| 摘要 |
PROBLEM TO BE SOLVED: To suppress the occurrence of clock path changeover as much as possible avoiding the occurrence of an independent synchronization state using an internal clock. SOLUTION: A master node 30 is operated with a clock signal extracted from data transmitted through an optical transmission line 50. Furthermore, the master node 30 transfers a quality code; Q=2 received from the optical transmission line 50 to a downstream node (slave node 40). In this state, when external clocks 1, 2 are recovered from their fault state, the master node 30 does not release the assignment of a quality code; Q=9 denoting inhibition of selection of the external clocks 1, 2. That is, the master node 30 does not execute the switch-back to the external clocks 1, 2 even when either or both of the external clocks 1, 2 are restored. Thus, a quality level is given to each of selectable clocks and on the occurrence of a fault in a clock in use, a clock with a highest quality level is selected among a higher clock or a selectable clock where the fault is restored. |
