From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-24-ewr.dyndns.com (mxout-030-ewr.mailhop.org [216.146.33.30]) by lists.bufferbloat.net (Postfix) with ESMTP id 6CB112E04AC for ; Tue, 8 Feb 2011 07:17:57 -0800 (PST) Received: from scan-21-ewr.mailhop.org (scan-21-ewr.local [10.0.141.243]) by mail-24-ewr.dyndns.com (Postfix) with ESMTP id 82C005CBB0F for ; Tue, 8 Feb 2011 15:17:55 +0000 (UTC) X-Spam-Score: 0.0 () X-Mail-Handler: MailHop by DynDNS X-Originating-IP: 74.125.82.41 Received: from mail-ww0-f41.google.com (mail-ww0-f41.google.com [74.125.82.41]) by mail-24-ewr.dyndns.com (Postfix) with ESMTP id 9A6A45D0AC4 for ; Tue, 8 Feb 2011 15:17:50 +0000 (UTC) Received: by wwi18 with SMTP id 18so663457wwi.4 for ; Tue, 08 Feb 2011 07:17:50 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:in-reply-to:references:date :message-id:subject:from:to:cc:content-type; bh=0bJbdW8WFVZBtXRjCTI0jFN7W1WmgYy+JRsly3pymCg=; b=g2bAUDSlh4Fs8tGs2EW6vExw3qdTMdk9IxhAe6StDbqkUC4qOkDUMnSkQbVTKNNb3P 0fSE/jQyhFM3ANIA6Y+FhkqIw5ldqtpg8IyKmCPt14mHPaf9augaEsv58/Uilli/SPpI mTejxv9PTIfVRa0bKQcZyAYG7j/XlbkScxQ6Y= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; b=n8wOjvNjIh/nYfWk4svUNopJ6sdo4wLpnYVNivznUDPutb1v0Qf1bHyJydqDC1SUwa W2MkpLjXahE6SLrjz8TNT0EOwO27x9sd29D/kT7CuyuJ+6kJ+55Ly2Mx8IeabUcLnYdQ T1ETpGIt60QKrFee4Cmm7mwsw8NAUwdFT5EWM= MIME-Version: 1.0 Received: by 10.227.153.204 with SMTP id l12mr15868263wbw.81.1297178269635; Tue, 08 Feb 2011 07:17:49 -0800 (PST) Received: by 10.227.2.208 with HTTP; Tue, 8 Feb 2011 07:17:49 -0800 (PST) In-Reply-To: <20110205132305.GA29396@thyrsus.com> References: <20110205132305.GA29396@thyrsus.com> Date: Tue, 8 Feb 2011 10:17:49 -0500 Message-ID: From: Justin McCann To: esr@thyrsus.com Content-Type: text/plain; charset=ISO-8859-1 Cc: bloat@lists.bufferbloat.net Subject: Re: [Bloat] First draft of complete "Bufferbloat And You" enclosed. 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: Tue, 08 Feb 2011 15:17:58 -0000 On Sat, Feb 5, 2011 at 8:23 AM, Eric Raymond wrote: > Please fix typos and outright grammatical errors. If you think you have spotted > a higher-level usage problem or awkwardness, check with me before changing it. > What you think is technically erroneous may be expressive voice. This may be intentional, but the text launches into an explanation of why bufferbloat is bad without concisely explaining what it is--- you have to read the whole first two sections before it's very clear. Maybe fitting Jim's phrase "the existence of excessively large (bloated) buffers" (from http://www.bufferbloat.net/projects/bloat/wiki/Bufferbloat) toward the beginning would help, bI guess your new third paragraph will have that. The second of the three main tactics states, "Second, we can decrease buffer sizes. This cuts the delay due to latency and decreases the clumping effect on the traffic." Latency *is* delay; perhaps "cuts the delay due to buffering" or "due to queueing" would be better, if more tech-ese. I've re-read through the Bell Labs talk, and some of the earlier posts, but could someone explain the "clumping" effect? I understand the wild variations in congestion windows ("swing[ing] rapidly and crazily between emptiness and overload"), but clumping makes me think of closely spaced packet intervals. This statement is one I find problematic: "A constantly spaced string of cars coming in tends to turn into a series of clumps coming out, with size of each clump controlled by the width of the exit from the the parking lot." If the bottleneck bandwidth is a constant 10 Mbps, then the outgoing packets will be spaced at the 10 Mbps rate (the ACK clocking effect). They aren't really more clumped going out than they came in-- in fact, with more traffic joining at the choke point, a given flow's packets will be spaced out even more than they were before. This isn't quite so true on a wireless link, where it's not the buffering so much as the variation in actual layer-2 goodput due to retransmissions and rate changes that cause clumping. The essential problem is that the increase in RTT slows the feedback loop, so if a queue is creating an 8 second delay, there can be 8 seconds of badness and changes before *any* connection slows down (or speeds up). The problem isn't clumping so much as it is the delay in feedback. Justin