Wavebanding in Bi-Directional WDM Ring Networks with Limited Reconfigurability

An important factor that affects the cost of WDM networks is the number of wavelengths to be added/dropped by reconfigurable optical add drop multiplexers (ROADMs). Limiting the range of wavelengths that can be accessed at a node reduces costs. In this paper, we study wavelength assignment (WA) in WDM bi-directional ring networks 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 tuning range (L-ROADMs) or have full range (F- ROADMs). In this work, a node can either possess a limited-add L-ROADM or an F-ROADM. 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 L-ROADMs at other nodes. For all-to-all traffic, we develop an integer linear programming (ILP) formulation, and also propose a new wavelength assignment algorithm that uses W_u = N²/4 - N/2 + 1/4 wavelengths. Our heuristic´s results are similar to the ILP´s. The results show that a saving of 85-93.3% in tuning range is achievable for this type of traffic.