From owner-freebsd-net@FreeBSD.ORG Fri Oct 19 02:10:47 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 25EC616A418 for ; Fri, 19 Oct 2007 02:10:47 +0000 (UTC) (envelope-from sandiegobiker@gmail.com) Received: from wx-out-0506.google.com (wx-out-0506.google.com [66.249.82.234]) by mx1.freebsd.org (Postfix) with ESMTP id CB4DC13C45A for ; Fri, 19 Oct 2007 02:10:46 +0000 (UTC) (envelope-from sandiegobiker@gmail.com) Received: by wx-out-0506.google.com with SMTP id i29so321577wxd for ; Thu, 18 Oct 2007 19:10:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=beta; h=domainkey-signature:received:received:message-id:date:from:to:subject:in-reply-to:mime-version:content-type:references; bh=393j4ZdYjXFnfal+UIgEkDBTAAfnY7beEwCkotOypIU=; b=S/ey02VCZ8uCYYO9Nf5Dw6kLVBOPbo39LBcxU9FZJu7Fym4MOt3zSD1Iopuo/bHMlRgA5Tzol9S79rU5G0OnHzpJkos7R/RWdl5S88xJHpQRRONKmXGr6GnV3xEKU/CJP49K5E0UslId538qrK6P6x5UlXh7hlD7bOZq8ZnkJ2I= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:to:subject:in-reply-to:mime-version:content-type:references; b=As/ovN/I5GyxJaVKnNySsdTrZXPBfcnWguwpNZ3g+DtJ36wm9PJyIeXKxIYrUsirioMgJTJEzgbQTLtPIdADH/eaWOQ530xG4FDn0tkEcI2DwTNIF6l1Ljxr4sb2uNd2xaxDdVs8NA114oFn0HSl7vr0xIHjeekp+vrB5fTa0OI= Received: by 10.70.108.18 with SMTP id g18mr2020281wxc.1192758130387; Thu, 18 Oct 2007 18:42:10 -0700 (PDT) Received: by 10.70.19.9 with HTTP; Thu, 18 Oct 2007 18:42:10 -0700 (PDT) Message-ID: <27cb3ada0710181842x4d214d31ob4f474ff790355b8@mail.gmail.com> Date: Thu, 18 Oct 2007 18:42:10 -0700 From: "Len Gross" To: "John-Mark Gurney" , "Len Gross" , freebsd-net@freebsd.org In-Reply-To: <20071018082056.GW39759@funkthat.com> MIME-Version: 1.0 References: <27cb3ada0710172051t536a4d11pfdfdb079ebd98932@mail.gmail.com> <20071018082056.GW39759@funkthat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Cc: Subject: Re: Disable Exponential Backoff (retry) on Ethernet? X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 19 Oct 2007 02:10:47 -0000 Thanks so much for the response. Here is some additional information. I'm trying to emulate an RF network where there are colisions (e.g. "Aloha" type protocol) so I actually need collisions! I had forgotten that modern hardware essentially eliminated them. So, lets say I can find/use an "old hub", can I control the number of retries? Maybe I have to find some old NICs and old drivers? -- Len On 10/18/07, John-Mark Gurney wrote: > > 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." >