Which protocol at the TCP/IP reference model Transport Layer ensures reliable, connection-oriented communication?

In the TCP/IP reference model, the Transport Layer plays a critical role in facilitating reliable communication between devices across a network. The Transmission Control Protocol (TCP) is specifically designed to provide reliable, connection-oriented communication. It establishes a connection between the sender and receiver before data transmission begins, ensuring that packets are delivered in order, without errors, and without duplication.

TCP accomplishes this through a variety of mechanisms, such as error checking, acknowledgment of received packets, and retransmission of lost packets. This ensures that the data sent across the network is accurate and complete.

In contrast, protocols like User Datagram Protocol (UDP) do not guarantee delivery or order of packets, instead opting for a connectionless approach that’s faster but less reliable. Likewise, Internet Control Message Protocol (ICMP) is used for error handling and diagnostics rather than data transmission, and Real-Time Protocol (RTP) is typically used for delivering audio and video over IP networks, focusing on timely delivery rather than reliable transmission.

Thus, TCP stands out in the Transport Layer of the TCP/IP model as the protocol that ensures reliable, connection-oriented communication, making it the correct answer to the question.