Transmission Design Criteria for a Synchronous Token Ring

This paper discusses the transmission design criteria and limiting factors of an experimental synchronous token ring implemented at the IBM Zurich Research Laboratory. The following key aspects are addressed: 1) ring topology and wiring, 2) transmission, and 3) ring synchronization with phase-locked loops. Wiring of a ring is based on a two-level hierarchy with passive wiring concentrators placed at convenient locations in a building. Data are transmitted with differential Manchester code. Special emphasis is placed on the synchronization methods and on the parameters and tolerances which limit distance and number of stations that can be attached to a ring. An analysis of the behavior of a chain of repeaters under growing jitter is given. Also the various procedures for guaranteeing high reliability are outlined. An experimental token ring has been running since 1981, and has been tested extensively under extreme jitter and noise conditions.