## 5 Simulation Results
Figure 6a,b display that the blocking rate of key service requests is affected by the change of protection threshold in two different networks. As shown in Figure 6a, the blocking rate of key service requests rises with the increase in \(\eta\). Because the  
Figure 4: (**a**) NSFNET topology; (**b**) USNET topology. Figure 5: Simulation results: (**a**) blocking rate of key service requests varies with link key resources in the case of different protection thresholds in NSFNET; (**b**) blocking rate of key service requests varies with link key resources in the case of different protection thresholds in USNET. protection threshold is the product of the remaining key resources of the link and variable quantity \(\eta\), the protection threshold is related to \(\eta\) in direct proportion. Therefore, the blocking rate of key service requests in Figure 6 rises with protection threshold increasing. The results can be explained by the results of the success rate of protection path construction in the following result. The increase in the number of protection paths affects the number of key resources allocated to the working paths of other services. From the vertical comparison of different curves in Figure 6a,b, the blocking rate of key service requests increases with the increase in the number of untrusted nodes. The reason is that an untrusted node cannot act as a relay between more than two nodes like a trusted node. When the protection threshold and the number of untrusted nodes are the smallest in Figure 6, the blocking rate of key service requests can reach close to 0. The change trend of the curves in Figure 6a is similar to that in Figure 6b, indicating that the results are common in the network. In this case, the percentage of key protection threshold \(\eta\) was set to 0.8 as shown in Figure 7. As shown in Figure 7a,b, the curves show the change of blocking rate of key service requests with link key resource increasing. Different from Figure 5a,b, the curves are distributed in the case of different untrusted node numbers. With the increase in key resources, the blocking rate of key service requests decreases in both figures. Comparing different curves vertically, it can be seen that the blocking rate of key service requests rises with the increase in the number of untrusted nodes. In Figure 7b, the key generation rate of the link, that is, the link key resource, is set to 80 unit/s. It can be seen from the curves that when the number of untrusted nodes changes from 3 to 2, the blocking rate of key service requests decreases by about 3%. With the increase in key resources, the gap of blocking rate of key service requests between different untrusted nodes gradually decreases. This is more obvious in the simulation results of USNET topology. When the number of untrusted nodes is the lowest and the key resource takes a higher value in the two figures, the blocking rate of key service requests can be close to 0. Figure 6: Simulation results: (**a**) blocking rate of key service requests varies with \(\eta\) in the case of different untrusted node numbers in NSFNET; (**b**) blocking rate of key service requests varies with \(\eta\) in the case of different untrusted node numbers in USNET. In order to observe the results more conveniently, the number of untrusted nodes in NSFNET is set to 2, while that in USNET is 3. The protection threshold is proportional to \(\eta\). Therefore, the change of \(\eta\) refers to the change of protection threshold. Figure 8a,b shows the change of protection path construction success rate with protection threshold with different untrusted node numbers. With the increase in key resources provided by the links, protection path construction success rate grows in both topologies. The reason is that more key resources can reduce the pressure of protection path construction.