[ntp:questions] Not-So-Newbie question

Martin Burnicki martin.burnicki at meinberg.de
Thu Mar 13 08:31:48 UTC 2008


Peter Laws wrote:
> Martin Burnicki wrote:
>> Depending on what causes the jitter and offset. If timekeeping by the
>> kernel is poor the this may also cause high jitter and offsets.
> 
> I'm really looking for more general answers to this question.
> 
> I know (or think I know) that delay is just a measure of how far away
> another server is, offset is just how far off the local system thinks the
> distant server is from the One True Time, and low jitter is good ...
> 
> But .... how low does jitter have to be to be "good enough"?  How do the
> three relate to one another?

I think this is one of the basic questions. Of course the lower the jitter
the better the results since (simply spoken) the packet turnaround times
are then constant and thus can be determined and compensated.

However, in practice the jitter can be large or small, but it will never be
zero. So it's good to configure several upstream time source (especially if
they are NTP servers on the internet), let ntpd determine the offset and
jitter of each time source, and let ntpd decide which time sources to use
to yield the best possible time synchronization.

Martin
-- 
Martin Burnicki

Meinberg Funkuhren
Bad Pyrmont
Germany




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