The unidirectional ring is usually composed of two optical fibers, one of which is the
working fiber, represented by S; the other is the protective fiber, represented by P.
Protection switching is accomplished by a reverse switch.
In addition to the unidirectional switching ring, there are also bidirectional
multiplexer switching double fiber ring and bidirectional multiplexing segment
switching four fiber ring. But the analysis shows that the unidirectional path switching
double fiber ring is the best considering the node cost, system complexity and
product compatibility.
The working mode is divided into recovery mode and non-recovery mode. In the
recovery mode, when the working section has recovered from the failure state, the
working path automatically switches back to the working section. In the non-recovery
mode, even if the working section has been restored to normal, the working path is
still unchanged in the protection section. Generally, 1 + 1 protection can work in both
recovery mode and non-recovery mode, while 1: N protection can only work in
recovery mode.
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