WHAT IS OSI REFERANCE MODEL?

The Open System Interconnection (OSI) model was created by the International organisation for standrsation (ISO) .  Basically OSI model is created to define the rule for making protocols. In OSI model there is seven layer and every layer has its own importance. A standard structure for open system interconnection is show below.



                                                  

Now I am going to explain all the function of all seven layer in detail.

1.Physical layer :-

This layer defines that how bits moves from one device to another. this layer deal with the physical characteristic of the media link. ETHERNET PROTOCOL are used in physical layer .The PDU(protocol data unit) of Physical layer is bits and different connectors and cables are used here.

2.Data-Link layer :-

Data-link layer is responsible for making frame. every frame contain header and trailor. The header has source and destination MAC address. The protocol used are PPP, HDLC, X.25 and ETHERNET.

PDU(protocol data unit) for data-link layer is FRAME .Basically SWITCHES are used on this layer.

3.Network layer :-

This layer is used for routing purpose. The logical address are used by router for determine the path. the logical address are used to identify a host on a NETWORK . IP,IPx and ICMP are used in network layer. The Protocol data unit of Network layer is Packet. and Router are used here.

4.Transport layer :-

This layer received data from lower layer and break data in segment .This layer provide reliable end to end data transfer, transmission control protocol (TCP) and user datagram protocols(UDP) are used.

         

TCP	UDP
1.it has 1-65535 port.	it has also 1-65535 port
uses acknowledgement.	it not uses acknowledgement
fast	very fast( used on video conferencing)
Connection oriented.	.Connection-less

The Protocol data unit used in transport layer is segment.

5.Session layer :-

The main purpose of using this layer is to make Connection , Maintain connection during conversation and Terminate connection when conversation over. SSL and NETBIOS are session layer protocol.The Protocol data unit used in Session layer is DATA.

6.Presentation layer:-

This Layer describe the format of data, encryption and decryption of data are performed in this layer. The Protocol data unit used in Presentation layer is DATA.

7.Application layer :-

Application layer provide user interface and enable network application to communicate with other Network application . HTTP. Telenet ,FTP protocol are used in Application layer.

NOW IF WE EXPLAIN IN SHORT THE BINARY BITS FROM PHYSICAL LAYER SEND TO DATALINK LAYER AND HERE FRAME OF 1 & 0 ARE MADE NEXT FRAME ON THE NETWORK LAYER GET BREAKED IN SMALL PACKET FORM AND TRANSPORT LAYER PROVIDE SPECIFIC ROUTE SO THAT THIS PACKET REACH ON HIS DESTINATION CORRECTLY ,AND REMANING FUNCTION ARE PERFORMRD IN YOUR PC.