[ntp:questions] Re: ntpd Not Converging

David J Taylor david-taylor at blueyonder.co.not-this-bit.nor-this-part.uk.invalid
Fri Nov 4 14:44:57 UTC 2005


David T. Ashley wrote:
[]
> But the replies did not zero in on the key question.  It is a control
> law question.  When ntpd starts and the server time is off of the
> true time by an offset (say, 2 seconds), what "control law" does it
> apply to reconverge the server's time and the true time?

A simple answer would be:

- if the clock is off by a large amount, it is first stepped

- a damped control loop is then used to keep the offset approaching zero

- recognising that there is a fixed rate offset which is the value stored 
in the drift file

I don't understand why you delete the drift file, as that file is supposed 
to speed the convergence process.  There is a limit of 500 ppm in the 
clock error beyond which NTP will not converge.

Now, please note that this is my simple and rough understanding - there 
are many far more expert than me here, so if my description is incorrect I 
hope they will correct me.  You should also read David Mills' 
authoritative papers:

  http://www.eecis.udel.edu/~mills/ntp.html

David 





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