Time Synchronisation

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.

In selecting a NTP time server it is important to think about where the device will be located and which timing reference would be most suitable for the applications it is required for. There are benefits and drawbacks to both the radio broadcasts and the GPS timing signals.

Unfortunately not every country transmits a national time and frequency broadcast so if a time server is to be located outside of the US, Germany, UK, France or Japan it may be doubtful that a signal could be received (although many of the these transmissions can be received in neighbouring countries).

Radio signals are also easily susceptible to atmospheric interference and can be blocked by mountains, sky-scrapers or other topography.

GPS on the other hand can be received literally anywhere on the planet. GPS is also a more accurate means of receiving a time code -  a typical GPS receiver can provide timing information to within a few nanoseconds of UTC (a nanosecond is a 1 billionth of a second) while national time and frequency transmissions are accurate to only 1 – 20 milliseconds (a millisecond is 1/1000 of a second).

However, one benefit of using a radio broadcast as a timing reference is that it is possible to receive the transmission from inside a building (although basements and rooms with lots of metal furnishings can cause problems), while a GPS antenna needs to be situated on the roof of a building and have a good view of the sky to be able to find and receive the signal broadcast from the satellites (although it is possible to receive a signal through a window depending on the topography outside).