Instances of the application layer first agree how the data to be exchanged is to be structured and which data types and values are to be used. This agreement in the form of a command set is called abstract transfer syntax. A corresponding description language is Abstract SyntaxNotation One, ASN.1, a standard proposed by ISO. The representation layer has the task of transferring the file units while preserving their information content. The instances of the representation layer make agreements on a concrete transfer syntax. The mapping between abstract and concrete transfer syntax is called the representation context. Examples of implemented presentation layer protocols are CCITT 's T.73 document architecture and EHKP-6 for screen text.
According to DIN, the description for the presentation layer is as follows: The presentation layer provides means of expression (e.g., character set, attributes) that enable application instances to name terms unambiguously and specifies the rules in the presentation protocol for how information presented in the common language is to be exchanged.