[ntp:questions] offline machines' time synchronization

unruh unruh at invalid.ca
Thu May 24 20:46:44 UTC 2012

On 2012-05-24, Dave Hart <hart at ntp.org> wrote:
> 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)?

Well, you could measure it while your ntp is up, and then use it as a
flywheel while other sources are down. Ie, run the rubidium, examine the
offset of the rubidium on a well controlled clock (eg by GPS) and then
run the rubidium as a source with a known offset.

> Cheers,
> Dave Hart

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