Using National Time and Frequency Signals as a NTP Timing Reference

December 17, 2017 by  Filed under: Computer 

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The importance of anauthenticated timing reference to synchronise a computer network to, cannot be stressedhighly enough.

While there arehundreds and quite possibly thousands of internet based timing sources thesecan’t be authenticated leaving a system open to viruses, malicious hackers ormalware.

Furthermore, a surveyby MIT (Massachusetts Institute of Technology) found that nearly half ofinternet timing sources were offset by over ten seconds and only a third could beregarded as being ‘useful ’ also it was discovered that many were too far awayfrom peers to provide any useful accuracy.

Most dedicated networktime servers are designed to receive a timing signal from the GPS (GlobalPositioning System), primarily because it is the most accurate and can be receivedfrom anywhere on the globe.

However, there aresituations where it may not be practical to use a GPS time server. A GPSantenna has to be situated on a rooftop and have a clear view of the sky whichmay prove difficult if the server is on the ground floor of a multi-storeysky-scraper. Many administrators also dislike the hassle and expense of havingto run a cable up a building and install an antenna or if there arepossibilities the server room maybe relocated and the process has to berepeated.

Fortunately manycountries’ national physics laboratories broadcast a time and frequency signalfrom a radio transmitter.  In the US thesignal is referred to as WWVB and is broadcast by NIST (National Institute forStandards and Technology) in Colorado. In the UK the National PhysicalLaboratory (NPL) broadcasts the MSF signal from Cumbria and similar systems arebroadcast in Germany (DCF-77), Japan (JJY) and France (TDF).

Unfortunately notevery country transmits a national time and frequency broadcast so if a timeserver is to be located outside of the US, Germany, UK, France or Japan it maybe doubtful that a signal could be received (although many of the thesetransmissions can be received in neighbouring countries).

Radio signals are alsoeasily susceptible to atmospheric interference and can be blocked by mountains,sky-scrapers or other topography. However, an upside to using a radio receiveris that it will receive a signal inside a building.

While a radiotransmission is not as accurate as a GPS time signal a dedicated network timeserver receiving a radio signal can still provide accuracy between 1 – 20 milliseconds (a millisecond is 1/1000 of a second) which ismore than adequate for the needs of network synchronisation.




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