From owner-freebsd-net Fri Jul 19 11:58:16 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 C714337B400 for ; Fri, 19 Jul 2002 11:58:14 -0700 (PDT) Received: from patrocles.silby.com (d100.as5.nwbl0.wi.voyager.net [169.207.137.228]) by mx1.FreeBSD.org (Postfix) with ESMTP id 4A29D43E3B for ; Fri, 19 Jul 2002 11:58:13 -0700 (PDT) (envelope-from silby@silby.com) Received: from patrocles.silby.com (localhost [127.0.0.1]) by patrocles.silby.com (8.12.4/8.12.4) with ESMTP id g6JJ2gcv095413; Fri, 19 Jul 2002 14:02:42 -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 g6JJ2dPI095410; Fri, 19 Jul 2002 14:02:40 -0500 (CDT) X-Authentication-Warning: patrocles.silby.com: silby owned process doing -bs Date: Fri, 19 Jul 2002 14:02:38 -0500 (CDT) From: Mike Silbersack To: Garrett Wollman Cc: Jonathan Lemon , Subject: Re: cvs commit: src/sys/netinet tcp_timer.h In-Reply-To: <200207182133.g6ILXHNl007758@khavrinen.lcs.mit.edu> Message-ID: <20020719134639.S95326-100000@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 Thu, 18 Jul 2002, Garrett Wollman wrote: > - He questioned whether the traditional VJ `srtt + 4*rttvar' > computation captures enough of the variance in the real Internet to > avoid unnecessary slow retransmits. > > - He also notes that there have not been screams of protest since > Linux adopted the 200-ms minimum, which suggests that it's not a > completely hare-brained value. > > -GAWollman Now that I've had a bit more time to think it over, I believe that Matt's 200ms slop + no floor on rtomin provides us with a very good system. In effect, Matt has seperated the delay necessary to avoid retrans because of delayed acks (200ms or less on modern systems) from rtt (quite variable.) This is an approach that seems quite obvious in hindsight, and should allow the tcp stack to adapt to varying link types quite dynamically. The main improvement upon this I could see is dynamically detecting the delayed ack period of the receiver, as suggesed by DG. Unfortunately, I suspect that such detection would be nearly impossible to get correct. In place of this, I'd suggest that the slop be bumped from 200ms up to 220ms; both linux and windows use a 200ms delayed ACK period, and we don't want to be exactly synchronized to that time period. Mike "Silby" Silbersack To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message