[nSLUG] timeout in congestion & congestion avoidance

Thomas Graham miguel at accesswave.ca
Thu Nov 15 16:48:17 AST 2001


you are chinese guy, right ?
I am come from HK!
----- Original Message ----- 
From: "Yuan Sha" <sha at cs.dal.ca>
To: "Linux User Group (NS)" <nslug at nslug.ns.ca>
Sent: Saturday, November 10, 2001 11:29 PM
Subject: [nSLUG] timeout in congestion & congestion avoidance


> 
> hi,
> 
> Recently, I have been doing a project where I have to implement
> "congestion avoidance algorithm". I checked RFC 2001/2581 and Steven's
> "TCP/IP Illustrated (Vol. 1)" but still have some questions.
> 
> 1. timeout:
> 
> In Karn's algorithm, it uses timer backoff strategy, which is:
> 
> new_timeout = r * timeout
> 
> In Cormer's "Internetworking with TCP/IP", he said "typically, r is 2".
> (In his new versionn of this bible, it can be found on page 229. But I 
> remember in the elder version, Comer also mentioned this thing.)
> 
> But I am wondering, if there are several congestion, the timeout will be
> larger than the max integer (in C/C++) or much longer than the period
> people can patiently wait.
> 
> For example, if the initial timeout is 30ms. After 11 times of 
> computation, the timeout will beyond 1 minute. Is that correct?
> 
> I guess that timeout may be decreased based on some algorithm or RFC in 
> some cases so that the timeout cannot be exponetially increased forever.
> But I cannot find any RFC yet :(
> 
> So could you pls tell me how to deal with timeout in the congestion?
> 
> 2. congestion avoidance
> 
> RFC 2001 (page 3, item 3) said "if the congestion is indicated by a 
> timeout, cwnd is set to one segment." But sometimes, an ICMP packet 
> arrives to report the congestion before timeout occurs in sender side. In
> this case, how to change the cwnd?
> 
> thank u very much,
> yuan
> 
> 
> 
> +-----------------------------+
> |         Yuan Sha            |
> |       MSc Student           |
> |                             |
> |   Email: sha at cs.dal.ca      |
> +-----------------------------+
> 
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