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Distributed Computer Control of Industrial Processes

出版	University of Cape Town, 1979*
ISBN	08699950659780869995068
URL	http://books.google.com.hk/books?id=ZX4TAAAACAAJ&hl=&source=gbs_api

註釋A communication subnetwork, HYDRA, suitable for use in distributed process-control systems has been designed, and is described here in general terms with the emphasis mainly on how the user sees the system. The HYDRA network consists of five nodes connected into a loop. The link between nodes is a single, bi-directional, twisted-pair cable, which operates in half-duplex synchronous mode at a speed of 38,4K-bits per second. Each node contains a node processor and a communications processor. The processors are connected by a shared-memory technique. Although further work is necessary before the HYDRA network can be used in the field, tests have indicated the following: (1) HYDRA provides secure, error-free communication between nodes, (2) HYDRA is extremely reliable with a high degree of fault tolerance, (3) the interfacing to HYDRA is simple, involving minimal overheads, (4) the network can accommodate a large variation in system size, ie, it is highly modular, (5) delays of messages through the network are very short, the average time for a response to be received from a remote node being little more than 200 ms, and (6) it exhibits these characteristics even in the harshest industrial environment.