OSI model, 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.225 or 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.

Within the service layering semantics of the OSI network architecture, the session layer responds to service requests from the presentation layer and issues service requests to the transport layer.

Services

• Authentication
• Authorization
• Session restoration

Protocols

• ADSP AppleTalk Data Stream Protocol
• ASP AppleTalk Session Protocol
• H.245 Call Control Protocol for Multimedia Communication
• ISO-SP OSI session-layer protocol (X.225, ISO 8327)
• iSNS Internet Storage Name Service
• L2F Layer 2 Forwarding Protocol
• L2TP Layer 2 Tunneling Protocol
• NetBIOS Network Basic Input Output System
• PAP Password Authentication Protocol
• PPTP Point-to-Point Tunneling Protocol
• RPC Remote Procedure Call Protocol
• RTCP Real-time Transport Control Protocol
• SMPP Short Message Peer-to-Peer
• SCP Session Control Protocol
• SOCKS the SOCKS internet protocol, see Internet socket
• ZIP Zone Information Protocol
• SDP Sockets Direct Protocol