Cost-effectivenesss of highly-accurate clocks for NTP

Baldur Norddahl baldur.norddahl at
Sat May 14 19:39:29 UTC 2016

On 13 May 2016 at 23:01, Baldur Norddahl <baldur.norddahl at> wrote:

> Ok how many hours or days of holdover can you expect from quartz,
> temperature compensated quartz or Rubidium? Should we calculate holdover as
> time until drift is more than 1 millisecond, 10 ms or more for NTP
> applications?
> I am thinking that many available datacenter locations will have poor GPS
> signal so we can expect signal loss to be common. Some weather patterns
> might even cause extended GPS signal loss.
I found some data points here:

Assuming that acceptable drift is 10 milliseconds due that being the
expected accuracy from NTP.

The common crystal oscillator can be as bad as 1E-4 => holdover time is 2
TCXO is listed as 1E-6 => holdover time is 3 hours.
OCXO is listed as multiple values, I will use 1E-7 => holdover time is 1
Rubidium is listed as 1E-9 => 3 months
Caesium is listed as 1E-11 => 30 years
Hydrogen Maser 1E-15 => 300 millennia

I clearly need three of those maser things for my network.



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