nanog mailing list archives
Re: Cost-effectivenesss of highly-accurate clocks for NTP
From: Baldur Norddahl <baldur.norddahl () gmail com>
Date: Sat, 14 May 2016 21:39:29 +0200
On 13 May 2016 at 23:01, Baldur Norddahl <baldur.norddahl () 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
Current thread:
- Cost-effectivenesss of highly-accurate clocks for NTP Eric S. Raymond (May 13)
- Re: Cost-effectivenesss of highly-accurate clocks for NTP Baldur Norddahl (May 13)
- Re: Cost-effectivenesss of highly-accurate clocks for NTP Baldur Norddahl (May 14)
- Re: Cost-effectivenesss of highly-accurate clocks for NTP Mel Beckman (May 14)
- Re: Cost-effectivenesss of highly-accurate clocks for NTP Eric S. Raymond (May 15)
- Re: Cost-effectivenesss of highly-accurate clocks for NTP Mel Beckman (May 15)
- Re: Cost-effectivenesss of highly-accurate clocks for NTP Eric S. Raymond (May 15)
- Re: Cost-effectivenesss of highly-accurate clocks for NTP joel jaeggli (May 15)
- Re: Cost-effectivenesss of highly-accurate clocks for NTP Mel Beckman (May 15)
- Re: Cost-effectivenesss of highly-accurate clocks for NTP Lamar Owen (May 16)
- Re: Cost-effectivenesss of highly-accurate clocks for NTP Mel Beckman (May 16)
- RE: Cost-effectivenesss of highly-accurate clocks for NTP Jameson, Daniel (May 16)
- Re: Cost-effectivenesss of highly-accurate clocks for NTP Baldur Norddahl (May 14)
- Re: Cost-effectivenesss of highly-accurate clocks for NTP Baldur Norddahl (May 13)
- Re: Cost-effectivenesss of highly-accurate clocks for NTP Valdis . Kletnieks (May 15)