| 摘要 |
PURPOSE:To reduce the probability that a line control is erroneous and to improve the reliability of a system as a whole by transmitting a sub-signal necessary only at the transmitting end office and the receiving end office without reducing the reliability more than necessary. CONSTITUTION:A line control signal as the first type sub-signal and a DSC signal as the second type sub-signal are handled as the separate signal and inserted and branched by using a different time slot. In a DSC multiplexing part 205, a DSC multiplexing separating part 216 and a DSC separating part 225, a digital ordering signal for all stations is multiplexed and separated with an ordering signal for inter-special stations instead of a line control signal. Further, in modulating parts 203 and 214 and demodulating parts 212 and 222, the modulation and the demodulation of an ASC signal are not executed. A line control signal is not separated and inserted in an intermediate station (b), and therefore, the reduction of the reliability will not occur. Since the ordering signal for all stations is multiplexed instead of the line control signal as the DSC signal, correcter carrier reproduction is executed and a receiving error ratio is reduced.
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