[ntp:questions] Strange jumps in PPM

unruh unruh at invalid.ca
Thu Aug 22 18:02:37 UTC 2013

On 2013-08-22, David Woolley <david at ex.djwhome.demon.invalid> wrote:
> On 21/08/13 21:24, A C wrote:
>> So the idea isn't that ntpd should figure out on its own without user
>> intervention.  Instead there would be some kind of
>> configuration/fudge/tinker options available so that the user can supply
>> baseline information that can help ntpd identify a rogue source versus
>> normal system behaviors.
> Actually, one of the main complaints about ntpd is that it favours the 
> theory that the source is the problem, when the crystal temperature is 
> the real problem.  (The exception to this is people who manually yank 
> the local clock and then complain that ntpd doesn't immediately reset it.)

ntpd assumes that the source is perfect. It has not choice. It does
assume that network delays etc can make the measurements inaccurate, and
tried to get rid of those by averaging, and filtering. (throwing away
87% of the emasurements) which makes its response slow. But it assumes
that the sources are perfect without other evidence (eg disagreement
between sources).

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