[ntp:questions] Thoughts on huff and puff

David L. Mills mills at udel.edu
Sat Oct 11 23:58:43 UTC 2008


Harlan,

It's not as simple as you think. In fact, it's not as simple as I 
thought. The scheme is a maximim a-posteriori (MAP) statisical 
estimation method. The estimator thinks it has a good measure of the 
correct value and then collects samples that reinforce that value.

The trick is to reliably estimate the minimum delay over a sufficient 
time span that insures at least one minimum delay sample is found. From 
theory, other samples tend to be found at the limbs of what I have 
called the wedge scattergram, where the limbs are at slopes of +-0.5. On 
the assumption the samples are on the limbs, just determine the sign and 
correct for the additional delay. It works equally well for one-sided or 
two-sided congested paths.

But, this works only if the apex of the wedge can be reliably 
determined, which is where the MAP method comes in. To do this 
successfully for diferent associations would require a separate 
pseudo-discipline for each association. This would be incredibly 
intricate, but in principle possible.

Dave

Harlan Stenn wrote:

> http://support.ntp.org/bin/view/Dev/NewNtpConfFormat#Individual_huff_n_puff_buffers_f
> 
> has been on the "good idea list" for a while.




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