The Application layer functions as a user platform in which the user and the software processes within the system can operate and access network resources. Applications and software suites that we use on a daily basis are under this layer. Common examples include protocols we interact with on a daily basis, such as FTP and HTTP.
Two mnemonics that I use to remember the order of layers are these:
- All People Seem To Need Data Processing, which uses the first letter of each layer (from the top down) as the first letter of each word in the sentence: Application, Presentation, Session, Transport, Network, Data Link, Physical.
- Please Do Not Teach Stupid People Acronyms, which does the layers in the opposite order—that is, from the ground up.