 base. The operations that an Standard ISO 7498, and the structure of the comprehensive family of International Standards that have been established for distributed AP requires may not be supported by its local processing resources, and therefore, it must share additional resources in a remotely information systems. located system to accomplish its task. Finally, upon completion of its operations, the AP may need to deliver the resulting data to a remotely-located data base for further processing or analysis. 12.2 OSI environment The interconnecting network shown in Figure 12.1 provides the telecommunication paths for information interchange between the The OSI architecture and family of standards, which specify the systems. The OSI architecture defines an orderly structure of func- services and protocols for interchange of information between sys- tionality to facilitate successful communications between APs. items, have been defined to provide an operating environment for the There are two basic components to ensure successful communica- POINT OF SALE ROBOT VIDEOTEX ELECTRONIC DATA BASE TELETEX VOICE Figure 12.1 Distributed information systems 12/4 Open systems interconnection reference model OPEN SYSTEM A OPEN SYSTEM B COBOL PASCAL UTILITIES PROCESSES INFORMATION Figure 12.2 Functional components of a computer based system tions. The first is the transparent movement of the data between are interchanging information. In the communication process, the systems. The second is ensuring that the data arriving for the functions of each of the layers (layer 7 through 1) are invoked in the destination AP is in a meaningful form that can be immediately originating system and conveyed to the destination system where recognised and processed. they are executed from layer 1 through 7 in the destination system. OSI standards only define those functions that are necessary to Very simply, in a point-to-point configuration, each layer is facilitate communications between systems. They do not describe traversed twice, firstly 