Date: Fri, 26 Jan 1996 11:06:48 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: lists@argus.flash.net (mailing list account) Cc: caj@tower.stc.housing.washington.edu, freebsd-questions@FreeBSD.org Subject: Re: good NTP servers Message-ID: <199601261806.LAA04921@phaeton.artisoft.com> In-Reply-To: <199601260755.BAA01748@argus.flash.net> from "mailing list account" at Jan 26, 96 01:55:25 am
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Since we are on a sort of tangent here, I might as well add to it. 8-). > tick.usno.navy.mil and tock.usno.navy.mil are sync'ed to Navy Cesium clocks, > I am assuming [someone please correct me if I am wrong] that these clocks > are sync'ed in a method similar to that described on pp 10 and 11 of NIST > Special Pub 432, as the Cesium sources at the USNO are traceable to NIST. > > The method described on pg 10 is accurate to less than 100ns, this is > utilizing GPS... this is pure assumption based on the fact that the > Cesium Primary Standards in use at the USNO are tracable to NIST, and > that NIST uses the GPS method as described to sync the Primary standards > at WWV, WWVB, and WWVH. > > Since all three sites are using NIST tracable Cesium Primary Standards, > I guess that would make all three sites stratum 1 servers... sorry folx... The inaccuracy on pg 10 is due to pseudo-random "jitter" in the GPS signal. The Navy, being a branch of the US military, has access to the generator and key pair and so GPS is significantly more accurate for them (many airports in the US are generating adjustment base references for GPS based on known lattitude/longitude positions of the adjusting signal source to defeat this intentional inaccuracy in the GPS position fixing for non-military grade GPS). The Navy's clocks are probably accurate to much better than 100ns if they are using military grade GPS. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.
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