| 摘要 |
PROBLEM TO BE SOLVED: To ensure the transmission of information, secure reliability, availabil ity, and maintainability by a single loop, and lower the cost by disconnecting a local terminal from a network and bypassing it when the terminal device gets out of order. SOLUTION: A terminal device 20 in a digital transmission network inserts and extracts a video signal and an audio signal into and from a reference signal inputted from an optical cable 421 through specific processes and sends the reference signal out to a next terminal device. At this time, if a frame synchronizing signal can not be received, a line control circuit 215 detects whether or not there is light input, judges that its device is faulty when the input is normal, and sends a fault signal out for a certain period and then passes transmit data through a bypass circuit 212. Consequently, when the network is constituted with a single loop, the network is maintained in the case of fault occurrence and a center device can specify a faulty terminal. Therefore, the constitution is simplified by adopting the single loop to constitute the network at low cost. |
