OSI Model

OSI model stands for OPEN SOURCE INTERCONNECTION . It was developed by ISO ( INTERNATIONAL STANDARD ORGANIZATION) in the year 1984. OSI model defines network communication and interconnection. OSI model also called reference model.  It has 7 Layers but we cant say which one is first layer and which is last layer. It depends upon sender and receiver.
These 7 Layers of OSI model are:

• APPLICATION LAYER
• PRESENTATION LAYER
• SESSION LAYER
• TRANSPORT LAYER
• NETWORK LAYER
• DATA LINK LAYER
• PHYSICAL LAYER 

OSI Model Design

1. APPLICATION LAYER :- Application Layer directly interacts data from the user. On the sender side it receive the data from user and receiver side it display data to the receiver. Software applications like MS Office, Web Browsers, Email ets, works on Application Layer.    
2. PRESENTATION LAYER :- Presentation Layer is responsible for data translation. The data received from Application Layer is extracted here and manipulate as per required format to transmit over the Network Layer. On the sender side data encrypted into another form i.e code and receiver side it decrypted .                                                                                                         
3. SESSION LAYER :- Session Layer establish the connection between sender and receiver until data transmission. The time between the communication is open and closed is known as session. When the data transmitted successfully, connection disconnect automatically.                 
4. TRANSPORT LAYER :- Transport Layer takes the data from session layer and brakes into segments before sending it to next layer. Transport Layer segments and reassemble the data. On sender side it brakes into segments and receiver side it reassemble the segments.                         
5. NETWORK LAYER :- In the Network Layer sender and receiver address are placed in the header .Network Layer takes care of packet routing ie. selection of shortest path to transmit the packet. It defines the root for packet received from transport layer.                                                
6. DATA LINK LAYER :- The main function of  Data Link Layer is make sure data transfer is error free. means error detection and correction. It provides a way for the sender to transmit set of bits that are meaningful to the receiver. It created the frames and adds physical address of sender and receiver on each frame.                                                                                                    
7. PHYSICAL LAYER :- Physical layer responsible for actual connection between devices. It contains the information in the form of bits. It transmit each bit from one node to another node. This layer includes the physical equipment involved in the data transfer such as cables , switches hub ets.

   

   OSI-Model