PURPOSE: To increase the relieve rate against a simultaneous fault or the like by not multiplexing an idle data before multiplexing as an invalid data but sending only a valid data.
CONSTITUTION: A multiplexer 49 selects a non-idle data among plural data sent to a digital transmission line and multiplexes the selected data, a demultiplex distributer 50 demultiplexes the sent data to demultiplexes the data based on a data identification signal provided to each data and a line changeover device 5 recognizes digital transmission lines not idle to be standby lines and relieves a faulty non-idle transmission line by using a standby line. Thus, when plural non-busy transmission lines exist, it is equivalent that plural standby lines are provided and when plural current lines are faulty simultaneously, they are relieved simultaneously.
TERAJIMA SHUICHI
NAKAJIMA TERUO
IKEDA HIDEO
