Time Synchronisation

Time synchronisation is now a critical aspect of network management enabling time sensitive applications to be conducted from across the globe. Without correct synchronisation computer systems would be unable to communicate with each other and transactions such as seat reservation, Internet auctions and online banking would be impossible.

For effective time synchronisation the global timescale UTC (Coordinated Universal Time) is a prerequisite. While a computer network can be synchronised to any single time source, UTC is employed by computer networks all over the world. By synchronising to a UTC time source a computer network can therefore be synchronised to every other computer network across the globe that also use UTC as their time source.

Receiving a reliable UTC time source is not as easy as it sounds. Many network administrators opt to use a UTC Internet time source. Whilst many of these time sources are accurate enough, they can be too far away to provide reliability and there are plenty of Internet time sources that are vastly inaccurate.

Another reason why Internet time sources should not be used as a source of time synchronisation is because an Internet time source is outside of a firewall and leaving a gap in the firewall to receive timing information can leave a system open to abuse.

So that UTC time can be opted as a civil time throughout the world several national physics laboratories broadcast a UTC timing signal that can be received and utilised as a network time source. Unfortunately, however, these time signals are not available in every country and even in those areas where a signal exists; they can be quite often obstructed by interference and local topography.

Another method for receiving a source of UTC time is to use the GPS satellite network. Strictly speaking the Global Positioning System (GPS ) does not relay UTC but it is a time based on International Atomic Time (TAI) with a predefined offset. A GPS NTP clock can simply convert the GPS time into UTC for synchronisation purposes.

The main advantage of using GPS is that a GPS signal is available anywhere on the planet providing that there is a clear view of the sky above (GPS transmissions are broadcast via line-of-sight) so UTC synchronisation can be conducted anywhere.

A network time server is responsible for ensuring that all devices on a network are synchronised to the same time. Without synchronisation problems with time sensitive applications can occur and can leave a network open to security issues and even fraud.

A network time server can synchronise a network to any timing source but to ensure security and accuracy a UTC (Coordinated Universal Time) time source is essential.

UTC was developed after the invention of the atomic clock. It is based on International Atomic Time (TAI) and Greenwich Mean Time (GMT). After atomic clocks were developed and the accuracy of a few nanoseconds that they can maintain it was discovered that the Earth was not as reliable in its rotation as the clocks.

UTC allows for the adding of leap seconds (and potential subtracting of them although that hasn’t happened yet) to allow UTC time to match up with GMT. If these leap seconds were not added then eventual day would creep into night (albeit in several millennia)

There are several possible sources for a UTC time source. Either the Internet, although these sources vary in accuracy and are not secure, the GPS network (Global Positioning System) through a roof mounted aerial or a national time and frequency transmission that are broadcast throughout several countries including the US, UK, Germany, France and Japan.

A network time server uses the protocol NTP (Network Time Protocol) to synchronise devices to UTC. NTP works by accounting for drift on the system clock and then adding or subtracting time depending on the difference. By utilising a network time server that uses a timing source from either the GPS network or radio transmission millisecond and even nanosecond accuracy to UTC is possible.