## 6 Case Study
### Structural Robustness Analysis
integrated replacement strategy both offer more significant robustness enhancement than the internal replacement strategy under the IB failure mode. 2.3 Structural Robustness Comparison of Three Substitution Strategies under Recomputed Node Degree Loss (RD) Failure Mode  
As shown in Figure 9, (1) in the RD failure mode, when the number of node attacks is high, the maximum connectivity subgraph values under all three substitution strategies decrease to 0, at which point the CMN has completely collapsed. This indicates that the RD failure mode is more destructive to the structural robustness of the CMS than either the ID or IB modes. (2) The \"external\" curve is always located above the \"internal\" curve, and the \"inter&exter\" curve is nearly always located above the \"external\" curve. This indicates that the maximum connectivity subgraph value is largest under the internal-external integration replacement strategy, followed by the external replacement strategy, and then the internal replacement strategy. Therefore, for the structural robustness of the CMS under the RD failure mode: internal-external integration replacement strategy > external replacement strategy > internal replacement strategy. 2.4 Structural Robustness Comparison of Three Substitution Strategies under Recomputed Node Betweenness Loss (RB) Failure Mode  
As shown in Figure 10, (1) in the RB failure mode, when the number of node attacks is high, the maximum connectivity subgraph values under all three strategies decrease to 0, at which point the CMN has completely collapsed. This indicates that the RB failure mode  
Figure 8: Variation of S under IB failure mode. Figure 9: Variation of S under RD failure mode. is more destructive to the structural robustness of the CMS than either the ID or IB modes. (2) The \"external\" curve is always located above the \"internal\" curve, and the majority of the \"inter&exter\" curve is located above the \"external\" curve. This indicates that the maximum connectivity subgraph value is largest under the internal-external integration replacement strategy, followed by the external replacement strategy, and then the internal replacement strategy. Therefore, for the structural robustness of the CMS under the RB failure mode: internal-external integration replacement strategy > external replacement strategy > internal replacement strategy. In summary, from the complex network perspective, all three resource substitution strategies significantly improved the structural robustness of the CMS. In the four failure modes (i.e., ID, IB, RD, and RB), the structural robustness levels under all three strategies were higher than those with no strategy. Further, the internal-external integration replacement strategy brought the greatest robustness enhancement to the CMS, followed by the external replacement strategy, and then the internal replacement strategy. This is reasonable because the essence of a resource substitution strategy is to add redundant nodes, so when a resource fails, redundant alternative resources will be there to replace it to complete the task. Therefore, as the number of node failures increased, the strategies with more initial redundant nodes (i.e., the internal-external resource integration strategy and the external replacement strategy) were more robust. Conversely, the strategy with fewer initial redundant nodes (i.e., the internal replacement strategy) was less robust. In addition, in the failure modes based on the initial topology (i.e., ID and IB), only the structural robustness under the no-replacement strategy and the internal replacement strategy significantly decreased. In contrast, in the failure modes based on the recomputed topology (i.e., RD and RB), the structural robustness under all strategies significantly decreased, indicating that the failure modes based on the recomputed topology were more destructive to the structural robustness of the CMS. However, for all four failure modes, all three resource substitution strategies could protect the structural robustness of the CMS to some extent.