The Transmission Control Protocol (TCP), part of the TCP/IP suite, provides reliable, flow-controlled, two-way, process-to-process transmission of data. TCP is a connection-based communication mechanism. This means that before data can be exchanged over TCP, the two communicating processes must first establish a connection through a distinct connection phase. Data is then sent and received as a byte stream at both ends.

Like UDP, TCP extends the connection address to include a port address in addition to the host Internet address. That is, a connection is established between a particular port in one host and a particular port in another host. TCP guarantees that the delivery of data is correct, in the proper order, and without duplication.