From owner-freebsd-hackers Sun Mar 31 9:32:21 2002 Delivered-To: freebsd-hackers@freebsd.org Received: from maild.telia.com (maild.telia.com [194.22.190.101]) by hub.freebsd.org (Postfix) with ESMTP id 36D2637B419 for ; Sun, 31 Mar 2002 09:32:15 -0800 (PST) Received: from d1o913.telia.com (d1o913.telia.com [195.252.44.241]) by maild.telia.com (8.11.6/8.11.6) with ESMTP id g2VHWE118076 for ; Sun, 31 Mar 2002 19:32:14 +0200 (CEST) Received: from falcon.midgard.homeip.net (h68n2fls20o913.telia.com [212.181.163.68]) by d1o913.telia.com (8.8.8/8.8.8) with SMTP id TAA12069 for ; Sun, 31 Mar 2002 19:32:13 +0200 (CEST) Received: (qmail 11685 invoked by uid 1001); 31 Mar 2002 17:32:01 -0000 Date: Sun, 31 Mar 2002 19:32:01 +0200 From: Erik Trulsson To: Paul Halliday Cc: Mike Silbersack , Leo Bicknell , hackers@FreeBSD.ORG Subject: Re: GPS time. Message-ID: <20020331173200.GB11505@student.uu.se> Mail-Followup-To: Paul Halliday , Mike Silbersack , Leo Bicknell , hackers@FreeBSD.ORG References: <20020331091304.U40871-100000@patrocles.silby.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.3.28i Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On Sun, Mar 31, 2002 at 10:44:55AM -0600, Paul Halliday wrote: > On Sun, 31 Mar 2002, Mike Silbersack wrote: > > > > > On Sat, 30 Mar 2002, Leo Bicknell wrote: > > > > > Your NTP servers are better. > > > > > > I tested a III Plus, and without a 1 PPS source (which that model > > > doesn't provide) it's accurate to about 100ms, give or take. Since > > > real NTP servers are < 1ms, they really aren't that good. It's > > > not that the time isn't accurate, it's that they were not designed > > > to communicate with that accuracy to an external device. > > > > OTOH, 100ms is pretty close; I doubt many people need time better than > > that. The one big advantage I can see with using a GPS receiver vs NTP > > servers is security & reliability; I've always worried that my clock > > might start to drift to a misconfigured NTP server. Taken to a paranoid > > level, you could worry that someone was faking NTP replies to throw your > > clocks off. :) > > This is the answer I was kinda hoping for. I think that accuracy > to ~100ms from a known source is a little more comforting than <1ms from a > server that I have no control over. I am not maintaining a space program, > just a dozen machines in my room that really serve no other purpose than > personal entertainment. Yes, but that is why one shouldn't rely on *a* server. When using NTP it is a good idea to get the time from several NTP servers. The chance that all of them are misconfigured at the same time is fairly small. OTOH, taking the time from a local GPS receiver doesn't sound like a bad idea either if one doesn't need extremely good timekeeping. -- Erik Trulsson ertr1013@student.uu.se To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message