Session Layer

The fifth layer of the OSI Reference Model is the session layer. The session layer is responsible for initiating the setup and teardown of connections. In order to perform these functions the session layer must determine whether data stays local to a computer or must be obtained or sent to a remote networking device.  In the later case the session layer initiates the connection. The session layer is also responsible for differentiating among multiple network connections ensuring that data is sent across  the correct connection as well as taking data from a connection and forwarding it to the correct application. The actual mechanics of this process however are implemented at the transport layer. To set up connections or tear down connections the session layer communicates with the transport layer. Remote Procedure Call (PRC) is an example of an IP session protocol the Network File System (NFS) which uses RPC is an example application at this layer.