Virtual topology reconfiguration in IP/WDM optical ring networks

Wavelength division multiplexing (WDM) has emerged as a promising technology for use in backbone transport networks. In an IP/WDM network, the optical layer provides circuit-switched lightpath services to the client Internet protocol (IP) layer. The set of all the lightpaths in the optical layer defines the virtual topology. Since the optical switches (cross-connects) are reconfigurable, the virtual topology can be reconfigured in accordance with the changing traffic demand pattern at the client layer in order to optimize the network performance. Although it is theoretically possible to implement any virtual topology on the physical topology, changing the virtual topology can be disruptive to the network since the traffic must be buffered or rerouted while the topology is being reconfigured. We develop a reconfiguration algorithm which is based on the concept of splitting and merging existing lightpaths, together with cost–benefit analysis to reduce the network reconfiguration cost. Our objective is to reduce the number of lightpaths that need to be reconfigured, while ensuring that the network congestion is low. The performance of the proposed algorithm for unidirectional and bidirectional ring networks is verified through simulation experiments. The experimental results show that the algorithm reduces the number of reconfiguration changes significantly while keeping the network congestion acceptably low. q 2002 Elsevier Science B.V. All rights reserved.