A time server is a common office tool but what is it for?
We are all used to having a different time from the rest of the world. When America is waking up, Honk Kong is going to bed which is why the world is divided into time zones. Even in the same time-zone there can still be differences. In mainland Europe for instance most countries are an hour ahead of the UK because of Britain’s seasonal clock changing.
However, when it comes to global communication, having different times all over the world can cause problem particularly if you have to conduct time sensitive transactions such as buying or selling shares.
For this purpose it was clear by the early 1970’s that a global timescale was required. It was introduced on 1 January 1972 and was called UTC – Coordinated Universal Time. UTC is kept by atomic clock but is based on Greenwich Meantime (GMT – often called UT1) which is itself a timescale based on the rotation of the Earth. Unfortunately the Earth varies in its spin so UTC accounts for this by adding a second once or twice a year (Leap Second).
Whilst controversial to many, leap seconds are needed by astronomers and other institutions to prevent the day from drifting otherwise it would be impossible to work out the position of the stars in the night sky.
UTC is now used all over the world. Not only is it the official global timescale but is used by hundreds of thousands of computer networks all over the world.
Computer networks use a network time server to synchronise all devices on a network to UTC. Most time servers use the protocol NTP (Network Time Protocol) to distribute time.
NTP time servers receive the time from atomic clocks by either long-wave radio transmissions from national physics laboratories or from the GPS network (Global Positioning System). GPS satellites all carry an onboard atomic clock that beams the time back to Earth. Whilst this time signal is not strictly speaking UTC (it is known as GPS time) because of the accuracy of the transmission it is easily converted to UTC by a GPS NTP server.