[ntp:questions] frequency adjusting only

Unruh unruh-spam at physics.ubc.ca
Tue Apr 29 17:27:26 UTC 2008

m.louvel at gmail.com (maxime louvel) writes:


>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. 

>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. 

>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.)

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