From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-vb0-f43.google.com (mail-vb0-f43.google.com [209.85.212.43]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id E689F21F0B4; Thu, 10 May 2012 07:25:11 -0700 (PDT) Received: by vbbfq11 with SMTP id fq11so3602719vbb.16 for ; Thu, 10 May 2012 07:25:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; bh=bon9KmMG7QX1QI14Ue4ftN/HritC3PBxLh/MhfWJTPc=; b=QSd6GcNAgOvYb2n07Mj7KnzluGx4GXsvIC/FmCSepFXFzVJTOU6KQW6tPaQc6Wtj8n IJ3AxX5v80IeEbd9pMuAByJBMjNOpixg6rL11nNrBb3cwzfhg0ftPxAOsoaixdpN8+j/ qDkuoAf82f1/o98nzESc2mjl5YWJCZPO8f9RRgqpzl/XstWc8dbPDnZ8zZNXLmgU5jZB IKZPxkTXcxfAazo40FrwNlXRuIR1o7LlVSK8oVG698ThtiQpn9TuocaElQvy2o5ICD2S JAN6X4tSM3g+b7jALewifMsqGFG1/iMHuZQYi8TdACmUodz4lKBYG7bBmzJimfI8pS9a mfJg== MIME-Version: 1.0 Received: by 10.52.67.199 with SMTP id p7mr1685018vdt.75.1336659910200; Thu, 10 May 2012 07:25:10 -0700 (PDT) Received: by 10.52.175.66 with HTTP; Thu, 10 May 2012 07:25:10 -0700 (PDT) In-Reply-To: <1336633359.27520.147.camel@shinybook.infradead.org> References: <532BA404-30FF-4395-9575-709A68E4C723@gmail.com> <1336631707.27520.136.camel@shinybook.infradead.org> <1336633359.27520.147.camel@shinybook.infradead.org> Date: Thu, 10 May 2012 10:25:10 -0400 Message-ID: From: Justin McCann To: David Woodhouse Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: codel@lists.bufferbloat.net, bloat Subject: Re: [Codel] [Bloat] The challenge X-BeenThere: codel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: CoDel AQM discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 10 May 2012 14:25:13 -0000 On Thu, May 10, 2012 at 3:02 AM, David Woodhouse wrot= e: > > If we overload the DSLAM, it drops one ATM cell out of N, which nixes > fairly much *every* IP packet by dropping a tiny part of each one, and > results in almost zero throughput. We don't let the DSLAM do > buffering :) Can't they turn on Early Packet Discard or something similar? This seems like a no-brainer. Dynamics of TCP Traffic over ATM Networks (1994), Allyn Romanow , Sally Flo= yd =A0 =A0 =A0http://citeseerx.ist.psu.edu/viewdoc/summary?doi=3D10.1.1.30.764= 7 "We investigate the performance of TCP connections over ATM networks without ATM-level congestion control, and compare it to the performance of TCP over packet-based networks. For simulations of congested networks, the effective throughput of TCP over ATM can be quite low when cells are dropped at the congested ATM switch. The low throughput is due to wasted bandwidth as the congested link transmits cells from `corrupted' packets, i.e., packets in which at least one cell is dropped by the switch. We investigate two packet discard strategies which alleviate the effects of fragmentation. Partial Packet Discard, in which remaining cells are discarded after one cell has been dropped from a packet, somewhat improves throughput. We introduce Early Packet Discard, a strategy in which the switch drops whole packets prior to buffer overflow. This mechanism prevents fragmentation and restores throughput to maximal levels."