The Network Time Protocol (NTP) is a networking protocol
for clock synchronization between computer systems over packet-switched,
variable-latency data networks. In operation since before 1985, NTP is one of
the oldest Internet protocols in current use. NTP was designed by David L.
Mills of the University of Delaware. NTP is intended to synchronize all
participating computers to within a few milliseconds of Coordinated Universal
Time (UTC). It uses the intersection algorithm, a modified version of Marzullo's
algorithm, to select accurate time servers and is designed to mitigate the
effects of variable network latency. NTP can usually maintain time to within
tens of milliseconds over the public Internet, and can achieve better than one
millisecond accuracy in local area networks under ideal conditions. Asymmetric
routes and network congestion can cause errors of 100 ms or more.