From owner-freebsd-net Tue Aug 13 22:40:48 2002 Delivered-To: freebsd-net@freebsd.org Received: from mx1.FreeBSD.org (mx1.FreeBSD.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 77A5937B400 for ; Tue, 13 Aug 2002 22:40:44 -0700 (PDT) Received: from patrocles.silby.com (d171.as13.nwbl0.wi.voyager.net [169.207.136.237]) by mx1.FreeBSD.org (Postfix) with ESMTP id BFD4543E6E for ; Tue, 13 Aug 2002 22:40:42 -0700 (PDT) (envelope-from silby@silby.com) Received: from patrocles.silby.com (localhost [127.0.0.1]) by patrocles.silby.com (8.12.5/8.12.5) with ESMTP id g7E5iVB1093352; Wed, 14 Aug 2002 00:44:31 -0500 (CDT) (envelope-from silby@silby.com) Received: from localhost (silby@localhost) by patrocles.silby.com (8.12.5/8.12.5/Submit) with ESMTP id g7E5iTkw093349; Wed, 14 Aug 2002 00:44:30 -0500 (CDT) X-Authentication-Warning: patrocles.silby.com: silby owned process doing -bs Date: Wed, 14 Aug 2002 00:44:28 -0500 (CDT) From: Mike Silbersack To: Oleg Polyakov Cc: freebsd-net@freebsd.org Subject: Re: Initial congestion window increase In-Reply-To: <20020812192549.24783.qmail@web10409.mail.yahoo.com> Message-ID: <20020814003743.U93223-100000@patrocles.silby.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-net@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org On Mon, 12 Aug 2002, Oleg Polyakov wrote: > Yes, real world is murky;) > RFC2414 references RFC2415 - Simulation Studies of Increased > Initial TCP Window Size which shows significantly increased > throughput and decreased delays and some increased drop rate - > around 1% more for connections with initial window=3. > It also references RFC2416 - When TCP Starts Up With Four > Packets > Into Only Three Buffers where experiment shows decreased delays > and "no harm" for transmission. I've read those over, and I'm still not sure what to believe. I have a few other TCP things on my plate right now, so I'd rather concentrate on those for the moment. > By the way looking into tcpdump revealed we have initial window > = 2 * mss in case of slowstart_flightsize = 1. I've seen it on > FreeBSD 4.5 and 4.6 . > What is this - an ancient bug in BSD stack? > > If I set slowstart_flightsize to 0 then tcpdump shows we > starting > with initial window 1... Hrm, interesting. If you can figure out how to fix it so that slowstart_flightsize is accurate, that would be appreciated. After that, then maybe we can worry about changing the default. Incidently, I think that the formula min (4*MSS, max (2*MSS, 4380 bytes)) is bogus. We really have three cases: MTU 512 bytes MTU 1500 bytes (and 1480 or whatever PPPoE uses) MTU 9000 bytes (jumbo frames) The formula above would penalize jumbo frames, while sending a lot of packets for the 512 byte case. Just using MSS * X, where X is a constant for all of the above seems like a better idea. Mike "Silby" Silbersack To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message