From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm1-x32c.google.com (mail-wm1-x32c.google.com [IPv6:2a00:1450:4864:20::32c]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 4E89F3B2A4 for ; Thu, 25 Aug 2022 16:27:12 -0400 (EDT) Received: by mail-wm1-x32c.google.com with SMTP id j26so10778574wms.0 for ; Thu, 25 Aug 2022 13:27:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc; bh=VS+2IgtLoXYcvg/RMAaBkTHcjhlLlVzc/AOfbyyVkig=; b=aTAAxj43pMY+AsPP5dmD4HjZShsGkuP4SGmjZyFMWxB7/Nj6l7qJ0ZZX17GKF35jwd DVM2fcaNj6k9l1hUU2RyhWdsmfdUmOQpMM23+NzeXgk8XFH9S6x/YarU3q72N5sULJCo uhKvoQcfEJNlL2SoPQZ9PoraguFFeUT1Bq8eeQfo1KJfIYaMa0RWgQfEy5ceiWBXeGX2 nITMVLL4eF2cFUEKEB4EwRztR9Y7DAw+ONVB/Sk00a2HZYMwVukvMmZNEjnlNxMBZxSF mJ490LCD0SXU4BBZKnZxK/g/9F/tuxiBB8a3Vrv/jfAsoLYFhWRIbtljoznTJeb+vG5n mfAw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc; bh=VS+2IgtLoXYcvg/RMAaBkTHcjhlLlVzc/AOfbyyVkig=; b=QKzZ+/5Qyj6d66nM6MZDol9xvbiYEGM4tDgqA31GW+vfvsUqrtVskN/hyK4Bvi8RkL dk/D6jJF9A2u4RCvikxVON8fmKApL6YsscLRP2JMKwNtYQwOAKrb9zSj9s/B00h5JN1N iJaQDH9oqgETV73C2ww8nFLFwB9HwWEpM+CN18Jo/L3fvsUQrNY8nS3zTs9gPosXz6vS bBwUhFqkmVyw2EvR2SPL7aentCYJgM+kU/pZT1SEmtEyMNyHaZQs7io9Kwty4M69BOxN SCx9aeonAoOa2rWbE0uz9ERLwrGYduyZbfrNWnWbyFgHww7cn+2o6SFmuY/I0kpDajYo av2w== X-Gm-Message-State: ACgBeo0h9XhhhE+odjvuo0bRtACos/1Lx3+FCjBzAk7ImT6bDRDwUoFa oMsGGSK/agnuqCSWpOnTiBpTTA/yKlb2xBHbO8ypBFzgW/I= X-Google-Smtp-Source: AA6agR6wzYE+NC7LfRsIpltfdX9l9cKzq2gTYSiKswjgiMBXLCuNkELZBrWoEKuaT9qZqOB1NqTp1QmDlRkGqL+t0kk= X-Received: by 2002:a05:600c:430c:b0:3a6:26e:88e8 with SMTP id p12-20020a05600c430c00b003a6026e88e8mr3219417wme.48.1661459230918; Thu, 25 Aug 2022 13:27:10 -0700 (PDT) MIME-Version: 1.0 References: <1660246489.6578887@apps.rackspace.com> In-Reply-To: <1660246489.6578887@apps.rackspace.com> From: Dave Taht Date: Thu, 25 Aug 2022 13:26:58 -0700 Message-ID: To: "David P. Reed" Cc: Dave Taht via Starlink Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Subject: Re: [Starlink] SIGCOMM MIT paper: Starvation in e2e congestion control X-BeenThere: starlink@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: "Starlink has bufferbloat. Bad." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 25 Aug 2022 20:27:12 -0000 btw, it won best student paper at sigcomm. twitter thread here: https://twitter.com/VenkatArun95/status/1555200399652814850 On Thu, Aug 11, 2022 at 12:34 PM David P. Reed via Starlink wrote: > > > > On Thursday, August 11, 2022 10:29am, starlink-request@lists.bufferbloat.= net said: > > > From: Hesham ElBakoury > > To: "David P. Reed" , > > starlink@lists.bufferbloat.net > > Subject: Re: [Starlink] SIGCOMM MIT paper: Starvation in e2e > > congestion control > > > > Hi David, > > > > I think someone such as Professor Hari who got many awards including th= e > > sigcomm 2021 life-achievement award or his student Venkat need to be > > educated on Fair Queuing. There are many publications and text books > > which describe FQ. The results of this paper is for network paths that > > do not use FQ or ECN. Venkat/Hari can provide more details. > > > > I would think that he knows about FQ in AQM, too. He should. > > My point is that this paper, which talks about *starvation*, doesn't ment= ion FQ at all, even though it is well known to mitigate "starvation effects= " - it was invented to solve exactly that problem! > > I'd suggest at minimum that the paper should point out that it *excludes*= FQ from consideration. And if possible, explain why it was excluded... > > > > I can think of reasons for excluding FQ in the specific paper, but should= n't the title and abstract say it applies only narrowly: Proposed revised = title: "Starvation in e2e congestion control if FQ is excluded within the n= etwork" > > > > Particularly since the paper makes *broad* generalizations - the only 2-o= ut-of-3 argument is stated as if it applies to ALL congestion control. > > > > > For the CAP theorem, do you think I can get C,A,P, if this is what I > > need ? if this is the case, then this theorem is wrong or has limited > > applicability, correct ? > > > > It has limited applicability for sure. Yet, it has become fashionable to = act as if it is a completely general truth. > > > > The CAP theorem, in the limited space of its assumptions, appears to be c= orrect. But because it is so easily trivialized, as encouraged by the "you = can have any two of C A an P, but not 3" without any qualification, problem= s with the definitions of the words C A and P - serious problems indeed tha= t matter to a first order in real distributed systems - it is often used to= derive "impossibility". > > > > I'll give you another example of a serious misuse of a theorem outside it= s range of applicability: > > > > Shannon proved a channel capacity theorem: C =3D W log(S / N). The proof = is mathematical, and correct. > > But hiding in the assumptions are some very strong and rarely applicable = conditions. It was a very useful result in founding information theory. > > > > But... it is now called "Shannon's Law" and asserted to be true and appli= cable to ALL communications systems. > > > > This turns out not to be correct. And it is hardly ever correct in practi= ce. An example of non-correct application turns out to be when multiple tra= nsmissions of electromagnetic waves occur at the same time. EE practice is = to treat "all other signals" as Gaussian Noise. They are not - they never a= re. > > So, later information theorists discovered that where there are multiple = signals received by a single receiving antenna, and only a little noise (us= ually from the RF Front End of the receiver, not the environment) the Slepi= an-Wolf capacity theorem applies C =3D W log(\sum(S[i]. i=3D1,N) /W). That'= s a LOT more capacity than Shannon's Law predicts, especially in narrowband= signalling. > > And noise itself is actually "measurement error" at the receiver, which i= s rarely Gaussian, in fact it really is quite predictable and/or removable. > > > > So a theorem can be correct (based on its assumptions) and inapplicable i= n most cases, because of its narrowness. > > > > And this is why a limited (not very general) theorem of the 2-out-of-3 fo= rm is dangerous. > > > > As for the CAP theorem, my Ph.D. thesis was in this very area - multi-cop= y consistency in distributed data systems. That was in 1978, 45 years ago. = I've followed that work since the time - both the pragmatics and the theor= y. I think I fully understand both the context and how the axioms chosen by= Brewer simplify reality in radical ways. > > > > C A and P are not booleans or binary quantities. So in a real sense the C= AP theorem is always inapplicable. But worse, the proof structure falls apa= rt as a mathematical proof if you assume any metric for C A or P that isn't= homomorphic to boolean algebraic quantities. > > > > And worse, there is no standard measure of C A and P that captures what m= atters on any dimension. > > > > So, aside from an intuition that maybe C, A, and P trade off in some way = in some model of reality, the theorem is meaningless, and not very useful. > > > > I hope this helps understand what's behind my comments. > > > > At core, a referee ought to have asked - how is this conclusion justified= as a general conclusion about ALL e2e congestion control in all networks, = when it is only shown in a narrow, unrealistic case? > > > > In my nearly 50 years of publishing in the computing and communications w= orld, I've done a LOT of refereeing, and served on program committees as we= ll. The obligation of a referee is to look at the conclusions of the paper,= in the context of the state of the science, and figure out if the conclusi= on is supported by the paper's contents. > > > > I'm not sure why this didn't happen here. > > > > David > > > > PS: compared to the post-publication comments to my first CS publication,= in a letter to my mentor from Edsgar Dijkstra, I think I'm being gentle. I= t's motivated by getting the science right. > > > > > > > Thanks > > > > Hesham > > _______________________________________________ > Starlink mailing list > Starlink@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/starlink --=20 FQ World Domination pending: https://blog.cerowrt.org/post/state_of_fq_code= l/ Dave T=C3=A4ht CEO, TekLibre, LLC