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

David L. Mills mills at udel.edu
Fri Jul 15 16:51:24 UTC 2011


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.


David J Taylor wrote:

> "Edward T. Mischanko" <etm1962 at ....> wrote in message 
> news:ivk80m$4uh$1 at speranza.aioe.org...
>> I am using GPS with PPS as my primary time source.  I don't want to 
>> set my back-up network servers to minpoll 10 in the configuration 
>> because if the GPS ever fails the servers would be fixed at minpoll 
>> 10.  I propose an enhancement to the current NTPD functions:  Have 
>> NTPD automatically set network clocks to minpoll 10 when using a 
>> stratum 0 clock as a time refference.  This would cut network traffic 
>> and server load while still allowing a minpoll 6 setting or lower in 
>> the configuration to be used if the refference clock ever fails.
> I like and support that suggestion.
> David
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