Hello to All, I have some interesting results using PPS to share.
Note that: - all my boxes run FreeBSD (6.1 and 6.2). - NTP v 4.2.2 - PPS is generated by a very stable Rubidium source - NTP server #1 provides the timebase (at the moment I cannot receive GPS in the building). All the others synchronise to it. - NTP server #1 provide a stability better than 10ppb - All servers use PPS kernel discipline (not ntpd PPS driver!) - The polling period was increased to 14 in order to maximise stability results (...other tinker parameters were also modified...) Setup n. 1: ----------- - NTP server #2 employs the same PPS signal as NTP server #1 - Time is synchronised by ntpd, only NTP server #1 is configured - The two servers sits on the same Ethernet switch - results of ntpq -crv: status=0644 leap_none, sync_ntp, 4 events, event_peer/strat_chg, version="ntpd [EMAIL PROTECTED] Wed Sep 27 20:58:11 UTC 2006 (2)", processor="i386", system="FreeBSD/6.1-RELEASE", leap=00, stratum=2, precision=-18, rootdelay=0.279, rootdispersion=5.003, peer=46944, refid=xxx.xxx.xxx.xxx, reftime=c97455bc.7f8c3ece Wed, Feb 7 2007 13:42:20.498, poll=6, clock=c974569e.33770463 Wed, Feb 7 2007 13:46:06.201, state=4, offset=0.949, frequency=-42.494, jitter=0.024, noise=0.028, stability=0.018, tai=0 NTP server #2 provides excellent accuracy and stability, to be expected given the low jitter. Setup n. 2: ----------- - NTP server #3 employs an unsynchronised version of the PPS signal available to NTP server #1 - Time is synchronised by ntpd, NTP server #1 and #2 are configured - The NTP server #3 connects to the other servers via a different ISP provider (albeit these are business grade connections) - Note that the peer filter algorithm always selects NTP server #1 (which is the stratum 1 after all) - results of ntpq -crv: status=0644 leap_none, sync_ntp, 4 events, event_peer/strat_chg, version="ntpd [EMAIL PROTECTED] Wed Jan 31 10:15:55 UTC 2007 (5)", processor="i386", system="FreeBSD/6.2-RELEASE", leap=00, stratum=2, precision=-19, rootdelay=49.455, rootdispersion=7.286, peer=47608, refid=xxx.xxx.xxx.xxx, reftime=c97427ab.9d96ca3f Wed, Feb 7 2007 10:25:47.615, poll=14, clock=c9745908.ea5119a3 Wed, Feb 7 2007 13:56:24.915, state=4, offset=1.459, frequency=23.129, jitter=5.380, noise=2.723, stability=0.057, tai=0 The NTP server #3 provides good offset, stability is affected by higher network jitter. Setup n. 3: ------------ - NTP server #4 employs the same unsynchronised version of the PPS signal as NTP server #3 - Time is synchronised by ntpd, only NTP server #1 is configured - The NTP server #4 connects to NTP server #1 via the same network path as NTP server #3 - results of ntpq -crv: status=0644 leap_none, sync_ntp, 4 events, event_peer/strat_chg, version="ntpd [EMAIL PROTECTED] Wed Jan 31 08:42:18 UTC 2007 (3)", processor="i386", system="FreeBSD/6.2-RELEASE", leap=00, stratum=2, precision=-19, rootdelay=41.177, rootdispersion=17.558, peer=27086, refid=xxx.xxx.xxx.xxx, reftime=c9741aed.6bcdf009 Wed, Feb 7 2007 9:31:25.421, poll=14, clock=c9744ef2.c5657e88 Wed, Feb 7 2007 13:13:22.771, state=4, offset=-11.474, frequency=27.642, jitter=5.628, noise=3.958, stability=0.129, tai=0 This experiment is very interesting... Although the network path is the same as NTP server #3 (measured jitter is the same), the stability of the servers is constantly worse (twice as big!). The only difference is that NTP server #3 employs two servers for time synchronisation, while NTP server #4 employs only one server. I think the only difference is the working of the clustering algorithm. The use of two NTP servers improves stability and accuracy when compared to only one servers. Regards, Mauro -- Mauro Fiacco ip.access Ltd URL: www.ipaccess.com _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
