This layer is essentially a translator and provides coding and conversion functions. A successful data-transfer technique is to adapt the data into a standard format before transmission. Computers are configured to receive this generically formatted data and then convert the data back into its native format for actual reading (for example, EBCDIC to ASCII). By providing translation services, the Presentation layer ensures that data transferred from the Application layer of one system can be read by the Application layer of another one.
The OSI has protocol standards that define how standard data should be formatted. Tasks like data compression, decompression, encryption, and decryption are associated with this layer. Some Presentation layer standards are involved in multimedia operations too.
The Presentation Layer is composed of two sublayers:
- CASE (Common Application Service Element)
- SASE (Specific Application Service Element)
CASE
The CASE sublayer provides services for the Application Layer and request services from the Presentation Layer. It provides support for common application services, such as:- ACSE (Association Control Service Element)
- ROSE (Remote Operation Service Element)
- CCR (Commitment Concurrency and Recovery)
- RTSE (Reliable Transfer Service Element)
SASE
The SASE sublayer provides application specific services (protocols), such as- FTAM (File Transfer, Access and Manager)
- VT (Virtual Terminal)
- MOTIS (Message Oriented Text Interchange Standard)
- CMIP (Common Management Information Protocol)
- JTM (Job Transfer and Manipulation) a former OSI standard
- MMS (Manufacturing Messaging Service)
- RDA (Remote Database Access)
- DTP (Distributed Transaction Processing)
- Tel Net(a remote terminal access protocol)
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