Wavelength Assignment in Optical Networks with Limited Reconfigurability

Reconfigurability of optical networks is a very important feature for supporting dynamic traffic demands and to enable new services. Optical network reconfigurability is enabled by reconfigurable optical add drop multiplexers (ROADMs) and tunable transceivers. Limiting the range of wavelengths that can be accessed at a node reduces costs, and possibly reduces flexibility in reconfigurability. The limited range (band-size) of wavelengths is a result of the limited add/drop range of the ROADMs and/or limited tuning range of transceivers. In either case, limited reconfigurability introduces a new constraint in the wavelength assignment of connections called as the wavelength termination constraint. In this paper, we consider a uni-directional ring network with limited reconfigurability and take up the problem of supporting two traffic types - permutation traffic and all-to-all traffic - while minimizing the worst-case wavelength range of the ROADMs and respecting the wavelength termination and continuity constraints. ROADMs can be limited in range (L-ROADMs) or have full range (F-ROADMs). For permutation traffic, we show that at least one F-ROADM is necessary, and we also give an upper bound on the number of F-ROADMs needed as a function of the range of the other nodes that are L-ROADMs. For all-to-all traffic, we give an integer linear programming formulation and present a heuristic algorithm to minimize the worst-case range. Our results show that all ROADMs can be L-ROADMs and the worst-case range is only about 65% of the full range for large network sizes.