The Session layer is responsible for dialog control between devices. It establishes, maintains, and terminates session between applications, as well as data transfer control between processes and management. It organizes communication between two presentation layer systems with three modes: simplex, half-duplex, and full-duplex. It splits a session into three phases: connection establishment, data tranfer, and connection release, which enables coordination of the requests and responses that result from the communication of different hosts. E.g. NFS, RPC, SQL, X Windows.