Now that we have an appreciation for the evolution of the Internet and the TCP/IP protocol suite, let us turn our attention to the structure of the protocol suite. However, since the TCP/IP protocol suite has a layered structure, we will ®rst examine the ISO Reference Model and the subdivision of its second layer by the Institute of Electrical and Electronic Engineers (IEEE) to provide a standardized frame of reference. THE ISO REFERENCE MODEL The International Organization for Standardization is an agency of the United Nations headquartered in Geneva, Switzerland. The ISO is tasked with the development of worldwide standards to. | 18 THE TCP IP PROTOCOL SUITE Now that we have an appreciation for the evolution of the Internet and the TCP IP protocol suite let us turn our attention to the structure of the protocol suite. However since the TCP IP protocol suite has a layered structure we will first examine the ISO Reference Model and the subdivision of its second layer by the Institute of Electrical and Electronic Engineers IEEE to provide a standardized frame of reference. THE ISO REFERENCE MODEL The International Organization for Standardization is an agency of the United Nations headquartered in Geneva Switzerland. The ISO is tasked with the development of worldwide standards to facilitate the international exchange of goods and services. The membership of the ISO consists of the national standards organization of most countries with over 100 countries participating in its work. One of the most notable achievements of the ISO in the field of data communications was its development of the seven-layer Open Systems Interconnection OSI Reference Model. This model defines the communications process as a set of seven layers with specific functions isolated and associated with each layer. Figure illustrates the seven layers of the ISO Reference Model. Each layer covers lower layer processes effectively isolating them from higher layer functions. In this way each layer performs a set of functions necessary to provide a set of services to the layer above it. Layer isolation permits the characteristics of a given layer to change without impacting the remainder of the model provided that the supporting services remain the same. This layering was developed as a mechanism to enable users to mix and match OSI-conforming communications products to tailor their communications systems to satisfy a particular networking requirement. Although OSI-conforming communications products never gained a significant degree of acceptance the OSI Reference Model provides a framework for comparing Application .
