From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-x234.google.com (mail-lj1-x234.google.com [IPv6:2a00:1450:4864:20::234]) (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 5F7FE3B2A4; Mon, 11 Mar 2019 12:13:51 -0400 (EDT) Received: by mail-lj1-x234.google.com with SMTP id l5so4613571lje.1; Mon, 11 Mar 2019 09:13:51 -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=aLcA0CBf0hRYwoP7VMSgDsTN7g4pnyHgKhgSF+/c0Yw=; b=Yye9anLzKP+HguhLC1KrnkaQ7V06nuw9HsKAOmPESA8SmAkt2GjpyeltNupvF5xgJq CIGKu3QqsN7rCiynWrPKjsX9hecPBSYii5JmGslW9/2WfexE34h9YjaFmN7UDZRBDux+ BQEABiyUw7sMkLsSjaCIMC+GoJxLNdb1L9qTJrsp38bo8dxPODRDNdCSQTu+F2uA0qXM MWxez8rhaq/T6ZlbObGhpDycQj5O8upLhSYrQZfe5L3AuIRwLzknsNBpE1spz/quOIn9 fW4mt6h3sW578n5+7w+SvzabbTZB6fMX11fOvZr0jXxAKVWJ0DTt1RGgnSW+OErmRnnY gt0A== 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=aLcA0CBf0hRYwoP7VMSgDsTN7g4pnyHgKhgSF+/c0Yw=; b=R7mW+VXgtNUuSPm4ApEN5NOB5UFSVM5BcYL0AnKBYKwz02xtE3AwoDLg4HbOs0+vF9 FQ2Ion7kqgP2xl1D6rLoEhLWvntnVjLQfB8JRcXrDKlai00/JN8QFjDbdB8pPGflsjle 7g62bAz43SWy7ZLzKr3CumO/pHkFKZmAS+YSku/rPi9qBh5eLvieFzX7bRvq4pKLirT7 GfaGfLCR+Ja1/e86NvOxLapaLf4fcpkybwxx8Qpta1XiFuT44JbV1hb0y6+aqZJ4JKSt aJU2VZbFXH+o5X8k9nKbW19NuBHUPKYEVn5gply3Y2lcvJnMGOWJrZpptvhTmIf4OPfM fkWQ== X-Gm-Message-State: APjAAAVh4te0sfxDHs9Xj7hLoGCvxDo8hJ0CADDco5OQ2EmoFyC1OCDV yAGLathQVEcBvyIxX4oqhsU= X-Google-Smtp-Source: APXvYqxe/ptwa4/9viuVY/tTedFnof9bLWlysVGFwLSgjST0Xkh27msU4JktjTr6AiXyFO4buGhZHg== X-Received: by 2002:a2e:161b:: with SMTP id w27mr14449104ljd.40.1552320830240; Mon, 11 Mar 2019 09:13:50 -0700 (PDT) Received: from jonathartonsmbp.lan (83-245-235-245-nat-p.elisa-mobile.fi. [83.245.235.245]) by smtp.gmail.com with ESMTPSA id z26sm1009207lja.33.2019.03.11.09.13.48 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 11 Mar 2019 09:13:49 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.1\)) From: Jonathan Morton In-Reply-To: <9C165094-DE2D-42AA-85F3-71760F01BD92@akamai.com> Date: Mon, 11 Mar 2019 18:13:47 +0200 Cc: Mikael Abrahamsson , Cake List , "ecn-sane@lists.bufferbloat.net" , Richard Scheffenegger , "codel@lists.bufferbloat.net" , bloat Content-Transfer-Encoding: quoted-printable Message-Id: <42826AC0-C4C4-4149-8994-EB6C95A3626B@gmail.com> References: <550C0248-1704-49DA-ABDC-49A91E0AC6F3@akamai.com> <1EE25778-8571-4506-A334-38C544470ACE@gmail.com> <9C165094-DE2D-42AA-85F3-71760F01BD92@akamai.com> To: "Holland, Jake" X-Mailer: Apple Mail (2.3445.9.1) Subject: Re: [Cake] [Ecn-sane] [Bloat] The "Some Congestion Experienced" ECN codepoint - a new internet draft - 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: Mon, 11 Mar 2019 16:13:51 -0000 > On 11 Mar, 2019, at 5:29 pm, Holland, Jake = wrote: >=20 > The key difference to me is that L4S doesn't work without a dual = queue. > It embeds a major design decision ("how many queues should there be at > a middle box?") into the codepoint, and comes with very narrow = requirements > on the sender's congestion control. It's certainly unclear to me what happens when an L4S flow passes = through a Classic ECN middlebox, especially one with only a single = queue. I get the impression that a DCTCP-like congestion response would = tend to starve out conventional flows competing with it. Unless you = have data showing otherwise? That has serious implications for incremental deployability, because you = can't safely deploy L4S endpoints until single-queue Classic ECN = middleboxes have all been replaced with L4S or flow-isolating types. = And without L4S endpoints in use, where's the impetus to do that? = Chicken and egg. Conversely, an SCE-aware flow passing through a Classic ECN middlebox = behaves just like a Classic ECN flow. The only question arises when a = single-queue AQM is made SCE-aware, and in that case the SCE-aware flows = are the ones that might get outcompeted (ie. they are friendlier, not = more aggressive). If necessary, it would be easy to specify that = single-queue AQMs "should not" produce SCE marks, only the = flow-isolating types - which in any case are easier to deploy at edge = devices where statistical multiplexing works less well. Incremental deployability is very important when tackling a project as = big as this. SCE takes it as a central tenet. L4S appears, in practice, = to have overlooked it. That's my objection to L4S. - Jonathan Morton