In the first paper at the 9th ITC [8], PCM (TDM) switching arrays having up to six stages and up to about 100 000 terminations were investigated with regard to their standardized costs per termination as a function of the cost ratio "gate to memory-bit." In this context, the following were considered: the influence of the number and sequence of stages (T-stages,S-stages), the number of terminations, the degree of multiplexing (30, 120 time slots per multiplex line). Furthermore, new PCM charts for the quick design of economic PCM switching arrays were developed. The second paper completes these studies by comparisons between PCM switching arrays and their equivalent SDM switching arrays. Handy formulas for the best possible economic design of PCM and SDM arrays, respectively, are presented and derived. The loss versus the carried traffic of PCM arrays havingS = 3up to six stages and withM = 30and 120 time slots per highway are compared with each other and with equivalent SDM link systems. Furthermore, the relative costs per termination are calculated for these PCM and SDM array structures and drawn versus the size of these arrays.

The problems of how group-selection link systems should be structured, wired, and hunted to achieve optimal traffic characteristics are studied. Furthermore, a loss-and-load-equivalent mapping of large group-selection link systems to smaller ones is presented. A new approximate loss calculation method is developed. All studies were supported by extensive Monte Carlo simulations.

This paper deals with some important practical applications of teletraffic theory to field engineering problems. It is shown that the following tasks concerning line switching telephone networks can be mastered by means of a few handy tables: loss calculation and dimensioning of trunk groups for full or limited access; very accurate loss approximation of link systems with an arbitrary number of stages, operating as group selection or traffic concentrating arrays with point-to-group selection mode (regarding this, and also optimal link structures, wiring, etc., see [7] in this issue); dimensioning groups with limited or full access for offered peaked overflow traffic; cost minimizing partition of the traffic in local or toll networks with alternate routing to the various trunk groups; and computerized dimensioning is of course also possible.