Feature Issue on Waveband Switching, Routing, and GroomingAs the number of wavelengths in wavelength-division-multiplexed (WDM) systems continues to increase, the switching fabrics of optical cross connects (OXCs) will become increasingly complex. This complexity can be reduced by introducing multigranular optical cross connects (MG-OXCs) into the network. A MG-OXC is capable of switching an entire group of wavelengths through a single switch port, thereby reducing the required number of switching ports and the complexity of the switch fabric. We consider the problem of establishing active and backup paths for connections in networks with MG-OXCs. The problem of establishing protected connections for a given traffic demand in multigranular networks differs from the protection problem in standard wavelength-routed networks in that the primary objective in multigranular networks is to minimize the number of switch ports in the network. The mode of protection (dedicated or shared) affects the ability to aggregate and route traffic together. We formulate the problems of dedicated and shared protection in the form of Integer Linear Programs (ILPs) to optimize the total number of ports. Since solving the ILPs for large networks is intractable, we propose a graph-based heuristic that attempts to solve the problem of routing and waveband assignment in an integrated manner. The heuristic reduces the total number of ports in the multigranular network. We also study the effect of shared protection on the port count.
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