Centralized Clock Synchronization Algorithm: Berkeley Algorithm
The Berkeley algorithm is an averaging scheme based on a single master. The master polls every slave for time value and on receipt of the same computes an average discarding the outliers. The correct value is sent to all slaves for adjustment of local clocks.
Decentralized Clock Synchronization:
Network Time Protocol (NTP)
Network Time Protocol (NTP) uses a hierarchy of multilevel servers exchanging time information for synchronization. Figure 2.6 illustrates this between two levels of servers i,i + 1.
The server at level i communicates a time value T1 to the server at level i + 1. If the offset between the two timelines is 5 and the latency of communication is L and T2 is the instant at which the server at level i + 1 receives this communication, then the following holds from Figure 2.6:
External clock synchronization: Network Time Protocol (NTP).
Substituting the value of T1,T2 from Equations 2.18 and 2.19 in Equation 2.20 yields
which is independent of the offset between the timelines of the two servers.
The term L + L represents the round-trip message transmission latency between the two servers on the network. If the interval 0 is known, then the accuracy of synchronization depends on the value of the round-trip message passing latency only.