This invention relates to a time-division transmission method for a plurality of terminals connected to a looped transmission line, in which a plurality of slots being provided with regions, where three kinds: "Free", "Busy" or "Neutral" of access control information are set, are made to circulate on...http://www.google.de/patents/US4685105?utm_source=gb-gplus-sharePatent US4685105 - Loop transmission method
