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.