[ntp:questions] Getting NTP to correct only the clock skew
bdebelius at intelesyscorp.com
Thu Apr 5 18:33:47 UTC 2007
Have you seen this?
> Maarten Wiltink wrote:
>> Spoon wrote:
>>> B is supposed to re-send the packets it receives at the rate they
>>> were originally sent by A.
>>> If the clocks on A and B do not tick at the same rate, the buffer
>>> used by B will either overflow or underflow.
>>> This is why I need A's clock and B's clock to tick at the same rate.
>>> But it is not important to me that A and B's clock give the same
>>> absolute time. ...
>> But nothing will break if they do, either. Right?
> Right. Of course :-)
>> The simplest solution
>> would be to have both synchronized to UTC, or either one to the other,
>> and accept that they will keep better time or at least closer time.
>> From the sound of it, you do not care about what time A keeps _at all_,
>> so if you simply slave it to B, your problem goes away.
>> The fact that you are concerned with reproducing timing but not with
>> good time is, frankly, suspect and leads me to propose a different
>> 'solution': could you monitor the buffer length and adjust frequency
>> on system B from that? If it's slowly draining, slow down B a little;
>> if it's growing, speed it up ever so slightly. Just like NTP does,
> The very hard part (for me) is seeing that B's buffer is in fact slowly
> draining when there is a lot of jitter on the link between A and B.
> I've tried using an exponentially-weighted moving average to filter the
> jitter out, but it didn't work as well as I had hoped. That is when I
> turned to NTP. I'm trying not to reinvent the wheel.
> Are you saying I should use the theory in NTP but not the daemon?
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