Frequently Asked Questions

General Questions
How are upgrades handled and what do they cost?
Are your products traceable to UTC?
What is Stratum?
Do your clocks use smearing techniques to handle the leap second?
GPS for Time & Frequency
How far can I install the antenna from the GPS receiver?
Will GPS work inside?
I don't have roof-top access.  What do I do?
CDMA for Time & Frequency
Do your CDMA products work with PCS or cellular and what is the difference?
How do I know if I am in a CDMA coverage area?
Do I have to pay a monthly cell phone service fee to use your products?
Does weak signal level affect the timing accuracy?
Why does the timing accuracy vary?
Since the timing accuracy varies why is the frequency so stable?
Can you tell if the basestation you are receiving is in a holdover mode?
How much longer will CDMA be around?
Precision Time Protocol (PTP/IEEE-1588)
For questions about PTP see this special PTP/IEEE-1588 FAQ.
Network Time Servers and NTP
How accurate is NTP?
Where can I get client software?
Our security guys did a scan on the time server and found a few vulnerabilities.
   Is there going to be a firmware update soon to address this?

How long will the time server deliver Stratum 1 performance if the signal is lost?
Why do I need a time server?
Why not use the network time services available over the Internet?


How are upgrades handled and what do they cost?
Software upgrades for all our products are freely available for download from our website at: www.endruntechnologies.com/download.htm.
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Are your products traceable to UTC?
Yes - the time and frequency outputs generated by our equipment are all traceable to UTC.  For a thorough explanation of traceability in regards to our GPS and CDMA Time Servers read this white paper called: Establishing Traceability to UTC.
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What is Stratum?
Stratum is a term that means different things depending on the context.  In the world of NTP, stratum is defined in RFC 1305.  NTP uses a hierarchical structure in which Stratum 0 is the reference clock, linked via a time signal, to a reliable source of UTC.  Stratum 1 is the time server with a direct link to the reference clock.  Stratum 2 is a client that receives time over a network connection from a Stratum 1 clock.  Stratum 3 is a client that receives time from a Stratum 2 clock.  And so on, up to Stratum 15.  For more details on strata in the NTP world, click here.

In the Precision Time Protocol (PTP/IEEE-1588) (version 1), stratum is indicative of its accuracy relative to UTC.  Stratum 1 means its accurate within 25 nanoseconds.  Stratum 2 is accurate within 100 nanoseconds.  Stratum 3 is accurate greater than 100 nanoseconds.  And Stratum 255 means it has never been locked.  Stratum is not used in PTP version 2.

In the telecommunications industry stratum level is indicative of oscillator performance.  It refers to the holdover performance of the oscillator in the event of loss of synchronization.  A Stratum 1 clock has an accuracy of 1.0 x 10-11, Stratum 2 has an accuracy of 1.6 x 10-8, Stratum 3 has an accuracy of 4.6 x 10-6, and Stratum 4 has an accuracy of 3.2 x 10-5.
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Do your clocks use smearing techniques to handle the leap second?
EndRun clocks do NOT use smear techniques, which are inconsistent with the definition of UTC.  For more information click here.
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How far can I install the antenna from the GPS receiver?
The standard antenna cable length is 50 feet.  If you need more we offer antenna lengths of up to 250 feet without a GPS preamplifier.  If you need more than 250 feet of cable then a preamp is required.  You can run an additional 200 feet of cable for every preamp installed and you can have up to 3 or 4 preamps.  This will allow you to run a total of 850 to 1050 feet of cable.  For more information on our GPS preamplifiers click here.
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Will GPS work inside?
Unlike CDMA, GPS will not work inside buildings.  To receive GPS signals the antenna must have a view of the sky.  The best location is on a roof-top with the antenna in view of a maximum amount of sky.  However, our GPS products have the ability to operate in a single-satellite mode.  This lets you avoid the trouble and expense of a rooftop installation by allowing you to mount the antenna in a window of your building with only a partial view of the sky.
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I don't have roof-top access.  What do I do?
You have two choices:
   1. Mount your GPS antenna in a window (see the question above), or
   2. Purchase a CDMA-synchronized product which works very well inside buildings (assuming your area has CDMA coverage).
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Do your CDMA products work with PCS or cellular and what is the difference?
The difference between PCS and cellular is the frequency band.  PCS frequencies are at 1960 MHz and cellular frequencies are at 881 MHz.  Our newest rackmount products use a dual-band CDMA receiver and can receive either cellular or PCS signals.  Some of our earlier products use CDMA at cellular frequencies only (Praecis Ct, Cf, Ce).
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How do I know if I am in a CDMA coverage area?
CDMA coverage is throughout the USA, China, Korea, India, Japan and elsewhere.  The best way to know if you have CDMA coverage is to find someone with a CDMA cellular or PCS phone and see if it indicates any signal level at all.  Our products work in very poor signal level conditions.

If you are unsure that you have the appropriate CDMA coverage contact us.  Also, since we offer a 60-Day Money-Back Guarantee there is no risk in trying it out.  We have shipped thousands of units throughout the world and our return rate has been less than 1%.
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Why does the timing accuracy vary?
CDMA basestation transmissions must be synchronous with UTC to within 10 microseconds, typically much better - less than 1 microsecond.  This variation is due to the possibility that a basestation might have a GPS outage, a rare occurrence.  Under these conditions the basestation must stay within 10 microseconds of UTC for as long as 24 hours.  This ensures the smooth operation of the CDMA telecommunications system.

Our products are synchronous with the CDMA basestation transmissions from one to tens of microseconds, depending on location.  This variation depends on the propagation delay from our receiver to the basestation.  The propagation delay is about 5 microseconds per mile (about 3 microseconds per kilometer).  In an urban environment, there are many basestations and you would probably be within a mile of one.  Therefore the accuracy of the unit would be within 5 microseconds of the CDMA transmissions and typically within 6-7 microseconds of UTC.  Our main facility is located in an urban environment and our products test here to within 2 microseconds of UTC.  This is very typical for an urban environment.

In suburban or rural areas the basestations are spaced further apart.  This increases the propagation delay and therefore the accuracy of the unit degrades.  At our suburban test facility the units are synchronous with UTC to within 20-25 microseconds.  At our rural test facility the best-case accuracy we have seen is 30 microseconds and the worst-case is nearly 90 microseconds.  That would put the received basestation at nearly 18 miles away!

If you know approximately how far away the basestation is from your location you can eliminate this propagation delay component by using the CAL command via the serial I/O port.  Refer to the user's manual for more details.
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Since the timing accuracy varies why is the frequency so stable?
Unlike the timing outputs, the 10 MHz frequency output is not affected by propagation delay.  Since both the basestation and the EndRun unit are stationary (they don't move in relation to each other) the frequency is extremely accurate, to parts in 10 to the 12th over 24-hour averaging times.  On rare occasions, a basestation might experience a GPS outage, as when the GPS antenna is damaged.  Under these conditions the basestation's GPS receiver would go into a holdover mode and its frequency could drift up to about a part in 10 to the 10th over 24 hours.  An outage is rare, and one lasting 24 hours would be very rare.

Note that the requirement to maintain basestation synchronization during long GPS outages requires that each basestation have at least one high performance GPS time receiver controlling either an ultra high stability quartz oscillator or a rubidium vapor atomic frequency standard. Since it is very difficult to meet this performance using quartz oscillators, most base stations have rubidium units and redundant GPS receiver/oscillator units are common.
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Can you tell if the basestation you are receiving is in a holdover mode?
No.
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How much longer will CDMA be around (USA)?
We expect Verizon to provide CDMA service until 2020.  We expect Sprint to provide CDMA service through 2020 and beyond.  Sprint CDMA coverage is extensive nationwide.  For a Sprint Voice coverage map click here.  For background and details, read the following:

CDMA service in the United States depends on the CDMA networks operated by Sprint and Verizon.  As of April 2017, Sprint has made no announcements to discontinue operation of their CDMA network.  Verizon announced in February 2016 that they intend to discontinue CDMA service by 2020 to reuse the spectrum.  Therefore we expect CDMA service to be available from both providers to at least 2020 and most likely beyond by at least Sprint.

Sprint:  Sprint completed a large investment in their Network Vision project in 2014 that completely upgraded the network infrastructure at 38,000 cell sites throughout the U.S.  Sprint has said that it plans to maintain its 2G CDMA network capability for the long term as part of its overall Network Vision strategy.  Sprint is also focused on the M2M market and is supporting the migration of many 2G GSM customers to their CDMA network.  "Now is the opportune time for any customers migrating off GSM or designing new products for telematics, telemetry, automotive and security applications to take advantage of Sprint's 2G platform", said Wayne Ward, vice president of Sprint's M2M Group, in May 2013.

Verizon:  In July 2016, Jeff Hamby, Verizon spokesman, stated that Verizon has set a goal to discontinue operations of it's CDMA 1X network by December 31, 2019.  However, Verizon is aware of the millions of CDMA based machine-to-machine (M2M) and Internet-of-Things devices that will need to transition to LTE.  Therefore Verizon has signaled that they "will work with these customers one-on-one" to transition and will consider operating the CDMA network into 2020 if necessary.  M2M includes communications for alarm systems, industrial equipment, vending machines, power company meters, and other "smart" equipment.

Reference articles:
Telecom Engine:  Sprint to Continue Supporting 2G for M2M Customers
Sprint:  Sprint Selects u-blox as a Preferred Provider for Long-term CDMA Network Support
Telit:  Sprint Selects Telit as a Preferred Provider and Approves CDMA 1xRTT M2M Module
Fierce Wireless:  Verizon to shut down 2G CDMA 1x network by the end of 2019
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How accurate is NTP?
Over WANs (Wide Area Networks), up to 100 milliseconds is typical.  It depends on how far away the public time server is, or more specifically, how many hops between you and the server.  Within a LAN (Local Area Network) using a dedicated NTP Time Server, 0.5 to 2 milliseconds is typical.  The internal accuracy of the CDMA Network Time Server is on the order of 10 microseconds.  It can easily keep all clients on a LAN synchronized to typically within 0.5 to 2 milliseconds.
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Where can I get NTP client software?
NTP client software is widely available as freeware and shareware.  Setting up an NTP or SNTP client is relatively simple once you have installed the software on your workstation and communicated with the time server over the network.  For a list of client software click here.
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Our security guys did a scan on the time server and found a few vulnerabilities.  Is there going to be a firmware update soon to address this?
Serious vulnerabilities that cannot be mitigated with a reasonable workaround will be addressed with a new firmware update as soon as possible.  For remaining vulnerabilities, we recommend you read this paper:

   Best Practices to Secure Your Time Server.

Taking the steps outlined in this paper will eliminate most, if not all, vulnerabilities.  It was written for the Sonoma Time Servers but the same general steps apply to our older models such as Tempus LX and Unison.
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How long will the time server deliver Stratum 1 performance if the signal is lost?
Exclusive EndRun oscillator-control algorithms provide extended Stratum 1 holdover performance when the unit is not locked to the synchronization signal (GPS or CDMA).  Typical NTP Stratum 1 holdover periods are:
   24 hours - TCXO (standard)
   35 days - OCXO (upgrade)
   140 days - Rubidium (upgrade)
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Why do I need a time server?
When two or more computers are involved, accurate time keeping is difficult, especially if they are not in the same physical location.  A dedicated time server inside your network perimeter is the most accurate, reliable and secure way to ensure accurate timekeeping for all computers on your network.  Accurate timekeeping is necessary to support eBusiness and other applications such as Stock Trades, Logs, B2B Transactions, File Operations, Packet Time Stamps, Software Configuration Management, Database Accuracy, Telecommunication Call Billing, etc.  For a more detailed response to this question click here.
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Why not use the network time services available over the Internet?
There are many public time servers available over the Internet.  Access to these public time servers is free of charge.  While public time servers are certainly less costly - accurate, reliable and secure time is best provided by a dedicated time server that resides under your control inside your network security perimeter.  Using public time servers available over the Internet is not recommended for the following reasons:

1.  Setting up your firewall to accept NTP packets (which is based on UDP/IP) introduces a security risk that many Network Administrators are not willing to take.

2.  Time accuracy degrades because of indeterminate network latency, up to 100 milliseconds is typical.
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