From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from eu1sys200aog112.obsmtp.com (eu1sys200aog112.obsmtp.com [207.126.144.133]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by huchra.bufferbloat.net (Postfix) with ESMTPS id ABBAC21F37B for ; Thu, 29 May 2014 00:36:05 -0700 (PDT) Received: from mail.la.pnsol.com ([89.145.213.110]) (using TLSv1) by eu1sys200aob112.postini.com ([207.126.147.11]) with SMTP ID DSNKU4bjYSWJDzL4bmGxelk5Vd91wFwrAZAl@postini.com; Thu, 29 May 2014 07:36:05 UTC Received: from [172.20.5.238] (helo=roam.smtp.pnsol.com) by mail.la.pnsol.com with esmtp (Exim 4.76) (envelope-from ) id 1Wpusa-0004uI-Dn; Thu, 29 May 2014 08:36:00 +0100 Received: from gw.eu-west-1b.aws.pnsol.com ([172.30.11.4] helo=[172.30.8.198]) by roam.smtp.pnsol.com with esmtpsa (TLS1.0:RSA_AES_128_CBC_SHA1:128) (Exim 4.82) (envelope-from ) id 1Wpusa-0000En-1b; Thu, 29 May 2014 07:36:00 +0000 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.2\)) From: Neil Davies In-Reply-To: <53861CEB.8060003@rogers.com> Date: Thu, 29 May 2014 08:28:35 +0100 Content-Transfer-Encoding: quoted-printable Message-Id: <768DCE2B-AB4D-41C2-B218-B2360D613666@pnsol.com> References: <53861CEB.8060003@rogers.com> To: davecb@spamcop.net X-Mailer: Apple Mail (2.1878.2) Cc: bloat@lists.bufferbloat.net Subject: Re: [Bloat] ipspace.net: "QUEUING MECHANISMS IN MODERN SWITCHES", > (Jonathan Morton) 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: Thu, 29 May 2014 07:36:06 -0000 On 28 May 2014, at 18:29, David Collier-Brown = wrote: > On 05/28/2014 11:33 AM, Jonathan Morton wrote >> It's a mathematical truth for any topology that you can reduce to a = black box with one or more inputs and one output, which you call a = "queue" and which *does > not discard* packets. Non-discarding queues don't exist in the real > world, of course. >>=20 >> The intuitive proof is that every time you promote a packet to be = transmitted earlier, you must demote one to be transmitted later. A = non-FIFO queue tends to increase the maximum delay and decrease the = minimum delay, but the average delay will remain constant. >=20 > A niggle: people working in queuing theory* make the simplifying > assumption that queues don't drop. When describing the real world, = they > talk of "defections", the scenario where a human arrives at the tail = of > the queue and "defects", either to another queue or to the exit door = of > the store! There is another mathematical approach that we've found very useful, = actually the original work goes back to the 1950's (M/M/1/K/K).=20 As mentioned in a reply just now in a different thread, it does give = some interesting insights into the underlying two-degrees of freedom = that are present in every finite queue.=20 > As you might guess, what I find intuitive the IP world finds wrong, = and > vice versa. >=20 > --dave > [* as opposed, perhaps, to queuing networks (:-)] > --=20 > David Collier-Brown, | Always do right. This will gratify > System Programmer and Author | some people and astonish the rest > davecb@spamcop.net | -- Mark Twain >=20 >=20 >=20 > --=20 > David Collier-Brown, | Always do right. This will gratify > System Programmer and Author | some people and astonish the rest > davecb@spamcop.net | -- Mark Twain > _______________________________________________ > Bloat mailing list > Bloat@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/bloat