On 5 Jan, 22:20, David Woolley <da...@ex.djwhome.demon.invalid> wrote: > B wrote: > > I want to know the accuracy on a certain NTP-server at stratum 3. It > > is easy to calulate the absolute error bounds that wont be exceeded > > with this equation > > OFFSET +/- [DELTA/2 + DISPERSION]. This will in my case be OFFSET +/- > > 4 seconds, but I need to know more precise, ie an indicator of > > In that case there is something wrong in your configuration! ntpd will > start ignoring servers if their root distance is rather less than this > and it would be an unusual system where the leaf nodes go so long > between polls that they can accumulate the additional dispersion needed > to reach 4 seconds.
Oh, sorry for my typo. In my case the absolute error bounds is -0,72 +/- 3,9 ms, not seconds! There is almost a dedicated network with optical fiber and no(very little) asymmetris. There is a huge network which got three GPS-clocks as stratum 0, reference clocks for the primary servers. Below you can see the selected servers, all in [milliseconds]. Stratum 2 ref clock st when poll reach delay offset disp .GPS. 1 55 64 377 0.7 0.02 0.1 Stratum 3 ref clock st when poll reach delay offset disp xx.xx.x 2 154 256 377 5.7 -0.74 0.6 For my logging application and master thesis report I need to know a more narrow interval, and I know it is more accurate than the absolute error bounds [-4.62, 3.18]. So a smaller interval of expected time is desirable. Unruh you are probably right, but aren't you talking about synchronization distance(sometimes called root distance), DELAY/2 + DISPERSION, as a conservative estimate of the error. I thinking if it is ok to use OFFSET with DISPERSION as the uncertainty about that value. If only DISPERSION is a conservative value for that too, at least I got a narrower interval of [-0.72 - 0.7, -0.72 + 0.7]=[-1.42, -0,02] milliseconds. I really appriciate your help! // B _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions