[ntp:questions] NTP makes a time jump

unruh unruh at invalid.ca
Mon Jul 8 20:19:12 UTC 2013


On 2013-07-08, John Hasler <jhasler at newsguy.com> wrote:
> unruh writes:
>> Do you mean none of the slaves ever have to jump to track it? Since
>> all ntpd does ever is either jump or slew.
>
> I mean so that none ever have to slew at the 500PPM max rate.

The problem is that ntpd will keep increasing the slew rate until it
hits the limit if the clock is out.  If the server  is out by 3 min say, it should
hit that limit pretty early on, and then be pegged there until the clock
catches up and eliminates the offset. And the clients will either have
to slew at 500PPM as well in order to keep up with the server, or they
will fall behind and develop a huge offset which will only be corrected
once the server has calmed down and has eliminated its offset. 

Now, If we know that the max difference between the client and server's
drift rate is say 200PPM, then if one could limit the server to only
slewing at 300PPM then the client should be able to keep up. But I do
not know of any way of telling the server it should never slew faster
than 300PPM. Is there one? Plus you would have to beforehand decide by
hand what the natural drift rates of all the clients are so you could
put in that limit. 

 



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