ISO OSI.Layers3

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The Session layer is responsible for setting up, managing, and then tearing down sessions between Presentation layer entities. The Session layer also provides dialog control between devices, or nodes. It coordinates communication between systems and serves to organize their communication by offering three different modes: simplex, half-duplex, and full-duplex. The Session layer basically keeps different applications’ data separate from other applications’


The following are some examples of Session-layer protocols and interfaces (according to Cisco):

Network File System (NFS) Was developed by Sun Microsystems and used with TCP/IP and Unix workstations to allow transparent access to remote resources.

Structured Query Language (SQL) Was developed by IBM to provide users with a simpler way to define their information requirements on both local and remote systems.

Remote Procedure Call (RPC) Is a broad client/server redirection tool used for disparate service environments. Its procedures are created on clients and performed on servers.

X Window Is widely used by intelligent terminals for communicating with remote Unix computers, allowing them to operate as though they were locally attached monitors.

AppleTalk Session Protocol (ASP) Is another client/server mechanism, which both establishes and maintains sessions between AppleTalk client and server machines.

Digital Network Architecture Session Control Protocol (DNA SCP) Is a DECnet Session-layer protocol.