Session Layer | Layer 5 | The OSI-Model

OSI Layer 5 – Session Layer

In the seven-layer OSI model of computer networking, the session layer is layer 5.

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.

Other examples of session layer implementations include Zone Information Protocol (ZIP) – the AppleTalk protocol that coordinates the name binding process, and Session Control Protocol (SCP) – the DECnet Phase IV session-layer protocol.

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.

Wikipedia

Services

• Authentication

• Authorization

• Session restoration

Popular Session Layer 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

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