The OSI reference model was proposed by J D Day and H Zimmermann in 1983 Open Systems Interconnection consists of seven layers and we will discuss each in brief. The principles that were applied to arrive at the model were a layer to be created where a different level of abstraction is needed. Each layer should performs a well defined function. All layers follow internationally established protocols.
Now lets see what are the different layers of the OSI model :
The physical layer
The physical layer transmits raw bits over a communication channel it deals with encoding and transmitting the bits received in form of 0’s and 1’s.
The data link layer
The data link layer upon receiving the encoded data from the physical layer organises the data into frames it deals with transmission errors, regulate data flow and provide interface to the next layer of OSI model.
This layer is mainly responsible for translating the logical addresses into physical addresses. It consists of routers that are responsible for forwarding packets from one network to another or within the same network the routers rely on algorithms to determine the best path for the packet to transfer.
The basic function of the Transport layer is to accept data from the layer above, split it up into smaller units, pass these data units to the Network layer, and ensure that all the pieces arrive correctly at the other end.
Furthermore, all this must be done efficiently and in a way that isolates the upper layers from the inevitable changes in the hardware technology. The Transport layer also determines what type of service to provide to the Session layer, and, ultimately, to the users of the network. The most popular type of transport connection is an error-free point-to-point channel that delivers messages or bytes in the order in which they were sent.
The Session Layer allows users on different machines to establish active communication sessions between them. A session allows ordinary data transport some of its services are :
> Dialog control
> Token management
This OSI layer allows systems with different internal codes to communicate by setting standard for the abstract data structures and representations inside to convert to network standard representation and back.
This layer is responsible for the process to process communication through the network. The application layer is a layer in the Open Systems Interconnection (OSI) seven-layer model and in the TCP/IP protocol suite. It provides a firm communication interface and end-user services.