Open Systems Interconnection-OSI reference model is a reference model which is based on a proposal developed by the international standards organization-ISO. This was the first step for international standardization of the protocols which are used in the various layers of computer network. This model is called as ISO OSI reference model. This name was kept because this reference model deals with open systems connection. The systems which are open for communication with other systems is called open systems interconnection. Seven layers are defined in this type of reference model. The principles that were applied to arrive at the seven layers are as follows.
- A layer should be created where a different level of abstraction is needed
- Each layer should perform a well defined function
- The function of each layer should be chosen with an eye toward defining internationally standardized protocols
- The layer boundaries should be chosen to minimize the information flow across the interfaces
- The number of layers should be large enough that distinct functions need not be thrown together in the same layer out of necessary, and small enough that the total architecture does not become unwieldy.
The seven layers are Application layer, Presentation layer, Session layer, Transport layer, Network layer, Data link layer and physical layer