Joint Routing and Wavelength Assignment
An alternate approach to selecting a route and wavelength separately is to consider them jointly. These approaches tend to more theoretical and not very practical. As this is a NP-complete problem, any exact solution is likely not be possible. The approximation techniques usually aren't very useful either, as they will require centralized control and, usually, predefined traffic demands. Two joint approaches are ILP formulation and Island Hopping.
The ILP formulation listed above can be solved using a traditional ILP solver. This is typically done by temporarily relaxing the integer constraints, solving the problem optimally, and converting the real solution to an integer solution. Additional constraints can be added and the process repeated indefinitely using a branch and bound approach.
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