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 changing the network structure in one way or the other, leading to a higher size of the largest connected component for a given fraction of nodes removed. 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 16-fold. We also analysed real-world networks using our algorithm, where the mean increase in robustness was nearly five-fold. To our knowledge, these numbers are significantly higher than those hitherto reported in literature. The normalized cost of this spare capacity and its effect on the operational parameters of the network have also been discussed. Instances of spare capacity in biological networks, termed as distributed robustness, are also presented.