GPS is generally associated with navigation. Less well known is the fact that it can also provide a very accurate source of time. Much of the internet is synchronized by GPS based time servers using the network time protocol (NTP). GPS Network Time Protocol servers utilize the Global Positioning System to provide the internet with a very accurate time reference from which a comprehensible order of events can be determined. The GPS system is a satellite based system which orbits high above the Earth. Each of the 24 satellites is positioned to provide global signal availability. Each individual satellite contains an ultra-precise atomic clock, which is periodically synchronized to a ground-based master atomic clock at USNO. The very accurate time is required by triangulation algorithms to provide positioning and navigation information but can also be used as a very precise source of time. Typically, the GPS system can provide time synchronization down to a few nanoseconds of UTC time.
Stratum 1 NTP Operation
A stratum-1 NTP server is of the highest stratum, as such it obtains time from a hardware reference clock rather than another NTP server. Lower stratum NTP servers (2 or more) are generally introduced to share the load of network time clients between multiple time servers. In this manner many stratum 2 or stratum 3 time servers may obtain time from a single stratum 1 server, but in turn serve many thousands of time clients.