From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wg0-f47.google.com (mail-wg0-f47.google.com [74.125.82.47]) (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 ACDC621F14B for ; Tue, 23 Oct 2012 17:39:42 -0700 (PDT) Received: by mail-wg0-f47.google.com with SMTP id ge7so2723890wgb.28 for ; Tue, 23 Oct 2012 17:39:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=subject:mime-version:content-type:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to:x-mailer; bh=WqozYUrJidioLz/gcv1XHXyKhJ3Gx5fT8e/CkxoxtrU=; b=G2NNGh972xBcWxYn0Bvt0XnZNOyQhr8CjsPeEl697CWB7pwT+HXRH9VuZv1+i3Uigq TqYtgdICrYy9qsfvyljj5ijPp3nb9mBzsn27KBtmDbEu4E5jnClwjubRis4t0ylkvVLd cKqTKCR/SIySpq0sZtNlmO1oxFZlJBG4wMw4msK8xIhdtNc7AfNolhTx3scweF07mY4c Udoq/1cmwet5SDwkRtOSJqo6QR7hjUsPzpebPIm9LC1v+p/gdVXiitfPJr7N80b4bpsY TO7UWSKr9oG62TGRli+clLEy3/QWVcSwvxtadK7UAZiZ3s4oMvP+lmqZM4FMAxPkPGZx VNbQ== Received: by 10.180.99.97 with SMTP id ep1mr1705786wib.9.1351039180706; Tue, 23 Oct 2012 17:39:40 -0700 (PDT) Received: from bass.home.chromatix.fi (xdsl-83-150-84-172.nebulazone.fi. [83.150.84.172]) by mx.google.com with ESMTPS id hv8sm1521154wib.0.2012.10.23.17.39.39 (version=TLSv1/SSLv3 cipher=OTHER); Tue, 23 Oct 2012 17:39:40 -0700 (PDT) Mime-Version: 1.0 (Apple Message framework v1085) Content-Type: text/plain; charset=us-ascii From: Jonathan Morton In-Reply-To: Date: Wed, 24 Oct 2012 03:39:38 +0300 Content-Transfer-Encoding: quoted-printable Message-Id: <4C04E6DB-F9A4-4326-818B-17D953CA1D39@gmail.com> References: To: Dave Taht X-Mailer: Apple Mail (2.1085) Cc: bloat Subject: Re: [Bloat] "a bandwidth breakthrough" X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 24 Oct 2012 00:39:43 -0000 On 24 Oct, 2012, at 12:24 am, Dave Taht wrote: > I've had 3 separate people send me this today. >=20 > http://www.technologyreview.com/news/429722/a-bandwidth-breakthrough/ >=20 > Sure wish we had a PR dept here that was this good vs a vs fq_codel. >=20 > I *think* I've read the relevant paper "Modeling network coded TCP > throughput"? But perhaps there is something newer driving this > announcement? That looks like a form of Forward Error Correction - you basically stick = a Reed-Solomon code or a trellis code across sections of data packets, = and unconditionally send extra packets containing the correction code. = This allows missing packets to be reconstructed at the receiver instead = of retransmitted. Most TCPs back off very heavily when subjected to = random loss, because they interpret it as congestion loss, and that is = what results in poor throughput. With Reed-Solomon, each extra packet sent allows one arbitrary dropped = packet from the group to be reconstructed, *provided* the total number = of dropped packets from the group doesn't exceed the number of extra = packets. Latency is however increased by the group size, which can be = over 250 packets in an extremely naive example. With a trellis code, the reconstruction would be more continuous, with = latency depending on the properties of the code rather than on the group = size. This might therefore be the better option. High speed hardware = trellis decoders are already in common use. The more common form of FEC operates within a packet, ensuring that low = levels of bitwise corruption don't invalidate the whole packet. A heavy = burst error can still squash the whole packet though. I'm actually sort of surprised that the inter-packet version isn't = already built into wireless technologies by default, especially the ones = that do packet aggregation. In any case it is not totally new - a very = similar idea is used in CDs. These people seem to be implementing it using a tunnelling protocol to a = proxy server. That makes it easy to test in public as they describe, = although I would be wary of their results until they can be replicated. - Jonathan Morton