David Woolley wrote: > 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?
Neither, directly. I mean the peak-to-peak variation in the reported offset, as "measured" by eye on a graph like the "Daily" graph here: http://www.satsignal.eu/mrtg/gemini_ntp.html > 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 noise. Yes, I'm looking for an approximate value only at the moment - an order of magnitude relationship to say whether its linear or quadratic (with number of seconds). I'm thinking of a system where the maximum polling interval might be set to 7, 8, 9 or 10. Thanks, David _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions