From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-la0-x22b.google.com (mail-la0-x22b.google.com [IPv6:2a00:1450:4010:c03::22b]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id BFDEE21F3ED; Fri, 15 May 2015 05:19:49 -0700 (PDT) Received: by lagr1 with SMTP id r1so35047814lag.0; Fri, 15 May 2015 05:19:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=content-type:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=MfODDdxb5a4husebN4bR8mz09WCXk87jjH96GOgL000=; b=Ube1a+K/9F/10cdM4Z5JPySPp5Vt4hI+c6e/GUhPXRDTjBEoEQpVJnTm6BNYt7bU2U qDZhixYHDvsvKX/R8WLXOHHsKY9WGnZ+oK5HTMHf6SEj507nUjwvfoKHWgMWYQwkhh+q MPnkn5ItLu1Euw6KiqdcofNaeMRAMFn66LYYf2ksDCH0+SD0I504hAQ5g55ycK/rHpr7 F+cM86HRjLYUxtulLU4CEJOpoVuboAf8+7uf3bFvCLwSLrmJZnebEKEUUN3kE8Mg4p0/ 00s9pXTeiai5+ICLv3SbmbPhjZ77knipDRHBMrshf5tmKhkArBbornou2Tokb7vDUZcm /Lcg== X-Received: by 10.152.204.7 with SMTP id ku7mr2177233lac.38.1431692386757; Fri, 15 May 2015 05:19:46 -0700 (PDT) Received: from bass.home.chromatix.fi (87-93-34-32.bb.dnainternet.fi. [87.93.34.32]) by mx.google.com with ESMTPSA id wl9sm424771lbb.11.2015.05.15.05.19.35 (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 15 May 2015 05:19:45 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2098\)) From: Jonathan Morton In-Reply-To: Date: Fri, 15 May 2015 15:19:15 +0300 Content-Transfer-Encoding: quoted-printable Message-Id: <916082F3-82DA-4B22-AB0C-818435471F58@gmail.com> References: <8C015B1B-EFBA-4647-AD83-BAFDD16A4AF2@netapp.com> To: "Bill Ver Steeg (versteb)" X-Mailer: Apple Mail (2.2098) Cc: "Klatsky, Carl" , "cake@lists.bufferbloat.net" , "cerowrt-devel@lists.bufferbloat.net" , bloat , "Eggert, Lars" Subject: Re: [Cerowrt-devel] [Bloat] heisenbug: dslreports 16 flow test vs cablemodems X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 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: Fri, 15 May 2015 12:20:20 -0000 > On 15 May, 2015, at 14:27, Bill Ver Steeg (versteb) = wrote: >=20 > But the TCP timestamps are impacted by packet loss. You will sometimes = get an accurate RTT reading, and you will sometimes get multiples of the = RTT due to packet loss and retransmissions. I would hate to see a line = classified as bloated when the real problem is simple packet loss. Head = of line blocking, cumulative acks, yada, yada, yada. TCP stacks supporting Timestamps already implement an algorithm to get a = relatively reliable RTT measurement out of them. The algorithm is = described in the relevant RFC. That=E2=80=99s the entire point of = having Timestamps, and it wouldn=E2=80=99t be difficult to replicate = that externally by observing both directions of traffic past an = intermediate point; you=E2=80=99d get the partial RTTs to each endpoint = of the flow, the sum of which is the total RTT. But what you=E2=80=99d get is the RTT of that particular TCP flow. This = is likely to be longer than the RTT of a competing sparse flow, if the = bottleneck queue uses any kind of competent flow isolation. - Jonathan Morton