[ntp:questions] broadcast client

David Woolley david at ex.djwhome.demon.co.uk.invalid
Sun Nov 23 09:11:36 UTC 2008


Danny Mayer wrote:

> 
> The simple answer is to talk about the proverbial spring yo-yoing around
> a fix point. However you don't want it to yo-yo you want it to be damped
> so that the fluctuations around the mean get smaller. By oversampling
> you are perturbing the calculated time and frequency and the increased
> perturbation means that you reduce the stability. This is what I call my
> pebble in the pond analogy. Your discussion above indicates that it is
> okay to have wild fluctuations around the mean even though it means that
> you may have taken a clock reading at one of the peaks of the
> fluctuation. You really need to damp the fluctuations as much as possible.

You compensate for oversampling by giving each sample a lower weight.  I 
think that NTP already does that.

In the limit the only effect of oversampling is to make the control loop 
behave more like the analogue control systems on which it is modelled. 
The effect of minimal sampling is to make the mathematical analysis more 
difficult.




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