Why a GPS Time Server

Just as your computer is only as good as the software it is running (and in most cases the operator too), a time server is only as useful as the timing source it uses.

Accuracy is of course the fundamental feature in time servers and Network Time Protocol (NTP) has been designed to ensure the highest accuracy possible is always obtainable.

Unfortunately many administrators opt to use an Internet timing source to run their time server with. Unfortunately several studies of Internet timing references discovered that nearly two thirds were inaccurate by over several seconds (almost an eternity in the world of NTP) and those that weren’t were often too far away from a client to provide reliable accuracy.

Probably the most accurate and widely used method of retrieving a reliable time reference is to use a dedicated GPS Time Server.

The Global Positioning System is ideal to provide an accurate timing reference as each global positioning satellite contains an atomic clock that beams timing information directly to Earth. As these satellites are in a relatively low and known orbit the distance the signal travels can be compensated for by the GPS time server ensuring a high level of accuracy.

Another benefit is that a GPS time server will always be able to receive a signal no matter where in the world it is situated as long as the GPS antenna can have a clear view of the sky, enabling it to communicate with a satellite.

A GPS time server are also relatively inexpensive and advances in GPS technology means the costs are perennially falling. There is a downside to a GPS server in that to ensure the antenna can spot a satellite it needs to be situated  on certain buildings this can be expensive, impractical or even impossible as the maximum cable length should never exceed 100 metres.

The NTP Choice – GPS Time Server or Radio Receiver

NTP (Network Time Protocol) has been around for a long time now. First conceived in the early eighties it has been providing synchronisation for over 25 years.

Many people assume that because they are running NTP then their networks are perfectly synchronised and running accurate UTC time (UTC – Coordinated Universal Time – the world’s standard timescale).

However, NTP is a protocol designed for synchronisation and does just that it synchronises. NTP can synchronise time from an atomic clock that doesn’t lose more than a second every million years or so or to a cheap plastic wrist watch that runs a minutes slow each week. A time server is therefore only as good as the timing reference that it uses to synchronise to.

Many administrators select a timing source from the Internet and automatically assume that their server is running accurate UTC time. However, many Internet timing sources are wholly inaccurate and those that are not can often be too far away from a client to provide any hope of an accurate time source, not to mention the fact that Internet timing references can’t be authenticated and can leave a system open to a malicious attack.

Fortunately there are two methods that can provide both accurate and secure timing information to a time server. The first method is to use a radio referenced time server. These simple pieces of kit receive the national time and frequency transmission that many countries broadcast. This signal can be picked up usually within a 1000km of the transmitter and provides accuracy to within a few milliseconds. unfortunately places outside the transmission’s country of origin or areas with topographical features such as mountains may struggle to receive a signal.

Fortunately a GPS time server can receive a signal anywhere on Earth as long as the antenna can see a patch of blue sky. Also a GPS time server provides slightly better accuracy than a radio referenced one. They are also relatively inexpensive, however, the antenna does normally have to go to the roof which can bring with it its own costs.

Galileo – GPS Time Server Implications

In the field of high precision time keeping and frequency measurement the Global Positioning System (GPS) has had its own way for a long time.

The signals broadcast by the American Military’s Global Satellite Navigation System (GNSS) has provided timing references since the late 1990’s and is used worldwide as a timing source in hundreds of thousands of GPS time servers. Now GPS is to receive competition from not just the proposed European Galileo system but the Russians and Chinese are attempting to get into the act.

Currently the GPS is the world’s only fully functioning, global navigation satellite system, however, the European Union and European Space Agency agreed in 2002 for a European alternative called Galileo which is scheduled to be fully operational by 2012-2013.

The Russian Glonass system, which was fully operational during the height of the Cold War but had fallen into disrepair after the collapse of Soviet Union, has also been vowed to be patched up and to be fully operational again by 2010. A Chinese system called Compass is also being developed although some doubt exists as to whether it will be a stand alone system or be incorporated into Europe’s Galileo network, India have also proposed there own system.

Galileo which is expected to work alongside the GPS system providing timing references from 2013. The broadcasts will be similar to those currently received by a GPS time server and the two systems should work well together as Galileo is designed to be interoperable with GPS.

This means there will be close correspondence between the signals from the two systems, and most of the frequencies used by the Galileo satellite signals will be similar to GPS signals. This will  increase accuracy of Galileo as well as increasing the capabilities of GPS as only minor software alterations will be needed for a  current GPS time server to be able to locate Galileo satellites too. The great advantage of this is that it will be able to see around twice as many satellites providing better accuracy

Although Galileo is intended to have somewhat better positioning and timing performance than the current GPS system, the difference will be reduced or even disappear with a planned modernisation of GPS, designed to ensure the US system doesn’t lag behind the next generation.

Galileo is expected to be fully operational, by 2013, with timing and positioning signals available at the same time.

Benefits of a GPS Time Server

The American GPS system is currently revolutionising the way we navigate. Once a secretive Cold War military weapon it now adorns the dashboards of one in three cars.

But GPS is much more than a handy navigational tool. The constellation of 24 satellites each contain some of the world’s most accurate chronometers in the shape of atomic clocks. These provide such accuracy in timing that a million years could pass and not even a second would have been gained or lost

These clocks are what enable us to pinpoint our location on Earth as a GPS receiver can workout how long the timing signal took to reach it and therefore how far away from the satellite it is. Using three or four satellites means an exact location can be pin-pointed by triangulation. Atomic clocks need to be used as just one seconds inaccuracy could mean a location could be hundreds of thousands of miles out because of the vast distances radio signals can travel in that time.

These timing signals can also be utilised to provide extremely accurate synchronisation for computer networks by receiving the timing signal via a GPS antenna connected to a GPS time server. A GPS time server uses NTP (Network Time Protocol) to synchronise machines on a network.

Because of the accuracy of the atomic clocks a GPS Time Server can obtain an accuracy to within a few hundred nanoseconds of UTC time (a nano is one billionth of a second)

UTC (Coordinated Universal Time) is a global timescale developed after the invention of the atomic clock. It is a standardised time scale base on Greenwich Meantime but allows for the minute slowing of the Earth’s rotation (caused by the Moon’s gravity).

A GPS time server can also receive a timing signal from anywhere in the world (as long as it can get a clear view of the sky)

Accuracy in Timekeeping – Using a GPS Time Server

Computer time synchronisation is becoming more and more important as we become ever reliant on the Internet for our day-to-day business.

Whether it doing the shopping from our PC at home or whether we work in a global trading company. The Internet is fast becoming the world’s new high street.

Time synchronisation is therefore more vital and relevant today than it has ever been. Time synchronisation errors are commonplace, just check your inbox you may find that email that has just arrived may technically not have been sent yet. This may not cause you any problems but what happens if you book and airline ticket on a computer system that is not synchronised?  You may find the plane seat has been sold after you had bought it or you could have the last bid on an Internet auction site only to find somebody else wins the lot because their earlier bid was on a computer with a faster clock.

In some industries time synchronisation is not only essential, but without it trading would become impossible, just think of the stock exchange where millions are won and lost in seconds.

Fortunately time synchronisation is not the headache it used to be. It is now possible to connect to an accurate UTC (Coordinated Universal Time – a global standardised time scale based on the time told by atomic clocks) time source with relatively low cost equipment.

A GPS time server is a relatively inexpensive and simple device that receives a timing signal directly from a global positioning satellite. Because GPS satellites contain atomic clocks (essential in providing accurate positioning) the signal of which can be picked up and used to synchronise an entire network.

A dedicated GPS time server is relatively simple and straightforward to install and comprises of a GPS receiver equipped with NTP software (network time protocol – software used to synchronise a network) and a GPS antenna. The only difficulties faced with the installation of a GPS time server is that the antenna needs a good view of the sky to ensure it can receive the satellite information.