Time Synchronisation

What is NTP?

NTP is a protocol developed over 25 years ago to deal with the problems of time synchronisation across the Internet. Network Time Protocol distributes a single time source to all computers and devices by using an algorithm to inspect the drift of each device and then correcting the time.

While NTP can distribute any time reference it was designed in particular to synchronise computer networks to UTC (Coordinated Universal Time). UTC is a global time scale used by computer networks around the world. It is based on the time told by atomic clocks and is therefore highly accurate.

What is GPS?

The Global Positioning System (GPS) is currently the world’s only global navigational satellite system (GNSS) and is controlled by the American military. GPS is most commonly thought of as a navigational tool but as the principles of GPS navigation involve an atomic clock onboard each GPS satellite transmitting its time, this information can be used by NTP as a highly accurate source of UTC.

What does a NTP GPS server do?

A NTP GPS server is a dedicated computer server that receives a GPS timing signal via a GPS antenna and then distributes it amongst the network.  NTP GPS servers can provide accuracy to within a few milliseconds of UTC time.

A NTP GPS server is the most effective, accurate, reliable and secure method of receiving a UTC time signal from an atomic clock source.

A NTP GPS server uses the precise timing information generated from the GPS satellite’s onboard atomic clock. It receives this information via a roof-mounted GPS antenna. The antenna, which is connected to either a rack mount NTP GPS server or a stand alone unit then distributes the signal to all devices on that network. All devices from workstations, routers, switches and other servers can be synchronised to this source.

The UTC time (coordinated universal time – based on the time told by atomic clocks) can then be displayed on a wall mounted digital clock or other time telling device.

Currently there is only one Global Navigation Satellite System (GNSS) the NAVSTAR GPS which has been open for civilian use since the late 1980’s.

Most commonly, the GPS system is thought to provide navigational information allowing drivers, sailors and pilots to pinpoint their position anywhere in the world.

In fact, the only information beamed from a GPS satellite is the time which is generated by the satellites internal atomic clock. This timing signal is so accurate that a GPS receiver can use the signal from three satellites and pinpoint the location to within a few metres by working out how long each precise signal took to arrive.

Currently a GPS NTP server can use this timing information to synchronise entire computer networks to providing accuracy to within a few milliseconds.

However, the European Union is currently working on Europe’s own Global Navigation Satellite System called Galileo, which will rival the GPS network by providing its own timing and positioning information.

However, Galileo is designed to be interoperable with GPS meaning that a current GPS NTP server will be able to receive both signals, although some software adjustments may have to be made.

This interoperability will provide increased accuracy and may make national time and frequency radio broadcasts obsolete as they will not be able to produce a comparable accuracy.

Furthermore, Russia, China and India are currently planning their own GNSS systems which may provide even more accuracy. GPS has already revolutionised the way the world works not only by allowing precise positioning but also enabling entire globe to synchronise to the same timescale using a GPS NTP server. It is expected that even more advances in technology will emerge once the next generation of GNSS begin their transmissions.

The Global Positioning System was developed by the United State s Military for their armed forces, however following the accidental shooting down of a Korean Airliner in 1983, the US government realised the benefits a civilian system would have in preventing such a disaster.

As a consequence the GPS network was opened up freely for civilian use and is currently the world’s only fully functioning global navigation satellite system (GNSS), although Europe and Russia are to have their own systems within the next decade.

Although the GPS system is primarily used for location finding the only information it relays is the time, which has proved beneficial in keeping computer networks synchronised using a GPS NTP server.

Each GPS satellite contains an atomic clock, these clocks beam to Earth an exact timing signal, precise to a second in several millions of years. The GPS receiver then works out the time each signal took to get to it (a minimum of three is therefore needed) and can work out its exact location by this triangulation.

GPS satellites have to provide exact timing information as light and radio waves can travel 300,000 km each second, a difference which would make navigation hopeless. However, this information can be used by a GPS NTP Server which converts the time signal from the satellites into UTC (Coordinated Universal Time) and then synchronises every clock on a network to that time.

Using the GPS network means a GPS NTP server can provide accuracy to a computer network to within a few milliseconds. GPS has therefore not only transformed the way in which the world navigates but also has also revolutionised computer networks with precise timing information making possible many of the Internet processes such as online purchasing and email that we all take for granted.

NAVSTAR was invented and developed by the US during the height of the Cold War. It was primarily meant for military use but after a Korean airliner was accidentally shot down the US administration at the time decided to open up their system for the ‘greater good.’

Since that time NAVSTAR, now commonly referred to as GPS (Global Positioning System), has revolutionised transportation around the world for mariners, pilots and car drivers alike.

The functioning of the GPS system is very simple. There are currently a constellation of 24 satellites, arranged in orbit so that four are always in line-of-sight to any spot on the Earth.

These satellites contain atomic clocks, the most accurate chronometers so far developed by mankind. These keep and broadcast a time code that is accurate to a few nanoseconds (nano = 1 billionth of a second). This time code is then received by a GPS receiver that uses the information from four satellites to triangulate its exact position. This can only be done because the atomic clocks provide such accurate time. If a clock on a GPS satellite was even just one second too slow or fast, the positioning information could be as much as 200,000 miles out (because of the distance light and therefore radio waves travels in that time).

As the timing source from GPS systems are so accurate they are ideal to be used as a reference for a NTP server. NTP (network time protocol) servers use a timing source to synchronise all machines on a network to that time. A dedicated GPS NTP server can receive the time signal from the NAVSTAR system and synchronise an entire network to within a few milliseconds.

A GPS NTP server is quite possibly the most accurate and efficient method of receiving a timing source to synchronise a computer network to.

A GPS NTP server can receive a timing signal from literally anywhere in the world using relatively low cost components. They are also incredibly easy to install.

The only difficulties ever encountered in installing a GPS NTP server is that they require an antenna with a good view of the sky, this is because the signals are broadcast by the satellites by line-of-sight so a clear view of the sky is a necessity (although some people have had success receiving a signal from a window).

The maximum length of cable from the antenna to the GPS NTP server is normally only 20 to 30 metres but using a signal amplifier and high quality coax cable can allow in excess of 100 metres.

The GPS NTP server decodes the time signal from the satellite and converts it to a computer readable format. NTP (Network Time Protocol) then checks all the clocks on a network and synchronises them by adding or subtracting time so it matches the GPS time signal.

A GPS NTP server is ideal in providing networks or stand-alone computers with a highly accurate reference for synchronisation. Even with relatively inexpensive equipment, accuracy to within a few hundred nanoseconds (a nanosecond = a billionth of a second) can reasonably be achieved.

GPS has already revolutionised the way the world works by allowing precise global positioning but it has also revolutionise4d the Internet and the way entire globe communicates.

NTP is the standard protocol for synchronising networks and is used throughout the world to ensure computers are all running the same UTC (Coordinated Universal Time) time.

UTC was developed after the invention of atomic clocks to enable the global community to synchronise to the same time. It is based on Greenwich Meantime but accounts for the slowing of the Earth’s rotation by occasional adding ‘leap seconds’.

There are many ways to receive a UTC time source to synchronise a network to. Most commonly the internet is used as a timing source but inaccuracies, distance and lack of authentication means many internet time sources are virtually useless as a way of maintaining accurate time.

The most accurate and efficient way a of receiving UTC time is by using a dedicated GPS NTP server. These comprise of a GPS antenna, GPS receiver and NTP software.

These time servers receive the time code from GPS (global positioning system) satellites which contain atomic clocks, necessary to provide positioning information. Although the time is not broadcast as UTC, NTP software converts it.

Using a GPS NTP server means that accuracy to within a few hundred nanoseconds is possible using relatively low cost equipment. GPS NTP servers can also receive this time signal from literally anywhere in the world as long as the GPS antenna can get a good view of the sky.

The only disadvantages of a GPS NTP server is that the antenna is limited in its distance from the time server. Although high quality coaxial cable and a signal amplifier may help to achieve distances of up to 300 feet (100 metres).

Because of the advances in GPS technology over recent years, GPS NTP Servers are now more accurate and less expensive as they have ever been.

A NTP GPS Server is a type of time server that uses Network Time Protocol (NTP) as a method for synchronizing the time on network devices and computers after receiving a time signal from he GPS network.

The GPS (Global Positioning System) network is a constellation of satellites owned and operated by the USA military. Most people are aware of GPS as an aid for satellite navigation. In actual fact, the basis of the transmissions broadcast by the GPS satellites is a time signal. This time signal is generated by the satellite’s onboard atomic clock. It is this information that a satellite navigation system receives and calculates by triangulation the distance away from the satellites.

This timing signal is what is used by a NTP GPS server as a reference to synchronize a network too. NTP then distributes this time to all routers and computers on that network.

A NTP GPS server comprises of a GPS receiver, GPS antenna and NTP software. The GPS antenna should be situated on a rooftop which will give the best possibility of receiving the transmissions from the satellites.

The GPS receiver then converts this information into timing information that can be read and distributed by NTP.

While the atomic clocks onboard the GPS satellites do not transmit a UTC timing code (Coordinated Universal Time). However, NTP has the ability to convert the atomic clock from the satellites to UTC. This allows computer networks to be synchronized to the same universal time source no matter where they are in the world.

Using a dedicated NTP GPS server a network can be synchronized to within a few milliseconds of UTC time with accuracies of a few hundred nanoseconds made possible over LAN’s.

A time server is a computer server that reads the time from an accurate clock and distributes this information to its clients across a computer network.

The reference used by a time server is normally a UTC (coordinated universal time) time source. UTC is a global time scale adopted all over the world and based on the time told by atomic clocks The most common source for UTC time is now the GPS system (global positioning system).

The most widely-used protocol for distributing and synchronising time is Network Time Protocol (NTP) which has been around almost as long as the Internet itself, having been developed in 1985 by Professor David Mills.

NTP receives the time from the time server and then checks or clocks on its networks to see if they need advancing or retreat.

To prevent overload of networks requesting timing information, NTP is hierarchical.  The term “stratum” is used to label the nearness to a stratum 0 server – that atomic clock. The higher the stratum number the further away the server is. A GPS time server is normally a stratum 1 device as it receives time from a stratum 0 device. However, stratum 2 and stratum 3 devices can still synchronise with each other.

Atomic clocks use an atomic resonance frequency standard as their timekeeping element and are by far the most accurate chronometers possible with the latest Strontium based atomic clocks boasting a precision of a less than a second lost in several hundred million years.

The clocks maintain a continuous and stable time scale called International Atomic Time (TAI). However, for civil time, another time scale, Coordinated Universal Time (UTC)which  is derived from TAI, but synchronized using leap seconds to UTC, to keep it based on the rotation of the Earth.

UTC is a global timescale that is commonly used to synchronise the clocks on computer networks allowing machines from across the globe to communicate together and conduct time sensitive applications.

Unfortunately atomic clocks are highly expensive pieces of equipment and are generally only to be found in high technology physics laboratories or onboard satellites. However, several national physics laboratories broadcast the time told by their atomic clocks via a long wave radio transmission.

These signals are commonly picked up and utilized by radio controlled wall and desk clocks and by NTP time servers (Network Time Protocol).

The transmissions from the national standards agencies maintain an accuracy of 10-9 seconds per day (approximately 1 part in 1014). MSF is the signal broadcast by National Physical Laboratory in, Anthorn, Cumbria. Other countries boast their own signals the most common being the DCF77 transmission broadcast from Mainflingen near Frankfurt, Germany and the USA’s WWVB signal broadcast from Fort Collins, Colorado.

All these times signals work in a similar way. At the start of each second the strength of the signal is either reduced by between 6 and 10 dB