[ntp:questions] time to sync vs ptp?
david at ex.djwhome.demon.invalid
Fri May 31 14:33:45 UTC 2013
matthew.garman at gmail.com wrote:
> OK. But at some point, when the drift file is established, it has a memory of sorts, right?
Not in the sense that unruh means. If you ignore the minimum delay
filter, ntpd uses an IIR filter with only z^0 and z^1 terms, so it only
remembers the state from one accepted sample back. Linear regression
based system actively use values from several back samples in each
The drift file provides a checkpoint of part of the state, but is only
used after an outage.
You can consider the minimum delay filter as using z^0 to z^7, but it
ends up only selecting one of these, even though it uses all of them to
make the decision.
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