[ntp:questions] Jitter versus polling interval

David Woolley david at ex.djwhome.demon.co.uk.invalid
Sun Mar 1 10:23:39 UTC 2009

David J Taylor wrote:

> Does anyone know an approximate relationship between polling interval 
> and peak-to-peak jitter for a non-ref-clock system?  I.e would the 
> jitter offset) go up linearly with polling interval, or as the square, 
> or what?

Do you mean true jitter (RMS error from true time) or the jitter 
statistic produced by NTP?

I may be completely wrong, but I thought that true jitter initially went 
down with increasing polling interval and that ntpd stopped increasing 
the polling interval before it started to go back up again.  That's 
because ntpd increases the loop time constant as it increases, which 
compensates for the increased poll interval and, in the Millsian world, 
measurement jitter has a 1/f spectrum.

In the real world, you'll need to specify the nature of the measurement 

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