Network Time Protocol (NTP) is a UDP protocol that provides a reliable way of transmitting and receiving the time over TCP/IP networks. It has become the de facto standard for synchronizing Internet computers and other networked devices to Universal Coordinated Time (UTC). The Internet Engineering Task Force formalized NTP in RFC 1305.
For a complete time synchronization solution client software is required to read the NTP packets generated by an NTP time server and synchronize the local clock. (see "How do I configure NTP clients" on the GPS Time Servers FAQ page)