[ntp:questions] high precision tracking: trying to understand sudden jumps

Danny Mayer mayer at ntp.isc.org
Thu Apr 3 03:04:30 UTC 2008

David Woolley wrote:
> starlight at binnacle.cx wrote:
>> The generic version of 'ntpd' has some sophisticated code that 
>> handles interpolation.  See the source.  Power management is 
> I know that.  But the problem is that normal applications just get a 
> more accurate time for the most recent tick, but still don't see any 
> times between ticks.
>> Pings are consistently 400 microseconds and 'ntpq -p' reports 800 
> Which is excessive for 1GHz network doing essentially nothing but NTP.
>> probably have make use of PTP (precision timing protocol).
>> Still très expensive.
> I assume by PTP you mean ethernet cards that extract a timestamp with a 
> very low latency.  I doubt that this will help with lost interrutps.  If 
> you really want extreme accuracy for applications you need to:
> 1) use hardware that maintains a high resolution time completely 
> independent of the software and is directly readable by application code 
> (I'm not sure if Windows supports such direct reading).

I suspect that what is being discussed here is IEEE1588 which can 
timestamp packets via the hardware. It requires device driver support 
and a number of other changes to NTP to work with it.


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