OSI ( Open system Interconnection ) Reference Model:

OSI ( Open system Interconnection ) Reference Model

The OSI was released in 1984 AD a standard network model. It decrease how information make its way from application program. Thus media to another application program in another computer.
The OSI reference model is described below:

1. Application layer

• It is service layer .
• It is closest to the user.
• It provide services to application program.
• It synchronizes the sending & receiving application.
• It determines weather the sufficient resources of the intended communication.

2. Presentation layer

• It is six layer .
• It ensure that information send by application layer of one system will be readable by the application layer of another system.
• It provide common format for transmitting data across various system. so, that data can be understand .
• It provides facilities to convert meaning to communicating application layer entities.
• It may perform such transformation as recording, decoding, code conversion, compares  and decompression, interruption and decryption on the message data.

3. Session layer

• It is fifth layer.
• It provides  means establishing, maintaining & combination a dialog or session between two in user end.
• It allows two parties authentic is before established a dialog session between them.
• It specifies dialog type one way, two way alternative of two way simultaneous ( simplex half tabular, fall duplex) an imitated diagnose session. It also provides purity management services which is useful for giving priority to important and time bound message over normal, place important message.

4. Transport layer

• It is fourth layer.
• It excepts message of any length from the session layer, segment package, submits them into the network layer for transmission and finally resemble the packet at the destination.
• It includes machines  for handing and lost and fat of sequence packet.
• The two most popular transport layer protocol are TCP ( Transport Control Protocol) and UDPC ( User Data Protocol).

5. Network layer 

• It is third layer.
• It is responsible for setting up a logical path between two notes for data communication.
• It is encapsulates  frames into packets, which can be transmitted from one node to another node by using a high level addressing & rotating, scheme, of the network.
• The two popular network layer protocol are: X2S and IP ( Internet protocol).

6. Data link layer

• It is second layer .
• It detect and correct any arrears in the transmitted data.
• It partition the raw bit streams into frames so that error detection and correction can be perform independently for each frames. 
• It also perform flow control of the frames.
• It is concern with topology.

7. Physical layer

• It is first layer .
• It creates a physical path in between sender and receiver .
• It is responsible for transmitting raw bit streams in between two nodes.
• It also deal with the mechanism details such as size and shape of connecting plugs, the number pins in  there plugs and function of each pins etc.