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.
