hey there Nanog,
I am trying to buy a GPS based NTP server like this one
https://timemachinescorp.com/product/gps-time-server-tm1000a/
but I will be placing this inside a data center, do these need an actual view of a sky to be able to get signal or will they work fine inside a data center building? if you have any other hardware requirements to be able to provide stable time service for hundreds of customers, please let me know.
mehmet
Dear Mehmet,
I am trying to buy a GPS based NTP server like this one
https://timemachinescorp.com/product/gps-time-server-tm1000a/
but I will be placing this inside a data center, do these need an
actual view of a sky to be able to get signal or will they work fine
inside a data center building?
This will *not* work if the antenna is placed *inside* the datacenter.
The trick is to order a spot on the roof of the datacenter, have the
facility staff place the antenna there, and run a cable to the NTP
server in your rack.
It'll depend on the facility what the MRC / NRC is for this service will
be.
Kind regards,
Job
You will need a clear view to the sky for at least the antenna.
Most GPS "antennas" are an antenna and Low Noise Amplifier (LNA) which is
powered via 5-12v on the coax. This sets the noise figure and gain of the
system, so you can run 50-100' of RG6 coax if needed. You'll need a F to sma
adapter for this unit it looks like. Don't worry about the impedance
mismatch, 50 to 75 ohm is not horrid, the RG-174 thin cable has more loss in
10' than 100' of RG6.
You will not want to use the low gain puck antenna, but rather get a proper
grounded/mounted/weatherproofed antenna such as the ubiquitous 26 dBi
Quadrifilar Helix antenna. https://www.ebay.com/itm/192899151132
thank you guys, looks like GPS based NTP is the way to go.
If you can't get a good spot for an antenna, you could be on the lookout for a CDMA NTP clock.
https://endruntechnologies.com/products/ntp-time-servers
We've got one as a backup to our SyncServer S200. Doesn't need an outdoor antenna as long as you can get a cellular signal in the DC.
EndRun's are Linux based and still getting software updates. As an added bonus, they also do IPv6.
Of course, you're putting a lot of trust into the wireless companies doing this, but its a nice alternative.
The link you provided answers that question:
“The built in high sensitivity GPS receiver is able to lock multiple satellites from within multiple buildings or from a window location, eliminating the requirement that an outdoor antenna be installed”. If you’re still worried about your specific use-case, I recommend contacting the manufacturer.
Hi,
If you can't get a good spot for an antenna, you could be on the lookout
for a CDMA NTP clock.
CDMA service is about to be retired in several places, please check
in your area before you install a "new" CDMA based time server.
C.f. https://www.verizonwireless.com/support/knowledge-base-218813/
I looked into the same thing and decided not to go with CDMA.
A simple check inside a (datacenter) building is to use one of the GPS
smart phone apps that display you number of Sats and signal strength then
walk around where you would place the NTP server appliance. Beware of
server CPUs and memory making RF noise in the same frequency spectrum of
1.2 - 2 GHz, completely blanking out any GPS indoors. I concur that
installing an amplified roof-top antenna and running coax to your receiver
is the best option.
-andreas
I had inquired with Frontier about installing a GPS antenna and they said they don’t allow antennas of any kind attached to the building anymore. I didn’t pursue that any further. I didn’t think to check what the signal strength was inside.
Mehmet,
I use the TimeMachines unit a lot. Usually we deploy these near any outside window, typically putting the box in the ceiling and the running the GPS antenna on its 20’ cable (or whatever it is) down to the window glass. Test different windows first before committing. Then use any of the may passive POE injectors to inject the TM’s power brick into the Cat5 and strip it out on the other end, over a little power plug jumper that plugs into the TM box. Works a treat!
-mel beckman
There's actually a few other CDMA networks in our area (Boise) besides Verizon, so it wouldn't hurt to look. I seem to remember Sprint is planning to go to 2021? There also appears to be a few smaller independent CDMA networks around as well.
I looked before at who had spectrum allocations in the frequencies my boxes supported. I then used Cell Mapper to figure out what technology was deployed on that frequency. IIRC, both US Cellular and Verizon had basic CDMA running in my area on those channels. Sprint was running LTE and 1x Advanced (or something like that), so probably wouldn’t have worked out. If Verizon is dropping theirs, then depending on only one company seems a bit unwise… which means I gotta find some kind of solution by then. sigh
Kinda sucks all the good 'backup' methods of time keeping are dwindling.
I've got a WWVB clock as well that I'd love to get hooked into my main NTP server, but I worry they're going to finally kill that off in the next year or so.
LORAN C clocks still have potential to work well too...
High accuracy time keeping is a fun hobby. 
So I gotta ask, just as a reality check:
- Why do folks want to have one or more NTP server masters that have at
least 1 refclock on them in a data center, instead of having their data
center NTP server masters that only get time over the internet?
- What % of data center operators provide time servers in their data
centers for their tenants (or for the general public)?
Perhaps using a rubidium source instead of GPS ? The actual time can be obtained thru NTP, all you actually need is a precision source to keep time accurate thereafter.
Rubens
- Why do folks want to have one or more NTP server masters that have at
least 1 refclock on them in a data center, instead of having their data
center NTP server masters that only get time over the internet?
I had that discussion before with the QSA for a compliance audit, pointing
to requirement "10.4.3 Time settings are received from industry-accepted
time sources" and "verify that the time server(s) accept time updates from
specific, industry-accepted external sources (to prevent a malicious
individual from changing the clock)" in the PCI-DSS document. He
non-jokingly suggested "why don't you use pool.ntp.org?", not really
realizing how many servers are in fact just someone's PC behind a cable
modem in their home, which negated the "do I trust the time I am
receiving?". My immediate answer was "we could use NIST servers",
but the easiest way out of this is "we operate our own NTP appliance
with a GPS receiver" and provide that as evidence.
Don't get me wrong, I support pool.ntp.org by operating and contributing
servers to it, but it is not deemed good enough if you need traceability
of your NTP time source(s), even though the pool will only admit members
above a certain quality threshold.
- What % of data center operators provide time servers in their data
centers for their tenants (or for the general public)?
My $employer does that in our datacenters and points of presence for
our customers.
-andreas
Some DCs also offer GPS antenna feeds fed from a splitter, though it's
important to get the total cable length from the antenna to your
receiver so you can set your propagation delay offset accordingly. I've
also been in facilities that distribute IRIG and 10MHz references so you
can feed a reference directly, but that's fairly rare.
It's worth asking what your facilities can provide, in either case. Many
DCs don't want a dozen GPS antennae cluttering the roof up but are happy
to provide the service from one they look after (for a cost, of course).
If you have external facilities, of course, so long as you can run
PTP/1588 back from them, you can always host your clocks there and
distribute to 1588 masters in the DC.
- Why do folks want to have one or more NTP server masters that have at
least 1 refclock on them in a data center, instead of having their data
center NTP server masters that only get time over the internet?I had that discussion before with the QSA for a compliance audit, pointing
to requirement "10.4.3 Time settings are received from industry-accepted
time sources" and "verify that the time server(s) accept time updates from
specific, industry-accepted external sources (to prevent a malicious
individual from changing the clock)" in the PCI-DSS document. He
non-jokingly suggested "why don't you use pool.ntp.org?", not really
realizing how many servers are in fact just someone's PC behind a cable
modem in their home, which negated the "do I trust the time I am
receiving?". My immediate answer was "we could use NIST servers",
but the easiest way out of this is "we operate our own NTP appliance
with a GPS receiver" and provide that as evidence.Don't get me wrong, I support pool.ntp.org by operating and contributing
servers to it, but it is not deemed good enough if you need traceability
of your NTP time source(s), even though the pool will only admit members
above a certain quality threshold.
I have no immediate agenda here. My sole purpose is to get information
about this, as I mostly work with people who a) believe accurate time is
important, and b) at least have an appreciation for how unexpectedly
difficult it is to synchronize time in a predictable and stable way
across a large population of systems in a diverse set of environments.
In my experience, people who don't fall in to either of those categories
are pretty well invested in their opinions.
- What % of data center operators provide time servers in their data
centers for their tenants (or for the general public)?My $employer does that in our datacenters and points of presence for
our customers.
Glad to hear it!
Accurate timing is also often required for telco gear.
Hello,
As other have commented before, it looks you need an outdoor antenna, however, reading the specs it says:
“The built in high sensitivity GPS receiver is able to lock multiple satellites from within multiple buildings or from a window location**, eliminating the requirement that an outdoor antenna be installed**.”
Weird.
Alejandro,
It can be extremely useful to have known-good timestamps to within several milliseconds, even in the event of a connectivity outage, when trying to figure out what went wrong from log entries spanning multiple systems and sites.
Think about what might happen if you lost time sync as a result of the incident causing said connectivity outage. Depending on your time sources available, you might see rapid drift or, worst case, lose your time reference entirely as a result of equipment restarts, etc. GPS, as long as you have a good view of the sky, provides extremely accurate "lights out" time info, both absolute and relative, from a single source with no (mostly) strings attached for that purpose.