Effect of dormant spare capacity on the attack tolerance of complex networks

The vulnerability of networks to targeted attacks is an issue of widespread interest for policymakers, military strategists, network engineers and systems biologists alike. Current approaches to circumvent targeted attacks seek to increase the robustness of a network by adding or swapping edges (Edge Addition (EA) or Edge Swapping (ES) method respectively) that ultimately leads to a higher size of the largest connected component for a given fraction of nodes removed when compared to that of the original network. In this work, we propose a strategy in which there is a pre-existing, dormant spare capacity already built into the network for an identified vulnerable node, such that the traffic of the disrupted node can be diverted to another pre-existing node/set of nodes in the network. Using our algorithm, the increase in robustness of canonical scale-free networks was nearly 14-fold. We also analysed real-world networks using our algorithm, where the mean increase in robustness was nearly 5-fold. We have compared our work with the results obtained from other EA and ES algorithms and have found the increase in robustness using our algorithm to be significant in light of what has been reported to our knowledge in the literature. The cost of this spare capacity and its effect on the operational parameters of the network have also been discussed.