A Routing and Wavelength Assignment Algorithm in Optical Burst Switching Networks

Abstract

One-way resources reservation and distributed control scheme are two notable features of routing and wavelength assignment (RWA) in optical burst switching (OBS) networks. These two features make the initial routing of bursts, i.e., the selection of the routes and wavelengths at source nodes, dramatically influence the network performance, especially the networks with limited-range wavelength conversions (LWCs). In this paper, we present a RWA algorithm called pre-defined lightpath RWA (PL-RWA). In PL-RWA, initial routing of bursts is precisely designed to avoid wavelength contentions at intermediate nodes. At the network design stage, for each source-destination pair (s,d), a dedicated set of alternate lightpaths is predefined to guide the initial routing of the bursts of (s,d). The alternate lightpaths subject to the wavelength continuous constraint and are clash free. Source node s will pour the bursts destined for d into the alternate lightpaths predefined for (s,d) as many as possible. For the bursts that cannot be carried by the alternate lightpaths, the shortest path of (s,d) is selected as the route and wavelengths are assigned hop-by-hop in real time. Using alternate lightpaths, the randomness and uncertainty of one-way resources reservation under distributed control are diminished. The selection of alternate lightpaths is formulated as an integer programming (IP) and solved by a heuristic algorithm based on tabu search. Simulation results obtained for NSFNET show that our algorithm, which can greatly reduce not only burst loss probability but also the number of used wavelength conversions, has advantage over the current algorithms.