Cost-effectivenesss of highly-accurate clocks for NTP

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


On 13 May 2016 at 23:01, Baldur Norddahl <baldur.norddahl at gmail.com> 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: https://en.wikipedia.org/wiki/Crystal_oven

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
minutes.
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
day.
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.

Regards,

Baldur


More information about the NANOG mailing list