Category: timekeepers

Atomic Clock Synchronization made easy with a NTP Time Server

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Atomic clocks are the ultimate in timekeeping devices. Their accuracy is incredible as an atomic clock will not drift by as much as a second within a million years, and when this is compared to the next best chronometers, such as electronic clock that can drift by a second in a week, an atomic clock is incredibly more precise.

Atomic clocks are used the world over and are the heart of many modern technologies making capable a multitude of applications that we take for granted. Internet trading, satellite navigation, air traffic control and international banking are all industries that rely heavily on

They also govern the world’s timescale, UTC (Coordinated Universal Time) which is kept true by a constellation of these clocks (although UTC has to be adjusted to accommodate the slowing of the Earth’s spin by adding leap seconds).

Computer networks are often required to run synchronized to UTC. This synchronisation is vital in networks that conduct time sensitive transactions or require high levels of security.

A computer network without adequate time synchronization can cause many issues including:

Loss of data

  • Difficulties in identifying and logging errors
  • Increased risk of security breaches.
  • Unable to conduct time sensitive transactions

For these reasons many computer networks have to be synchronized to a source of UTC and kept as accurate as possible. And although atomic clocks are large bulky devices kept in the confines of physics laboratories, using them as a source of time is incredibly simple.

Network Time Protocol (NTP) is a software protocol designed solely for the synchronisation of networks and computer systems and by using a dedicated NTP server the time from an atomic clock can be received by the time server and distributed around the network using NTP.

NTP servers use radio frequencies and more commonly the GPS satellite signals to receive the atomic clock timing signals which is then spread throughout the network with NTP regularly adjusting each device to ensure it is as accurate as possible.

Did you Remember the Leap Second this Year?

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When you counted down on New Year’s Eve to mark the beginning of the next year did you start at 10 or 11? Most revelers would have counted down from ten but they would have been premature this year as there was an extra second added to last year – the leap second.

Leap seconds are normally inserted once or twice a year (normally on New Year’s Eve and in June) to ensure the global timescale UTC (Coordinated Universal Time) coincides with the astronomical day.

Leap seconds have been used since UTC was first implemented and they are a direct result of our accuracy in timekeeping. The problem is that modern atomic clocks are far more accurate timekeeping devices than the earth itself. It was noticed when atomic clocks were first developed that the length of a day, once thought to be exactly 24 hours, varied.

The variations are caused by the Earth’s rotation which is affected by the moons gravity and tidal forces of the Earth, all of which minutely slow down the earth’s rotation.

This rotational slowing, while only minuscule, if it is not checked then the UTC day would soon drift into the astronomical night (albeit in several thousands of years).

The decision on whether a Leap Second is needed is the remit of the International Earth Rotation Service (IERS), however, Leap Seconds are not popular with everybody and they can cause potential problems when they are introduced.

UTC is used by NTP time servers (Network Time Protocol) as a time reference to synchronise computer networks and other technology and the disruption Leap seconds can cause is seen as not worth the hassle.

However, others, such as astronomers, say that failing to keep UTC in line with the astronomical day would make studying of the heavens nearly impossible.

The last leap second inserted before this one was in 2005 but there have been a total of 23 seconds added to UTC since 1972.

Dealing with Time across the Globe

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No matter where we are in the world we all need to know the time at some point in the day but while each day lasts for the same amount of time no matter where you are on Earth the same timescale is not used globally.

The impracticality of Australians having to wake up at 17.00 or those in the US having to start work at 14.00 would rule out suing a single timescale, although the idea was discussed when the Greenwich was named the official prime meridian (where the dateline officially is) for the world some 125 years ago.

While the idea of a global timescale was rejected for the above reasons, it was later decided that 24 longitudinal lines would split the world up into different timezones. These would emanate from GMT around with those on the opposite side of the planet being +12 hours.

However, by the 1970’s a growth in global communications meant that a universal timescale was finally adopted and is still in much use today despite many people having never heard of it.

UTC, Coordinated Universal Time, is based on GMT (Greenwich Meantime) but is kept by a constellation of atomic clocks. It also accounts for variations in earth’s rotation with additional seconds known as ‘leap seconds’ added once of twice a year to counteract the slowing of the Earth’s spin caused by gravitational and tidal forces.

While most people have never heard of UTC or use it directly its influence on our lives in undeniable with computer networks all synchronised to UTC via NTP time servers (Network Time Protocol).

Without this synchronisation to a single timescale many of the technologies and applications we take for granted today would be impossible. Everything from global trading on stocks and shares to internet shopping, email and social networking are only made possible thanks to UTC and the NTP time server.

European Time Synchronisation with DCF-77

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The DCF 77 signal is a long wave transmission broadcast at 77 KHz from Frankfurt in Germany. DCF -77 is transmitted by Physikalisch-Technische Bundesanstalt, the German national physics laboratory.

DCF-77 is an accurate source of UTC time and is generated by atomic clocks that ensure its precision. DCF-77 is a useful source of time that can be adopted all over Europe by technologies needing an accurate time reference.

Radio controlled clocks and network time servers receive the time signal and in the case of time servers distribute this time signal across a computer network. Most computer network use NTP to distribute the DCF 77 time signal.

There are advantages of using a signal like DCF for time synchronisation. DCF is long wave and is therefore susceptible to interference from other electrical devices but they can penetrate buildings that give the DCF signal an advantage over that other source of UTC time generally available – GPS (Global Positioning System) – which requires a open view of the sky to receive satellite transmissions.

Other long wave radio signals are available in other countries that are similar to DCF-77. In the UK the MSF -60 signal is broadcast by NPL (National Physical Laboratory) from Cumbria while in the USA, NIST (National Institute of Standards and Time) transmit the WVBB signal from Boulder, Colorado.

NTP time servers are an efficient method of receiving these long wave transmissions and then using the time code as a synchronisation source. NTP servers can receive DCF, MSF and WVBB as well as many of them also being able to receive the GPS signal too.

UTC What Time is it?

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From the early days of the industrial revolution, when railway lines and the telegraph spanned across time zones it became apparent that a global timescale was required that would allow the same time to be used no matter where you were in the world.

The first attempt at a global timescale was GMT – Greenwich Meantime. This was based on the Greenwich Meridian where the sun is directly above at 12 noon. GMT was chosen, primarily because of the influence of the British empire on the rest if the globe.

Other timescales had been developed such British Railway Time but GMT was the first time a truly global system of time was used throughout the world.

GMT remained as the global timescale through the first half of the twentieth century although people began referring to as UT (Universal Time).

However, when atomic clocks were developed in the middle of the twentieth century it soon became apparent that GMT was not accurate enough. A global timescale based on the time told by atomic clocks was desired to represent these new accurate chronometers.

International Atomic Time (TAI) was developed for this purpose but problems in using atomic clocks soon became apparent.

It was thought that the Earth’s revolution on its axis was an exact 24 hours. But thanks to atomic clocks it was discovered the Earth’s spin varies and since the 1970’s has been slowing. This slowing of the Earth’s rotation needed to be accounted for otherwise the discrepancies could build up and night would slowly drift in to day (albeit in many millennia).

Coordinated Universal Time was developed to counter this. Based on both TAI and GMT, UTC allows for the slowing of the Earth’s rotation by adding leap seconds every year or two (and sometimes twice a year).

UTC is now a truly global timescale and is adopted by nations and technologies across the globe. Computer networks are synchronised to UTC via network time servers and they use the protocol NTP to ensure accuracy.

Radio Controlled Clocks Atomic Clocks on Shortwave

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Atomic clocks are a marvel compared to other forms of timekeepers. It would take over 100,000 years for an atomic clock to lose a second in time which is staggering especially when you compare it to digital and mechanical clocks that can drift that much in a day.

But atomic clocks are not practical pieces of equipment to have around the office or home. They are bulky, expensive and require laboratory conditions to operate effectively. But making use of an atomic clock is straightforward enough especially as atomic time keepers like NIST (National Institute of Standards and Time) and NPL (National Physical Laboratory) broadcast the time as told by their atomic clocks on short wave radio.

NIST transmits its signal, known as WWVB from Boulder, Colorado and it is broadcast on an extremely low frequency (60,000 Hz). The radio waves from WWVB station can cover all of the continental United States plus much of Canada and Central America.

The NPL signal is broadcast in Cumbria in the UK and it is transmitted along similar frequencies. This signal, known as MSF is available throughout most of the UK and similar systems are available in other countries such as Germany, Japan and Switzerland.

Radio controlled atomic clocks receive these long wave signals and correct themselves according to any drift the clock detects. Computer networks also take advantage of these atomic clocks signals and use the protocol NTP (Network Time Protocol) and dedicated NTP time servers to synchronise hundreds and thousands of different computers.

Atomic Clock to be attached to International Space Station

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One of the world’s most accurate atomic clocks is to be launched into orbit and attached to the International Space Station (ISS) thanks to an agreement signed by the French space agency.

The PHARAO (Projet d’Horloge Atomique par Refroidissement d’Atomes en Orbite) atomic clock is to attached to the ISS in an effort to more accurately test Einstein’s theory of relatively as well as increasing the accuracy of Coordinated Universal Time (UTC) amongst other geodesy experiments.

PHARAO is a next generation caesium atomic clock with an accuracy that corresponds to less than a second’s drift every 300,000 years. PHARAO is to be launched by the European Space Agency (ESA) in 2013.

Atomic clocks are the most accurate timekeeping devices available to mankind yet they are susceptible to changes in gravitational pull, as predicted by Einstein’s theory, as time itself is slewed by the Earth’s pull. By placing this accurate atomic clock into orbit the effect of Earth’s gravity is lessened allowing PHARAO to be more accurate than Earth based clock.

While atomic clocks are not new to orbit, as many satellites; including the GPS network (Global Positioning System) contain atomic clocks, however, PHARAO will be among the most accurate clocks ever launched into space, allowing it to be used for far more detailed analysis.

Atomic clocks have been around since the 1960’s but their increasing development has paved the way for more and more advanced technologies. Atomic clocks form the basis of many modern technologies from satellite navigation to allowing computer networks to communicate effectively across the globe.

Computer networks receive time signals from atomic clocks via NTP time servers (Network Time Protocol) which can accurately synchronise a computer network to within a few milliseconds of UTC.

IEEE 1588 Time Protocol Promises More Accurate Time Synchronisation

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Despite being around for over twenty years, the current favoured time protocol by most networks, NTP (Network Time Protocol) has some competition.

Currently NTP is used to synchonise computer networks using network time servers (NTP servers). Currently NTP can synchronise a computer network to a few milliseconds.

The Precision Time Protocol (PTP) or IEEE 1588 has been developed for local systems requiring very high accuracy (to nano-second level). Currently this type of accuracy is beyond the capabilities of NTP.

PTP requires a master and slave relation ship in the network. A two-step process is required to synchronise devices using the IEEE 1588 (PTP). First, determination of which device is the master is required then the offsets and natural network delays are measured. PTP uses the Best Master Clock algorithm (BMC) to establish which clock on the network is the most accurate and it becomes the master whilst all other clocks become slaves and synchronise to this master.

IEEE (Institute of Electrical and Electronic Engineers) describes IEEE 1588 or (PTP) as designed to “fill a niche not well served by either of the two dominant protocols, NTP and GPS.  IEEE 1588 is designed for local systems requiring very high accuracies beyond those attainable using NTP. It is also designed for applications that cannot bear the cost of a GPS receiver at each node, or for which GPS signals are inaccessible.” (quoted in Wikipedia)

PTP can provide accuracy to a few nano-seconds but this type of accuracy is not required by most network users however, the target use of PTP appears to be mobile broadband and other mobile technologies as PTP supports time-of-day information, used by billing and service level agreement reporting functions in mobile networks.

Facts of Time

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From wristwatches to atomic clocks and NTP time servers, the understanding of time has become crucial for many modern technologies such as satellite navigation and global communications.

From time dilation to the effects of gravity on time, time has many weird and wonderful facets that scientists are only beginning to understand and utilise. Here are some interesting, weird and unusual facts about time:

•    Time is not separate from space, time makes up what Einstein called four dimensional space time. Space time can be warped by gravity meaning that time slows down the greater the gravitational influence.  Thanks to atomic clocks, time on earth can be measured at each subsequent inch above the earth’s surface. That means that every bodies feet are younger than their head as time runs slower the lower to the ground you get.

•    Time is also affected by speed. The only constant in the universe is the speed of light (in a vacuum) which is always the same. Because of Einstein’s famous theories of relativity anybody travelling at close to the speed of light a journey to an observer that would have taken thousands of years would have passed within seconds. This is called time dilation.

•    There is nothing in contemporary physics that prohibits time travel both forward and backwards in time.

•    There are 86400 seconds in a day, 600,000 in a week, more than 2.6 million in a month and more than 31 million in a year. If you live to be 70 years old then you will have lived through over 5.5 billion seconds.

•    A nanosecond is a billionth of a second or roughly the time it takes for light to travel about 1 foot (30 cm).

•    A day is never 24 hours long. The earth’s rotation is speeding up gradually which means the global timescale UTC (coordinated universal time) has to have leap seconds added once or twice a year. These leap seconds are automatically accounted for in any clock synchronization that uses NTP (Network Time Protocol) such as a dedicated NTP time server.

Choosing a Time Source what to do and what not to do

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Time synchronization is crucial for many of the applications that we do across the internet these days; internet banking, online reservation and even online auctions all require network time synchronization.

Failing to ensure their servers are adequately synchronized would mean many of these applications would be impossible to achieve; seat reservations could be sold more than once, lower bids could win internet auctions and it would be possible to withdraw you life savings from the bank twice if they didn’t have adequate synchronization (good for you not for the bank).

Even computer networks that on the face of it do not rely on time sensitive transactions also need to be adequately synchronized as it could be near impossible to track down errors or protect the system from malicious attacks if the timestamps on differ on various machines on the network.

Many organisations opt to use internet time servers as a source of UTC (Coordinated Universal Time) – the atomic clock controlled global timescale. Although there are many security issues in doing so such as leaving a hole in the firewall to communicate with the time server and not having any authentication for the time synchronization protocol NTP (Network Time Protocol).

However, in saying that many network administrators still opt to use online time servers as a UTC source regardless of the security implications although there are other issues that administrators should be aware of. On the internet there are two types of time server – stratum 1 and stratum 2. Stratum 1 servers receive a time signal direct from an atomic clock while stratum 2 servers receive a time signal from a stratum 1 server. Most internet stratum 1 servers are closed – unavailable to most administrators and there can be some shortfall in accuracy in using a stratum 2 server.

For the most accurate, secure and precise timing information external NTP time servers are the best option as these are stratum 1 devices that can synchronize hundreds of machines on a network to the exact same UTC time.