What does Layer 4 (Transport) primarily manage in the OSI model?

Layer 4 of the OSI model, known as the Transport Layer, is primarily responsible for ensuring the reliable delivery of data between systems. This layer facilitates data reliability through mechanisms such as error detection and correction, which helps guarantee that the data sent reaches its destination without errors. Additionally, the Transport Layer is tasked with flow control, which manages the rate of data transmission between sender and receiver to prevent overwhelming either party, ensuring a smooth and efficient communication process.

The other aspects associated with the Transport Layer, such as packet segmentation and reassembly, are also critical, but they are considered part of the overall reliability and management of data flow. While session initiation and termination are important tasks, they are the domain of Layer 5 (Session Layer) rather than Layer 4. Similarly, frame relay and addressing pertain more to the Data Link Layer (Layer 2) and the Network Layer (Layer 3) in terms of data communication and routing. Therefore, the focus on data reliability and flow control accurately captures the primary functions of Layer 4 within the OSI model.