network time protocol (Internet) (NTP)
The Network Time Protocol(NTP) is a synchronization protocol used to synchronize the time in distributed servers and clients of the Internet. The NTP protocol is implemented by synchronized time servers located at various points on the Internet. In this hierarchical model, multiple reference sources are connected as time servers at various network access points.
The time server hierarchy divides the time servers into up to 15 different levels, which differ in their time accuracy. The higher the hierarchy level, the more precise the accuracy. The master clocks are subject to a complex evaluation. They receive their reference time from the GPS system or from a highly stable internal clock.
As a time server protocol, the NTP protocol handles the synchronization between the primary and the subordinate time servers. The transport protocol used for data transport is the User Datagram Protocol( UDP). The resulting common time base is used for some applications, such as some authentication systems. The simpler version of the NTP protocol is called Simple Network Time Protocol( SNTP).
The Network Time Protocol (NTP) was specified by the Internet Engineering Task Force ( IETF) and is described in RFC 1305.