[ntp:questions] Re: polling algorithm

David L. Mills mills at udel.edu
Thu Aug 25 19:06:54 UTC 2005


Think about what you said. The only way the client knows the server is 
reachable is to poll it. Even if the server does not answer a poll you 
can't conclude it has become unreachable; a packet could have been lost.

The poll interval increases in the first place because the feedback loop 
has stabilized and doesn't need refresh very often. The design allows 
for some packets to be lost and for the server quality metric 
(synchronization distance) to accurately reflect the maximum error 
relative to that server. If the server comes back online after a few 
polls or a couple of hours, the clock discipline process just takes over 
as before and reducing the poll interval is unnecessary and 


Klas Bengtsson wrote:
> Hi all!
> Anyone out there who can describe how the polling algorithm for NTP works?
> My problem is that when the poll interval is 1024 seconds and I suddenly 
> lose synchronisation for some reason, I would expect the NTP server to 
> decrease the polling interval back to 64 seconds again, but it does not.
> That means that even if the reason for the synchronisation loss is fixed 
> I have to wait up til 17 minutes before I get the synchronisation back 
> again.
> Is this how it is supposed to work?
> What makes the polling interval decrease again once it has reached 1024 
> seconds?
> Where can I find information about how the polling algorithm works?
> BR,
> Klas
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