[189295] in North American Network Operators' Group
Re: Cost-effectivenesss of highly-accurate clocks for NTP
daemon@ATHENA.MIT.EDU (Mel Beckman)
Sat May 14 15:42:50 2016
X-Original-To: nanog@nanog.org
From: Mel Beckman <mel@beckman.org>
To: Baldur Norddahl <baldur.norddahl@gmail.com>
Date: Sat, 14 May 2016 19:42:13 +0000
In-Reply-To: <CAPkb-7AbRJJs2g4mOHxLsAVCdKTKhJmqfEHO7D5SSahWWCj3RQ@mail.gmail.com>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
> 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@gmail.com>=
wrote:
>=20
>> On 13 May 2016 at 23:01, Baldur Norddahl <baldur.norddahl@gmail.com> wro=
te:
>>=20
>> 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?
>>=20
>> I am thinking that many available datacenter locations will have poor GP=
S
>> signal so we can expect signal loss to be common. Some weather patterns
>> might even cause extended GPS signal loss.
>>=20
>>=20
>>=20
> I found some data points here: https://en.wikipedia.org/wiki/Crystal_oven
>=20
> Assuming that acceptable drift is 10 milliseconds due that being the
> expected accuracy from NTP.
>=20
> The common crystal oscillator can be as bad as 1E-4 =3D> holdover time is=
2
> minutes.
> TCXO is listed as 1E-6 =3D> holdover time is 3 hours.
> OCXO is listed as multiple values, I will use 1E-7 =3D> holdover time is =
1
> day.
> Rubidium is listed as 1E-9 =3D> 3 months
> Caesium is listed as 1E-11 =3D> 30 years
> Hydrogen Maser 1E-15 =3D> 300 millennia
>=20
> I clearly need three of those maser things for my network.
>=20
> Regards,
>=20
> Baldur
