Abstract: Line groups with doubled central switching network and connected via correspondingly two time division multiplex lines and having inter alia one sub-switching network and one group control system each are assigned to each other in pairs. The connection devices, which are individually assigned to the one and the other of two line groups, and which are connected via internal lines in normal operation to the sub-switching network in each instance of their own line group, can be changed over to the sub-switching network of the particular other line group.

Abstract: A circuit for a centrally controlled time division multiplex telecommunication exchange having PCM line/trunk groups connected to a switching network wherein each line/trunk group comprises a plurality of line units to connect one time division multiplex interexchange trunk each and is connected to a switching network over a time division multiplex line. Two line/trunk groups are assigned to each other in pairs. The connection devices which are assigned to one and to the other of two line/trunk groups and which in normal operation are connected with the time division multiplex switching device of each of their own line/trunk group can be changed over during emergency operation of one of the two line/trunk groups to the time division multiplex switching device of the other line/trunk group.