From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-x230.google.com (mail-lf0-x230.google.com [IPv6:2a00:1450:4010:c07::230]) (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 D8ADD3B2A0 for ; Wed, 21 Sep 2016 07:14:44 -0400 (EDT) Received: by mail-lf0-x230.google.com with SMTP id g62so37423254lfe.3 for ; Wed, 21 Sep 2016 04:14:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=UEgoKAec/IQAXlSaoC7ZkL5q2rBLevBKi1b0CVGYNQM=; b=Ny0zsOcht6NOedYBXrcDIJduIvcF9NBqFwEUv674q1MyVpttUL6FJARq28gqI6+GHF BwhmIOr5S2jQKPWAfvpSJw1GGrx7D481hLuCoCryA11OMRKh/frqhnu1RprPS2kN/ArC Fkqf0nIe0m/mBiZWXCtxSY5sAXe9Y/6gR2CUDrF9BryXlzQZGH7KGUys457LTjI+d/t+ 6tIPHNvnn4TZ6Pyy9IG2Ak9gIZaY40cyWYB5o1bYLbxM3fCRTCUHHDt0kyJcnyjpXOjs Zj/YkVzXrVb7zhPU8+ylDwCymG+eph2Is5CEG5+tzoU8UK9uJvQF3aGYRcoSspN3Mqv8 INOA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=UEgoKAec/IQAXlSaoC7ZkL5q2rBLevBKi1b0CVGYNQM=; b=Tx+IRw/3FIqH5BvYD8K3nUs7dt4CzcEcLOBUeIyYX9b0cwBOQCWIqZ/OJBJha5gDaV tURnAI/FguSt9owO0H4/40rF49EG6Ok+4J40FTq93Ubvg3mGSGCXuqaDtu1lU55oMvJI sJ6FVQQctmmeJtEgksVaO4yD10Xh8aPsjLg8BAOqfsBgcocbB1n4BNI5bS4Vz6MnQReF LR8rbZInSuh34mLEdGp/MA472ts2zZHjdQRFOjwkxVAutXGLCDp4LgoBP+I+9KXLdbfT RtzNMwUzKHsKHaup2IZb5qRNvBF7eCh5VjT5yaqGSCFlc7RS481UP/zTMBQY0JD4jYMS m6RQ== X-Gm-Message-State: AE9vXwP4b7SojDN0iNOvLp15//eNQKBFOAbE8xKJ94BPvZmJRiKBHAG1eaysm33KKlt6Xc9fl+w8epdSxZ+6+g== X-Received: by 10.25.23.29 with SMTP id n29mr12655757lfi.19.1474456483506; Wed, 21 Sep 2016 04:14:43 -0700 (PDT) MIME-Version: 1.0 Received: by 10.25.5.209 with HTTP; Wed, 21 Sep 2016 04:14:42 -0700 (PDT) In-Reply-To: References: <92a6ae25-530f-1837-addd-8a9ef07dd022@gmail.com> From: Alan Jenkins Date: Wed, 21 Sep 2016 12:14:42 +0100 Message-ID: To: Mikael Abrahamsson Cc: Dave Taht , "cerowrt-devel@lists.bufferbloat.net" Content-Type: text/plain; charset=UTF-8 Subject: Re: [Cerowrt-devel] BBR congestion control algorithm for TCP in net-next X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 21 Sep 2016 11:14:45 -0000 On 21/09/2016, Mikael Abrahamsson wrote: > On Wed, 21 Sep 2016, Dave Taht wrote: > >> I dunno, I'm just reading tea leaves here! >> >> can't wait for the paper! > > +1. > > I would like to understand how BBR interacts with a window-fully-open > classic TCP session and FIFO induced delay that is in steady-state before > the BBR session starts. > > So let's say I have 100ms of lightspeed-in-fiber RTT, and I am then > running a file transfer with some other TCP algorithm which is sitting > there, window fully open, creating an additional 100ms of > stupid-router-FIFO-buffering delay. > > So new BBR TCP session comes along, sees 200ms of RTT, and starts sending. > I guess the classic TCP algorithm still keeps its window fully open, and > doesn't care that RTT now increased to 210ms by the BBR flow packets. > > Now what? BBR flow sees increased latency, and backs off, right? So how > much of the bandwidth will each flow get? How do these interact? I don't know what you're reading, but the BBR code that's just been submitted does not back off when latency increases. Period. If less well-behaved flows drove up the minimum latency measured over the 10 second interval, BBR would treat this as a longer pipe, and will seek to fill it. It would *increase* the number of packets in-flight. That assumes the measured maximum bandwidth (over an interval of 10*rtt) remains constant. (Say there were 100 BBR flows, then you added one CUBIC flow to bloat the buffer). I don't have a good intuition for how the bandwidth estimation behaves in general.