Overview
NTP provides Coordinated Universal Time (UTC) including scheduled leap second adjustments. No information about time zones or daylight saving time is transmitted; this information is outside its scope and must be obtained separately.
NTP uses Marzullo's algorithm and is designed to resist the effects of variable latency. NTP can usually maintain time to within tens of milliseconds over the public Internet, and can achieve 1 millisecond accuracy in local area networks under ideal conditions.
As of June 2010, the current reference implementation is version 4 (NTPv4), which is a proposed standard as documented in RFC 5905. It succeeds version 3, specified in RFC 1305.
The protocol uses the User Datagram Protocol (UDP) on port number 123.
Read more about this topic: Network Time Protocol