Explain the functions of Presentation Layer.

The functions of the presentation layer are as follows:

  • It provides the users with a way to execute the session service primitives. For that, it uses the contexts, each consisting of some data types and their transfer syntaxes. When a session is established, the peer entities negotiate for one or more contexts. It can change these contexts as the session progresses.
  • Once the negotiations have been agreed upon, each machine is free to represent the data structures internally in the most convenient form. It is known that it should express that it can be transmitted and understood by the remote peer entity even if a different internal representation is used there.
  • It provides a way to specify complex data structures. The presentation layer provides services dealing with the representation of data. It accepts data types from the application layer and then negotiates for the syntax representation like ASCII, Videotex, teletype etc.
  • The layer also contains Abstract syntax negotiation as a language (ASN.I), which describes data structure and syntax. The layer manages the set of data structures currently required. It also converts data between internal and external forms. It uses data representations and data compression to perform this function.
  • It provides an establishment and release of the presentation connection. A particular functional unit, 'kernel', is used to establish and release the presentation connection. It is a unit that is always required. The negotiation of the defined ontext set and default context is done during the connection establishment phase. These negotiated contexts are used throughout the life of the connection
  • The presentation entities can modify the defined context set. This can be done only if the context management functional unit is chosen to establish the connection. During the connection, the user application entities inform the new abstract syntax to be added, deleted or changed, and the presentation entities negotiate the common transfer syntax. Such needs are in various situations. For example, if a file is required to be accessed which has a different syntax etc.
  • If a resynchronization occurs at the session layer, it must restore the defined context, and the presentation layer can do it. It chooses the context restoration functional unit for this function.
  • The presentation layer also encodes the defined abstract syntax into common transfer syntax. It uses various encoding and decoding rules/methods for that. The set of encoding and decoding rules are defined in ISO 8825, Specification of Basic Encoding Rules for ASN.1. They use a Type-Length-value form of encoding.
  • The presentation layer also provides privacy and network security by using end to end encryption. The encryption makes the data unintelligible to all but their intended recipient.
  • Using encryption can protect the data from being read by unauthorized persons. It also prevents them from inserting or deleting messages. It verifies each message’s sender and also makes it possible for users to send signed documents electronically.

Updated on: 04-May-2021


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