On 2013-08-15, unruh <[email protected]> wrote: > On 2013-08-14, Steve Kostecke <[email protected]> wrote: > >> The time server specified in each of those lines is the one which is >> currently selected as the "sys_peer". > > But as I understand it, it is simply one of the systems which is > not a false ticker, and has not real significance other than that. > Ie, its time is not treated any differently than any of the other > systems regarded as true chimers by the selection algorithm. Or do I > misunderstand something?
The sys_peer is chosen after the select[ion] alrorithm scans the associations for selectable candiates _and_ after the cluster (combine?) algorithm casts out the outliers. In the last paragraph at http://www.eecis.udel.edu/~mills/ntp/html/warp.html we see: "The algorithms described on the Mitigation Rules and the prefer Keyword page combine the survivor offsets, designate one of them as the system peer and produces the final offset used by the algorithm described on the Clock Discipline Algorithm page to adjust the system clock time and frequency." Section 6 of the Mitigation Rules page (http://www.eecis.udel.edu/~mills/ntp/html/prefer.html) clarifies how the process works: "As previously noted, the cluster algorithm casts out outliers, leaving the survivor list for later processing. The survivor list is then sorted by increasing root distance and the first entry temporarily designated the system peer. At this point the following contributors to the system clock discipline may be available: * (potential) system peer, if there are survivors; * orphan parent, if present; * local driver, if present; * modem driver, if present; * prefer peer, if present; * PPS driver, if present. The mitigation algorithm proceeds in three steps in turn. 1. If there are no survivors, the modem driver becomes the only survivor if there is one. If not, the local driver becomes the only survivor if there is one. If not, the orphan parent becomes the only survivor if there is one. If the number of survivors at this point is less than the minsane option of the tos command, the algorithm is terminated and the system variables remain unchanged. Note that minsane is by default 1, but can be set at any value including 0. 2. If the prefer peer is among the survivors, it becomes the system peer and its offset and jitter are inherited by the corresponding system variables. Otherwise, the combine algorithm computes these variables from the survivor population. 3. If there is a PPS driver and the system clock offset at this point is less than 0.4 s, and if there is a prefer peer among the survivors or if the PPS peer is designated as a prefer peer, the PPS driver becomes the system peer and its offset and jitter are inherited by the system variables, thus overriding any variables already computed. Note that a PPS driver is present only if PPS signals are actually being received and enabled by the associated driver. If none of the above is the case, the data are disregarded and the system variables remain as they are." -- Steve Kostecke <[email protected]> NTP Public Services Project - http://support.ntp.org/ _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
