[170708] in North American Network Operators' Group
Re: Recommendation on NTP appliances/devices
daemon@ATHENA.MIT.EDU (Will Orton)
Fri Apr 4 00:27:21 2014
Date: Thu, 3 Apr 2014 21:25:27 -0700
From: Will Orton <will@loopfree.net>
To: nanog@nanog.org
In-Reply-To: <CAK__KzvUxoRqkEaLjKgkXR6pVnAcYaqUtgLPHmrY+6zTH02qnQ@mail.gmail.com>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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
