From owner-freebsd-net@FreeBSD.ORG Thu Oct 18 08:20:57 2007 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 3160716A41A for ; Thu, 18 Oct 2007 08:20:57 +0000 (UTC) (envelope-from jmg@hydrogen.funkthat.com) Received: from hydrogen.funkthat.com (gate.funkthat.com [69.17.45.168]) by mx1.freebsd.org (Postfix) with ESMTP id 0445213C467 for ; Thu, 18 Oct 2007 08:20:56 +0000 (UTC) (envelope-from jmg@hydrogen.funkthat.com) Received: from hydrogen.funkthat.com (rawg0uhdjo336hx6@localhost.funkthat.com [127.0.0.1]) by hydrogen.funkthat.com (8.13.6/8.13.3) with ESMTP id l9I8Kuem036247; Thu, 18 Oct 2007 01:20:56 -0700 (PDT) (envelope-from jmg@hydrogen.funkthat.com) Received: (from jmg@localhost) by hydrogen.funkthat.com (8.13.6/8.13.3/Submit) id l9I8KuNN036246; Thu, 18 Oct 2007 01:20:56 -0700 (PDT) (envelope-from jmg) Date: Thu, 18 Oct 2007 01:20:56 -0700 From: John-Mark Gurney To: Len Gross Message-ID: <20071018082056.GW39759@funkthat.com> Mail-Followup-To: Len Gross , freebsd-net@freebsd.org References: <27cb3ada0710172051t536a4d11pfdfdb079ebd98932@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <27cb3ada0710172051t536a4d11pfdfdb079ebd98932@mail.gmail.com> User-Agent: Mutt/1.4.2.1i X-Operating-System: FreeBSD 5.4-RELEASE-p6 i386 X-Files: The truth is out there X-URL: http://resnet.uoregon.edu/~gurney_j/ X-Resume: http://resnet.uoregon.edu/~gurney_j/resume.html X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-3.0 (hydrogen.funkthat.com [127.0.0.1]); Thu, 18 Oct 2007 01:20:56 -0700 (PDT) Cc: freebsd-net@freebsd.org Subject: Re: Disable Exponential Backoff (retry) on Ethernet? X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: John-Mark Gurney List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 18 Oct 2007 08:20:57 -0000 Len Gross wrote this message on Wed, Oct 17, 2007 at 20:51 -0700: > I'm doing some protocol development and it is convenient to start it on > Ethernet. I will need to send a packet to the Ethernet device and only have > it be sent once, even if there is a colision. (Higher levels in the > protocol will detect the failure.) I've searched quite a bit, and haven't > found any place that talks about this. Are there any hardware cards, or > drivers, that let me turn off the backoff/retry behavior? Are you even using hardware that does collisions? Collisions pretty much went out w/ 10Mbit ethernet... Not completely as there are older 10/100mbit "switches" that only switched between the two segments (and each of 10/100 segments was hubbed)... All modern switches are full-duplex and don't suffer from the old CD part of CDMA that was part of the original ethernet specification.. For Gige, you can't even do half-duplex, as each side is transmitting on all four pairs at the same time... The physical layer handles the fact that both sides may transmit at the same time, and knows how to cancel their own interference out so they can hear the other side... -- John-Mark Gurney Voice: +1 415 225 5579 "All that I will do, has been done, All that I have, has not."