Cost-effectivenesss of highly-accurate clocks for NTP

Mel Beckman mel at beckman.org
Sat May 14 19:42:13 UTC 2016


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

Gives new meaning to the phrase "Set and forget". :)

 -mel beckman

> On May 14, 2016, at 12:40 PM, Baldur Norddahl <baldur.norddahl at gmail.com> wrote:
> 
>> 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


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