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Thursday, July 19, 2012

Presentation layer

Presentation layer is the 6th layer that we met in the OSI Reference Model. The Presentation Layer is composed of two sublayers such as CASE (Common Application Service Element) and SASE (Specific Application Service Element) This layer translates data between the formats that the network requires and the formats the computer expects.

In the same time the Presentation Layer is responsible for the delivery and formatting of information to the application layer for further processing or display. In the same time this is the layer which performs protocol conversion such as data translation, compression, and encryption; character set conversion and the interpretation of graphics commands.

The presentation layer encodes the data in various ways such as data compression, or encryption. But the receiving peer will convert the encoding back into its original meaning. If we concern about the presentation layer process we can identify that, it establishes a context between application layer entities which are the higher layer entities that can use different syntax and semantics as long as the Presentation Service understands both and the mapping between them.

Presentation layer includes,


  • Protocol
  1. LPP( Lightweight Presentation Protocol/0
  2. AFP(Apple Filing Protocol)
  3. ASCII( American Standard Code for Information Interchange)
  4. EBCDIC( Extended Binary Coded Decimal Interchange Code)
  5. NDR( Network Data Representation)
    1. X.25 PAD( Packet Assembler/Disassembler Protocol)
    2. NCP( NetWare Core Protocol)
  6. XDR,(eXternal Data Representation)
  7. ICA,(Independent Computing Architecture)

Functions & Servicers

  • Encryption and decryption of a message for security
  • Graphics formatting
  • Content translation
  • Compression and expansion of a message so that it travels efficiently
  • System-specific translation

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