail:    [email-masked],
>>Address: CoRiTeL c/o Università degli Studi di Salerno,
>>         Facoltà di Ingegneria,  via Ponte Don Melillo,
>>         84084 - FISCIANO (SA) - Italy
>>Tel:     +39 089 964012
>>Fax:     +39 089 964010
>>========================================================
>>
>>
>>
>
>
Thanks Michael,
best regards ,

-- Andrea
========================================================
Andrea Senatore,     
Mail:    [email-masked],
Address: CoRiTeL c/o Università degli Studi di Salerno,
         Facoltà di Ingegneria,  via Ponte Don Melillo,
         84084 - FISCIANO (SA) - Italy
Tel:     +39 089 964012
Fax:     +39 089 964010
========================================================

---

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Mon, 28 Oct 2002 23:35:23 -0700

Andrea,

What definition do you use for "path"?  And, how do you ensure
that such a definition of "path" has meaning in the underlying
network?

This was one of the difficulties in the original SCTP work.  Do
you use destination IP address?  Do you use source-destination
pairs?  Do you use interfaces?  Interface pairing?

In general there is not a definition of path which suits all
networks and all circumstances.  The approximation to treat all
paths as a single path with variable characteristics is a usable
compromise.

--brian

On Mon, 28 Oct 2002, Andrea Senatore wrote:
> control mechanism should keep congestion parameters for each used path.
> 

-- 
Brian F. G. Bidulock    ¦ The reasonable man adapts himself to the ¦
[email-masked]    ¦ world; the unreasonable one persists in  ¦
http://www.openss7.org/ ¦ trying  to adapt the  world  to himself. ¦
                        ¦ Therefore  all  progress  depends on the ¦
                        ¦ unreasonable man. -- George Bernard Shaw ¦

---

From: Andrea Senatore <[email-masked]>
Date: Tue, 29 Oct 2002 10:21:58 +0100

>Andrea,
Hi Brian,

>pairs?  Do you use interfaces?  Interface pairing?
An endpoint cannot control completely the path used to send packets 
(i.e. all routers), but can choose the source and destination IP address.
I believe that source-destination IP pairs identifies the path better 
than only destination IP address.
Why need I use different congestion control parameters for different  IP 
destination in SCTP ?
Because if I change the IP destination address, probably the path 
changes, and then all congestion control parameters MUST change.
But the path changes also if  I change IP source address (if is it 
possible..)  and, for the same reasons,  all congestion control 
parameters MUST change.
This is the reason for which I say that a good congestion control 
mechanism should keep congestion parameters for each used path..

Best Regards,

-- Andrea

---

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Tue, 29 Oct 2002 03:51:16 -0700

Andrea,

> than only destination IP address.

How so?  Source address typically has no bearing on the path
taken by a packet through an IP network (nor on which interface
the outgoing packet is sent).

> Why need I use different congestion control parameters for different  IP 

Because the only valuable use of SCTP multi-homing is to have
each destination IP address correspond to a different interface
on the destination host, which is, indeed, a different path for
each destination address.

> changes, and then all congestion control parameters MUST change.

The useful application of SCTP multi-homing means that the path
does change when the destination address changes and thus, per
RFC 2960, the congestion control parameters MUST change.

> possible..)  and, for the same reasons,  all congestion control 

No.  Path does not change when IP source address changes.  The
IP source address is merely a return address.  In a typical IP
stack or router, changing the source address has no bearing on
the path taken by the packet.  Only destination address does.
Source address has a bearing on the return path for packets, but
CC on the return path is the business of the peer.

> mechanism should keep congestion parameters for each used path..

The host will chose the outgoing interface based on the
destination address and will not consider the source address
when selecting the outgoing interface.  Some IP implementations
permit routing based on source address, but this is atypical.
Regardless, it is outgoing interface and destination address
that determines path, not source address.

In the absence of failures and network reconfigurations, it is
true that destination address alone determines path.

--brian