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.

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.

Why GPS?

Time synchronisation can be conducted in multiple ways on a computer network. There are many time protocols but NTP (Network Time Protocol) is by far the most used (probably close to 99% of networks use NTP).

Most time servers receive a UTC time signal UTC (Coordinated Universal Time) yet, there are multiple places that NTP can receive a signal from but each has it downsides. The most widely used source of UTC is the Internet but no serious network administrator would dare to use the Internet as a timing source.

Internet timing sources can’t be authenticated using NTP’s security measure and an Internet timing source will exist outside a networks firewall so a TCP/IP port would need to be left open both of these problems could leave a network open to malicious attacks, abuse or even fraud. Another reason why Internet sources should not be used is that a recent survey found less than a third were accurate enough to UTC to be useful and those that were depended on the distance from the client.

Time and frequency transmissions broadcast in longwave are far more secure and far more accurate than any Internet timing source. These transmissions are broadcast by several national physics laboratories and provide a safe, secure and highly accurate method of receiving UTV. Unfortunately not every country has a timing broadcast and even in a country that does the signals are vulnerable to local geography and interference.

GPS however, is available everywhere on the planet, the only downside at all in using a GPS time server is that it needs an antenna to be situated on the roof, which in most cases is not normally an issue.

GPS Time Server – Receiving Time from Space

GPS time servers are network time servers that receive a timing signal from the GPS network and distribute it amongst all devices on a network ensuring that the entire network is synchronised.

GPS is an ideal time source as a GPS signal is available anywhere on the globe. GPS stands for Global Positioning System, the GPS network is owned by the US military and controlled and run by the US air force (space wing). It is however, since the late 1980’s been opened up to the world’s civilian population as tool to aid navigation.

The GPS network is actually a constellation of 32 satellites that orbit the Earth, they do not actually provide positioning information (GPS receivers do that) but transmit from their onboard atomic clocks a timing signal.

This timing signal is what is used to work out a global position by triangulating 3-4 timing signals a receiver can work out how far and therefore the position you are from a satellite. In essence then, a global positioning satellite is just an orbiting clock and it is this information that is broadcast that can be picked up by a GPS time server and distributed amongst a network.

Whilst strictly speaking GPS time is not the same as the global timescale UTC (coordinated universal time), a GPS time server will automatically convert the time format into UTC.

A GPS time server can provide unbridled accuracy with networks able to maintain accuracy to within a few milliseconds of UTC.

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.

GPS Time Server – Utilising Satellite Navigation as a Timing Source

Satellite navigation has been around for the last few decades courtesy of the American military controlled GPS system (Global Positioning System). The GPS network is currently the World’s only GNSS (global navigation satellite system, although Europe, Russia and China are developing their own.

GNSS systems like GPS are based on the same principle. A constellation of satellites orbiting the Earth each have onboard an atomic clock. These clocks are accurate to within a few microseconds and it is this time-telling accuracy that allows satellite navigation possible.

The GPS satellite continually transmits its location along with the time told by its atomic clock. It is this information that is received by a satellite navigation unit that works out how long the message took to arrive from the satellite and therefore the distance away from it. By using four or more satellites a GPS receiver can triangulate its exact position.

Atomic clocks have to be used onboard the satellites as even tiny inaccuracies in time could cause huge errors in navigation. The signals from the satellites travel at the speed of light which can manage 300,000 km every second so even a millisecond out would make the satellite navigation inaccurate by hundreds of kilometres.

Because of its accuracy, this timing signal broadcast from the onboard atomic clocks can be utilised as a source of UTC time by a GPS time server. A GPS antenna connected to a dedicated time server can synchronise a computer network to within a few milliseconds of UTC time.