OSI Model - Network+ Certification Tutorial

The OSI (Open Systems Interconnections) Reference Model is one of the basic concepts of networks and one that you should learn for any networking exam.

The Reference Model sets up how communication should take place. The Reference Model addresses all of the communication processes that take place. These processes are broken down into logical groups called layers.

The seven layers of the OSI Reference Model are Application (7), Presentation (6), Session (5), Transport (4), Network (3), Data Link (2), and Physical (1).

Application Layer

The Application Layer is the layer at which software programs communicate with each other and establish communication. It synchronizes sending and receiving between programs. It also determines if sufficient resources exist for communication. The corresponding devices are gateways.

Popular Application Layer protocols include WWW, FTP, Telnet, SMTP.

Presentation Layer

The Presentation Layer controls the conversion of information from the Application Layer. It is also responsible for encryption, data compression and decompression. The corresponding devices are gateways.

Presentation Layer standards include JPEG, PICT, TIFF, MPEG, and ASCII.

Session Layer

The Session Layer is responsible for establishing and maintaining communications sessions. These communications are coordinated between protocols at this layer. The corresponding devices are gateways.

Session Layer protocols include Appletalk Session Protocol, NetBEUI, XWindows, NFS, SQL, RPC.

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