[ntp:questions] Compensating for asymmetric delay on a per-peer/server basis?

William Unruh unruh at invalid.ca
Wed Sep 10 15:14:19 UTC 2014


On 2014-09-09, Harlan Stenn <stenn at ntp.org> wrote:
> The issue is that the huff-n-puff filter will work in the case where a
> symmetrical delay becomes asymmetric, and it will "tolerate" or
> "accommodate" an asymmetric delay (caused by a large download, for
> example) for some period of time.
>
> This is a case where there is reasonably-understood asymmetry for a
> given server, or across a given interface.
>
> That one is really hard to figure out.

Not if you have gps reference at both ends, though why you would not use
the gps as the timesource then I do not know. (I guess you could have it
only temporarily). May home connections are much slower one way than the
other, and an assymmetric delay is very possible. If it really is
stable, it would be nice to be able to remove it (like the fudge time1
for refclocks). But I also could not see the equivalent for network
clocks. 
I agree that huff and puff is for temporary assymmetry. There is not way
a permanant assymmeter could be detected by ntpd.
But if there was a sudden onset, then one could use the free running
computer clock to notice that (delta t vs roundtrip would show it). 


>



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