[ntp:questions] Ignore one server except in extreme conditions?

A C agcarver+ntp at acarver.net
Wed Nov 16 16:11:26 UTC 2011

On 11/16/2011 00:15, Harlan Stenn wrote:
> What sort of offset/jitter are you seeing on the NMEA signal?  By
> default we expect it to be correct to about 2ms.

I posted more data in another reply but the NMEA tends to have offsets 
of +/- 50 ms and jitters of +/- 10 ms while the PPS and Internet servers 
are all much more stable.  PPS has a jitter of only 0.061 ms reported by 
ntpd (but probably better than that, the jitter value never drops below 
0.061 for any server, in fact it's present in the entire billboard 
jitter column when ntpd first starts up so it must be a floating point 
calculation/rounding issue).  A couple of the Internet servers can 
wander off if the network is bad but most of them stay within +/- 5 ms 
of offset and +/- 1 ms of jitter.

This is from my other reply:

By way of example, one of the Internet servers in my peer list has an 
offset of 1.887 and jitter of 0.586 and is labeled an outlier.  The NMEA 
data at that same moment has an offset of 21.863 and a jitter of 10.290 
and it's labeled as accepted.

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