Layer 5 - Session layer

The Session layer manages the communications between the workstation and network. The Session layer directs the information to the correct destination and identifies the source to the destination. The Session layer identifies the type of information as data or control. The Session layer manages the initial start-up of a session and the orderly closing of a session. The Session layer also manages Logon procedures and Password recognition and permissions. See Fig. 1.

Figure 1

The Session layer is concerned with managing the communications. Does the source have rights and permissions to access the destination? Is the destination alive and present? The session layer will periodically check to see if the both the source and destinations are still operating and will timeout if no communications has been seen for a while.

At this point, the data is contiguous and complete at this point (one large data file).

Remember, the OSI model is a theoretical model constructed to understand how protocols interconnect in a multiprotocol environment. Layer 5 is not clearly defined in many protocols. For example, the TCP/IP protocol's Application layer incorporates the functions of the Layer 6 - Session layer.

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Copyright July 2013 Eugene Blanchard