Time server – Synchronisation Methods

A time server is an essential piece of equipment responsible for ensuring all devices on a computer network are running the same time. Most time servers are dedicated devices that receive a time signal, normally UTC (Coordinated Universal Time), and distribute it to all devices on a network.

Most time servers use the Internet protocol NTP (Network Time Protocol) to synchronise all devices and are often referred to as NTP servers. NTP distributes a single time source throughout the network which is normally a UTC source (Coordinated Universal Time).

There are several places a time server can receive a time signal from. The internet is an obvious source for many although online time sources are not very accurate, can be too far away to give any useful precision, and more importantly are not secure being as they are external to the firewall.

As a dedicated time server is an external device they are extremely secure and impossible for malicious users to tamper with. Dedicated time server can receive a time signal from two sources the GPS network (Global Positioning System) , a highly accurate method and available everywhere on the globe with a good view of the sky; or the specialist long wave radio transmissions broadcast by national physics laboratories.

In Europe the two main radio transmissions are the UK’s MSF signal broadcast by NPL (National Physical Laboratory) in Cumbria, England and the German DCF-77 broadcast near Frankfurt.

These long wave signals are also highly accurate and can be picked up in most neighbouring countries too. The USA has a similar system called WWVB,  transmitted by the National Institute for Standards and Technology (NIST) from Boulder, Colorado.

Types of Dedicated Time Server

Dedicated time servers are used despite the numerous Internet time sources available. The advantages of a dedicated time server is that the device is behind a firewall so preventing any security issues, dedicated time servers can also guarantee accuracy that is just not possible over the Internet.

The dedicated time server checks the time stamp from the UTC source (Coordinated Universal Time) and uses the information to calculate if the network clocks are drifting and adds or subtracts a second to match. The time server will do this at set intervals. Most time servers utilise NTP (network time protocol) although other protocols do exist NTP is by far the most widespread.

For NTP to distribute the time it first needs a timing source and this is where the differences in dedicated time servers come in. As UTC is based on the time told by atomic clocks, it is an atomic clocks that is the source for a time servers timing reference. Atomic clocks are extremely expensive, large, and require a multitude of maintenance engineers. For this reason they are only to be found in large scale physics laboratories.

However, the time from an atomic clock can still be utilised by using either a radio clock attached to a time server or a GPS clock. A radio clock is just a simple radio receiver that picks-up the long-wave signal broadcast by several national physics laboratories. This UTC signal is not available everywhere and the broadcast can be blocked by buildings, mountains and bad weather etc.

The other type of dedicated time server utilise the signals sent by the GPS satellites (global positioning system). These signals are available literally everywhere on the globe although the only downside is that a GPS antenna needs to have a clear view of the sky and therefore ideally needs to be situated on a roof which can cause some problems if the server room is along way from the top of the building.

Some dedicated time servers can actually receive both signals; the radio and GPS. In doing so they can continue receiving time signals even if one signal fails or gets temporarily blocked.