Abbreviation for Transmission Control Protocol. In the Internet Protocol suite, a standard, connection-oriented, full-duplex, host-to-host protocol used over packet-switched computer communications networks. Note 1: TCP corresponds closely to the ISO Open Systems Interconnection–Reference Model (OSI–RM) Layer 4 (Transport Layer). Note 2: The OSI–RM uses TP-0 or TP-4 protocols for transmission control.