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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. Function of Application layer is to present data to users by enabling direct interaction between user and software applications. In simple words the major function of Application layer in OSI Reference Model is to provide user interface. User interface can be either command line based or GUI based. GUI based user interface is used in 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 application layer. These application layer protocols are classified in to 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) FTAM HTTPDHCP NFSPOP3NNTPIRC
OSI Seven Layer Structure Physical layer

Data link layer

Network layer

Transport laye…

Presentation Layer - Sixth Layer in OSI Reference Model

Presentation Layer is the sixth layer in Open Systems Interconnection (OSI) Reference Model. 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 user is the major duty of this layer. Data encryption is also one of the functions of presentation layer to ensure data security. Presentation layer is working as the intermediate between Application layer and Session layer in OSI Reference Model.

How Information is Presented in Presentation layer

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

Functions of Presentation Layer
Three functions of presentation layer are:

Encryption and Decryption Compression Translation
As we can see presentation layer is responsible for data encryption and decryption. Forms of data presentatio…