Subject: Re: initial window size

From: Mark Allman <[email-masked]>
Date: Fri, 30 Mar 2001 09:19:42 -0500

> Am I right in thinking that we can blame the existence of this on:
> a. the MTU of edge system (good old ethernet) not scaling upward?
> b. TCP's back-to-back busrtiness behaviour?
> 
> Fix either one of those, and an initial window of more than one
> segment looks less compelling.

I do not follow.  See RFC 2414 for (what I believe are) a number of
good reasons to use an initial cwnd of more than 1 segment.

allman

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From: Lloyd Wood <[email-masked]>
Date: Fri, 30 Mar 2001 15:46:35 +0100 (BST)

> good reasons to use an initial cwnd of more than 1 segment.

(section 3)

Those reasons are related to the (legacy, dammit!) TCP implementation.

1. is, I think, basically a problem with delayed-ack implementations,
which should ack the first packet immediately before going into delay.
(I'd guess that paced TCP should make the effects of delayed acks less
desirable; acking the first packet strikes me as a good idea
regardless.)

2. is made moot by a larger MTU on edge systems leading to larger path
MTU throughout.

3. as for 1., and the effect on slow-start should be ameliorated by 
byte-counting.

Sections 4 and 5 list the disadvantages of larger initial cwnd - it's
harder to encounter unnecessary retransmits when it's only 1 segment.

L.

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