Telnet uses the TELNET protocol, specified in RFC 854, to connect to a remote computer that is running telnet server software over the network. It provides a two-way communication facility that allows terminal devices and terminal-oriented processes to communicate with each other. Telnet uses TCP to transmit data and telnet control information. The default port for telnet is TCP port 23.
RFC 854 states: "The Telnet Protocol is built upon three main ideas: first, the concept of a 'Network Virtual Terminal;' second, the principle of negotiated options; and third, a symmetric view of terminals and processes."