Optical Wavelength Division Multiplexing (WDM) rings are being deployed to support multiple SONET/SDH selfhealing rings over a single physical optical ring. In such systems, the dominating cost is the SONET Add/Drop Multiplexers (ADMs). To minimize the system cost, algorithms must be developed to assign wavelengths to lightpaths in the system so that the number of ADMs required is minimized. However, the problem of optimal wavelength assignment to minimize SONET ADMs is NP-hard. Existing

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... ic algorithms for this problem include the assign first, the iterative matching and the iterative merging heuristics. In this paper, we propose a new wavelength assignment heuristic to minimize SONET ADMs. Our heuristic is on average 3% to 5% more effective in finding the opportunities to share ADMs (and thus to reduce the total number of ADMs required) than the most effective existing heuristic, the iterative merging algorithm.