| 摘要 |
PROBLEM TO BE SOLVED: To prevent that normal communication state cannot be returned to because of imperfect fault restoration in releasing loopback by constituting so that control pass can be loopback released while holding the loopback of a user pass after starting the loopback. SOLUTION: First, an ATM switch part 102 performs switch loopback of user paths 20' and 22', under this state, the continuity of a cell is confirmed by using control paths 26' and 28' and, with regard only to a transmission line 9 conductor confirmation of which can be obtained, the switch loopback is released. That is, when executing the loopback release at a node device, the user paths 20' and 22' set by as physical layer interface loopback is switched to switch loopback state in which the loopback is performed by the ATM switch part 102. Next, while maintaining communication between local communication terminals, control for releasing the physical layer interface loopback is performed with the control passes 26' and 28'.
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