| 摘要 |
PURPOSE:To attain the automatic extension of a loop and the quick recovery of a communication system by providing a means commanding the maintenance or release of loopback constitution based on the reception state of a signal on the transmission line of a required node after the loopback constitution is set. CONSTITUTION:When the loopback is constituted as shown in the figure, for example, a loopback control section 46 commands loopback setting, e.g., from the system 0 to the system 1 to nodes 34, 35. When transmission lines 41, 43 are normal and both the nodes are recovered, a loopback shown in broken lines is set in both the nodes 34, 35. Then the loopback control section 46 inquires about the state to the end node 36 of the loopback loop and detects that the reception from the outside of the loop is normal, the section 46 commands the loopback release to the node 36 to extend the loop up to the node 34, inquires similarly about the state to the node 34, and when the state is normal, the section 46 commands the loopback release.
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