Which OSI model layer is responsible for establishing, maintaining, and terminating connections?

Correct answer: Layer 5 (Session)

Option C is correct because Layer 5, the Session layer, is responsible for establishing, managing, and gracefully terminating logical sessions between applications, including synchronization and dialog control functions such as those used by NetBIOS and RPC. Option A is wrong because Layer 6, the Presentation layer, handles data translation, encryption, and compression to ensure that data is in a usable format for the application layer, not session management. Option B is wrong because Layer 4, the Transport layer, provides end-to-end reliable or unreliable data transfer and flow control via protocols such as TCP and UDP, but does not manage application-level sessions. Option D is wrong because Layer 3, the Network layer, handles logical addressing and routing of packets between networks and has no responsibility for session establishment or termination.