Layer 5. The Session Layer

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This functions as an interface between the hardware (the bottom four layers) and the software (the top two layers). This layer is the "dialog manager." The Transport Layer directs the data stream, but it is the Session layer that controls how data flows. It negotiates and creates a connection between two Presentation Layers when requested, then controls the data flow. More technically, it establishes, maintains and otherwise controls the use of the basic communications channels provided by the Transport Layer, by setting up, coordinating, and terminating conversations, exchanges, and dialogs between the applications at each end. It handles session and connection coordination. A session establishes the connection between communicating devices, providing synchronization, security authentication, and network naming. Protocols that function at this layer include RPC, XNS and LDAP. This layer is often combined with the Transport Layer.

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