[ntp:questions] NTP server with Garmin GPS 18 LVC
david at ex.djwhome.demon.invalid
Fri Dec 20 09:42:04 UTC 2013
On 20/12/13 00:48, David Lord wrote:
> If ntpd is throwing away 7 out of 8 polls I'd say their results
> could be similar to mine.
Throwing away polls is only relevant when there is an abrupt change in
local clock frequency. In the steady state, the real situation is that
ntpd is polling 8 times faster than it needs to given the low pass
filter it is then going to apply. In fact it is more than 8 times, as
ntpd oversamples, even after you apply the minimum delay from last 8 filter.
The only way that ntpd could use those extra polls more effectively is
to look to see if the offset was diverging consistently, indicating a
clock frequency change. The problem in doing that is how does it
distinguish that from, say, a batch of high network delays with each
delay longer than the previous one.
If it could, successfully, discriminate between the cases, it could
change the filter bandwidth sooner than it actually does.
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