While the OSI model separates the individual application, presentation, and session function, most widely known and implemented TCP/IP applications incorporate the functionality of all three layers.

The TCP/IP application protocols specify the format and control information necessary for many common Internet communication functions. Among these TCP/IP protocols are:

Application layer protocols are used by both the source and destination devices during a communication session. For the communications to be successful the application layer protocols implemented on the source and destination host must be compatible.