Summary :
So if two backup paths are fault disjoint, they can share the same backup wavelength under the single fault assumption, since only one of the sharing backup paths will be activated and thus no conflict will occur. We look at a path restoration strategy in which there exists a pre-com- puted restoration path for each primary path. This pre-computed path pro- tects the primary path against all failures and therefore has to be node-link disjoint with the primary path.