Which OSI layer handles communication between devices, with tasks performed by the OS when an application makes an API call?

• A. Data Link layer
• B. Transport layer
• C. Network layer
• D. Session layer

Answer: (D)

Managing ongoing conversations between two applications on different devices is the job of the Session layer. It handles establishing, maintaining, and terminating a dialogue between hosts, including who talks when and how the exchange is coordinated. When an application makes an API call to communicate, the OS typically sets up a session with the peer, negotiates dialogue rules, and inserts synchronization points so data can be resumed or coordinated if a interruption occurs. This is exactly what the Session layer is designed to do—control the conversation and keep the interaction organized throughout its lifecycle. The other layers handle different aspects: the Transport layer ensures end-to-end delivery of data, the Network layer handles routing between networks, and the Data Link layer manages node-to-node transfer on a single link.