COMPOSITE CONCENTRATION SYSTEM

In a composite concentration system of the type utilizing a time division system in which voice signals are digitallized and than concentrated in a traffic, there are provided a first subscriber line interface circuit means of a first type which connects subscriber's lines directly to subscriber line interface circuits, a second subscriber line interface circuit means of a second type which connects subscriber lines to subscriber line interface circuits via a space division concentration switch and a time division concentration switch connected to the first and second subscriber line interface circuit means via switching interfaces. The number of output terminals of the first subscriber line interface circuit means is equal to that of the output terminals of the second subscriber line interface circuit means when a concentration ratio of the space division concentration switch of the second subscriber line interface circuit means 1:1 and corresponding output terminals are connected such that the same channel is assigned to the time division concentration switch. The composite concentration system of this invention is not expensive and can readily expand a telephone system according to a variation in percentage of calls or change in a service performance.