A processor in a telephone exchange, monitoring the activity of r subscriber lines having each an incoming and an outgoing channel allocated to them, emits during respective halves of any 8-bit time slot in a 32-time-slot frame a pair of m-bit addresses x, y for each subscriber initiating or engaged in a conversation, these addresses respectively identifying an outgoing channel of a first (e.g. calling) subscriber and an incoming channel of a second (e.g. called) subscriber to be placed once per frame in communication with each other by a PCM switching network. The addresses of incoming and outgoing channels issuing from the processor during each time slot are separated in a distributor, the addresses y being inscribed in stages of a storage network respectively assigned to the 32.sup.. 32.sup.. n channels identified by addresses x. The storage network consists of n random-access memories, one for each of n channel groups, divided into 32 sections of 32 stages each for as many 32-channel families. Each of 32 scanning intervals composed of n phases, occurring within a time slot, is reserved for the successive readout of homothetic stages in a respective set of n corresponding sections of all the memories, the set being divided into two subsets respectively scanned in the presence of relatively staggered enabling pulses also spanning n phases each whereby the readout of each subset starts after the beginning and terminates before the end of the corresponding enabling pulse.