On-line reconfiguration of virtual topologies in wavelength-routed WDM networks

Wavelength-division multiplexed (WDM) networks employing wavelength-routing are considered to be potential candidates for the next generation wide-area backbone networks. In these networks, messages are carried in all-optical form using lightpaths. In a WDM network, the set of semi-permanent lightpaths which are set up in the network may be viewed as a virtual topology by higher layers such as SONET, ATM, and IP. The virtual topology is designed with an aim of minimizing certain objective function value. The underlying virtual topology may need to be changed in response to the changing traffic patterns in the higher layer. This process of changing the virtual topology to meet the traffic requirement is called as reconfiguration. The reconfiguration can be performed either on-line or off-line. We view the reconfiguration as an on-line process and it provides a trade-off between the objective function value and the number of changes to the virtual topology. The objective function value decides how best the topology is suited for the given traffic demand. The number of changes decides the extent of disruption of traffic in the network while making a transition to the new virtual topology. As the reconfiguration problem is computationally intractable, we propose four heuristic algorithms for reconfiguration of virtual topology, namely, Phasel, Phase2-Single, Phase2-Multi, and Two-Phase. These heuristic algorithms reconfigure the current virtual topology if traffic pattern changes from the existing one. The performance of these heuristic algorithms are compared in terms of objective function value of reconfigured topology, number of changes performed to get the reconfigured topology, and the amount of time taken by these algorithms to compute changes in the existing virtual topology.