Time Synchronisation

To receive and distribute and authenticated UTC time source there are currently two types of NTP server, the GPS NTP server and the radio referenced NTP server. While both these systems distribute UTC in identical ways the way they receive the timing information differs.

A GPS NTP time server is an ideal time and frequency source because it can provide highly accurate time anywhere in the world using relatively cheap components.  Each GPS satellite transmits in two frequencies L2 for the military use and L1 for use by civilians transmitted at 1575 MHz, Low-cost GPS antennas and receivers are now widely available.

The radio signal transmitted by the satellite can pass through windows but can be blocked by buildings so the ideal location for a GPS antenna is on a rooftop with a good view of the sky. The more satellites it can receive from the better the signal. However, roof-mounted antennas can be prone to lighting strikes or other voltage surges so a suppressor is highly recommend being installed inline on the GPS cable.

The cable between the GPS antenna and receiver is also critical. The maximum distance that a cable can run is normally only 20-30 metres but a high quality coax cable combined with a GPS amplifier placed in-line to boost the gain of the antenna can allow in excess of 100 metre cable runs. This can provide difficulties in installation in larger buildings if the server is too far from the antenna.

An alternative solution is to use a radio referenced NTP time server. These rely on a number of national time and frequency radio transmissions that that broadcast UTC time. 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 the USA (WWVB) and in France, Germany and Japan.

A radio based NTP server usually consists of a rack-mountable time server, and an antenna, consisting of a ferrite bar inside a plastic enclosure, which receives the radio time and frequency broadcast. It should always be mounted horizontally at a right angle toward the transmission for optimum signal strength. Data is sent in pulses, 60 a second. These signals provides UTC time to an accuracy of 100 microseconds, however, the radio signal has a finite range and is vulnerable to interference.

5. Synchronisation is vital for any network that conducts time sensitive transactions. Computers use time as the only point of reference between events and if computers on a network are all running different times then untold problems can occur. The problems increase many-fold if a network has to communicate with another network.

4. UTC (coordinated universal time) is a global timescale used all over the world ensuring that all networks linked to a UTC time source are running identical times. Not having synchronisation to UTC can mean that many International Transactions are just not possible.

3. A network time server is a dedicated device which means it receives time directly from an atomic clock source externally. UTC can be obtained from a variety of Internet time sources however this can leave a system open to abuse as the firewall needs to be open to receive the signal. Furthermore, the time protocol NTP has a security measure known as authentication – this does not work over the Internet.

2 A dedicated network time server can be legally audited which means in case of fraud or other legal issues the time provided by the time server is legally accepted as being accurate.

1. A dedicated network time server is a stratum 1 device a stratum 0 device is an actual atomic clock. A device that receives a time signal from a network time server is a stratum 2 device. The higher the stratum number the further away and therefore that less accurate the time signal is. The majority of Internet time servers are all stratum 2 devices and therefore cannot provide anywhere near as accurate timing information

NTP or Network Time Protocol is, like other protocols, merely a set of instructions. However, NTP is one of the Internet’s most successful and oldest of protocols. NTP was developed by Professor David Mills in the mid 1980’s when the Internet was in its earliest stages.

NTP is based on Marzullo’s Algorithm. Algorithms are mathematical equations and Marzullo’s algorithm is designed to set an optimal value from a set of estimates which is ideal for time synchronisation as the best estimate taken from several sources will provide far greater accuracy than relying on just one or two sources.

NTP has been an astronomical success and is now used in nearly 99 per cent of time synchronisation devices and a version of it is included in most operating system packages.

NTP owes much of its success to the development and support it continues to receives nearly three decades after its inception and is now used throughout the world in NTP time servers.

NTP GPS server is a time server that uses the protocol NTP (Network Time Protocol) receives its authoritative time source from the GPS satellite network (Global Positioning System).

Other varieties of time server exist most if not all dedicated devices use NTP as it is universally excepted as the most superlative time protocol, there are however numerous ways a network time server (whether NTP or not) can receive a time signal.

The internet is a common source for timing information although very few administrators who have a dedicated time server device would use the Internet. This is because external time sources across the Internet are the wrong side of a uses firewall and therefore pose a potential security risk not-to-mention many Internet timing sources are not very accurate and also most are stratum 2 devices and therefore further away from the original time source than a stratum 1 dedicated NTP server (stratum 0 devices are atomic clocks).

The other methods a dedicated NTP server (often called network time server) can receive a timing signal is via GPS or radio transmissions that are broadcast from national physics laboratories.

Radio signal are a good source of UTC time (coordinated universal time) as they are maintained and run by organisations such NPL (National Physical Lab. UK) or NIST (National Institute for Standards and Time – US). However, these long wave transmissions are not broadcast in every country and the signals are susceptible to local interference and topography.

On the other hand a dedicated NTP GPS server receives its time signal from the GPS satellite system (each satellite contains an atomic clock). These signals offer excellent accuracy and furthermore are available everywhere on the planet where there is a clear view of the sky.

GPS time servers are often called many things: NTP time servers, GPS network time servers, GPS NTP servers etc. A time server is merely a device to that computer’s can contact to receive timing information from for purposes of time synchronisation.

The way a time server receives the time is what defines it. A radio referenced time server will receive a time signal from a national physics laboratory via a long wave radio signal. A GPS time server receives a time signal from the Global Positioning System a constellation of satellites designed to provide navigation information.

What makes GPS possible is that onboard each global positioning satellite there is an atomic clock. The time from this clock is broadcast along with the position and velocity of the satellite. It is this information that a satellite navigation receiver uses to work out position by triangulation. It receives the same data from three or more satellites and works out by the time it takes for the transmission from each satellite to reach the receiver.

While the atomic clocks onboard the GPS satellites do not broadcast UTC (Coordinated Universal Time – the civil global timescale) because it is an atomic clock signal and therefore extremely reliable, a GPS time server can easily translate the GPS time into UTC.

Methods of keeping track of time have altered throughout history with ever increasing accuracy has being the catalyst for change.

Most methods of timekeeping have traditionally been based on the movement of the Earth around the Sun. For millennia, a day has been divided into 24 equal parts that have become known as hours. Basing our timescales on the rotation of the Earth has been adequate for most of our historical needs, however as technology advances, the need for an ever increasingly accurate timescale has been evident.

The problem with the traditional methods became apparent when the first truly accurate timepieces – the atomic clock was developed in the 1950’s. Because these timepieces  was based on the frequency of atoms and were accurate to within a second every million years it was soon discovered that our day, that we had always presumed as being precisely 24 hours, altered from day to day.

The affects of the Moon’s gravity on our oceans causes the Earth to slow and speed up during its rotation – some days are longer than 24 hours whilst others are shorter. Whilst this minute differences in the length of a day have made little difference to our daily lives it this inaccuracy has implications for many of our modern technologies such as satellite communication and global positioning.

A timescale has been developed to deal with the inaccuracies in the Earth’s spin – Coordinated Universal Time (UTC). It is based on the traditional 24-hour Earth rotation known as Greenwich Meantime (GMT) but accounts for the inaccuracies in the earth’s spin by having so-called ‘Leap Seconds’ added (or subtracted).

As UTC is based on the time told by atomic clocks it is incredibly accurate and therefore has been adopted as the World’s civilian timescale and is used by business and commerce all over the globe.

Most computer networks can be synchronised to UTC by using a dedicated NTP time server.

The GPS network (Global Positioning System), is commonly known as a satellite navigation system. It however, actually relays a ultra-precise time signal from an onboard atomic clock.

It is this information that is received by satellite navigation devices that can then triangulate the position of the receiver by working out how long the signal has taken to arrive from various satellites.

These time signals, like all radio transmissions travel at the speed of light (which is close to 300,000km a second). It is therefore highly important that these devices are not just accurate to a second but to a millionth of a second otherwise the navigation system would be useless.

It is this timing information that can be utilized by a GPS time server as a base for network time. Although this timing information is not in a UTC format (Coordinated Universal Time), the World’s global timescale, it easily converted because of its origin from an atomic clock.

A GPS time server can receive the signal from a GPS aerial although this does need to have a good view of the sky as the satellites relay their transmissions via line-of-sight.
Using a dedicated GPS time server a computer network can be synchronised to within a few milliseconds of NTP (milli=1000th of a second) and provide security and authentication.

Following the increase use of GPS technology over the last few years, GPS time servers are now relatively inexpensive and are simple and straight forward systems to install.

Network Time Protocol (NTP) designed to synchronise computers an devices on a network to an authoritative time source such as UTC (Universal Coordinated Time).
NTP distributes the timing information to all the devices on a network that require synchronisation and adjusts the clocks of these devices accordingly to keep it in line with the timing source.

May network administrators opt to use the Internet to retrieve timing information despite the fact that several surveys have found that many Internet based timing sources are inaccurate. There are Internet sources that are accurate to UTC but to use them as a timing source they need to be close as the distance travelled can reduce the accuracy. Furthermore, Internet timing sources can’t be authenticated. Authentication is a security measure utilised by NTP to ensure the timing source is what it says it is and not a malicious user.

There are several options available to receive an authenticated accurate timing source the first being the national time and frequency transmissions broadcast by several countries. However, these transmissions are not available everywhere and even in the country of origin the signal can be blocked by local geographical features.

The most assured way of receiving a UTC timing source is to use the onboard atomic clocks of the American GPS (Global Positioning System) network.
GPS, commonly known as a satellite navigation system actualy relays timing information. It is this information that is received by GPS receivers that can then triangulate the position of the receiver by working out how long the signal has taken to arrive from various satellites (four being the minimum to receive an accurate location).

Although this timing information is not in a UTC format, because it is from an atomic clock and incredibly accurate, NTP can convert the information into UTC and distribute it through the network using a NTP GPS time server.

A NTP GPS server can receive the signal from a GPS aerial although this does need to have a good view of the sky as the satellites relay their transmissions via line-of-sight.

Using a dedicated NTP GPS server a computer network can be synchronised to within a few milliseconds of NTP (milli=1000th of a second) and provide security and authentication.

Following the dramatic rise of GPS technology over the last few years, NTP GPS servers are now relatively inexpensive and are simple and straight forward systems to install.

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.

Telling the time is not as straight forward as most people think. In fact the very question, ‘what is the time?’ is a question that even modern science can fail to answer. Time, according to Einstein, is relative; it’s passing changes for different observers, affected by such things as speed and gravity.

Even when we all live on the same planet and experience the passing of time in a similar way, telling the time can be increasingly difficult. Our original method of using the Earth’s rotation has since been discovered to be inaccurate as the Moon’s gravity causes some days to be longer than 24 hours and a few to be shorter. In fact when the early dinosaurs were roaming the Earth a day was only 22 hours long!

Whilst mechanical and electronic clocks have provided us with some degree accuracy, our modern technologies have required far more accurate time measurements. GPS, Internet trading and air traffic control are just three industries were split second timing is incredibly important.

So how do we keep track of time? Using the Earth’s rotation has proven unreliable whilst electrical oscillators (quartz clocks) and mechanical clocks are only accurate to a second or two per day. Unfortunately for many of our technologies a second inaccuracy can be far too long. In satellite navigation, light can travel 300,000 km in just over a second, making the average sat-nav unit useless if there was one second of inaccuracy.

The solution to finding an accurate method of measuring time has been to examine the very small – quantum mechanics. Quantum mechanics is the study of the atom and its properties and how they interact. It was discovered that electrons, the tiny particles that orbit atoms changed the path that they orbit and released a precise amount of energy when they do so.

In the case of the caesium atom this occurs nearly nine billion times a second and this number never alters and so can be used as an ultra reliable method of keeping track of time. Caesium atoms are use din atomic clocks and in fact the second is now defined as just over 9 billion cycles of radiation of the caesium atom.

Atomic clocks are the foundation for many of our technologies. The entire global economy relies on them with the time relayed by NTP time servers on computer networks or beamed down by GPS satellites; ensuring the entire world keeps the same, accurate and stable time.

An official global timescale, Coordinated Universal Time (UTC) has been developed thanks to atomic clocks allowing the whole world to run the same time to within a few thousandths of a second from each other.