[ntp:hackers] NTP root dispersion.

Steven Sommars stevesommarsntp at gmail.com
Fri Nov 3 00:42:09 UTC 2017


Many NTP stratum one servers use a PPS signal to discipline a software
clock that uses the CPU's  oscillator.  E.g., GPS with PPS connected to a
Linux computer's serial port.  The deviation between the PPS signal and the
software clock can be used in a root dispersion calculation.

Some contemporary NTP servers have no software clock. They can be driven by
an external 10MHz (+PPS) or may contain their own GPSDO.    How should the
NTP root dispersion be computed?

Somewhat related.  One such commercial implementation uses the
Precision.field within the NTP reply message.to signal changes in
uncertainty; the root dispersion field is fixed at zero.    Are there NTP
clients that make use of a varying precision field in selection algorithms?


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