From owner-freebsd-ipfw@FreeBSD.ORG Tue May 6 19:34:24 2008 Return-Path: Delivered-To: freebsd-ipfw@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 6DF3C106566B for ; Tue, 6 May 2008 19:34:24 +0000 (UTC) (envelope-from mpope@oanda.com) Received: from mail.oanda.com (q9.oanda.com [216.220.44.222]) by mx1.freebsd.org (Postfix) with ESMTP id 268EB8FC22 for ; Tue, 6 May 2008 19:34:23 +0000 (UTC) (envelope-from mpope@oanda.com) Received: from localhost (localhost [127.0.0.1]) by mail.oanda.com (Postfix) with ESMTP id 8593DEC07E for ; Tue, 6 May 2008 15:34:23 -0400 (EDT) Received: from mail.oanda.com ([127.0.0.1]) by localhost (mail.q9.oanda.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 00970-04 for ; Tue, 6 May 2008 15:34:23 -0400 (EDT) Received: from gateway.oanda.com (unknown [216.235.10.210]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by mail.oanda.com (Postfix) with ESMTP id 6F839EC027 for ; Tue, 6 May 2008 15:34:23 -0400 (EDT) Received: from [10.1.5.123] (mpope.dev.oanda.com [10.1.5.123]) by eddie.dev.oanda.com (Postfix) with ESMTP id 2B73F64063 for ; Tue, 6 May 2008 15:34:23 -0400 (EDT) Message-ID: <4820B2BF.6090608@oanda.com> Date: Tue, 06 May 2008 15:34:23 -0400 From: Matthew Pope User-Agent: Thunderbird 1.5.0.14ubu (X11/20080306) MIME-Version: 1.0 To: freebsd-ipfw@freebsd.org References: <4820AB8F.2000204@oanda.com> In-Reply-To: <4820AB8F.2000204@oanda.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: dummynet queue size relative to bw setting? X-BeenThere: freebsd-ipfw@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: IPFW Technical Discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 06 May 2008 19:34:24 -0000 I must correct my test parameters: In one of the two pipes, the bw was 4K, not 48K as stated. When I just now moved it up to 48K to match the other pipe size, my ping times plummeted to 129-139ms throughout the Queue sizes listed below, again with Q=120 getting total packet loss. I thought a ping sent packets slowly, so that the 4K bw on the one pipe would not slow things down, but it seems I was wrong. Still I'm wondering why the measured delay is 130, without dummynet its 40, and I've set it to 5ms in each direction, so it should be measured as 50, not 130. Thx, Matthew > Hello, > I've been reading about dummynet for 2 weeks, including the seminal > ACM paper & I'm very impressed. I've configured and run some > preliminary simulations that have my colleagues quite interested too. > > However, I'm finding my delay settings are yielding delays of about > two orders of magnitude larger that requested. I believe I don't > understand the relationship very well that defines the setting of the > queue size to relative to the bandwidth setting (and plr?) Can > someone explain or point me to a source for this? > > I recall reading that with lower bandwidths one should use lower queue > sizes to avoid long queuing delays. So I presume that is why my > delays are so long. So I've run some tests with various queue sizes. > > With Queue sizes of 100, 80, 60, 40, 10 slots on a pipe with a bw of > 48Kbits/s, delay of 5ms, and plr 0.025 defined in each direction, I'm > consistently getting RT delays of 500-600ms with a ping test, packet > loss does come out around 5%. The target I'm pinging is normally a 40 > ms latency. At Queue size 120 I get 100% packet loss (but I can > ignore that). > > I am not a networking specialist, so I realize my question is ignorant > :-) I'm running this in VMWare Server on a dual core 2 GHz with 2 GB > RAM using a modification of the dummynet test network design described > at codefromthe70s.org > Thanks, > Matthew > >