[189265] in North American Network Operators' Group
Re: NIST NTP servers
daemon@ATHENA.MIT.EDU (Mel Beckman)
Fri May 13 10:39:03 2016
X-Original-To: nanog@nanog.org
From: Mel Beckman <mel@beckman.org>
To: Lamar Owen <lowen@pari.edu>
Date: Fri, 13 May 2016 14:38:58 +0000
In-Reply-To: <5735E0E1.6010807@pari.edu>
Cc: NANOG <nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
Lamar,
You make it sound like TXCOs are rare, but they're actually quite common in=
most single board computers. True, you're probably not gonna find them in =
the $35 cellular-based SBCs, but since these temperature compensated oscill=
ators cost less than a dollar each in quantity, they're quite common in mos=
t industrial species for well under $100.
An Ovenized XCO is absolutely not required for IT-grade NTP servers. If you=
need sub-microsecond low-jitter leading-edge clocks, for BITS timing of S=
ONET or radio networks for example, then an OXCO is helpful. But NTP itself=
is not that accurate. NTP can usually maintain time to only within tens of=
milliseconds over the public Internet, and can only achieve better than on=
e millisecond accuracy in local area networks under ideal conditions.=20
-mel=20
> On May 13, 2016, at 7:13 AM, Lamar Owen <lowen@pari.edu> wrote:
>=20
>> On 05/11/2016 09:46 PM, Josh Reynolds wrote:
>> maybe try [setting up an NTP server] with an odroid?
>>=20
> ...
>=20
> I have several ODroid C2's, and the first thing to note about them is tha=
t there is no RTC at all. Also, the oscillator is just a garden-variety no=
n-temperature-compensated quartz crystal, and not necessarily a very precis=
e one, either (precise quartz oscillators can cost more than the whole ODro=
id board costs). The XU4 and other ODroid devices make nice single-board A=
RM computers, but have pretty ratty oscillator precision.
>=20
> You really have to have at least a temperature compensated quartz crystal=
oscillator (TCXO) to even begin to think about an NTP server, for anything=
but the most rudimentary of timing. Ovenized quartz oscillators (OCXO) an=
d rubidium standards are the next step up, and most reasonably good GPS-dis=
ciplined clocks have at least an ovenized quartz oscillator module (the Agi=
lent Z3816 and kin are of this type).
>=20
