Presentation Layer Page

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Overview

What is the Presentation Layer?

The presentation layer is concerned with the representation (syntax) of the data in the messages associated with an application during the transfer between two application processes. The aim is to ensure that the messages exchanged between two application processes have a common meaning - known as shared semantics - to both processes. The presentation layer is also concerned with data encryption and data security.

We deal with the following aspects of the presentation layer:

OSI Definition of Presentation Layer and ISO Presentation Service

A quick run through the OSI Definition of the Presentation Layer, outlining among other things the services provided by the presentation layer and the functions of the presentation layer. The ISO Presentation Service is covered in detail.

ISO Presentation Protocol and Concepts

Presentation Layer Concepts and the ISO Presentation Layer. There is no mention of data encryption here because the actual presentation protocol is concerned only with the syntax of messages during their transfer across the network.

Abstract Syntax and Transfer Syntax

Application exchanges involve transmitting data structures which may be complicated. OSI introduced the notion of abstract syntax and transfer syntax. Included is a comparison between BER (Basic Encoding Rules) and Sun Microsystems' XDR (External Data Representation).

Data Encryption and Data Compression

Data Encryption is used to prevent listening or masquerading. In the context of the OSI Reference Model, the most appropriate layer to perform such encryption is the presentation layer. Data compression is done if required.

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David Smith / dpsmith@tcd.ie