[ntp:questions] Re: Box not synchronizing

Richard B. Gilbert rgilbert88 at comcast.net
Fri Jun 9 21:52:00 UTC 2006


John Pettitt wrote:
> Brian Utterback wrote:
> 
>>So, there you have it. I hope that helps you to understand how
>>a longer poll interval can lead to a more accurate clock, and
>>why it is a good idea to let NTP decide what the best poll interval
>>actually is.
>>
>>
> 
> 
> Great explanation - it also explains why sometime you do need to mess with minpoll and maxpoll.  If
> you have a machine that is prone to rapid changes in it's drift rate (typically due to thermal
> issues) when ntp moves to a longer poll it doesn't notice fast enough that the clock is drifting
> faster or slower that it was before.  This is very visible with PC based stratum 1 clocks where
> sporadic system loads (causing heat in the cpu) can push the clock off by hundreds of microseconds
> before ntp catches it and brings it back.  Setting minpoll and maxpoll to 4 for the refclock source
> can significantly improve the systems ability to remain relatively stable through these thermal events.
> 
> john

Yup!   Another factor is that hardware refclocks do not have the jitter 
problems that network servers do.  You can use a much shorter poll 
interval with a good refclock.




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