<P> In 1983, these two documents were merged to form a standard called The Basic Reference Model for Open Systems Interconnection . The standard is usually referred to as the Open Systems Interconnection Reference Model, the OSI Reference Model, or simply the OSI model . It was published in 1984 by both the ISO, as standard ISO 7498, and the renamed CCITT (now called the Telecommunications Standardization Sector of the International Telecommunication Union or ITU - T) as standard X. 200 . </P> <P> OSI had two major components, an abstract model of networking, called the Basic Reference Model or seven - layer model, and a set of specific protocols . </P> <P> The concept of a seven - layer model was provided by the work of Charles Bachman at Honeywell Information Services . Various aspects of OSI design evolved from experiences with the ARPANET, NPLNET, EIN, CYCLADES network and the work in IFIP WG6. 1 . The new design was documented in ISO 7498 and its various addenda . In this model, a networking system was divided into layers . Within each layer, one or more entities implement its functionality . Each entity interacted directly only with the layer immediately beneath it, and provided facilities for use by the layer above it . </P> <P> Protocols enable an entity in one host to interact with a corresponding entity at the same layer in another host . Service definitions abstractly describe the functionality provided to an (N) - layer by an (N - 1) layer, where N was one of the seven layers of protocols operating in the local host . </P>

The number of layers in iso osi reference model