Synchronising Computer Networks to an Atomic Clock

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Atomic clocks are well-known for being accurate. Most people may never have seen one but are probably aware that atomic clocks keep highly precise time. In fact modern atomic clock will keep accurate time and not lose a second in one hundred million years.

This amount of precision may seem overkill but a multitude of modern technologies rely on atomic clocks and require such a high level of precision. A perfect example is the satellite navigation systems now found in most auto cars. GPS is reliant on atomic clocks because the satellite signals used in triangulation travel at the speed of light which in a single second can cover nearly 100,000 km.

So it can be seen how some modern technologies rely on this ultra precise timekeeping from atomic clocks but their use doesn’t stop there. Atomic clocks govern the world’s global timescale UTC (Coordinated Universal Time) and they can also be used to synchronise computer networks too.

It may seem extreme to use this nanosecond precision to synchronise computer networks too but as many time sensitive transactions are conducted across the internet with such trades as the stock exchange where prices can fall or rise each and every second it can be seen why atomic clocks are used.

To receive the time from an atomic clock a dedicated NTP server is the most secure and accurate method. These devices receive a time signal broadcast by either atomic clocks from national physics laboratories or direct from the atomic clocks onboard GPS satellites.

By using a dedicated NTP server a computer network will be more secure and as it is synchronised to UTC (the global timescale) it will in effect be synchronised with every other computer network using a NTP server.

The World in Synchronisation

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Time synchronisation plays an ever more important role in the modern world with more and more technologies reliant on accurate and reliable time.

Time synchronisation is not just important but can also be crucial in the safe running of systems such as air traffic control that simply couldn’t function without accurate synchronisation. Think of the catastrophes that could happen in the air of aircraft were out of synchronisation with each other?

In global commerce too accurate and reliable time synchronisation is highly important. When the world’s stock markets open in the morning and traders from across the world buy stock on their computers. As stock fluctuates second by second if machines are out of synchronisation it could cost millions.

But synchronisation is also imperative in modern computer networking; it keeps systems secure and enables proper control and debugging of systems. Even if a computer network is not involved in any time sensitive transactions a lack of synchronisation can leave it vulnerable to malicious attacks and can also be susceptible to data loss.

Accurate synchronisation is possible in computer networking thanks to two developments: UTC and NTP.

UTC is a timescale -coordinated universal time, it is based on GMT but is controlled by an array of atomic clocks making it accurate to within a few nanoseconds.

NTP is a software protocol – Network Time Protocol, designed to accurately synchronise computer networks to a single time source. Both of these implementations come together in a single device which is relied upon the world over to synchronise computer networks – the NTP server.

An NTP time server or network time server is a device that receives the time from an atomic clock, UTC source and distributes it across a network. Because the time source is continually checked by the time server and is from an atomic clock it makes the network accurate to within a few milliseconds of UTC providing synchronisation on a global scale.

The Clocks to Spring Forward at the Weekend

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It’s that time of year again when we lose an hour over the weekend as the clocks go forward to British Summer Time. Twice a year we alter the clocks but in an age of UTC (Coordinated Universal Time) and time server synchronisation is it really necessary?

The changing of the clocks is something that was discussed just before World War I when London builder William Willet suggested the idea as a way of improving the nation’s health (although his initial idea was to advance the clocks twenty minutes on each Sunday in April).

His idea wasn’t taken up although it sowed the seed of an idea and when the First World War erupted it was adopted by many nations as a way to economise and maximise daylight although many of these nations discarded the concept after the war, several including the UK and USA kept it.

Daylight saving has altered over the years but since 1972 it has remained as British Summer Time (BST) in the summer and Greenwich Meantime in the winter (GMT). However, despite is use for nearly a century the changing of the clocks remains controversial. For four years Britain experimented without daylight changing but it was proved unpopular in Scotland and the North where the mornings were darker.

This timescale hopping does cause confusion (I for one will miss that hour extra in bed on Sunday) but as the world of commerce adopts the global civil timescale (which fortunately is the same as GMT as UTC is adjusted with leap seconds to ensure GMT is unaffected by the slowing of the Earth’s rotation) is it still necessary?

The world of time synchronisation certainly doesn’t need to adjust for daylight saving. UTC is the same the world over and thanks to devices such as the NTP server can be synchronised so the entire world runs the same time.

NTP Synchronization and FAQ

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With a variety of acronyms and timescales the world of time synchronisation can be quite confusing here are some frequently asked questions we hope will help enlighten you.

What is NTP?

NTP is a protocol designed to synchronize computer networks across the internet or LAN (Local Area Networks). It is not the only time synchronization protocol available but it is the most widely used and the oldest having been conceived in the late 1980’s.

What are UTC and GMT?

UTC or Coordinated Universal Time is a global timescale, it is controlled by highly accurate atomic clocks but kept the same as GMT (Greenwich Meantime) by the use of leap seconds, added when the Earth’s rotation slows down. Strictly speaking GMT is the old civil timescale and based on when the sun is above the meridian line, however, as the two systems are identical in time thanks to leap seconds, UTC is often referred to as GMT and vice versa.

And a NTP Time Server?

These are devices that synchronize a computer network to UTC by receiving a time signal and distributing it with the protocol NTP which ensures all devices are running accurately to the timing reference.

Where to get UTC time from?

There are two secure methods of receiving UTC. The first is to utilize the long wave time signals broadcast by NIST (WWVB) NPL in the UK (MSF) and the German NPL (DCF) The other method is to use a the GPS network. GPS satellites broadcast an atomic clock signal that can be utilised and converted to UTC by the GPS NTP server.

The Importance of the Atomic Clock

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Most people have vaguely heard of the atomic clock and presume they know what one is but very few people know just how important atomic clocks are for the running of our day to day lives in the twenty first century.

There are so many technologies that are reliant on atomic clocks and without many of the tasks we take for granted would be impossible. Air traffic control, satellite navigation and internet trading are just a few of the applications that are reliant on the ultra precise chronometry of an atomic clock.

Exactly what an atomic clock is, is often misunderstood. In simple terms an atomic clock is a device that uses the oscillations of atoms at different energy states to count ticks between seconds. Currently caesium is the preferred atom because it has over 9 billion ticks every second and because these oscillations never change it makes them a highly accurate method of keeping time.

Atomic clocks despite what many people claim are only ever found in large scale physics laboratories such as NPL (UK National Physical Laboratory) and NIST (US National Institute of Standards and Time). Often people suggest they have an atomic clock that controls their computer network or that they have an atomic clock on their wall. This is not true and what people are referring to is that they have a clock or time server that receives the time from an atomic clock.

Devices like the NTP time server often receive atomic clock signals form places such as NIST or NPL via long wave radio. Another method for receiving time from atomic clocks is using the GPS network (Global Positioning System).

The GPS network and satellite navigation are in fact a good example of why atomic clock synchonization is much needed with such high level of accuracy. Modern atomic clocks such as those found at NIST, NPL and inside orbiting GPS satellites are accurate to within a second every 100 million years or so. This accuracy is crucial when you examine how something like a cars GPS satellite navigation system works.

A GPS system works by triangulating the time signals sent from three or more separate GPS satellites and their onboard atomic clocks. Because these signals travel at the speed of light (nearly 100,000km a second) an inaccuracy of even one whole millisecond could put the navigational information out by 100 kilometres.

This high level of accuracy is also required for technologies such as air traffic control ensuring our crowded skies remain safe and is even critical for many Internet transactions such as trading in derivatives where the value can rise and fall every second.

The Hidden Cost of Free Time

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If you are reading this then you are probably aware of the importance time plays in IT systems and computer networks. Most computer administrators appreciate that precise time and accurate synchronisation are an important aspect of keeping a computer network error free and secure.

And yet, despite its importance many network administrators still rely on the Internet as a source of UTC time for their networks (UTC – Coordinated Universal Time), primarily because they see it as a quick and more importantly a free method of time synchronisation.

However, the drawbacks in using these free services may cost a lot more than the money saved on a dedicated NTP time server.

NTP (Network Time Protocol) is now present on nearly all computers and it is NTP that is used to synchronise computer systems. However, if an Internet time source is used then the source is outside the network firewall and this creates a serious vulnerability. Any external time source will require a port to be left open in the firewall to allow the time information packets through and this opening is too easy a way to exploit a network which can become victim to a DDOS attack (Distributed Denial of Service) or even allow malicious programmes through to take control of the machines themselves.

Another problem is the availability of stratum 1 time sources across the internet. Most online time sources come from stratum 2 time servers. These are devices that receive the time from a time server (stratum 1) that originally gets the information from an atomic clock (stratum 0).  While stratum 2 devices can be just as accurate as stratum 1 time servers, across the internet without NTP authentication the actual accuracy can not be guaranteed.

Furthermore, internet time sources have never been considered accurate or precise with surveys showing over half being inaccurate by over a second and the rest dependent on the distance from client as to whether they can provide any useful accuracy. Even organisations such as NIST publish  advisory notices on their time server pages about it unable to guarantee security or accuracy and yet millions of networks are still receiving time from across the internet.

With the decline in cost of dedicated radio referenced NTP time servers or GPS NTP server there has never been a better time to get one. And when you consider the cost of a computer breach or crashed network the NTP server will have paid for itself many times over.

Common Network Time Synchronisation (NTP) Server Errors (Part 2)

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Radio signal goes dead for several hours

The long wave transmissions such as MSF (NPL) or WWVB (NIST) are broadcast from large antennas that often need maintenance. This often requires a shut down of the broadcast while it is being done. These outages are normally posted with at least three months notice on the websites of the signals controllers (and can be automatically emailed if you register) to give prior notice.

These outages only tend to last a few hours leaving your computer network reliant on the electronic system clocks but it is doubtful there will be too much drift in that time (and any drift will be accounted for once the signal is back on. If these outages could be a potential problem than a simple solution is to invest in a dual system that will receive both GPS time server and radio signals ensuring a continuous time signal.

No time signal coming in despite the time server being powered up

This is most often caused by either lack of power going to the antenna or failing to connect to site the antenna where it can have a clear view of the sky. GPS antennas may have battery or power connections so it is always worth checking before switching the device on. Ensuring the antenna can ‘view’ the satellites when using GPS time servers is also important, remembering that windows and skylights may prevent signals getting through.

When using radio time reference such as MSF, DCF or WWVB the NTP server antennas can receive the long wave signal indoors but they are vulnerable to topography and local interference. If there is no signal or only a weak signal then try moving the antenna around until the signal strength increases enough.

Often users of these time and frequency signals find that the signal is weak throughout the day but is boosted at night. This is because the signals are ground state but have a residual skywave which can bounce of the ionosphere during the coolness of the night (ionospheric propagation).

Some users of these signals may find that despite being well within range the local topography can prevent a strong enough signal from getting through.

Common Network Time Synchronisation (NTP) Server Errors (Part 1)

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NTP servers are the easiest, most accurate and secure method of receiving a UTC time source (Coordinated Universal Time). Most dedicated NTP time servers will run in the background automatically synchronising the devices on a network completely automatically.

However, there are some common problems that occasionally occur in using a network time server but fortunately most can be solved relatively easily.

Losing A GPS time signal

GPS is one of the most efficient sources of UTC time. The GPS signal is available literally anywhere on the planet where there is a clear view of the sky. At any one time there are at least three satellites within range of any location and unlike radio referenced transmissions there are no maintenance outages so the signal is always uninterrupted.

However, some people find that they keep losing their GPS signal when using a GPS NTP time server. Very rarely this can be caused by extra terrestrial occurrences (solar flares – not little green men), however more commonly signal loss occurs when there has been insufficient time give for the initial acquisition lock.

To ensure a continuous signal make sure you follow manufacturer’s recommendation for obtaining acquisition. This usually means leaving the GPS time server to get a good lock for at least 24 hours (so all satellites have been in view). If not enough time is given to this then it is possible the GPS time server will lose a satellite and therefore timing information.

One second delay in a radio clock compared to internet or GPS

This is a very frequent occurrence when using a radio time server using signals such as the MSF transmission broadcast by the UK’s National Physical Laboratory. This occurs normally after the insertion of a Leap Second. Leap seconds are introduced once or twice a year to compensate for the slowing of the Earth’s rotation and to keep UTC in line with the Greenwich Meridian.
While NTP will automatically account for leap seconds with signals like the MSF it can often take some time as there is no Leap Second announcement. This announcement normally allows NTP to prepare for the leap second (which normally occurs in the last second of the last day in June or December). As signals such as MSF do not announce the upcoming leap second it can take some time for it to be accounted for. In some cases it can take a few days in others minutes. A simple solution is to manually announce the leap second.

However, if this is not done, NTP will eventually discover the leap second and adjust the network clocks.

Contiued……

Network Time Server Dual Signals

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A network time server (commonly referred to as the NTP time server after the protocol used in synchronisation – Network Time Protocol) is a device that receives a single time signal and distributes it to all devices on a network.

Network time servers are preferred as a synchronisation tool rather than the much simpler internet time servers because they are far more secure. Using the internet as a basis for time information would mean using a source outside the firewall which could allow malicious users to take advantage.

Network time servers on the other hand work inside the firewall by receiving source of UTC time (Coordinated Universal Time) from either the GPS network or specialist radio transmissions broadcast from national physics laboratories.

Both of these signals are incredibly accurate and secure with both methods providing millisecond accuracy to UTC. However, there are downsides to both systems. The radio signals broadcast by nation time and frequency laboratories are susceptible to interference and locality, while the GPS signal, although available literally everywhere on the globe can occasional be lost too (often due to bad weather interfering with the line-of-sight GPS signals.

For computer networks where high levels of accuracy are imperative, dual systems are often incorporated. These network time servers receive the time signal from both the GPS network and the radio transmissions and select an average for even more accuracy.  However, the real advantage of using a dual system is that if one signal fails, for what ever the reason, the network will not have to rely on the inaccurate system clocks as the other method of receiving UTC time should still be operational.

Atomic Clocks and the GPS Time Server

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Atomic clocks have been around since the 1950’s when NPL (National Physical Laboratory) in the UK developed the first reliable caesium based clock. Before atomic clocks, electronic clocks were the most accurate method of keeping track of time but while an electrical clock may lose a second in every week or so, a modern atomic clock will not lose a single second in hundreds of millions of years.

Atomic clocks are not just used to keep track of time. The atomic clock is an integral part of the GPS system (Global Positioning System) as each GPs satellite has its own onboard atomic clock that generates a time signal that is picked up by GPS receivers who can calculate their position by using the precise signal from three or more satellites.

Atomic clocks need to be used as the signal s from the satellites travel at the speed of light and as light travels nearly 300,000 km each second any slight inaccuracy could put navigation out by miles.

A GPS time server is a network time server that uses the time signal from the GPS network’s satellites to synchronise the time on computer networks. A GPS time server often uses NTP (Network Time Protocol) as a method of distributing time which is why these devices are often referred to as NTP GPS time servers.

Computer networks that are synchronised using a dedicated time server are normally synchronised to UTC (Coordinated Universal Time) and while the GPS signal is not UTC, GPS time, like UTC, is based on International Atomic Time (TAI) and is easily converted by NTP.