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In the Open Systems Interconnection (OSI) model, the session layer is the fifth layer, which controls the connections between multiple computers. The session layer tracks the dialogs between computers, which are also called sessions. This layer establishes, controls and ends the sessions between local and remote applications.
The session layer manages a session by initiating the opening and closing of sessions between end-user application processes. This layer also controls single or multiple connections for each end-user application, and directly communicates with both the presentation and the transport layers. The services offered by the session layer are generally implemented in application environments using remote procedure calls (RPCs).
Sessions are most commonly implemented on Web browsers using protocols such as the Zone Information Protocol, the AppleTalk Protocol and the Session Control Protocol. These protocols also manage session restoration through checkpointing and recovery.
The session layer supports full-duplex and half-duplex operations and creates procedures for checkpointing, adjournment, restart and termination. The session layer is also responsible for synchronizing information from different sources. For example, sessions are implemented in live television programs in which the audio and video streams emerging from two different sources are merged together. This avoids overlapping and silent broadcast time.