On Thu, Apr 03, 2014 at 09:06:57PM -0700, George Herbert wrote: > Sadly, right now that either means your own real clock, or WWV. The > cellphone time is (as far as I know, for the networks I saw data on) all > coming off GPS. > > Fortunately real clocks are coming way down in cost.
There are commercially available NTP servers with GPS + Rb oscillators... for NTP use you could basically let it sync up a couple days, disconnect the GPS and let it freerun. You'd still be within a millisecond of GPS even after a couple years most likely. Reconnect it to GPS for a couple days every 1-2 years to resync it. More fun and cheaper to build your own I'd bet, if you had the time. With clocks/oscillators designed to provide hold-over for synchronous networks and microwave RF systems (parts per million or billion) the demands of NTP for general use in an IP network are pretty modest. You lose more accuracy in NTP stratum 1->2 across a (relaively) jittery WAN link than a cheap atomic clock does in a long time. -Will
