A Study of Data Multiplexing Techniques and Delay Performance

One of the major functions of data communication networks is providing means by which users can access a distant computer in an interactive manner. Time-sharing, inquiry-response and credit checking are examples of applications which have a common communications requirement. They require rapid set up times for access to their respective computers and, as a consequence of their interactiveness, often require high-capacity return channels for return traffic. Providing access to a distant computer involves providing two major data transmission media, viz. long haul facilities and local distribution. (See Figs. 1 and 2.) While there are important problems associated with each part, we shall focus our attention on local distribution techniques. We are motivated in this direction by the relatively high cost of providing local distribution compared to the total cost of transmission. The results presented in the sequel are most appropriate to the situation where users desiring access to distant computers are geographically clustered. In this instance, traffic from several users is concentrated at what are designated as User Stations. We shall consider multiplexing techniques whereby traffic from User Stations is conveyed to a central point which we call the Central Processor. The role of the Central Processor is to route or direct message flow to and from User Stations and computers. This paper is devoted to an analysis of the roundtrip delay of three techniques which multiplex traffic onto common facilities.