The OSI Application Layer
The Application layer, layer seven of the OSI model, provides the interface between
applications and the Network Operating System (NOS). The Application layer provides
network services and applications such as HTTP (Hypertext Transfer Protocol), FTP (File
Transfer Protocol), TELNET, SNMP (Simple Netwrok Management Protocol) and SMTP (Simple
Mail Transport Protocol).
When you think of the Application layer, don't think in terms of applications, but
rather protocols. For example there are several different FTP applications that use
the FTP protocol at the Application layer.