From owner-freebsd-net@FreeBSD.ORG Tue Feb 8 19:22:06 2005 Return-Path: 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 4595116A4CE for ; Tue, 8 Feb 2005 19:22:06 +0000 (GMT) Received: from wyvern.icir.org (wyvern.icir.org [192.150.187.14]) by mx1.FreeBSD.org (Postfix) with ESMTP id 2121B43D49 for ; Tue, 8 Feb 2005 19:22:06 +0000 (GMT) (envelope-from mallman@icir.org) Received: from guns.icir.org (adsl-68-76-113-50.dsl.bcvloh.ameritech.net [68.76.113.50]) by wyvern.icir.org (8.12.9p1/8.12.8) with ESMTP id j18JLxuM092349; Tue, 8 Feb 2005 11:22:00 -0800 (PST) (envelope-from mallman@guns.icir.org) Received: from guns.icir.org (localhost [127.0.0.1]) by guns.icir.org (Postfix) with ESMTP id 6262377A6A5; Tue, 8 Feb 2005 14:21:56 -0500 (EST) To: Mohan Srinivasan From: Mark Allman In-Reply-To: <20050208184834.24690.qmail@web80602.mail.yahoo.com> Organization: ICSI Center for Internet Research (ICIR) Song-of-the-Day: Rocket Man MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha1; protocol="application/pgp-signature" Date: Tue, 08 Feb 2005 14:21:56 -0500 Sender: mallman@icir.org Message-Id: <20050208192156.6262377A6A5@guns.icir.org> cc: Ethan Blanton cc: freebsd-net@freebsd.org cc: Daikichi Osuga Subject: Re: SACK retransmits multiple segments respond to single dupack X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list Reply-To: mallman@icir.org List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 08 Feb 2005 19:22:06 -0000 --=-=-= Content-Type: text/plain > Which release are you experimenting with ? There was a bug > in 5.3 that would cause SACK to burst multiple segments on > a dupack reception. But that was fixed both in -current > and in RELENG_5 (1.100.2.3 and 1.102). From what I see, > the fix was never MFC'ed to RELENG_5_3. > > Referencing the code in -current, > > dupack handling starts at line tcp_input.c:1797. When SACK > recovery is first set up, upon reception of 3 dupacks, we > set cwnd to 3 (line 1867) and call tcp_output(), which would > cause 3 segments from the scoreboard to be retransmitted. I do not understand why receiving 3 dupacks would cause a retransmit of 3 segments. One retransmit I can understand. But, then we shouldn't be in packet conservation for a bit while some of the segments drain from the network to effectively halve the sending rate (because we noted congestion). allman -- Mark Allman -- ICIR -- http://www.icir.org/mallman/ --=-=-= Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.3 (FreeBSD) iD8DBQFCCRFUWyrrWs4yIs4RApp5AJ9nMx9QcYy8sRegfzOLrv088TvDuwCePJSM tuM27qCnMhj1i/xJMEuhIdw= =IMBD -----END PGP SIGNATURE----- --=-=-=--