List all seven layer of OSI model and describe function of application layer.

The layers of OSI model are as follows:

(1) The Physical Layer: It defines an interface in terms of the voltage levels, data rate, and connections in order for signals to be transmitted bit by bit.

(2) The link Layer: It provides correction for a link and error detection to make sure that the exchange of data is reliable. This may need the data stream to be divided in blocks, termed as packets, for synchronization or for inserting error-checking bits. Though, transparency is preserved for the data bits into these blocks.

(3) The network layer: It is concerned with the operation of the network among the terminals. This is responsible for establishing the corrections in between the suitable network nodes.

(4) The transport layer: It is responsible for establishing a network independent communication path appropriate for the particular terminal equipments (for example providing the suitable data rate and end-to-end error control). This therefore relieves the user from being concerned along with such details.

(5) The session layer: It is concerned with setting up and keeping an operational session among terminals. For illustration, 'signing on' at the commencement of a task and 'signing off' at its end.

(6) The presentation layer: It is concerned with the format of the data presented, so as to overcome difference in representation of the information as supplied to one terminal and needed at the other. Its reason is to make communication over the network machine-independent.

(7) The application layer: It defines the nature of the task to be performed. This supplies the user along with the applications programs required. Examples include word processing, electronic mail banking transactions and so on.