From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf1-x136.google.com (mail-lf1-x136.google.com [IPv6:2a00:1450:4864:20::136]) (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 648333B2A4 for ; Fri, 24 Jul 2020 23:13:24 -0400 (EDT) Received: by mail-lf1-x136.google.com with SMTP id i19so6208581lfj.8 for ; Fri, 24 Jul 2020 20:13:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=P0S+MHfHsdWgRbgC4sQpK2OM7vIJ9TACin2tcklMQNY=; b=tuQk1jKXIMFDAUtnfMCqPQFcCy4mOYJnWngFSFGRxaz52cKfCVf1DDA+oa0k13ylU4 ylcNxitPP7lUTpzNhGldziXEmJC3eZCF5FuM7L2loWz+Cvrs397G9JxET/KrcolYKj5A RC1RnLgsJ3qMfQvgjzfgi/s5TDaMaecP7eLb7gSKUk2QOD2tbNpdmhFJoxif1HNPX59t MUAtlfxOd3PC3tBmhxljthzqFSBfIqXw7I2R2xF9eDlWC7kULBP0FTZkcnewLd5iHv3Q mzFESaaSjNtcpBPxakQJY++A+BPuZ/P/T1TcUDoxKHYSdR0zQkSKFksD6qiFaQBmwtQ3 PILg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=P0S+MHfHsdWgRbgC4sQpK2OM7vIJ9TACin2tcklMQNY=; b=cvMsshcT8zF/LTIzY5DHLsbuM7Qc8DR5me+13Fs3PtpA6xyhk0843DjCtRRmK+wrOh 3qji2y70+r3pDPodl8vP3Hb0lNyu+xUUsRS26diN99/X3Mf+pmj77PJj4W/y/T1Inb2k cokThjBQnAehZL+baAWcrdQIZZwrTwXtszpyiQmCYdS3ArH/vpF0yf63UCK32kLq5jpA euPsikDS+pb7fkNLGWCHjjDNEypSVtReBzJmVjnfoemzfxYvNAoghEdjTfrsAiKUgLWs cgep+T6XJw+bvIE3haTvfVDV8qJrEZ2vAbZit474EcQF+cBIVrGB67A279vZ3bylmyXy 7VVA== X-Gm-Message-State: AOAM530CSc5Iiv9pw2aroKSE3nsqKVS5yEaH8SkZKiBFiePe68GVn6ou SLvrZzyHpd2+98PCfgdSBrY= X-Google-Smtp-Source: ABdhPJxuyOsaODkYZEY/vlodANcQiE1hMzvlxz1U/F6DOpImC5PyS54D6GvahmgRZ4QKZIsO2S8nmw== X-Received: by 2002:a05:6512:6d6:: with SMTP id u22mr6372638lff.13.1595646802514; Fri, 24 Jul 2020 20:13:22 -0700 (PDT) Received: from jonathartonsmbp.lan (83-245-252-162-nat-p.elisa-mobile.fi. [83.245.252.162]) by smtp.gmail.com with ESMTPSA id m6sm663344ljc.134.2020.07.24.20.13.21 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 24 Jul 2020 20:13:21 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.6\)) From: Jonathan Morton In-Reply-To: Date: Sat, 25 Jul 2020 06:13:20 +0300 Cc: cake@lists.bufferbloat.net Content-Transfer-Encoding: quoted-printable Message-Id: <1904547A-DC0A-497F-AB7C-624733E2F60A@gmail.com> References: To: Justin Kilpatrick X-Mailer: Apple Mail (2.3445.9.6) Subject: Re: [Cake] diffserv3 vs diffserv4 X-BeenThere: cake@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Cake - FQ_codel the next generation List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 25 Jul 2020 03:13:24 -0000 > On 24 Jul, 2020, at 6:56 pm, Justin Kilpatrick = wrote: >=20 > "sqm-scripts used 3 tiers of priority pretty successfully as does = free.fr. - de-prioritization seems a good idea, prioritization not so = much." >=20 > This is the best comment on why diffserv3 is the default that I could = find on bufferbloat.net. I'm interested in hearing about what data = (anecdotes welcome) lead to this conclusion. In Cake, Diffserv4 maps conceptually (but not in detail) to the four = priority buckets in Wifi - BK, BE, VI, VO. In Diffserv3 the VI bucket = is dropped, because Cake's flow isolation within BE is already good = enough to give decent video streaming performance. The BK and VO = buckets are still useful to deal with certain specific problems; BK is = the place to put "swarm" protocols which intend to be scavengers but = which flow-isolation tends to prioritise, and VO is for = latency-sensitive protocols which the user wants to specifically protect = from random traffic fluctuations. Thinking more broadly, I believe Diffserv would have been far more = successful if it had replaced Precedence/TOS with a simple two-bit, = four-way set of PHBs: 00: High Throughput - equivalent to traditional Best Effort service. 01: High Reliability - "Every Packet's Sacred". 10: Low Cost - a scavenging service for altruistic applications. 11: Low Latency - for the many protocols that are sensitive to delays = more than throughput. It may also have been reasonable to include a couple of extra bits for = uses internal to an AS, on the understanding that the basic two bits = would be preserved end-to-end as an indication of application intent. Of the above four classes, Diffserv3 provides three - omitting only the = High Reliability class. But that is a class most useful within a = datacentre, where it is actually practical to implement a lossless = backplane with backpressure signals instead of loss. What we *actually* have is a six-bit field with ill-defined semantics, = that is neither preserved nor respected end-to-end, is consequently = ignored by most applications, and consumes all the space in the former = TOS byte that is not specifically set aside for ECN (a field which could = profitably have been larger). It is a serious problem. Implementations of PHBs still tend to think in terms of bandwidth = reservation (a Bell-head paradigm) and/or strict priority (like the = Precedence system which was lifted directly from telegraphy practice). = Both approaches are inefficient, and go along with the misconception = that if we can merely categorise traffic on the fly into a large enough = number of pigeonholes, some magical method of dealing with the = pigeonholes will make itself obvious. However, both the easy, universal = method of categorisation and the magical delivery strategy have failed = to materialise. It rather suggests that they're doing it wrong. So that is why Diffserv3 is the default in Cake. It offers explicit = "low cost" and "low latency" service for suitably marked traffic, and = for everything else the Best Effort service uses flow and host isolation = strategies to maintain good behaviour. It usually works well. - Jonathan Morton