From owner-freebsd-stable@FreeBSD.ORG Tue Jan 30 20:03:08 2007 Return-Path: X-Original-To: freebsd-stable@freebsd.org Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id AA93B16A404 for ; Tue, 30 Jan 2007 20:03:08 +0000 (UTC) (envelope-from jandrese@mitre.org) Received: from smtp-bedford.mitre.org (smtpproxy1.mitre.org [192.160.51.76]) by mx1.freebsd.org (Postfix) with ESMTP id 6A40F13C4A8 for ; Tue, 30 Jan 2007 20:03:08 +0000 (UTC) (envelope-from jandrese@mitre.org) Received: from smtp-bedford.mitre.org (localhost.localdomain [127.0.0.1]) by smtp-bedford.mitre.org (8.12.11.20060308/8.12.11) with SMTP id l0UK373V029978 for ; Tue, 30 Jan 2007 15:03:07 -0500 Received: from smtp-bedford.mitre.org (localhost.localdomain [127.0.0.1]) by smtp-bedford.mitre.org (Postfix) with ESMTP id 95F75BEFB for ; Tue, 30 Jan 2007 15:03:07 -0500 (EST) Received: from imcfe2.MITRE.ORG (imcfe2.mitre.org [129.83.29.4]) by smtp-bedford.mitre.org (8.12.11.20060308/8.12.11) with ESMTP id l0UK37SK029966 for ; Tue, 30 Jan 2007 15:03:07 -0500 Received: from IMCSRV6.MITRE.ORG ([129.83.20.237]) by imcfe2.MITRE.ORG with Microsoft SMTPSVC(6.0.3790.1830); Tue, 30 Jan 2007 15:03:07 -0500 X-MimeOLE: Produced By Microsoft Exchange V6.5 Content-class: urn:content-classes:message MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Date: Tue, 30 Jan 2007 15:03:06 -0500 Message-ID: <53B52415C756A84E8A169F0E3673A3290E964A@IMCSRV6.MITRE.ORG> In-Reply-To: <20070124073602.B57678@xorpc.icir.org> X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: Dummynet and simulating random delay thread-index: Acc/zV6y5GL0saTySAeZU3UunOKlMgE2/6Ug References: <53B52415C756A84E8A169F0E3673A3290E8BA4@IMCSRV6.MITRE.ORG> <20070124071021.GG874@turion.vk2pj.dyndns.org> <20070124073602.B57678@xorpc.icir.org> From: "Andresen, Jason R." To: X-OriginalArrivalTime: 30 Jan 2007 20:03:07.0157 (UTC) FILETIME=[A890C450:01C744A9] Subject: RE: Dummynet and simulating random delay X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 30 Jan 2007 20:03:08 -0000 >From: Luigi Rizzo [mailto:rizzo@icir.org]=20 > >On Wed, Jan 24, 2007 at 06:10:21PM +1100, Peter Jeremy wrote: >> On Tue, 2007-Jan-23 14:22:54 -0500, Andresen, Jason R. wrote: >> >I have a project that requires me to simulate a link with=20 >varying but >> >well defined delay. The link is guarenteed to deliver packets in >> >order, so I wish to maintain that behavior with Dummynet. >>=20 >> I don't think dummynet can do this in its current form. Based on > >actually dummynet never does reordering within a single pipe, even >if you change the delay on the fly. > >But this said, you should explain "varying but well defined delay", >because if you use TCP or similar as the source, then you >have no control on when the userland write->tcp transmission delay >anyways so the concept is a bit vague and probably not a meaningful >experiment. And even in any common network (from switched >ethernet to wireless to dsl...) you have some variance on the delay, >ranging from a fraction of a millisecond to much larger values, >due to queueing and/or protocol issues (e.g. MAC channel allocation) >and/or switch/router/operating system issues. I'm trying to simulate a satellite link that has a normal delay of 1 second, but every 20-30 seconds or so the delay shoots up to 3.5 seconds for about 4 seconds and then settles back down to 1 second. >From what you said, I'm thinking that just twiddling the pipe on the fly will probably work. =20