GPS Time Server – Common Questions Answered

What is a GPS?

GPS (Global Positioning System) is the US controlled satellite navigation system which is commonly used by motorists, airlines and seafarers to find their position. The technology is based on time signals sent from atomic clocks that are onboard each GPS satellite. Atomic clocks have to be used as GPS positioning is based on triangulation of the time signals when they arrive at a receiver. As the signals travel the speed of light a second of inaccuracy could see positioning information out by hundreds of thousands of kilometres.

What is a GPS Time Server?

A GPS time server is a dedicated server that receives the time signal from the GPS satellites and distributes it around a network. Most GPS time servers use the protocol NTP (Network Time Protocol) to distribute the time to devices and computers on a network.

How accurate is a GPS time server?

Typically, GPS time servers can provide accuracy to within a few milliseconds (thousandths of a second) but a lot depends on a network layout. Time synchronisation can be affected by distance travelled and the speed machines process information

IS GPS time the same as UTC?

No, however, Coordinated Universal Time and GPS time are both based on International Atomic Time. The difference between the two is that UTC calculates for leap seconds that are added to adjust for slowing of the Earth’s rotation due to tidal and lunar effects. Since the GPS signal went online there have been 15 leap seconds which means GPS time is exactly 15 seconds slower than UTC but most GPS time server systems account for this ensuring that GPS time is converted to UTC.

Atomic Clocks and the GPS Time Server

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.

GPS Time Server – How they work

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.

GPS Time Server – Accuracy from space

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.

GPS Time Server – GPS Facts

From military hardware to GPS time servers

The Global Positioning System was designed and built by the US military in the late 1970’s, although it didn’t achieve initial operational capability until 1993. GPS was originally designed as a military only system but in 1983 after a USSR aircraft shot down a Korean airliner that had accidentally strayed into Soviet airspace, the then President of the United States, Ronald Reagan, vowed the system would be available for civilian use once completed.

Full Operational Capability was declared by the now named NAVSTAR GPS in April 1995 and in 1996 to fulfil his predecessors promise the U.S. President Bill Clinton issued a policy directive declaring GPS to be a dual-use system; one for US military use and one system for civilians.

Currently GPS is the World’s only GNSS (Global Navigational Satellite System) although the Russian GLONASS system that was operational during the Cold War but has since fallen into disrepair is being repaired and a European GNSS known as Galileo is expected to be operational by 2012, other systems developed by China and India are also being developed.

GPS is primarily a navigational system that transmits precise timing information via an onboard atomic clock. It is this information and the satellites location that is used to triangulate positioning. However, the GPS signal can also be used by a GPS time server as a timing source.

GPS Time Server – The First Choice for time synchronisation

GPS time servers have revolutionised the world of synchronisation. There advantages over other forms of timing references is many fold but as there are over 30 GPS satellites one will always be in range of a GPS receiver.

A GPS time server (Global Positioning System) bought fifteen years ago would have cost somewhere in the reason of £8,000-£10,000 ($15,000-$17,000) but thanks to the growing use of the technology the price of GPS receivers has plummeted and they can be bought for as little as £350 ($600). His has made GPS the dominate form of timing references for time synchronisation.

A GPS time server will come in several forms, some are designed to be fitted into standard server racks, these rack-mountable GPS time server will take up one or two standard U spaces depending on server type.

Other GPS time servers are smaller and more discrete, ideal to be located outside a server room. While GPS time servers offer unrivalled accuracy and a signal is available literally everywhere on the planet it does have one down-side in that a GPS antenna has to have a clear view of the sky. This means that the antenna has to be situated on a roof of a building otherwise there is a possibility that the signal will be lost.

GPS Time Server – The Synchronisation Choice

GPS (Global Positioning System) is now the preferred method of receiving a UTC (Coordinated Universal Time) time source for the purposes of synchronising a computer network.

GPS is an American military controlled system that was opened up for the use of civilians following a terrible air disaster in the late 1980’s. GPS receivers used to be astronomically expensive and all but the most wealthy network administrators would use the GPS signal as a source of UTC time.

However, due to advances in technology in recent years GPS technology has dramatically dropped in price and the GPS time server is now the globally preferred method of receiving a UTC timing source.

Other methods have continually been available of course with national time and frequency transmissions such as MSF in the UK, DCF in Germany and the WWVB signal in the USA having been the most popular method over the last decade.

However, there are drawbacks to using the national time and frequency transmissions. They are all broadcast on similar long-wave frequencies and are vulnerable to topography and interference from weather and other electrical appliances. These time and signal transmissions are also only available in a select few countries and even in the country of origin the local geography can prevent the signal getting through.

One of the reasons GPS is now so popular is that no matter where you are in the world the GPS receiver will always be able to receive a signal just as long as the GPS antenna can obtain a clear view of the sky.

GPS Time Server – NAVSTAR

NAVSTAR GPS is not an acronym although many people assume it is. NAVSTAR is the original name given to the US military’s Global Navigational Satellite System (GNSS).

Currently NAVSTAR is the world’s only fully functioning GNSS, although the European Galileo system is expected to be operational in a few years and the former Russian GLONASS system is being put back into commission after it fell into disrepair following the collapse of the Soviet Union.

NAVSTAR is controlled and run by the US Air Force’s 50th Space Wing but has been available for civilian use since the late 1980’s when a Korean passenger airliner was accidently shot down.

NAVSTAR is most commonly used as a positioning and navigational tool but the information it transmits is basic timing data that is generated by an onboard atomic clock.

It is these ultra precise timing signals that a satellite navigation system will use to work out positioning but they can also be utilised by a GPS time server as a source of UTC (coordinated universal time). Strictly speaking the time signal from NAVSTAR is not in UTC format but is kept very close to UTC (within 1 microseconds).

Using NAVSTAR GPS as a timing reference means that a UTC time source can be utilised safely, securely and reliably from anywhere on the globe.

GPS Time Server – A Revolution in Chronology

A GPS time server is often called a GPS clock although this is a misnomer. In fact a GPS time server simply relays the time from an external source around a network it doesn’t keep time itself.

The GPS time server receives its timing signal from the GPS network (Global Positioning System) and has revolutionised the way computers are able to keep track of time.

The GPS network is controlled by the US military and it was due to a military accident involving an airliner that the US government allowed the GPS network to be utilised by civilians around the globe.

The GPS system works by relaying precise time information which can be calculated by a GPS receiver to work out distances. This precise timing information is generated by an onboard atomic clock in the satellite and it is this atomic clock that a GPS time server receives the time from.

Without GPS the only other alternatives to receiving a time signal that relays UTC time (coordinated universal time) would be to use the national time and frequency radio broadcasts transmitted by several national physics laboratories, although these are not available everywhere. Alternatively the only other solution is to use the Internet which means using a device external to your firewall and also a time server that cannot be proven accurate.

GPS Time Server the Synchronisation Choice

Time servers, in reality, come in two flavours: the radio referenced time server and the GPS time server. Both are equally as good at receiving, distributing and synchronising to UTC (coordinated universal time).

However, while a radio signal is limited in range and vulnerable to interference the GPS signal, transmitted from one of the 33 NAVSTAR satellites in orbit, is available literally anywhere on the globe.

For this reason the GPS time signal is now the time reference of choice for network administrators needing a source of UTC time. The only prerequisite for a GPS time server is that that GPS antenna has to have a clear view of the sky.

This does pose some problems as the only place where an antenna can view the entire sky is on the roof. The antenna is also limited in the length of cable that it can run which means in some very large buildings there may be logistical problems in running the cable from the server room to the roof.

A GPS Time server can provide highly accurate timing information in a secure and safe environment. Using a GPS time server and a network can be synchronised to within a few milliseconds of UTC.