Abstract: Data packets are transmitted over a time-division multiplex system with CSMA-CD connecting multiple stations and having a signaling channel and message-switch channels. Collisions caused by simultaneous attempts by two or more stations to access the system for transmission are limited to the signaling channel, and are remedied by a retransmission procedure in which the unique station address number determines the frame number in which retransmission may start. This procedure guarantees that a station can access a message-switched channel within a short period of time.

Abstract: A power supply for supplying pulsed direct current from a central power source to a plurality of subscriber circuits in a telephone system. The variation of the terminal voltage of the central power supply due to the pulsating load is reduced by shifting the phases of the current pulses supplied to the various subscriber circuits so they are produced in different time intervals relative to each other.

Abstract: The matrix switch comprises a plurality of input lines (Y.sub.1 -Y.sub.4), a plurality of output lines (Y.sub.1 -Y.sub.4) and a plurality of crosspoint switches for selectively connecting one or more input lines to one or more output lines. When such a matrix switch is used for telephony systems the input lines are connected to the subscriber's lines and the output lines to the outgoing lines. Each of the input lines is coupled to input lines of an additional matrix switch via an impedance (which is equal to the characteristic impedance of the subscriber's line). The additional matrix switch has a first output line, which is connected via cross-point switches to the input lines of the additional matrix switch for terminating the selected input lines of the matrix switch with the impedance. A second output lines connects a tone generator to the input lines via the crosspoint switches.A further embodiment shows a matrix switch arranged for use with balanced lines.