DE 2538637 C UPAB: 19930901 The central telephone exchange, for digital decentralised exchanges, has incoming signals passed on to the receive cable alone that is connected to the subscriber for whom the incoming information is destined. The incoming information is temporarily stored in a memory using special switches. For time multiplexed operations, synchronisation at the beginning of a time frame ensures that the sync. signals appear on the transmit cable at the same time. This is achieved by holding the sync. signals in delay lines at each node in the telephone network until they all have the same phase.