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Computer Science
Computer Catlog
Comm Network Catlog

Network Components
Network Types
The OSI Model
Protocol Notations
Physical Layer
Transmission Media
Digitization and Synchronization
Physical Layer Standards
DataLink Layer
Error Checking
Retrans - Flow Control
Sliding Window Protocol
Data Link Layer Standards
Network Layer
Switching Methods
Congestion Control
Network Sub layers
Transport Layer
Transport Protocol
Transport Layer Standards
Session Layer
Session Layer Role
Session Protocol
Presentation Layer
Abstract Syntax Notation
Application Layer
Common Application
Specific Application
Message Handling
IEEE 802 Standards
ANSI FDDI Standard
Frame Relay
Broadband ISDN & ATM

Session Layer Role

    The exact role of the session layer in relation to other layers is worth some consideration. Although the session layer is positioned below and receives its requests from the presentation layer, its primary role is to serve the application layer by allowing applications to converse in a structured manner. The presentation layer is completely transparent to this process.

    The interface between the session layer and the transport layer is very simple. It provides for basic opening and closing of transport connections (a session connection directly maps to a transport connection) and reliable transfer of data over the connections. This simple interface is enriched by the session layer into a diverse set of services for the ultimate use by the application layer.

Session Layer

Functional Units

    It is generally rare for an application to require the use of all session services. Often a relatively small subset will suffice. To facilitate this, the session layer services are divided into 13 functional units. Each functional unit is a logical grouping of related session services. Functional units are negotiated and selected during connection establishment using the requirements parameter in the connection request. The functional units selected determine what services will be available for the duration of the session. Kernel represents the most basic set of services that applications could live with. All session layer implementations must provide this minimal subset.