Presentation Layer (Layer 6)

The presentation layer's basic function is to convert the data intended for or received from the application layer into another format. Such conversion is necessary because of the way in which data is formatted, so it can be transported across the network. This conversion is not necessarily readable by applications. Some common data formats handled by the presentation layer include the following:

  • Graphics files JPEG, TIFF, GIF, and so on are graphics file formats that require the data to be formatted in a certain way.

  • Text and data The presentation layer can translate data into different formats such as American Standard Code for Information Interchange (ASCII) and the Extended Binary Coded Decimal Interchange Code (EBCDIC).

  • Sound/video MPEGs, QuickTime video, and MIDI files all have their own data formats to and from which data must be converted.

Another very important function of the presentation layer is encryption, which is the scrambling of data so that it can't be read by anyone other than the intended recipient. Given the basic role of the presentation layerthat of data-format translatorit is the obvious place for encryption and decryption to take place.

Application Layer (Layer 7)

In simple terms, the function of the application layer is to take requests and data from the users and pass them to the lower layers of the OSI model. Incoming information is passed to the application layer, which then displays the information to the users. Some of the most basic application-layer services include file and print capabilities.

The most common misconception about the application layer is that it represents applications that are used on a system such as a Web browser, word processor, or a spreadsheet. Instead, the application layer defines the processes that enable applications to use network services. For example, if an application needs to open a file from a network drive, the functionality is provided by components that reside at the application layer.