From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.gmx.net (mout.gmx.net [212.227.17.22]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "mout.gmx.net", Issuer "TeleSec ServerPass DE-1" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 1B11721FDD5 for ; Thu, 9 Jul 2015 03:55:16 -0700 (PDT) Received: from u-088-d142.biologie.uni-tuebingen.de ([134.2.88.142]) by mail.gmx.com (mrgmx102) with ESMTPSA (Nemesis) id 0LtUHA-1Z3MRQ3GVw-010yAD; Thu, 09 Jul 2015 12:55:12 +0200 Content-Type: text/plain; charset=windows-1252 Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) From: Sebastian Moeller In-Reply-To: <20150709100723.CB767406057@ip-64-139-1-69.sjc.megapath.net> Date: Thu, 9 Jul 2015 12:55:09 +0200 Content-Transfer-Encoding: quoted-printable Message-Id: References: <20150709100723.CB767406057@ip-64-139-1-69.sjc.megapath.net> To: Hal Murray X-Mailer: Apple Mail (2.1878.6) X-Provags-ID: V03:K0:MqyZAHh/HtqpJV6hTDuFC7rDuLbW17z7vkY+0H303y1urkh17bb xecTyzbcMKTepGmokWZ58YifJ18khKPy+waF0CHa7Z0wUD80FhU6jb0OBdVtSksA3TkdOge Z/M+s0klOZ0vwx33qIyeIJGSEUwcCOmrfnvc37mWQDXFV/ffGe6Ac9nVkNRJ5X6jKkZh5dK K72PY3LlJZ5iqS6MpC3ew== X-UI-Out-Filterresults: notjunk:1;V01:K0:ouc8vy6r66M=:6sVq+NxPguzZIVG+nnmc1I 1HwBDemNNk+iXjlLn3o8OSIWN8MBJgNERIqftfRtcnFDfUGa54mrIxRWem64rGdzDBKAluJrT SgUTanXY8wGjmldk86CDzbYLI63dQ9jt9PvEmDTMg8ihrBqKVeU9jUluNe0nrQVqOH9z/k2qh IY2ppXOEyBha1VXYQgxKl2obz3igyMt0Tjx2F1dql3AgzGoqi5xM6xeLPF+JLjThrVGY0lKoZ Bn/mXpGV54GEU3/c3JyD0eIxAbczvXI/Yz4S518RUQ30/gtlP0u4lbfrvJy5B76JopOUrKPjD Qfu+e2YpWOGK9pS2Zgq65Gn1z2Jr2hdDf/8hK0K35N+8dmxiTbEvLixrSHfs9KJ4m2gSWqOzM K4ldGdQDlKbvv9osNY0E+AaYAXasPHO67MVcbAFzxjYf/tLTMIihH/yp9EBP4MbC2pp0XAM2t 9DcatJk3DlDIB75p20P0c4+kvrGWdJxlzph1wVfC0+CFY94IoC/+kCj+FO5GmCZ4CENmiMq/S jCf/qg/rXYx/2RzRyE4PZVVgglC9GcPxzGOB212sP7Qajq1TvyrCxtwRZE8l/bU2Zuk/dYvyd HBit113OgE8sdqMv1sy5x3QAmduyZ0DqhYaAS+W5TTC7QBWHxmbFNQC0p/Pqki7qDzPL1Lt8p UTRIRI4Id5Hw6ayxOu+mHefyDQyCUEItoBoKphhIJdnvXpbnvUGw+oDOumGJ6oJvj8HUXsB3q D252WArD6HAnGzt/ Cc: bloat Subject: Re: [Bloat] Graph of bloat X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 09 Jul 2015 10:55:45 -0000 Hi Hal, On Jul 9, 2015, at 12:07 , Hal Murray wrote: > [=85] > NTP makes the assumption that the network delays are symmetric. = Without bloat, that's generally reasonable. It does screwup on long = links with asymmetric routing. If you watch NTP servers over a long = distance, you can see steps when the routing changes. On the scale of = bloat, those errors are minor. If you had a fast link rather than my = slow DSL link they would be significant. > [...] What about the inherent bandwidth and delay asymmetry of DSL = links? The bandwidth imbalance alone can reach 10:1 and more easily = (faster for ingress). And as far as I know classical reed-solomon = forward error correction is most often combined with interleaving (to = help against error bursts), and that interleaving often is asymmetric as = well (but this asymmetry can go in both directions, so ingress might see = more interleaving delay than egress. How much asymmetry can NTP cope = with, and does NTP try to assess the one-way delay for both legs of the = path to a server (without much thought I can fool myself into believing = that if NTP would start with the symmetric connection fiction, sync the = clocks and then use the synced clocks to asses the link delay asymmetry = and then try to re-sync the clocks taking the just measured asymmetry = into account might be a viable way around the issue; this seems simple = so most likely it must be wrong ;) )? Best Regards Sebastian=