| 摘要 |
PURPOSE:To execute smoothly switching to a stand-by device by holding and updating the information of line switching in the control information which is detected from a frame to be transmitted and received between an existing highway supervisory device and a communication device, by a stand-by highway supervisory device. CONSTITUTION:A stand-by highway supervisory device 2 is connected to an annular data transmission line 6. The supervisory device 2 O/E-converts 7 a data from the upstream, S/P-converts 9 it, brings it to buffering by registers 10, 11 and P/S-converts 12 it, brings it to a data conversion 15 through a changeover switch 13 and sends it out to the downstream. Also, an output of the data converting part 7 is outputted to a frame counter 8, and from in its counter, a processor 17 always supervisors a command through an inter-node communication control part 16, that which is related to line switching is extracted and written in a management table, and also updated. In this way, when the existing supervisory device becomes faulty, even if it is switched to the stand-by supervisory device immediately, the line connection is secured, and switching is executed smoothly.
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