[ntp:questions] Re: What modulates polling interval?

Richard B. Gilbert rgilbert88 at comcast.net
Sat Jan 29 02:31:14 UTC 2005


Chris Richmond - MD6-FDC ~ wrote:

>Hi Folks,
>
>   So, the poll time was out to 1024 earlier today.  Now it 64.  What
>causes this to modulate?
>
>Also, what units are offset and jitter?  Is is ms or us?  In any case,
>this is a home network, so no big deal.
>
>CMD: [/usr/local/bin/ntpq -p -n]
>     remote           refid      st t when poll reach   delay   offset  jitter
>==============================================================================
>+216.27.190.202  140.142.16.34    2 u   59   64  377   22.290   -0.767   1.800
>*63.192.96.2     63.192.96.10     2 u   96   64  377   28.060   -1.166   0.600
>-192.83.249.28   207.126.98.204   2 u   48   64  377   18.010    3.338   0.470
>+204.87.183.6    128.9.176.30     2 u   59   64  377   27.080    2.489   8.180
>
>Chris
>
>  
>
The offsets are in milliseconds.  I think the jitter is also 
milliseconds but I'm not sure.

The poll interval is adjusted automatically.  When you have tight 
synchronization, the poll interval increases from 2^6 to 2^10 seconds.  
If you lose synchronization the poll interval drops back to 2^6 again.  
The non mathematicians explanation is that you can make large 
corrections quickly at short poll intervals and you can make small 
corrections accurately at longer poll intervals.



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