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Layer 5: Session

A person switching between two telephone conversations.  Source: Microsoft.

The Session layer allows two applications on different computers to open, use, and close a connection, i.e. a session. A session is a highly structured dialogue between two workstations. The session layer is responsible for managing this dialogue. It performs name recognition and other functions, such as security, that are needed to allow two applications to communicate over the network.

The Session layer synchronises user tasks by placing checkpoints in the data stream. The checkpoints break the data into smaller groups for error detection. This layer also implements dialogue control between communicating processes, such as regulating which side transmits, when, and for how long. Common protocols used by the session layer include RPC, SQL and NetBIOS names.

Layer 5 PDU: Data

Next: Layer 4: Transport