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Date:      Sun, 2 Jan 2000 15:05:49 -0800
From:      "David Schwartz" <davids@webmaster.com>
To:        "Karl Denninger" <karl@Denninger.Net>, "Warner Losh" <imp@village.org>
Cc:        <current@FreeBSD.ORG>
Subject:   RE: xntpd - VERY old folks, how about updating? :-)
Message-ID:  <000101bf5575$e8b342e0$021d85d1@youwant.to>
In-Reply-To: <20000102164519.A25992@Denninger.Net>

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> Now explain to me how stability of your timing source ON THOSE MACHINES
> is MATERIALLY different to any process WHICH THAT DEVICE MAY INTERACT WITH
> between 10ns and 1us, AS SEEN FROM THE UNIX MACHINE.

	A battle you would win is if you said, "synchronizing the time of other
UNIX machines without specialized hardware over a LAN or WAN". :)

	You can see 2 microsecond differences inside a single machine with no
specialized hardware. You can see 5 microseconds over a good LAN. For
example, youknow.youwant.to is synchronized to both tick.gpsclock.com and
tock.gpsclock.com through a full-duplex 100Mbps LAN switch. Watch this:

> ntpdate -q -p 8 209.133.29.16 209.133.29.20
server 209.133.29.16, stratum 1, offset -0.000298, delay 0.02579
server 209.133.29.20, stratum 1, offset -0.000302, delay 0.02579
 2 Jan 15:01:01 ntpdate[2491]: adjust time server 209.133.29.20
offset -0.000302 sec

	Note that it claims that Tick and Tock agree with each other to 5
microseconds. But it has been unable to keep its own time to any better than
300 microseconds (it's been under heavy load, swapping in fact).

	In actual reality, the GPSClock 200 is better than the specifications
indicate. If it really did alternate between 1us early pulses and 1us late
pulses, stability would be measurably impacted. NTP is very good at
smoothing things out anyway, especially since it only probes the clock every
64 seconds or so.

	David Schwartz
	http://www.gpsclock.com/



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