Memory Requirements in a Telephone Exchange

A General telephone exchange with N subscribers is indicated schematically in Fig. 1. The basic function of an exchange is that of setting up a connection between any pair of subscribers. In operation the exchange must “remember,” in some form, which subscribers are connected together until the corresponding calls are completed. This requires a certain amount of internal memory, depending on the number of subscribers, the maximum calling rate, etc. A number of relations will be derived based on these considerations which give the minimum possible number of relays, crossbar switches or other elements necessary to perform this memory function. Comparison of any proposed design with the minimum requirements obtained from the relations gives a measure of the efficiency in memory utilization of the design.