IP-Subnet Aware Routing in WDM Mesh Networks

We explore the problem of routing bandwidth guaranteed paths in wavelength-routed, WDM optical mesh networks. A WDM mesh network offers great flexibility in dynamically reconfiguring the optical core to match the IP layer demands. In this paper, we argue that, IP subnets can limit the re-configurability potential of the WDM mesh network. We show that finding the shortest IP-hop path, normally admitting a straightforward polynomial solution on the WDM mesh, is NP-hard in the presence of subnets. We propose a new algorithm called MobiTwist that finds the optimal shortest path when accounting for subnets. We also observe that subnets impose a routing penalty by forcing longer paths for bandwidth demands. Consequently, they create a trade-off between lower network efficiency if subnets are honored (due to longer paths) or, higher utilization at the expense of upfront overhead of dynamically changing subnets to derive shorter paths. We propose the MobiFlex algorithm that attempts to achieve a balance by finding the shortest path, given an upper limit on the number of subnet violations acceptable. The inherent hardness of the routing problem due to subnets precludes a solution with low worst case complexity. However, we present performance results that show that both the algorithms proposed are extremely efficient in routing demands, and in practice, do so in polynomial time.