Posts by: Richard N Williams

Finding the Time

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Finding out what the time is, is something we all take for granted. Clocks are everywhere and a glance at a wristwatch, clock tower, computer screen or even a microwave will tell us what the time is. However, telling the time has not always been that easy.

Clocks didn’t arrive until the middle ages and their accuracy was incredibly poor. True time telling accuracy didn’t arrive until after the arrival of the electronic clock in the nineteenth century. However, many of the modern technologies and applications that we take for granted in the modern world such as satellite navigation, air traffic control and internet trading require a precision and accuracy that far exceeds an electronic clock.

Atomic clocks are by far the most accurate time telling devices. They are so accurate that the world’s global timescale that is based on them (Coordinated Universal Time) has to be occasionally adjusted to account for the slowing of the Earth’s rotation. These adjustments take the form of additional seconds known as leap seconds.

Atomic clock accuracy is so precise that not even a second of time is lost in over a million years whilst an electronic clock by comparison will lose a second in a week.

But is this accuracy really necessary? When you look at technologies such as global positioning then the answer is yes. Satellite navigation systems like GPS work by triangulating time signals generated by atomic clocks onboard the satellites. As these signals are transmitted at the speed of light they travel nearly 100,000 k m each second. Any inaccuracy in the clock by even a thousandth of a second could see the positioning information out by miles.

Computer networks that have to communicate with each other across the globe have to ensure they are running not just accurate time but also are synchronised with each other. Any transactions conducted on networks without synchronisation can result in all sorts of errors.

Fort his reason computer networks use NTP (Network Time Protocol) and network time servers often referred to as an NTP server. These devices receive a timing signal from an atomic clock and distribute it amongst a network in doing so a network is ensured to be as accurate and precise as possible.

Difficulties in telling the time!

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Precision in telling the time has never been as important as it is now. Ultra precise atomic clocks are the foundation for many of the technologies and innovations of the twentieth century. The internet, satellite navigation, air traffic control and global banking all just a few of the applications that is reliant on particularly accurate timekeeping.

The problem we have faced in the modern age is that our understanding exactly of what time is has changed tremendously over the last century. Previously it was thought that time was constant, unchanging and that we travelled forward in time at the same rate.

Measuring the passing of time was straight forward too. Each day, governed by the revolution of the Earth was divided into 24 equal amounts – the hour.  However, after the discoveries of Einstein during the last century, it was soon discovered time was not at all constant and could vary for different observers as speed and even gravity can slow it down.

As our timekeeping became more precise another problem became apparent and that was the age old method of keeping track of the time, by using the Earth’s rotation, was not an accurate method.

Because of the Moon’s gravitational influence on our oceans, the Earth’s spin is sporadic, sometimes falling short of the 24 hour day and sometimes running longer.

Atomic clocks were developed to try to keep time as precise as possible. They work by using the unchanging oscillations of an atom’s electron as they change orbit. This ‘ticking’ of an atom occurs over nine billion times a second in caesium atoms which makes them an ideal basis for a clock.

This ultra precise atomic clock time (known officially as International Atomic Time – TAI) is the basis for the world’s official timescale, although because of the need to keep the timescale in parallel with the rotation of the Earth (important when dealing with extra terrestrial bodies such as astronomical objects or even satellites) addition seconds, known as leap second, are added to TAI, this altered timescale is known as UTC – Coordinated Universal Time.

UTC is the timescale used by businesses, industry and governments all around the world. As it is governed by atomic clocks it means the entire world can communicate using the same timescale, governed by the ultra-precise atomic clocks. Computer networks all over the world receive this time using NTP servers (Network Time Protocol) ensuring that everybody has the same time to within a few milliseconds.

How to Install and Configure a NTP Server

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Network Time Protocol (NTP) is one of the Internet’s oldest protocols still utilised. Invented by Dr David Mills from the University of Delaware it has been in use since 1985. NTP is a protocol designed to synchronize the clocks on computers and networks across the Internet or Local Area Networks (LANs).

NTP (version 4) can maintain time over the public Internet to within 10 milliseconds (1/100th of a second) and can perform even better over LANs with accuracies of 200 microseconds (1/5000th of a second) under ideal conditions.

NTP works within the TCP/IP suite and relies on UDP, a less complex form of NTP exists called Simple Network Time Protocol (SNTP) that does not require the storing of information about previous communications, needed by NTP. It is used in some devices and applications where high accuracy timing is not as important.

Time synchronisation with NTP is relatively simple, it synchronises time with reference to a reliable clock source. This source could be relative (a computer’s internal clock or the time on a wrist-watch) or absolute (A UTC – Universal Coordinated Time – clock source that is accurate as is humanely possible).

Atomic clocks are the most absolute time-keeping devices. They work on the principle that the atom, caesium-133, has an exact number of cycles of radiation every second (9,192,631,770). This has proved so accurate the International System of Units (SI) has now defined the second as the duration of 9,192,631,770 cycles of radiation of the caesium-133 atom.

However, atomic clocks are extremely expensive and are generally only to be found in large-scale physics laboratories. However, NTP can synchronise networks to an atomic clock by using either the Global Positioning System (GPS) or a specialist radio transmission.

The most widely used is the GPS system which consists of a number of satellites providing accurate positioning and location information. Each GPS satellite can only do this by utilising an atomic clock which in turn can be can be used as a timing reference.

A typical GPS receiver can provide timing information to within a few nanoseconds of UTC as long as there is an antenna situated with a good view of the sky.

There are also a number of national time and frequency radio transmissions that can be used to synchronise a NTP server. In Britain the signal (called MSF) is broadcast by the National Physics Laboratory in Cumbria which serves as the United Kingdom’s national time reference, there are also similar systems in Colorado, US (WWVB) and in Frankfurt, Germany (DCF-77). These signals provides UTC time to an accuracy of 100 microseconds, however, the radio signal has a finite range and is vulnerable to interference.

The distance from the reference clock is known as the stratum levels and they exist to prevent cycles in the NTP. Stratum 0, are devices such as atomic clocks connected directly to a computer. Stratum 1, are computers attached to stratum 0 devices, while Stratum 2 are computers that send NTP requests to Stratum 1 servers. NTP can support up to 256 strata.

All Microsoft Windows versions since 2000 include the Windows Time Service (w32time.exe) which has the ability to synchronise the computer clock to an NTP server (or an SNTP server – a simplified version of NTP) Many LINUX and UNIX based operating systems also have a version of NTP but the source code is free to download (current version 4.2.4) at the NTP website (ntp.org).

It is strongly recommended by Microsoft and others, that external based timing should be used rather than Internet based, as these can’t be authenticated. Specialist NTP time servers are available that can synchronise time on networks using either the MSF (or equivalent) or GPS signal.

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.