From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lars Eggert Subject: Re: 3 packet TCP window limit? Date: Thu, 6 May 2010 08:15:03 +0200 Message-ID: <0C1FD143-5588-4455-B08F-85ADD19E0E02@nokia.com> References: <4BE171EC.20904@athenacr.com> <4BE1D3B0.9000207@hp.com> Mime-Version: 1.0 (Apple Message framework v1078) Content-Type: multipart/signed; boundary=Apple-Mail-46-614044316; protocol="application/pkcs7-signature"; micalg=sha1 Cc: Rick Jones , Brian Bloniarz , "netdev@vger.kernel.org" To: dormando Return-path: Received: from smtp.nokia.com ([192.100.122.233]:62065 "EHLO mgw-mx06.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751100Ab0EFGPx (ORCPT ); Thu, 6 May 2010 02:15:53 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: --Apple-Mail-46-614044316 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii Hi, On 2010-5-5, at 23:31, dormando wrote: > The RFC clearly states "around 4k", no, it doesn't. RFC3390 gives a very precise formula for calculating the = initial window: min (4*MSS, max (2*MSS, 4380 bytes)) Please see the RFC for why. More reading at = http://www.icir.org/floyd/tcp_init_win.html I believe that Linux = implements behavior this pretty faithfully. > but these other OS's/products have an > extra kilobyte snuck in? Could this be on purpose via rfc > interpretation, or an off by one on the initcwnd estimator? :) I'm surprised to hear that OpenBSD doesn't follow the RFC. Can you share = a measurement? Are you sure the box you are measuring is using the = default configuration? I don't think the RFC can be misread (it's pretty clear), and the = formula is also not exactly complicated. My guess would be that some = vendors have convinced themselves that using a slightly larger value is = OK, esp. if they can show customers that "their" TCP is "faster" than = some competitors' TCPs. An arms race between vendors in this space would = really not be good for anyone - it's clear that at some point, problems = due to overshoot will occur. (We can definitely argue about whether the current RFC-recommended value = is too low, and Google and others are gathering data in support of = making a convincing and backed-up argument for increasing the initial = window to the IETF. Which is exactly the correct way of going about = this.) 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