ABSTRACT
This chapter describes the various Network Time Protocol (NTP) algorithms, including the filter, select, cluster, and combine algorithms that represent the heavy machinery. At the very navel of the belly are the algorithms used to groom time values from a flock of redundant servers via diverse network paths and produce the most accurate and reliable time. The particular choice of offset and delay computations used in NTP is a variant of the returnable-time algorithm used in some digital telephone networks. The NTP clock filter algorithm is designed to select the best sample data while rejecting noise spikes due to packet collisions and network congestion. The cluster algorithm sifts the truechimers of the select algorithm to identify the survivors providing the best accuracy. The result of the cluster algorithm is a set of survivors that represent truechimers or correct clocks.
