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Showing posts from January, 2009

Application Layer - Seventh Layer in OSI Reference Model

Application Layer is the seventh layer in Open System Interconnection (OSI) Reference Model. The function of the Application layer is to present data to users by enabling direct interaction between user and software applications. In simple words, the major function of the Application layer in the OSI Reference Model is to provide a user interface. The user interface can be either a command line based or GUI based. GUI based user interface is used in a web browser and Command Line Interface(CLI) is used in Routers and Switches (IOS high-end Routers and Switches).

Application Layer Protocols
A set of protocols are working on the application layer. These application layer protocols are classified into two.

Common Application Specific Elements (CASE)Specific Application Specific Elements (SASE)
The major Application Layer protocols are:

TelnetFile Transfer Protocol (FTP)Simple Mail Transfer Protocol (SMTP)FTAMHTTPDHCPNFSPOP3NNTPIRC
OSI Seven Layer Structure Physical layer

Data link layer


Presentation Layer - Sixth Layer in OSI Reference Model

Presentation Layer is the sixth layer in Open Systems Interconnection (OSI) Reference Model. The presentation layer is responsible for how data is presented to the user. Presentation of various forms of information like graphics, text, audio, video etc in various forms to the user is the major duty of this layer. Data encryption is also one of the functions of the presentation layer to ensure data security. The presentation layer is working as the intermediate between the Application layer and Session layer in OSI Reference Model.

How Information is Presented in the Presentation layer

Text information is presented in either ASCII or EBCDIC form to the user. In the case of graphical information, we can see various standards to present it to the user. Some examples are JPEG, BMP, GIF etc.

Functions of Presentation Layer
Three functions of the presentation layer are:

Encryption and DecryptionCompressionTranslation
As we can see the presentation layer is responsible for data encryption and …