[ntp:questions] Setting back-up network servers to minpoll 10 automatically when sychronizied to a referrence clock.

David J Taylor david-taylor at blueyonder.co.uk.invalid
Fri Jul 15 17:52:02 UTC 2011

> David,
> Something like this was done in NTPv3 (xntpd) and it turned out to be a 
> bad idea. The poll interval is determined by the time constant, which 
> for PPS and other low-stratum sources is relatively small. If a backup 
> is switched in at a poll interval much larger than this, it takes awhile 
> for the time constant and backup poll interval to stabilize and 
> meanwhile the Nyquist limit is exceeded. In NTPv3 this sometimes 
> resulted in an evil twitch until things calmed down.
> It gets worse in the general case where sources of unequal stratum are 
> configured. The algorithms can result in more than one stratum survivor 
> is present and the combine algorithm uses them all. They must all run 
> the same poll interval or evil twitches can result. All in all, to do 
> what you suggest requires an intricate evaluation of what already is a 
> complicated and fragile algorithm, so this might not happen soon.
> Dave

Thanks, Dave.  It's a pity it can't work easily, but (for me) it's not a 
show stopper, as I have four GPS/PPS sources here.


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