[ntp:questions] offline machines' time synchronization

David J Taylor david-taylor at blueyonder.co.uk.invalid
Fri May 25 05:44:42 UTC 2012


"Dave Hart" <hart at ntp.org> wrote in message 
news:CAMbSiYBLnxaj_x4vch3eNDqwUDX+d5sGcHyr8zBe3Jh0C2K=yg at mail.gmail.com...
> On Thu, May 24, 2012 at 4:24 PM, Chris Albertson
> <albertson.chris at gmail.com> wrote:
>> Lots of good discussion here but I found an easy way to stay "on-time"
>> while the Internet is down and GPS is not available.  There are some
>> people on eBay selling Rubinium oscillators for about $40.  They have
>> a pulse per second output.    These Rb clocks will keep NTP within
>> reasonable specs for a LONG time.  It does required some effort to set
>> up.  Just wanted to point out one more option.
>
> ntpd requires reference clocks provide time, not just frequency.  How
> do you discipline the Rb PPS to occur at the top of the UTC second (or
> a fixed offset from the top)?
>
> Cheers,
> Dave Hart

Agreed, Dave.  The way I read the message was for /temporary/ coverage, 
not a fully disconnected solution.  For US $40 (or somewhat more) you 
could easily get a secondary GPS reference such as:

  Trimble Resolution SMT Timing GPS OEM board
  eBay 290696970497  (price has gone up, though)

  Sure Electronics GPS evaluation board
  http://www.sureelectronics.net/goods.php?id=99
  http://www.satsignal.eu/ntp/Sure-GPS.htm

  Garmin GPS 18x LVC
  http://www.satsignal.eu/ntp/FreeBSD-GPS-PPS.htm
  http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html

and use these to provide backup servers to cover the outage.

Cheers,
David 



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