| 摘要 |
PROBLEM TO BE SOLVED: To effectively use network resources by providing a timer means which detects an abnormal state of a signal on an in-use transmission line and then newly detects the states of signals on the in-use and standby transmission lines. SOLUTION: State detection parts 11a and 11b judge the states of signals on the in-use transmission line 1a and standby transmission line 1b newly a time ΔT later by using the timer 15. This time ΔT is obtained by adding a preliminary time to the propagation time difference between the two transmission lines at a node. At this time, a switching control part 13 informs a switching part 21 of a switching instruction for the transmission lines through a control information signal line 14 when the signal of the in-use transmission line 1a is abnormal and the standby transmission line 1b is normal, and the switching part 21 selects the standby transmission line 1b and performs switching. When, however, the signal of the in-use transmission line 1a is normal, the switching is not performed. |
