(Or connection-based, stream-oriented). A type of transport layer data communication service that allows a host to send data in a continuous stream to another host. The transport service will guarantee that all data will be delivered to the other end in the same order as sent and without duplication. Communication proceeds through three well-defined phases: connection establishment, data transfer, connection release. The most common example is Transmission Control Protocol (TCP).
Opposite of connectionless, datagram. See also circuit switching, packet switching, virtual circuit.