Summary :
Because it is a pure waste in the tunnel layers without being covered by any tunnel, CB-STA needs to reduce the network resources uncovered by a tunnel as much as possible. We will also investigate a combination of the previous two approaches (termed "mixed" in the following context), in which the network is deployed with tunnels at the planning stage that will never be torn town, while dynamic allocation of tunnels is allowed and performed while the network is running. Derive a combination of feasible tunnels along an alternate path under inspection (including the existing tunnels and establishable tunnels), such that a lightpath can be built from the source to the destination.