Time and Timing Servers

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1

There were a lot of NTP threads several weeks ago, but I didn’t get an answer to my question amongst all of the other chatter.

I’m looking for a device that can receive GPS inside a building without the assistance of an external antenna (Frontier says they no longer allow external antenna), will provide traditional NTP services, and will provide a timing signal that my Metaswitch can work with.

I know that MicroSemi via Symmetricom makes these kinds of devices, but I’m hoping to look at multiple manufacturers and compare.

Thanks.

2

I'm looking for a device that can receive GPS inside a building without the assistance of an external antenna (Frontier says they no longer allow external antenna), will provide traditional NTP services, and will provide a timing signal that my Metaswitch can work with.

GPS inside a building probably isn't going to work unless you have the antenna up against a window.

Look at CDMA NTP Servers like the EndRun Sonoma. They use the cellular network which requires accurate timing and has good building penetration.

     - Ethan O'Toole

3

Isn’t a major problem with CDMA-based sources that the networks they depend on are getting shut down?

4

Unfortunately, L band satellite signals are incredibly weak by
the time they reach the surface. It's very unlikely this is going to
work for you (unless it's a wood framed single story building.)

  Generally, I try to ensure that a GNSS antenna is built into the
contract, to avoid games like this.

  You have two options:

  A) Find a new colocation provider. This may already be on your
to-do list for other reasons.

  B) Rely on the Internet for timing, using NTP or PTP from
another location to backfeed the site, and use a box with a good
stable oscillator to keep time (this can actually be a commercial
time server with decent holdover characteristics.

  If you're just looking for alternatives to Microsemi, I highly
recommend talking to the fine folks at Meinberg.

  --msa

5

Domestically, yes.

  Not only are you dependant on Sprint if you go that route
(Verizon is already pulling the plug on CDMA this year.), it was never
any better than +/- 10 ms or so. You can get that via NTP pointed at
the Internet.

  At best, all you were doing with CDMA was relying on a cell
site's GPS receiver and holdover characteristics -- which were totally
opaque to you. At least you can monitor NTP.

  --msa

6

Yes, expect CDMA cellular to disappear before too long.

Verizon is shutting down their CDMA network at the end of this year.

Sprint announced in February 2019 that it is no longer activating CDMA-only devices starting May 1 2019. No sunset date has been announced yet but suffice it to say the ball is in motion to sunset their CDMA network.

Any of the regional carriers that run CDMA networks are likely to follow suit in short order.

Ryan Wilkins

7

Since it’s a telco facility, maybe they can provide BITS service. Worth asking.

—Chris

8

There were a lot of NTP threads several weeks ago, but I didn’t get an answer to my question amongst all of the other chatter.

I’m looking for a device that can receive GPS inside a building without the assistance of an external antenna (Frontier says they no longer allow external antenna), will provide traditional NTP services, and will provide a timing signal that my Metaswitch can work with.

I know that MicroSemi via Symmetricom makes these kinds of devices, but I’m hoping to look at multiple manufacturers and compare.

I have a Symmetricom S250 with the Rb option – it has an active antenna; while it does technically work inside buildings it really needs to be jammed right up against a window to work. In my (top floor in my house) office it gets no reception unless against a window…

W

9

I’ll look into Meinberg.

I recent thread mentioned high-sensitivity receivers often allow GPS to work inside. Obviously “inside” has a lot of definitions.

I will need this facility for the TDM timing signals. It’s a central office, not a datacenter.

I don’t know that Internet-based NTP would be accurate enough for the timing signals that I need. Maybe, maybe not.

10

They can do BITS, but that doesn’t solve all of my problems. That said, I may have to do many things if I can’t find my wonder box.

11

Isn't a major problem with CDMA-based sources that the networks they depend on are getting shut down?

If so, I would imagine there will be timing servers based on the replacement cellular technology. Might ask EndRun or one of their competitors about it.

       - Ethan

12

My experience with Dave Mills NTP algorithm is that, giving sufficient diversity in higher stratum sources, GPS versus Internet sources makes no practical difference. This assumes that you are concerned with Time for event logging and scheduling and not concerned with frequency and phase for clocking data on TDM instances.

If you are worrying about backhoe fade — it’s consequences will most likely affect other things more strongly than Time differences.

James R. Cutler
James.cutler@consultant.com
GPG keys: hkps://hkps.pool.sks-keyservers.net

13

I think you are referencing their chip scale atomic clocks. Which are very frequency stable. But still need phase alignment. (Mobile UPS anyone?)

Maybe some peers can provide transparent or boundry clock support. Or someone close by in the DC can add an antenna splitter.

Karsten

14

Ethan O'Toole <telmnstr@757.org>:

> I'm looking for a device that can receive GPS inside a building without
> the assistance of an external antenna (Frontier says they no longer
> allow external antenna), will provide traditional NTP services, and will
> provide a timing signal that my Metaswitch can work with.

GPS inside a building probably isn't going to work unless you have the
antenna up against a window.

Concur. But if you have that, my microserver build on a Raspberry Pi
will do nicely.

https://www.ntpsec.org/white-papers/stratum-1-microserver-howto/

No need for expensive proprietary hardware.

15

James R Cutler <james.cutler@consultant.com>:

My experience with Dave Mills NTP algorithm is that, giving sufficient diversity in higher stratum sources, GPS versus Internet sources makes no practical difference. This assumes that you are concerned with Time for event logging and scheduling and not concerned with frequency and phase for clocking data on TDM instances.

If you are worrying about backhoe fade — it’s consequences will most likely affect other things more strongly than Time differences.

I'm a subject-matter expert in Internet time service (tech lead of NTPsec) and I concur.

Local GPS sources are nice to have and fun to play with but not essential unless you
have a mission requitement to run autonomous.

Note by the way that you *can* run completely autonomous with NTPsec,
but not with the NTF version.

https://blog.ntpsec.org/2017/08/30/achieving-autonomy.html

16

A couple of thoughts here:

  1. I know at some sites there is an external, shared, GPS antenna which is run through a distribution amplifier to clients. Worth checking into just in case it exists and they forgot to offer it to you.

  2. Do you have any specs on what you need for the TDM clock? If you don’t have GPS or any other reasonable way to discipline your local clock you could conceivably get an accurate freerunning clock and use that. However, if this is even possible is going to be based on the accuracy/precision needed for the clock. The spec should be something like 10E-11 or something like that, possibly with jitter or other specs specified as well. The more accurate, the fewer options you will have and the more it will cost. If you only need 10E-6, you can do this dirt cheap. If you need 10E-13, you’re going to need a Cesium clock which will set you back a good five figures (and then some).

  3. Do you have spare, dark fiber or perhaps even a WDM color to somewhere you can get GPS? Copper might even work depending on the needs of the switch. The thought here is if you have a stable, non-packetized link to somewhere with GPS you then have quite a few options for transferring time back to the site.

I agree with you that NTP time transfer isn’t probably accurate enough by itself to discipline a clock for TDM… of course depending on the exact needs.

17

I'll look into Meinberg.

Meinberg are nice people with good hardware. They can do 2048KHz from
GPS and other timing signals, for instance. Then again, some router
vendors do that in boxes you need anyway. As long as the controlling
clock is PTP.

I recent thread mentioned high-sensitivity receivers often allow GPS to work inside. Obviously "inside" has a lot of definitions.

Indeed. Colo buildings rarely are on the forgiving side of "inside".
In Sweden, most older central offices are built to some degree of bomb
proofness (certainly not safe from direct hit) , with some 10mm of steel
in shutters for all windows, etc. GPS fares not well there.

I will need this facility for the TDM timing signals. It's a central office, not a datacenter.

Then you're concerned with frequency and phase to ITU-T G.812, I
suspect. Unless this is your "central central" office, in which case
you need G.811.

I don't know that Internet-based NTP would be accurate enough for the timing signals that I need. Maybe, maybe not.

The current trend in today's large frequency/phase consumers, ie. mobile,
is to run PTP over backhaul. Well behaved NTP _could_ make it, I suspect,
given a good enough clock in the facility, but PTP will definitely work,
assuming you have transmission and hardware capable of doing it.

"Capable" here, means dark fibre or WDM is required together with
routers and switches that can act as boundaries in PTP sense. If you
rent MPLS or are using plain Internet infrastructure, it becomes a lot
more complicated.

There are frequency/phase transmission solutions (mostly broadcast
related) that easily can transfer your central central cæsium clock
frequency to another site using reasonable-quality IP transport, but
those are neither cheap nor fire-and-forget.

18

I think you are referencing their chip scale atomic clocks. Which are very
frequency stable. But still need phase alignment. (Mobile UPS anyone?)

This is not a new problem.

http://www.leapsecond.com/hpj/v15n11/

Fascinating reading.

19

Oh, is *that* why Tracfone's telling it's customers to get new phones by
December...

Cheers,
-- jra

20

Or, there may be someone else in the facility who *is* "important" enough to
justify being permitted a roof antenna, who could put in a DA and share it
with you...

Cheers,
-- jra