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.