Abstract: The establishment of connections between two subscriber or trunk locations or line terminating groups (TG1 . . . TGm) in a communication switching system in which the individual subscriber or trunk locations or line terminating groups are interconnected on a ring-shaped bus arrangement (BUS 0, BUS 1) are carried out through the application of two computers (SB1 . . . SBn) one of which interacts with or serves the calling subscriber location or line terminating group while the second computer interacts with or serves the subscriber location or line terminating group being called. The transmission of communications signals between subscriber locations or line terminating groups occurs through only one of the two computers.

Abstract: There is disclosed a circuit arrangement for receiving unipolar DC signals from a transmission line of a telecommunication system. An opto-coupler circuit is coupled with a light-emitting element at the input side to two wires of the receiving branch of the transmission line. A current reflector circuit arranged at the input side of the opto-coupler circuit is composed of a pair of transistors with a common base connection coupled to one wire of the transmission line. One of these transistors is connected in series by its collector-emitter path with the light-emitting element. The second transistor is symmetrically arranged between both wires of the transmission line. A resistor is arranged in the emitter circuit of one transistor for controlling the current reflection ratio.