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.

This paper deals with the design of economically structured PCM switching arrays for traffic distribution. The presented switching arrays are symmetrically structured, and have one up to six stages and use different combinations of time stagesTand space stagesS, respectively. It is shown how such arrays can be designed for a required grade of service having a prescribed number of terminations and a prescribed carried traffic per time slot. Their relative costs per termination equal to that per time slot are calculated. These are costs for the gates and costs for memory bits, i.e., speech memories and all control memories. All presented PCM switching arrays are mapped into the corresponding space division multiplex (SDM) arrays. This allows a simple comparison with SDM link systems and an easy calculation of the point-to-point loss. The paper concludes comparing the traffic behavior and costs of the various PCM switching arrays. Finally, new "PCM charts" are developed as useful means for the design of economic PCM switching arrays. A second paper of this congress [14] compares traffic equivalent PCM and SDM switching arrays, respectively, with regard to their economic design, their traffic behavior, and their costs per termination.