On a preemptive multi-class routing scheme with protection paths for WDM networks

A large optical network may carry multiple traffic classes with different priorities and fault-tolerance requirement. A higher priority traffic may require to have a backup path so that the traffic can be switched quickly to this path in case of a failure in the primary path. The lower priority traffic classes may not have any such requirement. In the path protection schemes currently in use for the WDM networks, a backup path is computed for all traffic, whenever a primary path is established between a source-destination pair. The resources needed for communication using the backup path are reserved (or set aside) for data communication between a source-destination pair, and are utilized only when the primary path is unavailable due to a failure in the network. The traffic carrying capacity of a network can be increased, if the resources set aside for the backup paths are utilized for data communication. In this paper we propose a path protection scheme for networks with multiple classes of traffic. The key features of our scheme are (i) Not all traffic classes have backup paths - only higher priority classes have backup paths, (ii) Primary paths of lower priority traffic share wavelengths with secondary paths of higher priority traffic, and (iii) Lower priority traffic can be preempted by higher priority traffic in case of a failure. The sharing of a wavelength between the primary path of a lower priority communication with the secondary path of a higher priority communication allows the network to satisfy more call requests, thereby reducing the call blocking probability. We provide a mathematical programming formulation for computing the primary and backup paths for call requests in a dynamic environment. We also compute the call blocking probability of our scheme and compare it with the call blocking probability of the conventional scheme through simulation. Our experimental results show significant gain by the proposed scheme over the conventional scheme.