On Sun, Nov 9, 2014 at 3:44 PM, Poul-Henning Kamp <[email protected]> wrote:
> NTP does indeed find the best clock from the subset of clocks > which pass its sanity check, and then it uses only that one. Normally I wouldn't question your NTP assertions but I suspect a great many people believe "NTPv4 Algorithms Specification" or the 18-Jul-2012 document on Mitigation Rules. >From <http://www.eecis.udel.edu/~mills/ntp/html/prefer.html#miti> "2. Combine Algorithm The clock combine algorithm uses the survivor list to produce a weighted average of both offset and jitter. Absent other considerations discussed later, the *combined offset* is used to discipline the system clock, while the *combined jitter* is augmented with other components to produce the system jitter statistic inherited by dependent clients, if any. The clock combine algorithm uses a weight factor for each survivor equal to the reciprocal of the root distance. This is normalized so that the sum of the reciprocals is equal to unity. This design favors the survivors at the smallest root distance and thus the smallest maximum error." Or more succintly (from a Mills ppt) Θ=combine(θj) where Theta is the (estimated) system clock offset and the theta_j are the survivor offsets. You're saying these documents affirming clock combining are wrong? Or have I gone terribly astray? _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
