From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ve0-x22c.google.com (mail-ve0-x22c.google.com [IPv6:2607:f8b0:400c:c01::22c]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 1502921F36C for ; Thu, 29 May 2014 07:09:56 -0700 (PDT) Received: by mail-ve0-f172.google.com with SMTP id oz11so437429veb.3 for ; Thu, 29 May 2014 07:09:55 -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; bh=ahLV5Vk0RjJV9t6wPM1nz8fy6180n18S7Lgt+dBnVbQ=; b=v7mxGv7v0E3r5E2CvfVbXRcZF3hRQVYzjpRc/GQKNrPsrwntzlqVzWkORmNPbmQSX7 LlYjQUKliWdimXbktjxPIHqYfEcewQiHoMNC/hUgTdHzHZVx3x07F88voYkvNz2sRhQU 31jvtX+9MsSVpR8o73y4DgPUaza6NTxjuoqqlHoVieSorT6KwtT97J95HevtL/yLzw+R 9n3DJFXjv00XoyR+pzczwT3DWNmIGbmTv4NpubZ7PSOmQPp+/E3TnuRVLsMI0MXUbIby PLlHHQAmTiTqNF+up8W170WkVT5Hl/AW/+h3YIepsP/X/K6qAg7nwgKybcDJzC0K4X8I FBEQ== MIME-Version: 1.0 X-Received: by 10.52.53.69 with SMTP id z5mr5818827vdo.42.1401372595781; Thu, 29 May 2014 07:09:55 -0700 (PDT) Received: by 10.52.14.99 with HTTP; Thu, 29 May 2014 07:09:55 -0700 (PDT) Received: by 10.52.14.99 with HTTP; Thu, 29 May 2014 07:09:55 -0700 (PDT) In-Reply-To: <53861CEB.8060003@rogers.com> References: <53861CEB.8060003@rogers.com> Date: Thu, 29 May 2014 17:09:55 +0300 Message-ID: From: Jonathan Morton To: davecb@spamcop.net Content-Type: multipart/alternative; boundary=089e01183caec5043904fa8a7b9f Cc: bloat 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 14:09:57 -0000 --089e01183caec5043904fa8a7b9f Content-Type: text/plain; charset=UTF-8 On 28 May 2014 20:31, "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. > > > > 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. > > 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! I think my description of the black box is still valid: a "defection" must imply a second output from the box, otherwise it will appear as either a reordering (preserving the property) or a discard. - Jonathan Morton --089e01183caec5043904fa8a7b9f Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

On 28 May 2014 20:31, "David Collier-Brown" <davec-b@rogers.com> wrote:
>
> On 05/28/2014 11:33 AM, Jonathan Morton <chromatix99@gmail.com> wrote
> > It's a mathematical truth for any topology that you can reduc= e to a black box with one or more inputs and one output, which you call a &= quot;queue" and which *does
> not discard* packets. =C2=A0Non-discarding queues don't exist in t= he real
> world, of course.
> >
> > The intuitive proof is that every time you promote a packet to be= transmitted earlier, you must demote one to be transmitted later. =C2=A0A = non-FIFO queue tends to increase the maximum delay and decrease the minimum= delay, but the average delay will remain constant.
>
> 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 e= xit door of
> the store!

I think my description of the black box is still valid: a &q= uot;defection" must imply a second output from the box, otherwise it w= ill appear as either a reordering (preserving the property) or a discard.

- Jonathan Morton

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