"Richard B. Gilbert" <rgilber...@comcast.net> writes: >George R. Kasica wrote: >> On Sat, 27 Dec 2008 23:53:49 GMT, Unruh <unruh-s...@physics.ubc.ca> >> wrote: >> ... >> # ntpq -p >> remote refid st t when poll reach delay offset >> jitter >> ============================================================================== >> xGPS_NMEA(0) .GPS. 0 l 16 16 377 0.000 12.677 >> 5.862 >> xSHM(0) .PPS. 0 l 12 16 377 0.000 8.410 >> 93.475 >> -eagle-local 192.43.244.18 2 u 99 128 37 0.166 724.868 >> 0.714 >> -apollo-local 128.233.154.245 2 u 98 128 37 0.215 706.214 >> 0.787 >> mumnunah.csse.u .INIT. 16 u - 64 0 0.000 0.000 >> 0.000 >> +tick.usask.ca .GPS. 1 u 97 128 37 105.157 702.859 >> 0.756 >> *clock.isc.org .GPS. 1 u 95 128 37 63.669 702.671 >> 3.087 >> -time.nist.gov .ACTS. 1 u 94 128 37 72.814 691.122 >> 24.052 >> -server.donkeyfl 18.26.4.105 2 u 93 128 37 30.919 706.994 >> 22.203 >> +ip-72-167-54-20 164.67.62.194 2 u 93 128 37 83.165 702.973 >> 137.172 >> -ns1.bluebottle. 64.202.112.75 2 u 88 128 37 25.726 712.661 >> 3.246
>An ntpq "banner" is not much use until at least thirty minutes have >elapsed since startup! >I question the selection of servers! Round trip delays of 63, 72, 83, >and 105 milliseconds seem unreasonable to me! The uncertainty in the I believe he used the pool.ntp.org servers, so he has no choice. And besides if the PPS is working then the fact that those servers at 40ms away is really irrelevant (By the way, the accuracy I get from a server 40ms away as measured by the offset it 10 times better than that from one 5ms away. ) >time reported by a server may be as great as one half of the round trip It MAY be. But usually is not. >delay. This suggests that you should strive to have the lowest possible >round trip delays. If the nearest servers are 1000 miles, or more, away >from your site, there's not much you can do but not many places are >that far away from any NTP server. Note that "network distance" rather >than physical distance is what counts here; e.g. if you are in New York, >a server in New Jersey that can only be reached by relaying through Los >Angeles is, effectively 3000 miles away! >The use of ten servers also seems a little extreme. Four, five, and >seven are the magic numbers that protect you from the failure of one, >two, or three servers; e.g. given seven servers, of which three are >"bad" (wrong time or not responding) the remaining four are sufficient >to "outvote" the bad servers. >Since you have a GPS receiver, three internet servers should be >sufficient as backup and a sanity check for the GPS. Agreed. _______________________________________________ questions mailing list questions@lists.ntp.org https://lists.ntp.org/mailman/listinfo/questions
