The presentation layer, also called the “presentation layer”, interacts very closely with the application layer that follows it. Its main mission is to present the data so that they can be understood and interpreted by the two interlocutors concerned, that is to say the system which sends and the one which receives. The application layer always begins by determining how the data should be structured and by defining the different types and values allowed.
Then it automatically creates a set of instructions or a abstract transfer syntax from this information. The objective of the presentation layer is then to transfer the data concerned in a readable manner, without however modifying the information that they contain.
A second most important mission is very often entrusted to the presentation layer, that of encrypt and decrypt data. To carry it out, one must first encrypt the data on the sender’s side and then send it in this form to the recipient. Keys and other encryption methods are therefore exchanged via the presentation layer. The recipient can thus decipher the otherwise unreadable data and view it in a format that is both understandable and usable.
The third function of the OSI presentation layer relates to the serialization of objects, managed directly by the « presentation layer ». Complex application data objects are converted for easier transfer and better storage at the recipient. This facilitates data transfer, even for the most ambitious files. The recipient can then reconstruct the object quickly and infallibly. To do this, the latter is again converted into an executable format by the application concerned. Thus, it is not necessary to integrate compression functions into the application itself.
