SPAN SWITCHING & RING SWITCHING
Span switching :
This type of switching uses only protection fibers on the span where fault is detected.
Ring switching :
In this type of switching, traffic is switched away from filed span to adjacent node via the protection fibers on the long path.
REVERTIVE & NON-REVERTIVE SWITCHING
We can implement two modes of protection switching in SDH networks, revertive or non-revertive.
In revertive switching, once the fault condition has cleared, the network enters a "wait to restore state. One the configured WTR time is elapsed, traffic will be switched back to main path. This will be useful, wjen main path is much shorter than protection path.
In non-revertive mode, even after clearance of fault condition, traffic will not switch back to main path automatically.