Finally, Ethernet also offers a convergence mechanism that ensures packe t can
be forwarded along a new spanning tree should the original spanning tree fail.
However, this mechanism is typically slow and does not scale to larger networks.
Given these protection mechanisms, what is the role of the WDM layer in
protecting traffic? Quite a bit of research has been performed on how WDM
protection can coexist with service layer protection and how the layers coordinate
and benefit from the respective protection mechanisms [13, 14]. However in
reality, most SPs prefer to keep protection to one layer for simplicity. Naturally,
when protection does exist in the service layer, it is more beneficial to use it, as it
covers failure mode s that are unrecoverable ...