Posted by Richard N Williams on May 15th, 2012
Computer networks need to be synchronised. Keeping an accurate, precise and synchronised form or time is essential for security, preventing errors and communicating with other computer networks. If two computers are running different time scales, all sorts of problems can ensue, from information getting lost, applications failing to occur and the whole network becoming vulnerable to unauthorised and malicious intrusion.
To keep precise time, computer networks have to find a source of accurate, precise and secure time, which enables all devices to be synchronised together. One of the most common used devices for achieving this are radio time synchronisation receivers.
Coordinated Universal Time
In today’s world of global communication and the internet, computer networks don’t only have to be synchronised internally, but also to prevent errors when communicating other computer networks, have to be synchronised with every network with which it communicates.
To achieve this, a global time scale was developed based on the time told by atomic clocks. Atomic clocks are the most accurate and precise form of timekeeping devices as they do not drift and keep time to within a few nanoseconds. The only problem with atomic clocks is that they are expensive pieces of equipment and only normally found in physics laboratories such as NPL (National Physical Laboratory) in the UK and NIST (National Institute of Standards and Time) in the USA.
Radio Time Synchronisation Receiver
Fortunately, computer networks can utilise atomic clocks because these physics laboratories broadcast time signals. To receive these time signals for synchronising a computer network, radio time synchronisation receivers are used. Radio time synchronisation receivers not only receive the atomic clock signal, but also they distribute this signal around a computer network, ensuring all computers, routers and switches on the network are kept synchronised to this atomic clock time.
Radio time synchronisation receivers use NTP (Network Time Synchronisation) to maintain synchronisation across the network using the atomic clock signal.
The time signals and frequencies that radio time synchronisation receivers use vary country to country. In the UK, the signal broadcast by NPL is known as the MFS signal and it is transmitted from Cumbria. The signal is available across the UK, although as with most radio signals it is susceptible to interference caused by local topography.
In the USA, the NIST signal is known as WWVB and is broadcast from Boulder, Colorado and radio time synchronisation receivers across North America can receive it. Other nations have their own radio transmissions, such as the DCF signal in Germany, which can also be picked up by neighbouring countries.
For areas where a local time signal is unavailable, there is another solution for receiving an atomic clocks source – the GPS time synchronisation receiver. These are similar devices to the radio time synchronisation receivers, but rather than use a radio source, they make use of the GPS signal, which is then distributed around a network using the same NTP protocol. The big advantage of GPS time servers is that the signal is available anywhere, no matter where you are on the planet, although their main disadvantage is that an antenna needs a clear view of the sky to receive the signal.