What OSI layer corresponds to the Transport Layer?

The Transport Layer is defined as Layer 4 in the OSI (Open Systems Interconnection) model. This layer is responsible for providing end-to-end communication services for applications. It ensures that data is transferred from one host to another reliably and without errors. Functions of the Transport Layer include segmentation of data from the Session Layer above it, establishing connections, and managing the flow of data, which can include both connection-oriented and connectionless communication protocols.

Protocols such as TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) operate at this layer. TCP, for instance, provides reliable data delivery through its mechanism of error checking, retransmission, and flow control, while UDP allows for faster transmission with less overhead but without guarantees of reliability.

In contrast, the other layers mentioned—Layer 1 pertains to the Physical Layer, which deals with the transmission of raw bit streams over a physical medium; Layer 3, known as the Network Layer, is responsible for packet forwarding including routing through different routers; and Layer 5, which is the Session Layer, manages sessions and controls the dialogues between computers. Therefore, the designation of Layer 4 is specifically reserved for the Transport Layer and its critical role in network communication.