A novel approach for assigning wavelengths in multihop WDM optical networks Sahadeb Jana a , Debashis Saha b, * , Amitava Mukherjee c , Pranay Chaudhuri d a STPI, Bangalore, Karnataka, India b MIS & Computer Science Group, Indian Institute of Management Calcutta (IIM-C), Joka, D.H. Road, Kolkata 700104, India c IBM Global Services, Salt Lake, Calcutta 700 091, India d Department of Computer Science, Mathematics & Physics, University of the West Indies, Cave Hill Campus, P.O. Box 64, Bridgetown, Barbados Received 13 September 2006; received in revised form 25 November 2007; accepted 25 November 2007 Available online 4 December 2007 Abstract This paper presents a new algorithm for effectively assigning wavelengths to ligthpaths in a multihop wavelength division multiplexed (WDM) optical network, wherein the physical medium consists of optical fiber segments interconnected by wavelength selective optical switches. WDM permits a limited number of wavelengths to be re-used among various fiber links, thereby offering a very high aggregate capacity. For a given network, we first construct its auxiliary graph and then formulate wavelength assignment as a graph coloring prob- lem on the auxiliary graph. However, we do not follow the conventional two-step procedure, unlike most of the existing techniques. While generating the auxiliary graph from the given physical topology and the given set of ligthpath requests, simultaneously we apply a dynamic coloring technique to assign colors (i.e., wavelengths) to nodes (i.e., lightpaths) on the fly. The number of colors needed at the end of the algorithm represents the number of wavelengths required for the network. The algorithm is proven to be correct, and its com- plexity is analyzed. The performance of the algorithm is tested on several networks for various lightpath demands through extensive simulations. The coloring scheme, blocking performance and timing efficiencies are studied and compared with the existing best-known wavelength assignment heuristics. It is found that, for a wide range of network sizes and lightpath requests, the proposed algorithm per- forms equally well, when compared with the existing ones. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Optical networks; WDM; Wavelength assignment; Auxiliary graph; Graph coloring 1. Introduction Fiber optic technology holds out the promise of catering to the ever-increasing demand for bandwidth intensive end- user applications of future [1]. The technique of Wave- length Division Multiplexing (WDM) [2], due to its efficient use of bandwidth, has emerged as the most promising transmission technology for optical networks. It divides the enormous bandwidth of an optical fiber into a number of channels, where each channel corresponds to a different wavelength. Typically, a WDM network consists of optical wave- length routers interconnected by pairs of point-to-point fiber links. A wavelength router receives a message at some wavelength from an input fiber and redirects it to any one of the output fibers at the same wavelength. Hence, a mes- sage can be transmitted from one routing node to another routing node through a wavelength continuous path by configuring the intermediate routing nodes on that path. Such a wavelength continuous path is known as a lightpath [3]. The requirement that the same wavelength must be used on all the links along the selected path is known as the wavelength continuity constraint. This constraint is unique to WDM networks, and, due to this constraint, 0140-3664/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.comcom.2007.11.016 * Corresponding author. Tel.: +91 33 24678300. E-mail addresses: sahadeb_jana@rediffmail.com (S. Jana), ds@iimcal.ac.in (D. Saha), amitava.mukherjee@in.ibm.com (A. Mukherjee), pchaudhuri@ uwichill.edu.bb (P. Chaudhuri). www.elsevier.com/locate/comcom Available online at www.sciencedirect.com Computer Communications 31 (2008) 1751–1762