Application Layer(Layer 7) of OSI model

Ø  Provides a user interface for the users to interact with application services or network services.

Ø  For example : Web browser etc

Ø  It is user oriented layer.

Ø  It is the 7^th layer of OSI reference model.

Ø  It is considered as software layer because most of the things happens inside the protocol or inside application program.

Ø  Application layer is the top most layer in OSI and TCP/IP layered model.

Ø  Application layer is where the actual communication is initiated and reflects. Because this layer is on the top of the layer stack, it does not serve any other layers.

Ø  Application layer takes the help of Transport and all layers below it to communicate or transfer its data to the remote host.

Ø  When an application layer protocol wants to communicate with its peer application layer protocol on remote host, it hands over the data or information to the Transport layer. The transport layer does the rest with the help of all the layers below it.

Specific Services

Ø  Network virtual terminal: A network virtual terminal is a software version of a physical terminal, and it allows a user to log on to a remote host. To do so, the application creates a software emulation of a terminal at the remote host.

Ø  File transfer, access, and management: This application allows a user to access files in a remote host (to make changes or read data), to retrieve files from a remote computer for use in the local computer, and to manage or control files in a remote computer locally.

Ø  Mail services. This application provides the basis for e-mail forwarding and storage.

Ø  Directory services. This application provides distributed database sources and access for global information about various objects and services.

Example of Understanding Application Layer Services:

Ø  An Application: Installed at the client side, usually meant to Request data from a Servers. Hence, PC’s Applications receive data from servers.

Ø  A Service: Installed at the Server side, usually meant to Receive requests from Client’s Application. Hence, Server’s Services respond to clients request with required data.