Wavelength band switching in multigranular all-optical networks

In this paper, we address the problem of wavelength band switching (WBS) in multi-granular, wavelength division multiplexing optical networks. The purpose of WBS is to reduce the increasing control complexity and port numbers in ordinary optical cross-connects. We classify the WBS problem into eight variations and then focus on one of them, wherein there are a fixed number of wavebands in each fiber, each with a fixed number of wavelengths and in fact, consisting of a fixed set of wavelengths. We develop an integer linear programming (ILP) model, which for a given set of lightpath requests, determines the routes and assigns wavelengths for the lightpaths so as to minimize the number of ports needed. Our model is more generic than existing solutions, as it takes into account the grouping of lightpaths having different sources and destinations and hence maximizes the benefits of WBS. Since the subproblem of minimizing the port count with WBS is NP-complete, we also develop and compare two heuristic algorithms: namely Waveband Oblivious optimal Routing and Wavelength Assignment (or WBO-RWA), and Balanced Path routing with Heavy-Traffic first waveband assignment (or BPHT). For small networks, our results indicate that the performance of the BPHT heuristic is quite close to that achievable using the ILP. For larger networks, the ILP model is no longer feasible, but BPHT can perform considerably better than WBO-RWA. Our results also provide valuable insights into the effect of wavelength band granularity on the performance of WBS algorithms, as well as the tradeoffs between the wavelength-hop and the port count.