What is the OSI reference model?
OSI stands for Open Systems Interconnection. It is a type of conceptual model that is intended to characterize the communication functions of a telecommunication or computing system. Basically, it breaks down the communication functions of a system into layers. The system defines seven layers, each one corresponding to one segment of system communications.
The primary purpose of the OSI reference model is to allow vendors and developers to define how their products and software programs will interoperate, i.e. work with each other.
However, in reality the OSI model is rarely fully implemented as few network products or standard tools define their communication functions in strict layers as per the OSI model.