SESSION LAYER
The session layer provides the mechanism for opening, closing and managing a session between end-user application processes, i.e., a semi-permanent dialogue. Communication sessions consist of requests and responses that occur between applications. Session-layer services are commonly used in application environments that make use of remote procedure calls (RPCs).
An example of a session-layer protocol is the OSI protocol suite session-layer protocol, also known as X.225or ISO 8327. In case of a connection loss this protocol may try to recover the connection. If a connection is not used for a long period, the session-layer protocol may close it and re-open it. It provides for either full duplex or half-duplex operation and provides synchronization points in the stream of exchanged messages.
This layer is very much important for exchange of messages in the form of stream ,it basically depends on requests and responses in network traffic.
Other examples of session layer implementations include Zone Information Protocol (ZIP) – the AppleTalkprotocol that coordinates the name binding process, and Session Control Protocol (SCP) – the DECnetPhase IV session-layer protocol.
Within the service layering semantics of the OSI network architecture, the session layer responds to service requests from thepresentation layer and issues service requests to the transport layer.
When a website says session expires ,it means communication with server through this not possible and again should be refreshed.
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