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)...http://www.google.se/patents/US5018059?utm_source=gb-gplus-sharePatent US5018059 - Method and apparatus for telecommunications signal processing and switching
