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Networking Fundamentals · Foundational

Session Layer (L5)

OSI Layer 5, which establishes, manages and terminates sessions (dialogs) between applications.

Definition

The Session layer controls dialog between communicating applications, including setup, checkpointing, synchronization and teardown. Functions such as RPC session handling and NetBIOS session service are commonly associated with it. In the TCP/IP model its functions are folded into the Application layer.

Example

Restarting a large transfer from the last checkpoint instead of from the beginning is a Session-layer function.

Exam tip

Session-layer functions are folded into the TCP/IP Application layer, so a question about the four-layer model will not list a separate Session layer.

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