Traffic Analysis of a Ring Switched Data Transmission System

Abstract

This paper is concerned with a study of traffic and message delay in a ring switched data transmission system. The system, by asynchronous multiplexing and data storage, shares transmission facilities among many users. It is the random component of message delay due to buffering that is the focal point of our study. The basic configuration of the system is a ring connecting stations where traffic enters or leaves the system. A mathematical model of the ring is developed which accommodates an arbitrary number of stations and any given pattern of traffic between stations. Studied in detail is the uniform traffic pattern in which each user is identical and communicates equally to all others. Intrinsic to the model is a recognition of the bursty nature of data sources. Other factors that are taken into account are line and source rates as well as the blocking of data into fixed size packets. Formulas are derived from which average message delay induced by traffic in the ring can be calculated. The results of the study are presented in a set of curves where normalized delay due to traffic within specific system configurations is plotted as a function of the number of stations and source activity. The delay here is normalized to average message lengths. An important parameter of these curves is the ratio of source rate to line rate. The results show that, in certain quite reasonable circumstances, the delay is less than two average message lengths. Rings of 10, 50, and 100 users have been simulated on a digital computer. Data obtained from these investigations are presented and compared to the theoretical estimates for line busy and idle periods and message delay. The results of simulated average message delay show that, for inter-station link utilizations of about 60 percent, the difference between the theoretical estimates and experimental observations is small.