[ntp:questions] Using a "composite clock" time source?

Kevin Oberman oberman at es.net
Tue Nov 6 18:32:25 UTC 2007

> From: "scott.baker at gmail.com" <scott.baker at gmail.com>
> Date: Mon, 05 Nov 2007 16:34:02 -0800
> Sender: questions-bounces+oberman=es.net at lists.ntp.org
> My NTP server is run at the local phone company. They already have a
> GPS fed stratum 2 (?) time source fed via GPS on the roof. The CO guy
> told me that they have lots of leads off their "composite clock" and
> we could have one if we needed. Apparently this timing source feds all
> their telco gear (OC-X equipment, class 5 switch, etc).
> I asked him what I should google up and he said "composite clock." Is
> there some way to hook up a "composite clock" to the serial port on my
> server? It appears that a composite clock is three wires: tip, ring
> and ground? Any help on if it's possible to use this would be great.

This looks like it's probably a T1 connection to provide sync, not time,
to telco equipment.

Telcos think of "clock" as a highly synchronized T1 clocking signal to
keep all of their equipment in sync. It provides very accurate clocking
to ADMs, routers, switches and the like, but does not provide actual
time. The GPS is used to assure that the clocking is consistent around
the world.

Make sure that they are providing time code, not just a clock signal. IF
they are, it is most likely IRIG-B timecode and there are several ntpd
supported reference clocks that support IRIG-B.

We went through this last year when we moved our colos to a new provider
and they told us that they could provide a a GPS based clock. They
handed us a T1 and we had to explain that some of use actually want to
know what time it is, not just how fast time is passing.
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634
Key fingerprint:059B 2DDF 031C 9BA3 14A4  EADA 927D EBB3 987B 3751
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