| 摘要 |
PROBLEM TO BE SOLVED: To provide a method of high-speed protective switching from a work circuit to a protective circuit. SOLUTION: The high-speed protective switching from work OSU 404 to protection OSU 406 is possible, and the arrival time of a corresponding upstream ranging response PLOAM cell is measured in both of the work OSU 404 and the protection OSU 406 during the ranging work of the work OSU 404. A cell description procedure is started in the protection OSU 406 during the normal nonranging operation of the work OSU 404, and next the arrival time of a corresponding upstream cell is measured in both of the work OSU 404 and the protection OSU 406. A propagation delay is produced based on the measured arrival time, so that it may be used by the protection OSU 406 for communication with one or more ONT's, in the case that protective switching is executed when trouble is detected in the work circuit, without necessity of the protective OSU 406 performing the ranging as to one or more ONT's. |
