Abstract: A control unit of a subscriber line termination module has access via a programmable interface to the transmitting and receiving arms of a time division multiplex line connected to the switching network. At intervals which are long in relation to the pulse frame length, during the course of existing connections, PCM-words which occur N-times on the receiving arm and, in each case following a reflection time, during a plurality of pulse frames, a plurality of PCM-words occurring on the transmitting arm are received, subjected to amplitude evaluation and, if recognized as valid, subjected to cross-correlation. The result of the cross-correlation provides a control value for the dummy impedance.

Abstract: For subscriber termination circuits of a digital time multiplex telecommunications system comprised in a group, an injection circuit is provided, individual to a group. The injection circuit comprises a switch exhibiting a gradual change of state both in switching on and switching off for providing timing for meter pulses provided by a meter pulse generator. The meter pulses are applied to the individual subscriber termination lines in a multiplex manner by way of contacts as well as test relays already present.