From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wy0-f171.google.com (mail-wy0-f171.google.com [74.125.82.171]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id C0217200ABA for ; Fri, 23 Sep 2011 02:24:45 -0700 (PDT) Received: by wyh13 with SMTP id 13so3173562wyh.16 for ; Fri, 23 Sep 2011 02:24:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=message-id:date:from:user-agent:mime-version:to:subject:references :in-reply-to:content-type:content-transfer-encoding; bh=Uhl13Kvn5foxQ8R8xWGTcSoYmMZ7pH/VVHZQttLmsYc=; b=VKUzBqkTVQowopV2GP2e2NpMX+aBCXqRUu7AeYYRGwxBnYlGwmj6XvSEL1WiasjGwg y12TwY77H1rnG5t1yigZUR8DmNbecg0tKGh3RlaigI0YHDdZO+Bt6zacOaUgBhPKgc5Q gF9yIQvZ64DS7AMgw1o9ISCRItdvsBXSEHa4g= Received: by 10.227.9.219 with SMTP id m27mr1853363wbm.61.1316769882477; Fri, 23 Sep 2011 02:24:42 -0700 (PDT) Received: from [192.168.1.6] (68.3-64-87.adsl-dyn.isp.belgacom.be. [87.64.3.68]) by mx.google.com with ESMTPS id z9sm15479803wbn.19.2011.09.23.02.24.41 (version=SSLv3 cipher=OTHER); Fri, 23 Sep 2011 02:24:41 -0700 (PDT) Message-ID: <4E7C5058.8090504@gmail.com> Date: Fri, 23 Sep 2011 11:24:40 +0200 From: Jan Ceuleers User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.21) Gecko/20110831 Thunderbird/3.1.13 MIME-Version: 1.0 To: bloat-devel@lists.bufferbloat.net Subject: Re: Preliminary results of using GPS to look for clock skew References: <20110921230205.2275820C2E5@snark.thyrsus.com> In-Reply-To: <20110921230205.2275820C2E5@snark.thyrsus.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: bloat-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: "Developers working on AQM, device drivers, and networking stacks" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 23 Sep 2011 09:24:46 -0000 Eric, Can I suggest another method for your comparisons of GPS time to ntp (or rather network) time? The whole purpose of ntpd is to compare multiple sources of time, whether local refclocks such as a GPS receiver or remote-ones. In fact, when acquiring a new refclock and before pressing it into service it is necessary to calibrate the offset between its PPS signal (as seen by the ntpd process, and therefore incorporating the propagation delay in the cable, in the receiver circuit and the processing delay in the OS) and the true UTC second. This is done by adding the new refclock to the ntpd config file, but by also telling ntpd to distrust it (using the noselect keyword). You can then leverage all of ntpd's stats for comparing the refclock to all other available time sources. More info at www.ntp.org. HTH, Jan