ABSTRACT A reference model is a conceptual blueprint of how communication should take place. It addresses all the process required for effective communication and divides these processes into logical grouping called layers. When a communication system is designed in this manner, it is known as layered architecture. The OSI isn’t a physical model, though. Rather, it’s a set of guidelines that application developers used to create and implement application that run on a network. It also provides a framework for creating and implementing networking standards, devices, and internetworking schemes. Due to the urgency in the need for standards for heterogeneous computer networks, International Standard Organization (ISO) created a new subcommittee for “Open System Interconnection” (ISO/TC97/SC16) in 1977. The first priority of subcommittee 16 was to develop architecture for Open System Interconnection which could serve as a frame work for the definition of standard protocols. As a result 18 months of studies and discussions, SC16 adopted a layered architecture comprising seven layers (Physical, Data Link, Network, Transport, Session, Presentation, and Application). In july 1979 the specifications of this architecture, established by SC16, were passed under the name of “OSI Reference Model” to Technical committee 97 “Data processing” along with recommendations to start officially, on this basis a set of protocols standardizations to start projects to cover the most urgent needs. These recommendations were adopted by TC97 at the end of 1979 as the basis for the following development of standards for Open System Interconnection within ISO.