This layer is responsible for ensuring that information is presented to the eventual user in a meaningful manner. Whereas the lower layers are solely interested in moving bits reliably from point to point the Presentation Layer is concerned with the syntax or representation of the data in the network. It should be made clear that this layer is not concerned with the semantics or meaning of the data.

For instance, it is responsible for accepting data of a specified type (character or integer) from the application layer and passing it on to the session layer in a suitable format (ASCII or signed bit).

The Presentation Layer is also concerned with other aspects of information representation. Typical examples are data compression, used to reduce the number of bits that have to be transmitted, and cryptography, frequently required to ensure privacy and authentication.

In essence it provides for a common representation to be used between applications, thus making applications independent of syntax. The applications can use any syntax and the Presentation provides the transformation between these syntaxes and a common syntax.

Services provided to the Application Layer

• Transformation of syntax - This is concerned with code and character set conversions and the layout of the data (on for example a VDU screen).
• Selection of syntax

Below are some of the functions available in the Presentation Layer:

• Data transfer
• Transformation of syntax
• Negotiation and renegotiation of syntax

Layer six in the Reference Model, the Presentation Layer, fulfills the requirement for identifying and agreeing the common syntax to be used between two applications.