Distributed-queue multiple-access (DQMA) and cyclic-reservation multiple-access (CRMA) access schemes for gigabit-per-second local and metropolitan area networks are described. These schemes are based on a slotted unidirectional bus structure, with both folded and dual-bus configurations. Like the distributed-queue dual-bus (DQDB) scheme, both the DQMA and the CRMA access schemes achieve full throughput independent of network speed and distance. They have two significant advantages over DQDB. They provide throughput fairness even at high speeds and large distances, where DQDB exhibits dramatic unfairness, and, by allowing reservation of multiple consecutive slots, they make segment labeling unnecessary and facilitate packet reassembly significantly.>

In digital transmission systems employing PLL repeaters, timing jitter is produced mostly by intersymbol interference (ISI). Despite the fact that IS1 represents a narrow-band disturbance to the PLL for a long chain of N repeaters, it is responsible for cycle slips of the PLL repeater. It is demonstrated that the cycle slip rate is the key parameter determining the error performance of the system. It is shown that the accumulated jitter for a large chain becomes a narrow-band process, which can be replaced by an equivalent low-pass jitter-noise process, which lends itself to analytical treatment. Numerical results of the cycle slip rate are given, based on the solution of a time-dependent Fokker-Planck equation. The results are useful for a wide range of loop transfer functions and phase-detector characteristics. The theoretical findings are confirmed by experimental results.

Architecture, performance, transmission system, and wiring strategy of a token-ring local area network implemented at the IBM Zurich Research Laboratory are described. In the design of the system, particular emphasis was placed on high reliability, availability, and serviceability. To ensure robustness of the token-access protocol, we employ the concept of a monitor function which is responsible for fast recovery from access-related errors. Our protocol supports asynchronous transmission of data frames concurrently with full-duplex synchronous channels, e.g., for voice services or other applications requiring guaranteed delay. The delay-throughput performance of the token ring is shown to depend very little on data rate and distance. The transmission system of the ring is fully bit synchronous and allows insertion/removal of stations in/from the ring at any time. A mixed ring/star wiring strategy is used which provides the means for both fault detection and isolation, and system reconfiguration, and allows wiring of a building systematically.

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.