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Wavelength Assignment to Minimize the Number of SONET ADMs in WDM Rings




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Wavelength Assignment to Minimize the Number of SONET ADMs in WDM Rings Xin Yuan Amit Fulay Department of Computer Science, Florida State University, Tallahassee, FL 32306 fxyuan, [email protected] Abstract— Optical Wavelength Division Multiplexing (WDM) rings are being deployed to support SONET/SDH self-healing rings. The cost of such a system is dominated by the SONET Add/Drop Multiplexers (ADMs). To minimize the system cost, algorithms must be developed to assign wave- lengths to lightpaths in the system so that the number of ADMs required is minimized. This problem of optimal wavelength assignment to minimize the number of SONET ADMs is NP–hard. In this paper, we develop an in- teger linear programming (ILP) formation for this problem, propose a new wavelength assignment heuristic, and evaluate the existing and the newly proposed heuristic using the ILP formation. We conclude that the perfor- mance of the newly proposed heuristic is very close to optimal. I. INTRODUCTION Optical Wavelength Division Multiplexing (WDM) rings are being deployed to support SONET/SDH self-healing rings. One of the fundamental design problems for such networks is how to assign wavelengths to the lightpaths in the system so as to mini- mize the system cost. Since the system cost is dominated by the SONET Add/Drop Multiplexers (ADMs)[3], [4], we must de- velop effective wavelength assignment algorithms to minimize the number of SONET ADMs in the system. In a WDM ring supporting multiple SONET/SDH rings, the SONET ADMs are used to terminate lightpaths. Each lightpath uses two ADMs, one at each end of the lightpath. Although the origin node only needs the downstream ADM function and the termination node only needs the upstream ADM function, full ADMs are installed on both nodes to complete the protection path around the ring. Each wavelength around the ring provides the connectivity for a single SONET ring. Two adjacent light- paths that are assigned the same wavelength can share an ADM at the common node. Fig. 1 shows an example of ADM sharing. In the figure, we use the notion (s; t) to represent a lightpath from node s to node t. Fig. 1 (a) depicts the case when light- path l1 = (a; b) and lightpath l2 = (b; c) are assigned different wavelengths. In this case, 4 ADMs are needed to support the two lightpaths. Fig. 1 (b) depicts the case when l1 and l2 are assigned the same wavelength. In this case, the ADM at node b is shared by both lightpaths and only 3 ADMs are needed. This example shows that wavelength assignment directly affects the number of SONET ADMs needed in the system. Notice that the wavelength assignment problem has been extensively stud- ied [1], [2]. However, most of the existing wavelength assign- ment algorithms have a different optimization objective, that is, to minimize the total number of wavelengths required in the sys- tem. These algorithms cannot be directly applied to solve the problem of minimizing the number of SONET ADMs and new This project was supported in part by NSF grants: ...





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