[time-nuts] sync computer clock ticks
John Ackermann N8UR
jra at febo.com
Fri Jan 4 14:17:00 UTC 2008
Michael Di Domenico wrote:
> I've used NTP for years, but i was under the impression that it is not
> able to synchonize the clocks below 1 or 2 seconds. Can you point me
> towards a specific article that speaks about the configuration
> parameters to get ntp sync'd that low?
Hi Michael --
PC hardware and operating systems can put some limits on NTP
performance, though with some attention to detail getting ~1 microsecond
with an attached hardware reference clock is fairly straightforward. On
a lightly loaded LAN, machines can be sync'd to a server on the same LAN
to a few hundred microseconds.
Challenges may be (a) in the Windows world, earlier versions (prior to
some SP level of XP) have inherent limitations on timekeeping accuracy,
and (b) Linux does not directly support high accuracy timekeeping with
hardware clocks that provide a PPS signal. For various (mainly
political, it seems) reasons you need to do a kernel patch to enable use
of the PPS signal.
I have a bunch of statistics showing NTP performance at
http://www.febo.com/time-freq/ntp/stats/index.html. There, you can see
how a group of very high performance stratum 1 servers (with directly
connected reference clocks) look across the local LAN, as well as how
some local stratum 2 and external stratum 2 servers look. There's also
a link there to a page that describes what is probably the most accurate
hardware available for an NTP server (and which costs less than $300 to
implement).
John
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