Which OSI layer is responsible for maintaining connections between systems?

The Session Layer is responsible for maintaining connections between systems, managing sessions in a network. It establishes, maintains, and terminates connections between applications at each end of the communication process. This layer ensures that sessions are properly initiated and terminated, allowing for organized communication. It controls the flow of data, helps manage dialogues (such as half-duplex or full-duplex), and keeps track of which user is talking to which application, thus ensuring that the connections remain stable and reliable during the session.

In contrast, the Transport Layer focuses on the end-to-end communication between systems, providing services like segmentation and flow control, but does not specifically manage sessions. The Network Layer is primarily responsible for routing data packets between devices across different networks, while the Data Link Layer deals with MAC addresses and error detection/correction on a local network segment. Each of these layers plays a critical role in the OSI model, but only the Session Layer is dedicated to the maintenance and management of sessions between systems.