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Wednesday, August 10, 2011


OSI stands for Open System Interconnection. OSI model is also known as OSI reference model. It is used for designing network architecture. It was designed by the International Standard Organization to provide a logical framework for how data communication processes should take place across networks.
There are seven layers in the OSI model. Each layer is responsible for a particular aspect of data communication. The seven layers of OSI models are:
  • Physical Layer
  • Data Link Layer
  • Network Layer
  • Transport Layer
  • Session Layer
  • Presentation Layer
  • Application Layer
Application Layer
The application Layer provides services directly to the application programs, to access the network. It provides user interface to send and receive information by the user.
Presentation Layer
This layer of OSI model performs data transformations to provide a common interface for user applications. It means that data is translated between the formats the network requires and the format the computers of the end users expect.
Session Layer
This layer of OSI model establishes, maintains and manages connections between communicating systems, so that they can talk to each other. These connections are called sessions.
Transport Layer
This Layer of OSI model provides a mechanism for the exchange of data between source and destination. It breaks large message from the session layer into segments to be sent the the destination computer. At the destination computer, it reassembles the data segments and presents the data to the session layer and also send acknowledgement of receiving of data.
Network Layer
This Layer of OSI model ensures the delivery of data packet from source to destination. It means that this layer is responsible for carrying data packets from one computer to another. If source and destination are connected to the same link, then there is no need for a network layer. It is because the data link layer can perform the necessary function of managing the links.
Data link Layer
The data link layer is responsible for carrying a packet of data from one computer to the next and also responsible for the reliability of the physical link established at physical layer. This layer provides for the error free transfer of data from one computer to another.
Physical Layer
The physical layer of OSI model is bottom-most layer. This layer is related to the transmission media for data transmission. This layer controls and coordinates the transmission of data in the form bit stream over a physical medium.