Layer 7 of the Open Systems Interconnection (OSI) reference model, in which network-aware, user-controlled software is implemented—for example, e-mail, file transfer utilities, and terminal access.
The application layer represents the window between the user and the network. Examples of protocols that run at the application layer include File Transfer Protocol (FTP), Hypertext Transfer Protocol (HTTP), telnet, and similar protocols that can be implemented as utilities the user can interface with.
Originally the OSI model consisted of two kinds of application layer services with their related protocols:
These terms have largely been replaced with the term Application Service Elements (ASE) to describe the elements of the application layer.
In most real-world networking, such as TCP/IP networking, many of these application layer services have no meaning.