Date: Sun, 31 Mar 2002 19:32:01 +0200 From: Erik Trulsson <ertr1013@student.uu.se> To: Paul Halliday <dp@penix.org> Cc: Mike Silbersack <silby@silby.com>, Leo Bicknell <bicknell@ufp.org>, hackers@FreeBSD.ORG Subject: Re: GPS time. Message-ID: <20020331173200.GB11505@student.uu.se> In-Reply-To: <Pine.LNX.4.43L0.0203311040090.8980-100000@saruman.xwin.net> References: <20020331091304.U40871-100000@patrocles.silby.com> <Pine.LNX.4.43L0.0203311040090.8980-100000@saruman.xwin.net>
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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. -- <Insert your favourite quote here.> Erik Trulsson ertr1013@student.uu.se To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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