| 摘要 |
PURPOSE:To reduce a processing time of fall back by outputting a stop control signal of a fall back control signal and a transmission data after a multilex line concentrator receives deterioration of a relay line so as to bring an opposite modulator-demodulator into a fall back state. CONSTITUTION:If a fault such as open line takes place in relay lines l71, l72, modulator-demodulator 21, 22 stop carrier detection signals S11, S12 to a multiplex line concentrator 1 to inform deterioration of the relay lines l71, l72. Thus, fall back control signals S21, S22 are outputted, the speed is subject to fall back and control signals S31, S32 stopping the transmission signal are outputted. The speed of the modulator-demodulators 21, 22 is subject to fall back to stop a signal outputted to relay lines l31, l32. The opposite modulator-demodulators 31, 32 inform deterioration of relay lines to the multiplex line concentrator 4, which falls back the speed of the modulator-demodulators 31, 32, then all devices are subject to fall back.
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