What is the stratum?
The stratum is a measure for synchronization distance. Opposed to jitter or delay the stratum is a more static measure. Basically (and from the perspective from a client) it is the number of servers to a reference clock. So a reference clock itself appears at stratum 0, while the closest servers are at stratum 1. On the network there is no valid NTP message with stratum 0. A server synchronized to a stratum n server will be running at stratum n + 1. The upper limit for stratum is 15. The purpose of stratum is to avoid synchronization loops by preferring servers with a lower stratum.
