unruh wrote:
more responsive to frequecy shifts. Also ntpd's averaging time is NOT of
the order of 100 poll intervals ( which you would need to get your order
Fair comment. However, it is still measuring the difference between a
filtered estimate of true time and an instantaneous measurement. It is
not measuring the difference between true time and the system clock
time, which is how a lot of people seem to treat it.
of magnitude) Especially as ntpd uses only one of every 8 polls, the
actual statistical improvement is less than 3, not an order of
magnitude.
No. a fast poll also corrects wander faster. ntpd is horribly slow at
correcting wander, but doing it quickly corrects it faster. What it does
Depends whether the wander is in the clock or the measurement.
loop time constant will report higher offsets, but the time will
actually be more correct.
sorry, but that is just wrong. The offsets are the best estimate of the
"correct time" Higher offsets means higher errors.
The offsets are the difference between the best estimate of the correct
time, before it is updated, and the time from a specific, selected
measurement.
This may be complicated in that I'm not sure that the loop time constant
is actually clamped by the poll rate, so it is possible that setting a
high rate over samples without changing the overall behaviour. Maybe it
is clamped by maxpoll?
No, it is determined by the number of readings, not by time. More
readings in a given time means shorter time constant. Fewer readeings,
I am pretty certain that they are decoupled internally, and the degree
of over-sampling can vary. Essentially, though, it is the time constant
that is tuned, and the poll interval has to over sample that and the 1
out of 8 filter.
longer. ntpd throws away 7 out of 8 readings, so the actual poll
interval of used reading is 8 times as long as the set poll interval,
and the time constant is about 5 times that if I remember correctly.
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