[ntp:questions] 500ppm - is it too small?

Richard B. Gilbert rgilbert88 at comcast.net
Thu May 7 16:23:18 UTC 2009


David J Taylor wrote:
> I've recent been suggesting the Windows port of NTP as a program 
> suitable for an application where the timekeeping needed to be within a 
> second or two.  Yes, NTP is overkill, but it has the advantages of 
> multiple servers, best server selection, adaptive poll rate, and memory 
> of the clock drift etc.  However, on quite a few installations - at a 
> guess between 1% and 5% - NTP has failed because the click frequency 
> error appears to be too great for NTP to correct.
> 
> Is there any feeling for changing the 500ppm limit, perhaps to 1000ppm 
> or even as much as 5000ppm (to pull a figure out of the hat)?  Or is 
> 500ppm generally believed to be the worst error which should be 
> compensated?
> 
> One possibility is that some of the problem PCs are portables, with some 
> sort of power-saving or even hibernation scheme.  I don't have direct 
> visibility of the type of PC.
> 
> Thanks,
> David

An error greater than 500 PPM suggests seriously broken hardware!  There 
might be some way to "kludge" the software to compensate for this 
brokenness but I think it would be easier and cheaper to fix or replace 
the broken hardware.




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