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The paper presents a description of a synchronization system suitable for among others, multi-exchange local networks. It includes mathematical formulation and analysis, hardware design, and computer simulation of network operation. The mathematical model is formulated within a framework of a specific control system design that employs digital techniques. A perstation control loop takes the form of a multiple-input PLL with an up-down counter operating as noncyclic phase comparator common to all of the incoming lines. The digital control system is mainly "single ended" mutual synchronization for which the problems of initial phase differences and effects of sampling are minimized, and the problem of "wrong-mode operation" is avoided. Central to the design is the generation of signals, denoted by "beats", upon which simple processing is performed to provide for the different subfunctions of the equipment.A combined discrete-event and continuous simulation model, based on hardware implementation of the bit-by-bit method, has been deve1oped to study the dynamic behavior of the system over long time periods. Factors such as transmission delays, delay variation, jitter, oscillator drift and various control strategies have been taken into account in the simulation.
Date of Publication: Jul 1979