OSI MODEL

Introduction to OSI Model

— OSI model is based on the proposal developed by the International Standards Organization (ISO).

— This model is called ISO OSI (Open Systems Interconnection) Reference model because it deals with connecting open systems (systems that are open for communication with other systems)

— We call it as OSI Model.

Physical Layer :

•          Provides physical interface for transmission of information.

•         Defines rules by which bits are passed from one system to another on a physical communication medium.

Data Link Layer:

•         Data link layer attempts to provide reliable communication over the physical layer interface.

•         Breaks the outgoing data into frames and reassemble the received frames.

Network Layer:

•         Implements routing of frames (packets) through the network.

•         Defines the most optimum path the packet should take from the source to the destination

•         Defines logical addressing so that any endpoint can be identified.

Transport Layer:

•         Purpose of this layer is to provide a reliable mechanism for the exchange of data between two processes in different computers.

•         Ensures that the data units are delivered error free.

•         Ensures that data units are delivered in sequence.

•         Ensures that there is no loss or duplication of data units.

Session Layer:

•         Session layer provides mechanism for controlling the dialogue between the two end systems. It defines how to start, control and end conversations (called sessions) between applications.

•         This layer requests for a logical connection to be established on an end-user’s request.

Presentation Layer:

•         Presentation layer defines the format in which the data is to be exchanged between the two communicating entities.

•         Also handles data compression and data encryption (cryptography).

Application Layer:

•         Application layer interacts with application programs and is the highest level of OSI model.

•         Application layer contains management functions to support distributed applications.

•         Examples of application layer are applications such as file transfer, electronic mail, remote login etc.