The OSI Reference Model

One of the greatest functions of the OSI(Open Systems Interconnection) Specifications is to assist in data transfer between disparent hosts.

The OSI isnt't a physical model, though. Rather, its a set of guidlines that application developers can use to creat and implement application that run on a network.

The OSI have seven different layers, divided into two groups. The top three layers define how the application within the end stations will communicate with each other and with users.

The bottom four layers define how data is transmitted end to end.

The upper layers:-

• Application:- Provides a user interface.

• Presentation:- Present data, Handles processing such as encryption.

• Session:- Keeps different application data separate.

The lower layers:-

• Transport:- Provides reliable or unreliable delivery, performs error correction before retransmit.

• Network:- Provides logical addressing which routers use for path determination.

• Data Link:- Combines packets into bytes and bytes into frames, performs error detection not correction.

• Physical:- Moves bits between devices, Specifies voltage,wire speed.