[ntp:questions] Speed of ntp convergence

Unruh unruh-spam at physics.ubc.ca
Sun Nov 2 17:19:59 UTC 2008

"David J Taylor" <david-taylor at blueyonder.neither-this-part.nor-this-bit.co.uk> writes:

>Unruh wrote:
>> So how long does it take your system to correct a bad drift file?

>Oh, much longer, but that just suggests that your drift file is bad, not 
>any inherent fault in NTP.

>>>> Note, if you are running gps, why have a poll level 6? The
>>>> recommendation
>>>> for ref- clocks is poll level 4?
>>> Probably because the system is also polling Internet servers, and I
>>> didn't want to hammer them at 16 second intervals.  It seems that
>>> the Internet poll interval /must/ be the same as the ref-clock poll
>>> interval, and that it doesn't automatically adjust upwards (which
>>> would be nice).
>> No, each source has its own poll interval. They do NOT need to be the
>> same.

>It's not what Dave Mills told me on this newsgroup, when PPS reference 
>clocks are included.

Well, the evidence is that teh different clocks DO have and use different
poll intervals. My refclock is on poll level 4 and a reading is taken from
it every 16 seconds as recorded in peerstats. My outside reference servers
are on the standard poll 6-10 and they are read every 64 seconds intially
and later at longer intervals. 
Here is teh output of ntpq -p

+tick.usask.ca   .GPS.            1 u   14   64  377   44.904    0.147 0.074
+ntp.ubc.ca      2 u  586 1024  371    0.666    9.912 1.265
*SHM(0)          .PPS.            0 l    2   16  377    0.000   -0.004 0.002

Note that the refclock is read every 16 seconds, ntp.ubc.ca is read every
1024 sec (poll 10) and tick.usask.ca is read every 64 sec (poll 6) and
looking at peerstats confirms this.

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