Application Layer of the OSI Model

The seventh layer of the OSI model. It provides a means for the user to access information on the network using an application. It also supports services such as electronic mail, remote file access and transfer and shared database management.

Services provided by application layer are:

Network Virtual Terminal - It is a software version of physical terminal. Using this software the user can log on to a computer that is remotely connected on the network. The application layer emulates a terminal at the remote host. When the user's computer wants to communicate with the remote host, it communicates with the virtual terminal that converts the data in the intermediary format used by the virtual terminal and sends it to the remote host. After processing the data the remote host replies to the terminal in the reverse order.

File Transfer, Access and Management (FTAM) - Using this application user can access files (to make changes) in a remote host. It also enables the user to retrieve and manage files from a remote computer so that the files can be used on a local computer.

Mail Services - Using this application e-mails can be forwarded to another device. Message handling system (MHS) is the OSI protocol used to transfer mail over the internet.

Directory Services - Another service provided by the Application layer is directory services. A directory is a source of information about objects such as people, organizations, programs and files. These objects are managed by directory services.

Summary of Layers

Each layer in the OSI model performs distinct functions on the data in accordance with the previous layer functions. Layers accept functions from the below layer and transfer the functionality to the layers above. The functions of the layers in the OSI model can be summarized as below:

• User information is converted into data in the upper layers

• Data is converted into segments in the transport layer

• Segments are converted into packets in the network layer

• Packets are converted into frames in the data link layer

• Frames are converted into bits in the physical layer

You may also be interested in understanding the other seven layers of the OSI Model

Presentation Layer of the OSI Model

Session layer of the OSI Model

Transport Layer of the OSI Model

Network Layer of the OSI Model

Data Link Layer of the OSI Model

Physical Layer of the OSI Model