[EMAIL PROTECTED] (maxime louvel) writes: >On Tue, Apr 29, 2008 at 6:27 PM, Unruh <[EMAIL PROTECTED]> wrote:
>> [EMAIL PROTECTED] (maxime louvel) writes: >> >> >Hi, >> >> >I have know run a lot of tests. >> >Just to let you know what I've got so far. >> >I have tried NTP, and NTP + PTP (Precision Time Protocol). >> >I haven't tried Chrony nor TSClock. >> >I have used the software only implementation of PTP (ptpd). >> >> >With NTP only I have got an accuracy around 1ms, >> >> accuracy? Do you mean the variation of the offset between ntp and the >> remote ntp server? YOu need to tell us what you mean by the term. >> >By accuracy I actually meant the offset between my nodes. And that offset is measured how? With a GPS receiver on each of the nodes? >From teh peerstats of the ntp? From ntpq -p? And is the offset constant or fluctuates by 1msec. Note that the ntpq -p offset is in milliseconds, so you would get things like 1.453 for the offset not .001, if that is how you determine it, for msec jitter. >> >> >> >with one node synchronising to public NTP server, the others nodes >> >synchronising to it with PTP I got 10 usec (between the nodes). >> >I haven't used any hardware support (not GPS,PPS, for PTP). >> >> Then you do not really know what the accuracy is of the other nodes. For >> example, your system could have a 100us assymmetry in communication which >> would make the accuracy 50us, but with a fluctuation of 10us. >> >You're right on this point, what I actually get with PTP is delay of 100 >usec, with a variation of 10 usec. >But I'm only interested in the variation as the 100usec can be removed >easily because it's constant >> >> >> >I might try the other solutions, if yeI do I'll send an email to complete >> >the results. >> >> As I said, I am completely at a loss to know why you would only be getting >> 1ms using ntp to synchronize. That is much worse than my experience. (Look >> at flory on www.theory.physics.ubc.ca/chrony/chrony.html which uses ntp vs >> the other machine which all use chrony. flory's fluctutations are >> certainly not 1ms.) >> >I have to say that I 'm also surprise of the bad performance of NTP, I will >try chrony if it is suitable to my nodes (embedded cards, with the latest >linux kernel). >> _______________________________________________ >> questions mailing list >> questions@lists.ntp.org >> https://lists.ntp.org/mailman/listinfo/questions >> >-- >Maxime Louvel >0044 7964 5555 80 >43 Allen road >Whitemore reans >WV60AW Wolverhampton >United Kingdom _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
