The OSI Model

Keith R. Barry

Strayer University

CIS 532

The Seven Layers

• Application

• Presentation

• Session

• Transport

• Network

• Data Link

• Physical

Application Layer

• Topmost Layer

• User-interface: How the user communicates with the network

• Responsible for interprocess communication

Presentation Layer

• Performs data compression and encryption

• Essentially interprets data for use in the Application Layer

Sessions Layer

• Controls the connections/dialogues between computers on a network.

• Utilizes checkpointing, adjournment and termination procedures in both half & full-duplex to control these connections.

Transport Layer

• Provides clear, transparent transfer of data so that upper level layers do not have to concern themselves with data reliability.

• Data Packet switching is entirely handled on this layer.

• Network devices such as Routers operate on this layer.

Network Layer

• Ethernets operate on this layer.

• The Network Layer and Transport Layer can sometimes be confused; however, the Networking Layer deals with complex networking matter whereas the Transport Layer reside on the network itself.

• Routing and Routers reside on this layer.

Data Link Layer

• This Layer provides procedural and functional means to transfer data from one network entity to another.

• HDLC and ADCCP are protocols on this layer.

• Networking devices such as bridges and switches operate on this layer.

Physical Layer

• Defines all electrical and physical specifications for a device on a network.

• Devices like hubs, repeaters and network adapters operate on this layer.

• A major function of this layer is the establishment and the termination of a connection with a network.