Computers advance at a remarkable rate; in effect computers double in power, speed and memory every five years, and with such advances in technology many people assume that the clocks that control the time of a computer are just as powerful.

However, nothing could be further from the truth; most system clocks are crude crystal oscillators that are prone to drift, which is why computer time synchronisation is so important.

In modern computing, nearly every aspect of managing a network is reliant on time. Timestamps are the only frame of reference a computer has to ascertain if an event has occurred, is due to, or shouldn’t occur.

From debugging, to conducting time sensitive transactions over the internet, accurate time is essential. But how accurate does it have to be?

Coordinated Universal Time

Coordinated Universal Time (UTC) is a global timescale derived from atomic clocks. UTC was developed to allow technological devices, such as computer networks, to communicate with a single time.

Most computer networks use time servers governed by NTP (Network Time Protocol) to distribute UTC across the network. For most applications, accuracy to within a few hundred milliseconds is sufficient – but achieving this accuracy is where the difficulty lies.

Getting an accurate source of time

There are several options for synchronizing a network to UTC. Firstly, there is the internet. The internet is awash with time servers that proclaim to supply an accurate source of UTC. However, surveys of these online sources of time indicate that many of them are wholly inaccurate being seconds, minutes and even days out.

And even the most accurate and respected sources from NIST (National Institute of Standards and Time) and Microsoft, can vary depending on the distance your network is away.

Dedicated Time servers

Dedicated NTP time servers use a more direct approach to achieve accurate synchronisation. Using atomic clocks, either from the GPS satellite network or from physics laboratories (like NIST and the UKs NPL); the time is beamed directly to the NTP time server that is connected to the network.

Because dedicated devices like this receive the time directly from atomic clocks they are incredibly accurate, enabling the entire network to be synchronised to within just a few milliseconds of NTP.

Time synchronisation becomes more and more relevant as we become more dependent on the internet. With so man time sensitive transactions conducted across the globe, from banking and commerce to sending emails, the correct and accurate time is vital in preventing errors and ensuring security.

Increasingly, more and more people are relying on sources of internet time especially with many of the modern flavours of Microsoft’s Windows such as Windows 7 having NTP and time synchronisation abilities already installed.

Windows 7 and Time Synchronisation

Windows 7 will, straight out of the box, attempt to find a source of internet time; however, for a networked machine this does not necessarily mean the computer will be synchronised accurately or securely.

Internet time sources can be wholly unreliable and unsecure for a modern computer network. Internet time has to come through the firewall and as a gap is left for these time codes to come through, malicious software can take advantage of this firewall hole too.

Not only can the accuracy of these devices vary depending on the distance away your network is but also an internet time source very rarely comes direct from an atomic clock.

In fact, most internet time sources are known as stratum 2 devices. This means they connect to another device – a stratum 1 device – namely a NTP time server which gets the time directly from the clock and transmits it to the stratum 2 device.

Stratum 1 NTP time servers

For true accuracy and security, there is no replacement for your network’s own stratum 1 NTP server. Not only are these devices secure, receiving a time source externally to the firewall (often using GPS) but also they receive these signals direct from atomic clocks (The GPS satellite that transmits this signal has an onboard atomic clock that generates the time.

Accurate time is so important for modern computer systems that it is now unimaginable for any network administer to configure a computer system without any regard to synchronisation.

Ensuring all machines are running an accurate and precise time, and that the entire network is synchronised together, will prevent problems arising such as data loss, failure of time sensitive transactions and enable debugging and error management which can be near impossible on networks that lack synchronicity.

There are many sources of accurate time for use with NTP time servers (Network Time Protocol). NTP servers tend to use time that is controlled by atomic clocks to ensure accuracy, and there are advantages and disadvantages to each system.

Ideally as a source of time you want it to be a source of UTC (Coordinated Universal Time) as this is the international time standard as used by computer systems worldwide. But UTC is not always accessible but there is an alternative.

GPS time

GPS time is the time as relayed by the atomic clocks on board GPS satellites. These clocks form the basic technology for the Global Positioning System and their signals are what are used to work out positing information.

But GPS time signals can also provide an accurate source of time for computer networks – although strictly speaking GPS time does differ to UTC.

No Leap Seconds

GPS time is broadcast as an integer. The signal contains the number of seconds from when the GPS clocks were first turned on (January 1980).

Originally GPS time was set to UTC but since GPS satellite have been in space the last thirty years, unlike UTC, there has been no increase to account for leap seconds – so currently GPS is running exactly 17 seconds behind UTC.

Conversion

Whilst GPS time and UTC are not strictly the same as they were originally based on the same time and only the lack of leap seconds not added to GPS makes the difference, and as this is exact in seconds, conversion of GPS time is simple.

Many GPS NTP servers will convert GPS time to UTC time (and local time if you so wish) ensuring you can always have an accurate, stable, secure and reliable source of atomic clock based time.

“Time is what prevents everything from happening at once,’ said eminent physicist John Wheeler. And when it comes to computers his words couldn’t be any more relevant.

Timestamps are the only method that a computer has to establish if an event has occurred, is meant to occur or shouldn’t be occurring just yet. For a home PC, the computer relies on the inbuilt clock that displays the time on the corner of your operating system, and for most home uses this is satisfactory enough.

However for computer networks that have to communicate with each other, relying in individual system clocks can cause untold problems:

All clocks drift, and computer clocks are no different and problems occur when two machines are drifting at different rates as the time does not match up. This poses a conundrum for a computer as it is unsure of which time to believe and time critical events can fail to occur and even simple tasks like sending an email can cause time confusion on a network.

For these reasons, time servers are commonly used to receive the time from an external source and distribute it around the network. Most of these devices use the protocol NTP (Network Time Protocol) which is designed to provide a method of synchronising time on a network.

However, time servers are only as good as the time source that they rely on and when there is a problem with that source, synchronisation will fail and the problems mentioned above can occur.

The most common cause for time server failure or inaccuracy is the reliance on internet based sources of time. These can neither be authenticated by NTP nor guaranteed to be accurate and they can also lead to security issues with firewall intrusion and other malicious attacks.

Ensuring the NTP time server continues to get a source of highly accurate time is fairly straight forward and is all a matter of choosing an accurate, reliable and secure time source.

In most parts of the world there are two methods that can provide a secure and reliable source of time:

• GPS time signals
• Radio referenced time signals

GPS signals are available anywhere on the planet and are based on GPS time which is generated by atomic clocks onboard the satellites.

Radio referenced signals like MSF and WWVB are broadcast on long wave from physics laboratories like NIST and NPL.

Keeping the clock on a PC system synchronised is important for many systems, networks and users that need time accuracy for applications and transactions. Nearly everything on a modern computer system is time reliant so when synchronisation fails all sorts of issues can arise from data getting lost and debugging becoming near impossible.

There are several methods of synchronising a computer system’s clock but the majority of them rely on the time synchronisation protocol NTP (Network Time Protocol).

By far the most common method is to make use of the myriad of online NTP time servers that relay the UTC time (Coordinated Universal Time). However, there are many common issues in using internet based time servers – here are some of them:

Can’t access the Internet time server

A common occurrence with Internet time sources is the inability to access them. This can be caused by several reasons:

• Too much traffic trying to access the server
• Website is down
• Your connection is down

The time from the time server is innacuurate

Most online sources of time are what are known as stratum 2 time servers. This means they get their time from another time server (stratum 1) that it connected to an atomic clock (stratum 0). If there is an error with the stratum 1 device the stratum 2 device will be wrong (and every device that is trying to get the time from it).

The time server is leading to security problems with the firewall

Another common problem caused by the fact that all online time servers need access through your firewall. Unfortunately this gives the opportunity for malicious users to make use of this back door into your system.

Eliminating Time Server Issues

Internet time sources are neither guaranteed to be accurate, reliable or secure so for any serious time synchronisation requirements an external source of time should be used. NTP time servers that plug into a network and receive the time from GPS or radio sources are a much more secure and reliable alternative. These NTP servers are also highly secure as they do not operate across the Internet.

NTP (Network Time Protocol) is perhaps the oldest and most commonly used protocol employed by computers and yet it is probably the least understood.

NTP is used by nearly all computers, networks and other devices that are involved in communicating across the internet or internal networks. It was developed in the very earliest stages of the internet when it became evident that some method of ensuring accuracy over distance was required.

The protocol works by selecting a single time source, of which NTP has the ability to establish the accuracy and reliability of, which it then distributes around every device on the NTP network.

Each device is regularly checked against this reference clock and adjusted if any drift is noticed. A version of NTP is now deployed with virtually every operating system allowing any machine to be synchronized to a single time source.

Obviously if every network in the world selected a different time source as its reference, the reason for of all this synchronization would be lost.

Fortunately, a global timescale based on an international consortium of atomic clocks has been developed to provide a single time source for the purposes of global synchronisation.

UTC (Coordinated Universal Time) is used by computer networks worldwide as a time reference which means any device that is synchronised to UTC with NTP will in effect be synchronised with every network that uses UTC as its base time.

There are many different methods that NTP can access UTC time. The internet is a common location although this does provide security and firewall issues. A more secure (and accurate) method is to use a dedicated NTP time server that takes the time from external sources such as the GPS network (GPS works by broadcasting an atomic clock timestamp that is easily converted to UTC by a NTP server).

With NTP, a dedicated time server and access to UTC an entire network can be synchronised to within a few milliseconds of the universal time providing a secure and accurate network that can operate in complete synchronicity with other networks across the globe.

Atomic clocks are much underrated technologies their development has revolutionised the way we live and work and has made possible technologies that would be impossible without them.

Satellite navigation, mobile phones, GPS, the internet, air traffic control, traffic lights and even CCTV cameras are reliant on the ultra precise timekeeping of an atomic clock.

The accuracy of an atomic clock is incomparable to other time keeping devices as they don’t drift by even a second in hundreds of thousands of years.

But atomic clocks are large sensitive devices that need team of experienced technicians and optimum conditions such as those found in a physics laboratory. So how do all these technologies benefit from the high precision of an atomic clock?

The answer is quite simple, the controllers of atomic clocks, usually national physics laboratories, broadcast via long wave radio the time signals that their ultra precise clocks produce.

To receive these time signals, servers that use the time synchronization protocol NTP (Network Time Protocol) are employed to receive and distribute these timestamps.

NTP time servers, often referred to as network time servers, are a secure and accurate method of ensuring any technology is running accurate atomic clocks time. These time synchronization devices can synchronise single devices or entire networks of computers, routers and other devices.

NTP servers that use GPS signals to receive the time from the atomic clock satellites are also commonly used. These NTP GPS time servers are as accurate as those that receive the time from physics laboratories but use the weaker, line of sight GPS signal as their source.

GPS is not the only technology that is dependent on atomic clocks. The high levels of accuracy that are supplied by atomic clocks are used in other crucial technologies that we take for granted everyday.

Air traffic Control Not only are all aeroplanes and airliners now equipped with GPS to enable pilots and ground staff to know their exact location but atomic clocks are also used by air traffic controllers who need precise and accurate measurements and time between planes.

Traffic Lights and Road Congestion Systems – Traffic lights are another system that relies on atomic clock timing. Accuracy and synchronization is vital for traffic light systems as small errors in synchronization could lead to fatal accidents.

Congestion cameras and other systems such as parking metres also use atomic clocks as a basis of their timekeeping as this prevents any legal issues when issuing penalty notices.

CCTV – Closed circuit television is another large scale user of atomic clocks. CCTV cameras are often used in the fight against crime but as evidence they are ineffective in a court of law unless the timing information on the CCTV camera can be proved to be accurate. Failure to do so could lead to criminals escaping prosecution because despite the identification by the camera, proof that it was at the time and date of the offence can’t be clarified without accuracy and synchronization.

Internet – Many of the applications we now entrust to the internet are only made possible thanks to atomic clocks. Online trading, internet banking and even online auction houses all need accurate and synchronized time.

Imagine taking your savings from your bank account only finding that you can withdraw them again because another computer has a slower clock or imagine bidding on an internet auction site only to have your bid rejected by a bid that came before yours because it was made on a computer with a slower clock.

Using atomic clocks as a source for time is relatively straight forward for many technologies. Radio signals and even the GPS transmissions can be used as a source of atomic clock time and for computer systems, the protocol NTP (Network Time Protocol) will ensure any sized network will be synchronized perfectly together. Dedicated NTP time servers are used throughout the world in technologies and applications that require precise time.

Synchronization is vital for most computer networks. Timestamps are the only reference a computer can use to analyse when and if processes or applications are completed. Synchronized timestamps are also vital for security, debugging and error logging.

Failure to keep a network adequately synchronized can lead to all sorts of problems. Applications fail to commence, time sensitive transactions will fail and errors and data loss will become commonplace.

However, ensuring synchronization no matter the size of network is straight forward and not costly, thank to the dedicated network time server and the time protocol NTP.

Network Time Protocol (NTP)

NTP has been around even longer than the internet but is the most widely used synchronization protocol available. NTP is free to use and makes synchronization very straight forward. It works by taking a single time source (or multiple ones) and distributes it amongst the network. It will maintain high levels of accuracy even when it loses the original time signal and can make judgements on how accurate each time reference.

NTP Time Server

These come in several forms. Firstly there are a number of virtual time servers across the internet that distributes time free of charge. However, as they are internet based a network is taking a risk leaving a firewall port open for this time communication. Also there is no control over the time signal so if it goes down (or becomes unstable or wholly inaccurate) your network can be left without adequate synchronization.

Dedicated NTP time servers use GPS or radio references to receive the time. This is far more secure and as GPS and radio signals like WWVB (from NIST) are generated by atomic clocks there accuracy is second to none.

Because the NTP protocol is hierarchical it also means that only one dedicated time server needs to be used for a network, no matter the size, as other devices on the network can act as time servers after having rece9ved the time from the primary NTP server.

The National Physical Laboratory has announced scheduled maintenance this week (Thursday) meaning the MSF60kHz time and frequency signal will be temporarily turned off to allow the maintenance to be conducted in safety at the Anthorn radio Station in Cumbria.

Normally these scheduled maintenance periods only last a few hours and should not cause any disturbance to anybody relying on the MSF signal for timing applications.
NTP (Network Time Protocol) is well suited to these temporary losses of signal and little if no drift should be experienced by any NTP time server user.

However, there are some high level users of network time servers or may have concerns on the accuracy of their technology during these scheduled periods of no signal. There is another solution for ensuring a continuous, secure and equally accurate time signal is always being used.

GPS, most commonly used for navigation and wayfinding it actually an atomic clock based technology. Each of the GPS satellites broadcasts a signal from their onboard atomic clock which is used by satellite navigation devices that work out the location through triangulation.

These GPS signals can also be received by a GPS NTP time server. Just as MSF or other radio signal time servers receive the external signal from the Anthorn transmitter, GPS time servers can receive this accurate and external signal from the satellites.

Unlike the radio broadcasts, GPS should never go down although it can sometimes be impractical to receive the signal as a GPS antenna needs a clear view of the sky and therefore should preferably be on the roof.

For those wanting to make doubly sure there is never a period when a signal is not being received by the NTP server, a dual time server can be used. These pick up both radio and GPS transmissions and the onboard NTP daemon calculates the most accurate time from them both.