[time-nuts] sync computer clock ticks

John Ackermann N8UR jra at febo.com
Fri Jan 4 09:17:00 EST 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 


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