NEASIM: A General-Purpose Computer Simulation Program for Load-Loss Analysis of Multistage Central Office Switching Networks

Determining the traffic performance of complex multistage central office switching systems without actual measurement can be a major problem for the communications engineer. While probability theory has been successfully applied to a wide variety of telephone traffic problems, 1,2 ' 3 a precise formulation of a mathematical model completely describing the multistage switching system has thus far not been found. No systematic approach exists which completely accounts for the gross complexity encountered in large-scale congestion systems, but several authors have contributed significantly to the theory, notably C. Jacobaeus, 4 6 K. Lundkvist, 5 A. Jensen, 7 C. Y. Lee,8 A. Elldin, 9 R. Fortet, 10 and P. LeGall.11 More recently, V. E. BeneS12"15 has initiated "an attempt to describe a comprehensive point of view towards the subject of connecting systems." 12 Although the engineer does not yet have a comprehensive theory, he does have a valuable tool in computer simulation. Simulation of telephone traffic flow has a long history in the Bell System. As early as 1907, a rudimentary simulation was undertaken to improve switchboard performance. Artificial traffic was generated by a card-drawing technique, and the simulation was used to verify a semimathematical analysis of the loads which could be handled by a team of operators meeting an average delay criterion. In the ensuing years, simulation techniques have been aids in the study of complex traffic problems, such as the effect of limited sources 011 graded multiple capacities, the efficiency of random slipped multiples, the capacities of various alternate routing plans, and the distribution of delays under various trunking plans.