Testing ntpd and/or timing from gpsd

[Hal Murray]

dan-ntp at drown.org said:
> I've found the built-in measurement to be useful.  I have this
> configuration: 

Yes, but you have to be suspicious.  Consider a PPS over USB setup without 
any fudging.  Without any other clock sources, you can't tell that the 
histogram is actually offset rather than centered around zero.

> statistics loopstats peerstats clockstats

rawstats is interesting too.  If you have good clocks at both ends, you can 
see network asymmetries.


> However, looking the data "over time" is useful to see the impact of
> various events.

That's also a good way to spot network congestion.

ntpd uses the best of the last 8 samples where "best" means lowest round trip 
time on the assumption that will give the lowest distortion due to queuing 
delays.  That filter is between rawstats and peerstats.  I think the local 
refclocks always return a RTT of 0 and the filter returns the most recent 
sample when the RTTs are equal.


-- 
These are my opinions.  I hate spam.