| 摘要 |
Devices (13.1, 31.1) communicate with each other on a wavelength channel using wavelength specific signals on a working WDM fiber (21) having a parallel protection WDM fiber (23). An SDH system (13.S, 31.S) uses one channel of the WDM system of the fibers as one of the fibres of the working pair of the SDH system and has a separate fibre (37) constituting that fibre of the protecting fibre pair for the SDH-system. To provide an unambiguous or predictable protection behaviour for the SDH system for the working WDM fibre being cut the RETs (29.1, ..., 29.S) have two modes. In the first mode a RET will be on and always carry traffic when the input power is high enough. In the second mode a RET they will not automatically turn on again after it has firstly lost the input signal and thereupon the input signal has returned. The RET can then be manually restarted or restarted after some suitable delay. Then the sequence of events will always be unambiguously defined. For a fibre break on the working WDM fibre, the RET will loose the input signal, turn off, and will not immediately turn on again. Thereby there will always be enough time for the SDH protection scheme to be carried out. The SDH-system will thus automatically have a working protection path, i.e. the now working, former WDM protection fibre. <IMAGE>
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