[ntp:questions] Speed of ntp convergence

David J Taylor david-taylor at blueyonder.neither-this-part.nor-this-bit.co.uk
Sat Nov 1 21:32:06 UTC 2008


Unruh wrote:
[]
> Nope, it is not my "ssytem" if by that you mean my computer. The
> convergence is a beautiful exponential convergence with a time scale
> of 1
> hour almost exactly. That is not hardware. That is the software ntp
> protocol.

Just along the lines that if my system converges in 10 minutes, I am at a 
loss to see why yours takes ten hours.  It seems to me that there is 
nothing inherently wrong with the NTP version I have.

[]
> Try switching it off, changing the value int he drift file by say
> 50PPM and
> then switching it on again, and see how long it takes to recover from
> that.

Why would I do that?  The drift values rarely change by more than five, 
certainly not by 50.  If you are seeing a change of 50, then perhaps that 
it part of your problem?

> 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).

Where did you get your information from, by the way?  I found this:

  http://sunsite.ualberta.ca/Documentation/Misc/ntp-4.0.99a/clockopt.htm

  "For most directly connected reference clocks, both minpoll and maxpoll 
default to 6 (64 s)."

from a quick Google search, but I don't know if that's in the official 
documentation.

Cheers,
David 




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