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[176.93.88.52]) by smtp.gmail.com with ESMTPSA id g4sm90610ljk.64.2021.09.28.18.37.57 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 28 Sep 2021 18:37:58 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.100.0.2.22\)) From: Jonathan Morton In-Reply-To: Date: Wed, 29 Sep 2021 04:37:56 +0300 Cc: rpm@lists.bufferbloat.net, Ben Greear , Karl Auerbach , Bob McMahon , bloat Content-Transfer-Encoding: quoted-printable Message-Id: <3176E6B1-CD4E-41E0-8BDA-62D3C73811D7@gmail.com> References: To: Dave Taht X-Mailer: Apple Mail (2.3654.100.0.2.22) Subject: Re: [Rpm] [Bloat] Relentless congestion control for testing purposes X-BeenThere: rpm@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: revolutions per minute - a new metric for measuring responsiveness List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 29 Sep 2021 01:38:00 -0000 > On 29 Sep, 2021, at 2:17 am, Dave Taht wrote: >=20 > In today's rpm meeting I didn't quite manage to make a complicated = point. This long-ago proposal of matt mathis's has often intrigued = (inspired? frightened?) me: >=20 > = https://datatracker.ietf.org/doc/html/draft-mathis-iccrg-relentless-tcp-00= >=20 > where he proposed that a tcp variant have no response at all to loss = or markings, merely replacing lost segments as they are requested, = continually ramping up until the network basically explodes. I think "no response at all" is overstating it. Right in the abstract, = it is described as removing the lost segments from the cwnd; ie. only = acked segments result in new segments being transmitted (modulo the = 2-segment minimum). In this sense, Relentless TCP is an AIAD algorithm = much like DCTCP, to be classified distinctly from Reno (AIMD) and = Scalable TCP (MIMD). Relentless congestion control is a simple modification that can be applied to almost any AIMD style congestion control: instead of applying a multiplicative reduction to cwnd after a loss, cwnd is reduced by the number of lost segments. It can be modeled as a strict implementation of van Jacobson's Packet Conservation Principle. During recovery, new segments are injected into the network in exact accordance with the segments that are reported to have been delivered to the receiver by the returning ACKs. Obviously, an AIAD congestion control would not coexist nicely with AIMD = based traffic. We know this directly from experience with DCTCP. It = cannot therefore be recommended for general use on the Internet. This = is acknowledged extensively in Mathis' draft. > In the context of *testing* bidirectional network behaviors in = particular, seeing tcp tested more than unicast udp has been, in more = labs, has long been on my mind. Yes, as a tool specifically for testing with, and distributed with = copious warnings against attempting to use it more generally, this might = be interesting. - Jonathan Morton=