[ntp:questions] Indirect GPS time source options

Jochen Bern Jochen.Bern at LINworks.de
Thu Mar 13 15:24:14 UTC 2014


On 13.03.2014 13:00, questions-request at lists.ntp.org digested:
> From: Olivier Drouin <ol.drouin at gmail.com>
> 
> For exemple, Endrun Technologies sells the Sonoma N12 which seems to
> allow time synchronization against CDMA signal without the need for
> a carrier subscriptions.

(This thing supposedly answers more requests per second than I've set up
NTP clients in my entire life:
	http://www.endruntechnologies.com/ntp-server.htm
- do you have thousands of *local* clients to serve and/or a Gigabit
uplink to bring that throughput to *remote* ones?)

> If not, do I have other options beside a GPS antenna with a sky view?

Horror story: I once set up a customer's housing rack, right next to a
window, with a DCF77 receiver cable-tied onto its top. (That was less
than 50km from the DCF77 antenna array supposedly serving the whole of
Central Europe, mind.) Half a year into operation, reception plain
stopped and never came back, with no change in nearby racks apparent to
the naked eye. If quietly watching your N12 turn into a $5,000 rack
weight is not an option, then IMHO neither is an indoor antenna that the
building administration doesn't officially know about and support.

(I've also seen server rooms where you have to actually stand next to a
specific window a dozen meters from the nearest rack to get any GSM
reception, so potential reception problems are definitely not limited to
DCF77 and/or GPS.)

You specifically asked about syncs where the ultimate source is GPS.
There are lots of forms of time syncing built into building automation
systems (ISDN, single-wire, fire alarms, ...), as well as into WAN
connections you might have in your very rack, but there's likely some
DIY involved and you very likely will not get the same precision ...

(Personal opinion: I just don't get why there apparently are so many
hosting/housing/colo providers where you *cannot* get access to a local
NTP server or other central sync source even if you threaten to throw
money at them. Tamperproofness-wise, two miniature PCs with GPS
receivers on a roof your provider owns and controls run circles around
everybody and his VMs talking to public no-crypto NTP servers through a
plain Internet uplink ...)

Regards,
								J. Bern
-- 
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