OSI Model: Application Layer and its Functions

In OSI model, application layer is the top most layer. The application layer user interface to enable user to access the network, user may be either human or software. Application layer contains communication protocols and interface to perform process to process communication on network.  Application layer acts as the user interface responsible for displaying received information to the user. Application layer supports many services such as electronic mail, remote file access and transfer, shared database system, directory services, network resource etc.

Functions of Application Layer

Network Virtual Terminal: Network virtual terminal allows user to log on to a remote host. Application creates a software emulation of a terminal at the remote host. User communicates with the software terminal which in turn communicates with the host and vice versa. The remote host assumes that it is communicating with one of its own terminals and allows user to log on.

File Transfer, Access and Management: The application layer allow user to access files in a remote host. User can make changes in files and read data from the file. 

Mail Services: The application layer provides services like E-mail forwarding and storage.

Directory Services: It provides distributed database sources and access for global information about various services.