In early 1980s,the International Standards Organization (ISO),developed the OSI (Open System Interconnect -ion) reference model.

The OSI model consists of 7 layers and it works on a layer approach,where each layer is responsible for performing certain function,like error control.

Between hosts,each layer communicates to its corresponding layer on the other machine,but only thorough the lower layers on both machines.

The seven layers of the OSI Reference Model are:

7.Application Layer

This is the layer at which communication partners are identified,quality of service is identified,user authentication and privacy are considered.The Application layer represents the level at which applications access network services.

This layer is not  application itself,although some applications may perform application layer functions.

6.Presentation Layer

This is the layer that converts incoming and outgoing data from one presentation format to another.Sometimes called also the Syntax layer,

(It describes the syntax of data being transferred).

5.Session Layer

Session layer allows two applications to establish,use and disconnect a connection between them called a session.

Session layer provides for name recognition and additional functions like security, which are needed to allow applications to communicate over the network.

4.Transport Layer

Transport layer provides end-to-end control.

This layer ensures complete data transfer,also it defines if and how retransmissions will be used to ensure data delivery.

3.Network Layer

This layer handles the routing of the data (sending it in the right direction to the right destination on outgoing transmissions and receiving incoming transmissions at the packet level).The network layer does routing and forwarding.

2.Data-Link Layer

This layer provides reliable transit of data across a physical link.Data-Link layer defines the framing,addressing,network topology,error notification,flow control.

1.Physical Layer

The physical layer is primarily concerned with transmission of bits.

It also defines the cable or physical medium itself.