[ntp:questions] does this make sense?

[Terje Mathisen]

Thanks William, I will go with GPS.
Maria

That's a good choice. These boxes are low-cost (but not yet multiple
GNSS systems - check with the vendor), and have good hold-over in the
http://www.leobodnar.com/shop/index.php?main_page=product_info&products_id=272

In (parts of?) the US you can get a receiver which uses the US-centric
cell phone modulation system which requires clock synchronization
between towers and phones, I installed one of these in Tampa, FL.

It provided ~12 us afair.

Terje

[William Unruh]

Thanks for your reply, David. Accuracy to within milliseconds is fine
for us. We currently have four old GPS appliances in four data
centers that we are replacing, and my thought is that some vendor
diversity would be good.
We are only staying in two of those data centers, so that was where I
was thinking of using GPS as we already have a cable to an antenna to
the roof. We have a third data center where we currently don't have
any ntp appliance, and that's where I was thinking it would be
convenient to put a WWVB device. But we do have access to the roof,
and from what you say it sounds like we would be better off putting a
GPS using all three services there.
We have a network of 12 stratum 2 servers that get time from our
appliances, and most of our infrastructure points to those, so maybe
three GPS appliances using all three services at the three data
centers?

I've designed similar setups a couple of times: Since we're located in
Europe my backup was the German radio transmitter since that one uses
spread spectrum modulation of the carrier, enabling 10-15 us precision.

That is about 2 miles light travel time. I suspect you are further than that
from the tranmitter. And propagation is all in the atmosphere, and the speed
of radio varies in the atmosphere, depending on the pressure, the humidity,
clouds,.... Ie, I am doubting the 10-15us. Maybe 10-15 ms.?

With a modern multi-system GNSS receiver and multiple geographical
locations I would probably be happy with a very good local clock (at
least TCXO, maybe a second-hand Rb?) to provide holdover and using
multiple internet sources as a sanity check.
Terje

[Terje Mathisen]

Post by William Unruh

I've designed similar setups a couple of times: Since we're located
in Europe my backup was the German radio transmitter since that one
uses spread spectrum modulation of the carrier, enabling 10-15 us
precision.

That is about 2 miles light travel time. I suspect you are further
than that from the tranmitter. And propagation is all in the
atmosphere, and the speed of radio varies in the atmosphere,
depending on the pressure, the humidity, clouds,.... Ie, I am
doubting the 10-15us. Maybe 10-15 ms.?

Bill, please!

This was of course with an initial propagation time measurement period,
where we used the GPS PPS signal to verify the ground wave propagation
time of the radio signal, then adjusting for that offset in the radio
driver.

Yes, propagation time will vary a bit over a 24H period, but this
provides a very useful backup.

Terje

[Thomas Laus]

I'm purchasing ntp appliances to put into three datacenters. Does it make sense to purchase two that use GPS and two that use WWVB, and configure them as peers?

The USA Bureau of Time Standards has a link for timing receiver
vendors:
https://www.nist.gov/pml/time-and-frequency-division/time-services/manufacturers-time-and-frequency-receivers

There are a few manufacturers of CDMA systems that receive the timing
signals from the USA cellphone systems. They have a high degree of
accuracy and are a better choice than WWVB in most cases.

Tom

[Steven Sommars]

Search for: CDMA shutdown

CDMA NTP servers lack an automated leap second mechanism, as far as I can
tell.

I'm purchasing ntp appliances to put into three datacenters. Does it

make sense to purchase two that use GPS and two that use WWVB, and
configure them as peers?
The USA Bureau of Time Standards has a link for timing receiver
https://www.nist.gov/pml/time-and-frequency-division/time-
services/manufacturers-time-and-frequency-receivers
There are a few manufacturers of CDMA systems that receive the timing
signals from the USA cellphone systems. They have a high degree of
accuracy and are a better choice than WWVB in most cases.
Tom
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GnuPG KeyID = 0x620836CF
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[Thomas Laus]

Search for:   CDMA shutdown
CDMA NTP servers lack an automated leap second mechanism, as far as I
can tell.

My CDMA experience dealt with an Endrun Tempus LX receiver only. It
received and used the leap second information that was sent along with
the rest of the CDMA time broadcast transmissions. It has been a long
time since setting up that receiver and my memory might be a little
foggy. I seem to remember that there was also a way to enter the IERS
file manually.

Tom

[Steve Sullivan]

There is this now too.
https://swling.com/blog/2018/08/nist-fy2019-budget-includes-request-to-shutd
own-wwv-and-wwvh/

What did you end up doing Maria?

Steve
Network Time Foundation

-----Original Message-----
From: questions [mailto:questions-
Sent: Monday, August 13, 2018 7:10 AM
Subject: Re: [ntp:questions] does this make sense?
Search for: CDMA shutdown
CDMA NTP servers lack an automated leap second mechanism, as far as I can
tell.

I'm purchasing ntp appliances to put into three datacenters. Does it

make sense to purchase two that use GPS and two that use WWVB, and
configure them as peers?
The USA Bureau of Time Standards has a link for timing receiver
https://www.nist.gov/pml/time-and-frequency-division/time-
services/manufacturers-time-and-frequency-receivers
There are a few manufacturers of CDMA systems that receive the timing
signals from the USA cellphone systems. They have a high degree of
accuracy and are a better choice than WWVB in most cases.
Tom
--
PGP KeyID = 0x5F22FDC1
GnuPG KeyID = 0x620836CF
_______________________________________________
questions mailing list
http://lists.ntp.org/listinfo/questions

_______________________________________________
questions mailing list
http://lists.ntp.org/listinfo/questions

[Ruslan Nabioullin]

Post by Thomas Laus

I'm purchasing ntp appliances to put into three datacenters. Does it make sense to purchase two that use GPS and two that use WWVB, and configure them as peers?

The USA Bureau of Time Standards has a link for timing receiver
https://www.nist.gov/pml/time-and-frequency-division/time-services/manufacturers-time-and-frequency-receivers
There are a few manufacturers of CDMA systems that receive the timing
signals from the USA cellphone systems. They have a high degree of
accuracy and are a better choice than WWVB in most cases.

What's the point? From what I know, cellular systems typically use
the following metrological hierarchy: 1. GPS, possibly redundant; and
2. onsite telecom-grade rubidium, possibly redundant. Therefore,
using CDMA would partially defeat the purpose of seeking an alternate
source as a fallback/for corroboration (the only utility would be that
rubidium standard, which would be civilian and moreover telecom-grade,
and of course the GPS receiver is almost certainly civilian and
therefore be susceptible to spoofing). Plus it's a for-profit
civilian commercial service (from which timing is extracted as a
byproduct of its operation), which will likely be decommissioned from
the entire US in a few years anyway...

WWVB should be a good fallback source to GNSS, due to the
significantly-different nature of the technology (terrestrial in lieu
of space, groundwave propagation in lieu of line-of-sight, and VLF in
lieu of L band), though I am concerned about it (and/or one's
receiver) employing civilian technology (that could be damaged or
taken out by nuclear EMPs) and the potential for *targeted* malicious
jamming/spoofing employed by adversaries (for general-coverage
malicious jamming/spoofing, obviously it would be more difficult due
to the need to erect VLF antennae and powerful transmitters, which
would be visible by authorities, one of the merits of terrestrial
hyperbolic radionavigation services, e.g., Loran).

It's quite unfortunate that WWV could be taken down (I am involved in
a number of projects which utilize WWV/CHU-derived timing for public
NTP services), though on the other hand I don't see too much of a
utility from it for T&F (it's skywave/groundwave in lieu of
groundwave, and HF in lieu of VLF) compared to VLF services (WWVB,
DCF77, et al.), due to its crude accuracy as a result of the skywave
propagation mode, apart from greater coverage during favorable
ionospheric conditions and there being WWV/CHU NTP decoders (try doing
that for WWVB...they changed the signal format in '12, thereby turning
virtually all metrological receivers into paperweights). It's the
best GNSS alternative out there for NTP users (in North America, at
least) (just connect an HF AM receiver to the server's soundcard),
unless one resorts to purchasing a WWVB receiver (which to my
knowledge is made by only 2--3 corporations, one of which is not
metrological-grade).

-Ruslan