[ntp:questions] ntpdate.c unsafe buffer write

Maarten Wiltink maarten at kittensandcats.net
Thu Feb 14 08:57:40 UTC 2008


"David L. Mills" <mills at udel.edu> wrote in message
news:fp0fpa$p5c$1 at scrotar.nss.udel.edu...

>>>> Is there also a random backoff after an increase of the polling
>>>> interval?

>>> No. However, there is a small dither of a few percent at all poll
>>> intervals to resist self-synchronization.

> The natural behavior of a bunch of oscillators near the same frequency
> is to become one giant phase-locked oscillator. Adding a bit of random
> fuzz at each poll turns each oscillator into a mini random-walk which
> breaks up that tendency. The fuzz is not a lot, like 10 percent.

Do you mean the dither alluded to above is cumulative?

I was never much good with statistics and remember only that the
expectation of the offset after N steps in a random walk is sqrt(N)
times the average step size. Not a clue what the distribution might
be. Intuitively, I would be aiming for uniform, and randomly adding
half a polling interval delay when doubling it seemed to me like it
would do that.

Groetjes,
Maarten Wiltink





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