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[173.246.8.242]) by smtp.gmail.com with ESMTPSA id g2sm24974664qkb.80.2019.07.26.16.40.16 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 26 Jul 2019 16:40:17 -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: Date: Fri, 26 Jul 2019 19:40:15 -0400 Cc: "Holland, Jake" , Sebastian Moeller , Bob Briscoe , "ecn-sane@lists.bufferbloat.net" , "tsvwg@ietf.org" , Dave Taht , "De Schepper, Koen (Nokia - BE/Antwerp)" Content-Transfer-Encoding: quoted-printable Message-Id: <9C42D7E8-734A-4620-B95B-5FFDDF1D3D95@gmail.com> References: <364514D5-07F2-4388-A2CD-35ED1AE38405@akamai.com> <17B33B39-D25A-432C-9037-3A4835CCC0E1@gmail.com> <52F85CFC-B7CF-4C7A-88B8-AE0879B3CCFE@gmail.com> <87ef2myqzv.fsf@taht.net> <4B02593C-E67F-4587-8B7E-9127D029AED9@gmx.de> <34e3b1b0-3c4c-bb6a-82c1-89ac14d5fd2c@bobbriscoe.net> <77522c07-6f2e-2491-ba0e-cbef62aad194@bobbriscoe.net> <619092c0-640f-56c2-19c9-1cc486180c8b@bobbriscoe.net> <3A454B00-AEBC-48B6-9A8A-922C66E884A7@gmx.de> <21E40F44-2151-4565-970E-E1CEBE975036@gmx.de> <58F8052E-A56B-4E1F-8E1D-CBE75A0F7332@akamai.com> To: "Black, David" X-Mailer: Apple Mail (2.3445.9.1) Subject: Re: [Ecn-sane] [tsvwg] Compatibility with singlw queue RFC3168 AQMs X-BeenThere: ecn-sane@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Discussion of explicit congestion notification's impact on the Internet List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 26 Jul 2019 23:40:18 -0000 > On 26 Jul, 2019, at 4:07 pm, Black, David = wrote: >=20 >> I believe under this nomenclature, L4S in a queue with RFC3168-style >> marking at a bottleneck should be classified as a flow that is >> responsive but not TCP-compatible, and therefore poses a significant >> threat to internet performance within this context. >>=20 >> I'm not sure how best to describe this discrepancy, but I think it's >> fair to call it an incompatibility between a RFC3168-style marking >> queue and L4S. >=20 > Based on the L4S slides in today's meeting and related discussion, the = L4S folks are starting to deal with this concern. >=20 > I share your technical view that this concern is not safe to ignore. Based on our post-session discussions, I feel that it may not actually = be entirely clear to the L4S people just how serious the situation with = L4S and Codel is. The impression I gained was that they consider *Codel* to be broken, and = that *it* should be changed to match what L4S expects. This is = impractical given how widely Codel is already deployed, and the fact = that it was carefully designed specifically with RFC-compliant transport = flows in mind. The result of their proposed changes would no longer = resemble Codel at all. Unfortunately contributing to their apparent confusion, TCP Prague is = currently broken in such a way as to mask the problem if tested = directly. To experimentally verify our hypothesis, we had to synthesise = a pseudo-Prague implementation by inserting a firewall rule (mangling CE = into SCE) in front of our DCTCP-SCE implementation, the results of which = matched our mathematical predictions perfectly. We saw no evidence of a = Classic ECN detector in our TCP Prague tests. Codel is itself documented in an Experimental RFC, authored by no less = personages than Kathy Nichols and VJ. The derivative FQ-Codel is = similarly documented in an RFC. The variant I use named COBALT (aka = Codel-BLUE Alternate) is not yet in an RFC (nor even a draft), but = possibly it should be made into one, as the improvements are at least = interesting and are proven by both research and deployment. - Jonathan Morton=