Inter-similarity between coupled networks

Recent studies have shown that a system composed of several randomly interdependent networks is extremely vulnerable to random failure. However, real interdependent networks are usually not randomly interdependent, rather pairs of dependent nodes are coupled according to some regularity which we coin inter-similarity. For example, we study a system composed of an interdependent world wide port network and a world wide airport network and show that well-connected ports tend to couple with well-connected airports. We introduce two quantities for measuring the level of inter-similarity between networks: i) the inter degree-degree correlation (IDDC); ii) the inter-clustering coefficient (ICC). We then show both by simulation models and by analyzing the port-airport system that as the networks become more inter-similar the system becomes significantly more robust to random failure.