Any transport layer protocol that establishes a connection in order to reliably send packets over the network. Connection-oriented protocols guarantee delivery of packets by making use of acknowledgments and retransmission of data. Connection-oriented protocols are used primarily for reliable delivery of large packets of data, as opposed to the unreliable connectionless protocols that are used to deliver small datagrams.
An example of a connection-oriented protocol is the Transmission Control Protocol (TCP), which is part of the TCP/IP protocol suite. The TCP protocol uses a TCP three-way handshake to establish a connection between two hosts on a network.
During session establishment, the hosts negotiate the TCP window size, segment size, and other information needed to ensure reliable and efficient communication. A TCP connection is terminated using a similar handshake procedure.