[ntp:questions] Tighter regulation?

unruh unruh at invalid.ca
Mon May 20 20:20:24 UTC 2013


On 2013-05-20, David Woolley <david at ex.djwhome.demon.invalid> wrote:
> Mischanko, Edward T wrote:
>
>> Does anyone know what setting can be changed that will cause
>> tighter regulation of the offset.  My goal is to get clk_wander to
>
> Why do you want to track network propagation delay changes, at the 
> expense of accurate time keeping?
>
>> equal as close to zero as possible more often.  I would also like
>> to see the frequency adjusted with every change in offset data;
>> it currently does not appear to do that; it seems to be random.
>
> I think you are seeing the effects of the 8 stage minimum delay filter. 
>   Defeating this is likely to increase jitter against true time, as it 
> will cause the frequency to be adjusted based on low quality measurement 
> samples, increasing the variability of the frequency.

Well if the prop delays were wildly varying, the network jitter can be
small, and ntpd will still throw out 7 of 8.

>
> Note that the time constants for the frequency adjustment loops are 
> significantly larger than 8 times the sample interval.



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