NTP is the
network time protocol. It's used to keep all the computers in a network syncronized to the same time source. It uses
stratums which are just trust levels to determine who has an authoritative time. The lower the number the better the trustworthiness. So a
Stratum 1 clock is the best, and it would be syncronized to a Cesium clock, or some other accurate timesource. Some very large sites will sync to Stratum 1 clocks, but if you wish to do so you need to ask permission first. Most large networks sync to one, or multiple public
Stratum 2 servers that are available.
Cheap,
accurate clocks that sync to sattalites can be bought for $3000 (US) now. But I can't remember the company that makes them.