[ntp:questions] Slow convergence of NTP with GPS/PPS

Unruh unruh-spam at physics.ubc.ca
Sat Oct 25 15:24:28 UTC 2008

"Maarten Wiltink" <maarten at kittensandcats.net> writes:

>"Unruh" <unruh-spam at physics.ubc.ca> wrote in message
>news:UJyMk.3986$fF3.1213 at edtnps83...

>> [...] The longer poll intervals are mainly about keeping packets off
>> the servers. In principle it is always better to poll more. ...

>Yes, but. One of the given reasons for polling less often is to let
>the host clock accrue more error so that it becomes better measureable
>amid other error sources, for example jitter from random network delays.

>But you can poll every second and still correct very small frequency
>errors, if only you don't _forget_ polls from very long ago. Keeping
>a simple FIFO queue of poll results is too simple.

Agreed. But even a simply fifo is ok, if you keep a long enough train of
values. If you keep none, as ntp does, then it is tougher, and more
frequent polling does degrade the frequency accuracy in the presence of
noise. (but increases the phase accuracy).

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