[ntp:questions] Compensating for asymmetric delay on a per-peer/server basis?
nomail at example.com
Thu Sep 11 16:47:47 UTC 2014
Paul <tik-tok at bodosom.net> wrote:
> Not to suggest that someone is doing something unreasonable but again
> why does time derived from the back-up clock need to be as accurate as
> the local clock (say .5ms versus 2ms)? If there's a legitimate need
> then trying to solve the problem with the wrong tool will only lead to
> frustration and complaints that NTP is buggy.
One possible explanation is that people don't want their clock to suddenly
track the changed offset in such cases. If only because ntpd will think
that the frequency offset it has calculated over a long time period is
suddenly wrong, and will change it to reflect a sudden time offset in a
short time interval. It will then slew to the correct time, overshoot,
and when the correct reference comes back online this will repeat in
the other direction.
This problem can partly be mitigated by ensuring that the offset between
your local clock and the external references is as small as possible.
(with some tweaking I can get these well below .5ms, often below .1ms)
More information about the questions