Our research investigates the use of generalized loop-back over mesh networks. In particular, we investigate bandwidth management to take advantage of the choice of routings afforded by generalized loop-back. To illustrate the issue of bandwidth management and choice of routings for recovery, we give a brief example of how such flexibility is afforded. The figure shows the situation we consider. We have single network, with a recovery subgraph built for link failure restoration. In case of failure of the link between node 2 and node 3, the recovery back-up path is shown by a curving directed line. The shortest back-up path uses the link between nodes 9 and 10, as shown in part a of the figure. Suppose that the link between nodes 9 and 10 becomes unusable for the back-up path, for instance because the link has failed or because all the wavelengths on that link are used to accommodate extra traffic. Then, the back-up path for a failure between nodes 2 and 3 can be the path node 3 -> node 10 -> node 6 -> node 7 -> node 9 -> node 2, shown by a curved line on figure 11.b. Thus, the same back-up subgraph can be used both when the link between nodes 9 and 10 is available and when it is not available.

Note that not all links can be allowed to become unavailable. If the link between nodes 3 and 10 becomes unavailable, the restoration after failure of the link between nodes 2 and 3 is not possible. However, it is possible to determine whether certain links are necessary for recovery in the case of failure of other links. Since there are two paths in the back-up subgraph from node 10 to node 9, the link between nodes 9 and 10 is not necessary and that link can be freed up to carry extra traffic, if the need arises. Note that the traffic carried on the back-up graph may or may not be protected by the primary subgraph. In general, it will not. However, the ability to re-assign some wavelengths from protection to primary use adds significant flexibility which is not present in BLSR rings. Which links can be allowed to re-assign their back-up wavelengths to primary use may be part of the criteria taken into account when designing the primary and back-up graphs.