[ntp:questions] Strange jumps in PPM

Harlan Stenn stenn at ntp.org
Wed Aug 21 22:02:26 UTC 2013

unruh writes:
> NTP of course cannnot tell the difference between your source going
> wild, or your computer ( say a sidden temp rise due to heavy work load)
> clock going wild. It HAS to trust the sources. Now if you have 5 sources
> all of similar accuracy, then it could throw away one or two as false
> tickers. but with only one PPS, it HAS to assume that the signal from
> the source is good. It has nothing else to go by. 

I've long thought that there would be benefit to having some "quality"
metrics regarding a PPS signal.  Some devices do not do this - all you
get is a pulse.  Some devices will withhold the PPS pulse if its quality
is "insufficient" (I say this like I know it's true, and I don't know if
it's true).  Some devices will offer information (over an RS232 port,
for example), that will report "health/quality" information about the
PPS signal it is providing.

I'd love to see NTP be able to query and use this sort of information.


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