Re: Recommendation on NTP appliances/devices

[Saku Ytti <saku () ytti fi>]

On (2014-04-03 21:25 -0700), Will Orton wrote:

> 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.

Meinberg[0] pegs rubidium at ±8ms per year, if you need NTP to do say single
direction backbone SLA measurement you want to have microsecond precision.

I think most GPS chipsets today do Glonass also, maybe it's partly because
Russia has import sanctions for those who don't do, or maybe simply because it
gives better user experience as sync is found earlier.

But is there NTP product which you can configure to GPS-only mode or
Glonass-only mode, which I think might be closer to Rob's idea of redundancy.
As if you use both, 'poisoned' source would break all of your kit.
But that is probably not easy to solve with two sources, if half is GPS and
half is Glonass, and Glonass starts sending bad timing information, what do
your NTP clients do, average to the middle?

[0] http://www.meinbergglobal.com/english/specs/gpsopt.htm

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  ++ytti