From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-x235.google.com (mail-lj1-x235.google.com [IPv6:2a00:1450:4864:20::235]) (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 52C653B29D; Sat, 4 Jul 2020 14:02:35 -0400 (EDT) Received: by mail-lj1-x235.google.com with SMTP id z24so15641266ljn.8; Sat, 04 Jul 2020 11:02:35 -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=MJ40AuzdGcmYm7sSta2xCdge4/0Daz0Xf7h8nSNeEbQ=; b=XNaM7MjezrMXQGuGCnc1NTTN0ihxjiRzXVt8uqyHzzkpZWJM98mv8kiOZlyJ2Hmgch kEyCy0YVAew/UJOfpJUfX9D2HJkwNyJXFTSjUSwiTKg5PxX/qN3w3wra0pXUItxEQVJH 91Tkoxaoj0VvcZ1dz2HV9/ATBCsNjtgpqehfxUzMf8olwDfzqZQx7HNGSlltzalvhhAM 4PpS4t98xGQkQjVSkVSYdTlWqXRKeS8Fkbwvcz4Ki02Xi8m42MjxemXTdjQym1uSnuEL hBn1NDPhEr/6qVaseAVRJHaM2g3cO8Ci9LwnTQ2mNj5ayTqH2dpqhOIZZK3W0RSgCV8T AYng== 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=MJ40AuzdGcmYm7sSta2xCdge4/0Daz0Xf7h8nSNeEbQ=; b=uoaUMt/3Y8gLVCpEADC6chGh/+y3fyxeIWM5G2349/hHIIjwElgPBWQ3MWxVPmdOUq Yf5vPrgmQSHorapjAi2g4aSYOD0+AuVJq5FH1mIEQwFE3qfbhz/kD8xKbrKyZig0a/HF rnXrxaRlpM3lt6muBzDkAmvn+y/C+I8XoO4kcpLVfQNRg/b5bocM5+TJiwk2nZNc9Air e6C0nHu/73R9r8UuGKaknWOcb2f7PFWX918CQ+iUoS/UQwk6vWn8W5jWSqVVnYOnSGxQ DvQL36daEFet21gwV+PVQnDL/fEyVsf0boGvTLTTPzHptpf2Gb5YrlDuMhO5FgZdSXze ieUw== X-Gm-Message-State: AOAM53258ni5832OQgE/zTB7iIQ8wa/x9quDk7r034hlG7fCNStq+k51 5ZAnbivx1/0nJT6+RIYHNh4= X-Google-Smtp-Source: ABdhPJyzcobezlI0pcNthv1+5Tpvr+j0DGN/GNqy3q8HzUWzbGY0k1sI5LaSrCkHTrQdSfzKCfDnDA== X-Received: by 2002:a2e:2242:: with SMTP id i63mr24018624lji.370.1593885754256; Sat, 04 Jul 2020 11:02:34 -0700 (PDT) Received: from jonathartonsmbp.lan (83-245-228-203-nat-p.elisa-mobile.fi. [83.245.228.203]) by smtp.gmail.com with ESMTPSA id n25sm5278456lji.28.2020.07.04.11.02.30 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sat, 04 Jul 2020 11:02:33 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.5\)) From: Jonathan Morton In-Reply-To: Date: Sat, 4 Jul 2020 21:02:26 +0300 Cc: Matt Mathis , Make-Wifi-fast , Carlo Augusto Grazia , bloat , jamshid@whatsapp.com Content-Transfer-Encoding: quoted-printable Message-Id: <26B050EB-25D5-4545-B6A6-5265ED146617@gmail.com> References: To: Daniel Sterling X-Mailer: Apple Mail (2.3445.9.5) Subject: Re: [Make-wifi-fast] [Bloat] the future belongs to pacing X-BeenThere: make-wifi-fast@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 04 Jul 2020 18:02:35 -0000 > On 4 Jul, 2020, at 8:52 pm, Daniel Sterling = wrote: >=20 > could someone explain this to a lay person or point to a doc talking > about this more? >=20 > What does BBR do that's different from other algorithms? Why does it > break the clock? Before BBR, was the clock the only way TCP did CC? Put simply, BBR directly probes for the capacity and baseline latency of = the path, and picks a send rate (implemented using pacing) and a = failsafe cwnd to match that. The bandwidth probe looks at the rate of = returning acks, so in fact it's still using the ack-clock mechanism, = it's just connected much less directly to the send rate than before. Other TCPs can use pacing as well. In that case the cwnd and RTT = estimate are calculated in the normal way, and the send rate (for = pacing) is calculated from those. It prevents a sudden opening of the = receive or congestion windows from causing a huge burst which would tend = to swamp buffers. - Jonathan Morton