Time synchronisation in the modern age is highly precise. Modern atomic clocks can keep time so accurately that in 100 million years these timekeeping devices will not lose even a second.

Bit is this sort of accuracy necessary in the modern world? How important can a second possibly be, after all, a second has always been seen as one of the smallest units of time.

However, when you consider modern technology such as the satellite navigation then a second suddenly becomes a huge gulf in time. Modern satellite navigation devices work by calculating distance by using the time form the atomic clocks on GPS (Global Positioning System) satellites.

However, when you consider that the speed of light is close to 300, 000 km a second then you can understand that if a GPS clock is a second out then your navigation could be inaccurate by hundreds of thousands of kilometres.

The same is true for modern computer networks. Computers can process thousands of transactions a second so when it comes to global network communication a second can be a huge amount of time.

That is why modern NTP server’s, responsible for synchronising networks offer precision to the millisecond, ensuring that network across the globe are within a hare’s breath of each other.

For users of MSF time server or other NTP related devices:

Notice of Interruption MSF 60 kHz Time and Frequency Signal – NPL
The MSF 60 kHz time and frequency signal broadcast from Anthorn Radio Station will be shut down over the period:

11 December 2008 – from 10:00 UTC to 14:00 UTC

The interruption to the transmission is required to allow scheduled maintenance work to be carried out in safety.

If you require any additional information, please contact NPL

Or alternatively please see the NPL time website.

A public NTP Server is a time server on the Internet that, as the name suggests, members of the public can use as a timing source. The best location on the Internet to find a list of public NTP servers is the home of NTP – www.ntp.org

There are two lists of public NTP servers on ntp.org, one for primary servers and one for secondary servers. Primary servers have up to several hundred clients each. However, many primary servers are ‘closed access’ meaning that only agreed clients can access them. This is because if there is too much traffic attempting to receive a timing source from a primary source then it will clog the network making the server useless.

Primary servers are known as a stratum 1 server in that they get their timing source direct from an atomic clock often using the GPS or national time and frequency transmissions. Secondary NTP servers tend to be stratum 2 time servers, that is a time server that receives its timing source from a stratum 1 server.

Most users that require a public NTP server will find that most primary servers are closed access and that they will have to use a secondary NTP server. When using a public NTP server it is important that access policies are adhered to as many institutions require on these servers for timing information.

Network Time Protocol (NTP) is an Internet based protocol designed to distribute and synchronise time across a network.

NTP is in fact one of the oldest Internet protocols having been developed in the late 1980’s at Delaware University when the Internet was still in its infancy. It was devised by Professor David Mills and his team when they realised the need for accurate time synchronisation if computers were needed to communicate with each other.

A NTP server is a dedicated device that receives a single timing source and then distributes it amongst all network devices. A NTP server will receive the timing information through a number of ways but normally it is a UTC source (coordinated universal time) a global timescale based on the time as told by atomic clocks.

NTP handles the time in a different way to how humans perceive and deal with it. While we may split a time into seconds, minutes, hours, days, months and years; NTP regards time  as a single number which is the number of seconds since the ‘prime epoch’.

The prime epoch is a date set for when NTP began counting seconds. For NTP the prime Epoch is 00.01 on 1 January 1900 so that means on 1 January 2008 the time according to NTP will be 3405888000, which is the number of seconds since 1900.

Time synchronisation is vital for the modern computer network particularly when computer networks across the globe need to communicate with each other.

A lack of synchronisation would make impossible many online activities such as Internet auctions, seat reservation and trading in stocks and shares. It can also leave a system open to security threats and even fraud.

The NTP server (Network Time Protocol) can provide the most secure and accurate method of synchronising a network.  Many NTP servers are rack-mountable devices that can connect to a network and distributes time information between all devices on that system.

They work by using a single time reference, most commonly a source of UTC (Coordinated Universal Time), which NTP then checks all the system clocks to ensure all devices are keeping the same time. When it finds a computer or device that is drifting it advances or retreats the system clock until it matches UTC.

A NTP server will receive a timing source from either across the Internet (although not very secure or accurate), a specialist long-wave radio transmission or from the GPS network (global positioning system).

By utilising dedicated NTP server, not only can all devices on a network be synchronised together but also by using UTC the network will be synchronised with millions of computer networks all over the world.

Using a long wave time and frequency transmission is perhaps the simplest and most efficient way of receiving an accurate and secure UTC timing reference (coordinated universal time). Dedicated NTP servers are available that receive a time code this way and distribute the timing information to a network. Often these time servers are referred to as radio clocks, although this title is a little misleading.

The long wave transmissions are usually broadcast at 60 khz but are not available everywhere. Only certain countries have these broadcasts and most come from their country of origin’s national physics laboratory.

In the UK the signal is known as MSF as is broadcast by the NPL (National Physical Laboratory) in Cumbria. The USA signal, WWVB, is broadcast Near Fort Collins in Colorado while the signal in Germany is known as DCF and is broadcast near to Frankfurt. Other nations such as Switzerland, Japan and Finland also have their own signals.

These transmissions are not however, available everywhere. While in many neighbouring countries it is possible to receive one of these transmissions, the long-wave signal is finite in range and susceptible to interference from topography and other electrical devices

However, where they are available, these time and frequency signals make an ideal source for a NTP server to synchronise a network too making them a logical choice for securing UTC time.

The NTP server is now an essential part of the modern computer network. Without a dedicated NTP server administrators are forced to rely on unsecure and inaccurate Internet sources to synchronise their network clocks too.

The potential risks involved in this, namely leaving a hole open in the network firewall and the lack of the NTP security measure: authentication, means that networks that use an Internet based timing source are risking their system to attacks from malicious user and hackers.

It should also be noted that a survey of Internet based timing sources found less than a third were accurate to UTC time and those that were could still be too far away from client to make any useful synchronisation.

There are two types of dedicated NTP server, the GPS NTP server and the radio referenced NTP server. The difference between the two is based solely on the method they receive their UTC time source from. A GPS NTP server will use the signals broadcast from the GPS satellites above the Earth’s atmosphere. These signals are very reliable and can be picked up anywhere in the Worlds as long as the GPS antenna has a clear view of the sky.

The alternative is to use a dedicated NTP server that can receive a signal from the national time and frequency transmissions broadcast by several national physics laboratories. While not available in every country and quite vulnerable to interference these long-wave time signals are still an accurate and secure method of receiving UTC time. They are also ideally suited for network administrators who, for reasons of logistics can’t place a GPS antenna on the roof.

The NTP server is an essential network tool. Whilst other protocols do exist, NTP is by far the standard time synchronisation protocol and is utilised in the majority of time servers.

A NTP server is reliant on a single time source it is this time reference that it uses to distribute amongst the network and synchronise to. This timing reference tends to be a UTC time source (coordinated universal time) which is a global time source based on the time told by atomic clocks.

There are only two viable options for receiving a UTC timing source. Although the Internet can be used, the signal can’t be authenticated this is a security measure used by NTP to ensure the reference is what it says it is. Also by using an Internet time source a hole must be left open in the network firewall to allow for communication to the server, this has its own security risks.

The only two secure methods for receiving a UTC time signal is to either use the GPS network or national time and frequency transmissions that are broadcast by several countries’ national physics laboratories.

In selecting a timing source for a NTP server, location is the key consideration. The national time and frequency transmissions are not available in every country. Whilst the USA, UK, Germany, France, Japan and Finland have a signal there are many countries that do not. Furthermore being a long wave radio transmission it can easily be blocked by local topography, although the radio aerial can pick op a signal indoors which is something a GPS NTP server can’t do.

GPS antennas have to be situated on a roof. This can have logistical problems if the server room is in the basement of a high storey building but on the plus inside the GPS signal can be received literally anywhere in the world.