| 摘要 |
PURPOSE:To specify a faulty port without using a mechanism for adding a port number identifier by sending data for constitution control out of a constitution control station when a network becomes abnormal and performing constitution control over a transmission line by a constitution control station which never receives the data until the data is received. CONSTITUTION:A control station ST2 which detects abnormality sets a mode wherein a frame RCF for constitution control is sent out to a downstream side continuously, and an RCF reception monitor timer (TWR) is started to monitor the reception of the RCF, thereby judging whether the control ST should perform constitution control or not. When the RCF is received, it is evident that there is another control ST which should perform constitution control at the upstream side of the control ST, so the TWR is stopped, the continuous transmission mode of the RCF is reset, and the received RCF is relayed to the downstream side. If the TWR enters a time-out state without receiving the RCF, it is judged that there is a faulty port in a line concentrator under the control of the control ST, and the constitution control is started.
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