Cristian's algorithm

Cristian's algorithm is a method of clock synchronization introduced by Flaviu Cristian in 1989. It is used in distributed computing and is primarily suited to low-latency intranets. A process asks a time server, which is connected to a time reference source, for the current time. The server replies with a reading from its own clock, and the process sets its clock to that reading plus half of the measured round-trip time. The result is error-free only when the delay is split equally between request and reply, which unpredictable influences often prevent, so the algorithm is probabilistic and achieves good synchronization only when the round-trip time is short compared with the required accuracy. Accuracy can be improved by choosing the best round-trip times from many request and reply pairs. Because it relies on a single server it is unsuitable for applications where redundancy is crucial.