An Algorithm for Waveband Routing and Wavelength Assignment in Hierarchical WDM Mesh Networks

Aggregation of wavelengths into wavebands is an attractive, cost-efficient way to facilitate switching and routing in optical networks. In this paper, we study the waveband routing and wavelength assignment (WRWA) tasks in hierarchical WDM mesh networks with optical crossconnects that can route multiple granularity (wavelengths and wavebands) at the same time. We solve the waveband routing and wavelength assignment subproblems as a single problem, rather than separating them into two separate problems. We propose a waveband routing and wavelength assignment algorithm, which is designed to minimize the number of wavelength conversions. The algorithm is solved by using Dynamic Programming, sequentially on one lightpath request at a time. We comment on the WRWA performance under various traffic scenarios. Our results demonstrate a significant cost reduction compared to the WDM mesh networks with a single granularity, i.e., without using wavebands. I . INTRODUCTION AND RELATED WORK Wavelength division multiplexed (WDM) networks using wavelength routing by optical crossconnects (OXCs) [ 11 have emerged as the most feasible architectural solution for wide area backbone networks. The key enabling technology of Dense WDM (DWDM) is optical wavelength multiplexing and demultiplexing. The benefits of DWDM come at the expense of increased complexity of managing the wavelengths. Large numbers of available wavelengths result in increased complexity of OXCs and increased difficulty in implementing and maintaining OXCs. A way of reducing the complexity and size of OXCs is to group the wavelengths, thus creating a layered structure of optical paths. This is achieved by using a concept called wavebands, which was recently introduced in [2], [3]. A waveband consists of a group of several wavelengths and it is routed as a group through the optical switches. A waveband path occupies only two (input and output) ports of an optical switch in a node. The path hierarchy reduces node costs since a waveband can be switched optically as a single unit, thus reducing the number of expensive optical-electronic-optical (OEO) ports required for processing individual wavelengths. This, coupled with well designed routing and wavelength assignment algorithms may enable a cost-efficient implementation of optical networks. The potential benefits of wavelength aggregation into wave0-7803-7710-9/03/$17.00