Layer 5 of the Open Systems Interconnection (OSI) reference model, which enables sessions between computers on a network to be established and terminated.
The session layer does not concern itself with issues such as the reliability and efficiency of data transfer between stations because these functions are provided by the first four layers of the OSI reference model.
The session layer is responsible for synchronizing data exchange between computers, structuring communication sessions, and other issues directly related to conversations between networked computers.
The session layer is also responsible for name recognition functions at the level of logical network names and for assigning communication ports. For example, the NetBIOS protocol is considered to run at the session level.
The session layer of the OSI reference model is not widely implemented in common local area network (LAN) protocol suites such as TCP/IP and IPX/SPX. Instead, the top three layers of the OSI model - the application layer, presentation layer, and session layer - are often thought of best as a homogeneous whole subsumed within a generalized application layer.