Subject: [Tsvwg] Congestion Control

From: "kedar sovani" <[email-masked]>
Date: 19 Sep 2001 13:51:19 -0000

Hi,
   I had a question. Why is it that SCTP defines the same algorithms for Congestion control that r used for TCP. Aren't any enhancements possible. Some specific to SCTP. Why use algos from the TCP?

Kedar.

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From: Lloyd Wood <[email-masked]>
Date: Wed, 19 Sep 2001 15:00:47 +0100 (BST)

On 19 Sep 2001, kedar sovani wrote:

>    I had a question. Why is it that SCTP defines the same
> algorithms for Congestion control that r used for TCP. Aren't any
> enhancements possible. Some specific to SCTP.

(see RFC2960 section 7.1)

> Why use algos from the TCP?

If SCTP used algorithms that made it more congestion-sensitive than
TCP, then TCP flows would outcompete SCTP flows for capacity.

If SCTP used algorithms that made it less congestion-sensitive than
TCP, then SCTP flows would outcompete TCP flows for capacity.

This is the trap of 'TCP friendliness' that ensures that congestion
avoidance will suck (but suck _consistently_ and possibly
adequately) for the rest of eternity.

Besides, we are short of credible alternatives. TCP Vegas congestion
avoidance is entirely different from that of other TCPs, but the Vegas
guys have had trouble explaining why it works - and, in any case, TCP
Vegas is more congestion-sensitive and will be outcompeted by other
TCP implementations, which is one reason why it hasn't been deployed.

(And you need to be as aggressive as TCP, or slightly moreso, to 
 ensure deployment.)

L.

<[email-masked]>PGP<http://www.ee.surrey.ac.uk/Personal/L.Wood/>