- The decision of buying a GPS is not mine ... So let's say for now that's still not possible, if no other solution is found I'll conclude that a GPS has to be bought.
- Danny, you're talking about the delay I got with ntpq -p ? - I have chosen a broadcast configuration for two reasons : - easier to install - I am doing the tests on only 2 nodes, thus with broadcast I assumed that more nodes won't change the accuracy I though it was possible to achieve the same precision with broadcast than with C/S, that's erroneous ? maxime On Wed, Apr 23, 2008 at 12:42 PM, Danny Mayer <[EMAIL PROTECTED]> wrote: > maxime louvel wrote: > > > Thanks, > > > > I am actually using 4 public NTP server, which whom my node-1 > > synchronises to. > > Then node-1 broadcasts the time to all the other nodes in the subnet. > > > > > If you are using broadcast mode then you have two additional issues that > you need to deal with: > > 1) authentication is required by default > 2) you are not measuring the delay for every packet > > With autokey, the delay gets measured during the autokey dance which > happens in client/server mode and then it switches to broadcast when it > completes. You cannot measure the delay in broadcast mode since the server > sends out the packets and the client just receives them. Broadcast can only > apply the delay estimates that it got when in the autokey dance and cannot > account for changes until the next autokey dance. > > If accuracy is critical in this environment, don't use broadcast. At least > in client/server mode you get to measure the delay with each packet. > > Danny > > > > My goal is to achieve a synchronisation between the nodes (not with the > > public NTP server) within 50 usec. > > I don't care if the synchronisation to the public NTP is accurate around > > half a second. > > I think it's possible, because the nodes are close to each other and > > every communication is using gigabit ethernet (cards + switch). > > > > I achieve to get a small offset when nothing else than linux and ntpd is > > running on the nodes > > (offset arount 10 usec). > > > > I have a program which sends data from one node to another. > > The sending/reception are timestamped and the delay is then computed. > > > > I would like the measured delay to be constrained in a 50usec wide > > range. > > > > Do you think it should be possible ? > > > > I have tried to run the test for 24h and didn't get the expected > > results. > > The range of the measured delay is 2 milliseconds (between -1ms and > > +1ms) with some spikes (ten or so for a milion measurments). The mean delay > > is -0.066087 (ms) and the std dev is 0.22849 > > Do you think the spikes can influence ntp ? > > > > thanks very much > > > > Maxime > > > -- Maxime Louvel 0044 7964 5555 80 43 Allen road Whitemore reans WV60AW Wolverhampton United Kingdom _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
