[ntp:questions] Polling interval in FreeBSD vs. Windows

David Woolley david at ex.djwhome.demon.invalid
Tue Jan 18 09:02:55 UTC 2011


unruh wrote:

> ?? Surely what you want is that your computer's clock shows the correct
> time. If your computer disciplines the clock to have the true rate (1
> sec of computer time equals one second of UTC time) but was 10 hours
> off, I think most people would count that as a failure of ntp. 
> Not sure what you mean with "You cannot do that in an unqualified way".
> 

The actual error, when locked, should be almost an order of magnitude 
less than the typical offsets.  Moreover, if there is both jitter and 
wander, and you set a very fast poll, you could get low offsets but a 
high error, because the real error is in the wander.  Increasing the 
loop time constant will report higher offsets, but the time will 
actually be more correct.

This may be complicated in that I'm not sure that the loop time constant 
is actually clamped by the poll rate, so it is possible that setting a 
high rate over samples without changing the overall behaviour.  Maybe it 
is clamped by maxpoll?




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