| 摘要 |
A method of switching an optical bidirectional ring composed of a plurality of nodes. At an add node into which a signal is inserted, signals are simultaneously inserted into a currently used route and an auxiliary route in the opposite direction to the currently used route for a path where no momentary interruption is set. At a drop node from which a signal of a designated path is extracted, the signal extracted from the currently used route when a failure occurs in the path of the currently used route is switched without any momentary interruption to the signal extracted from the auxiliary route. When the switching with no momentary interruption is unnecessary at the drop node due to a failure, at the add node, the signal of the path of no momentary interruption is not inserted into the momentary route, but the folded-back path is passed through the auxiliary route. As a result, the UPSR system can be fused into the BLSR system to realize a path of no momentary interruption by the BLSR system. Thus, it is possible to have the two advantages of the line capacity efficiency and the line reliability and to decrease the memory capacity.
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