Transmission system linking PBX with external circuits - includes input and output buses for each unit linked via controlled switching unit

摘要

The transmission system ensures a bidirectional connection between two or more terminal units of different hierarchial level (1,2) and between additional circuits such as the transmitters and receivers of multifrequency and tone signals. The terminal units are grouped into two sections (1,2) within which the terminal units have the same hierarchy level. The data receiving inputs of all the terminal blocks are connected in each section to a first bus (4,5). A switching circuit (23) allows either the connection of the first and second bus of one assembly to the second and first bus of the other assembly respectively, or the isolation of one pair of buses from the other pair.