## 4 Network Simulation  
As shown in Figure 6, to evaluate the performance of the CPSR-HQKDN routing scheme proposed in this paper, we conducted simulation experiments to compare the performance among different schemes. The network topology used for the experiment is shown in Figure 6. It consists of 17 nodes and 24 links. The weights of the links are marked in the diagram. Furthermore, for data packets with different security requirements, it is necessary to consider the links they can pass through. For example, L-class packets can only pass through the blue links generated using the BB84 protocol for quantum key generation, while H-class packets can only pass through the orange links generated using the MDI-QKD protocol for quantum key generation. On the other hand, N-class packets can pass through all links as they do not require the use of quantum keys. The comparative schemes used in the simulation experiments are the APR-QKDN [35] scheme and the KL-SPRA [36] scheme. The CPSR-HQKDN routing scheme targets specific scenarios with significant differences in key requirements due to high concurrency and a large number of data packets with different security requirements. Therefore, it is necessary to reproduce this specific scenario when comparing the performance of each scheme. In each simulation experiment, the number of data packets to be forwarded is distributed in proportions of 50%, 30%, and 20% for the N-class, L-class, and H-class packets, respectively. Approximately 1000 data packets are forwarded at once, and the request time interval is continuously adjusted to observe the overall service quality and packet loss rate in the network environment. Figure 6: Topology diagram of simulation experiment. As shown in Figure 7, the average packet loss rate for each class of data packets decreases as the data packet request time interval increases. When the data packet request time interval is sufficiently large, the number of keys stored in the node's key pool exceeds the total number of keys required by the data packets. It can be observed that when the data packet request interval reaches 250 ms, the packet loss rates for the three classes of data packets are very close to each other. This indicates that one of the main factors affecting the packet loss rate is the request time interval, which reflects the overall key consumption. By observing the average packet loss rate for N-class data packets, it can be seen that although it shows a decreasing trend, the fluctuation is not significant. This is because of the pre-emptive mechanism provided by CPSR-HQKDN, which prevents N-class data packets from being stuck in the waiting queue due to the lack of quantum keys. As shown in Figure 8, the average packet loss rate for CPSR-HQKDN and the other schemes decreases as the data packet request time interval increases. This is because the local storage of remaining quantum keys at the quantum nodes increases with the growing data packet request time interval, making network resources gradually abundant to serve more requests. Meanwhile, CPSR-HQKDN exhibits a significant performance improvement compared to APR-QKDN and KL-SPRA in terms of the packet loss rate. The performance difference between CPSR-HQKDN and APR-QKDN remains around 9%, while the difference between CPSR-HQKDN and KL-SPRA is around 16%. This is attributed to the appropriate path cost calculation strategy adopted by CPSR-HQKDN, along with the provision of additional delay-based retransmission opportunities for those data packets requiring quantum keys, which reduces the network packet loss rate and improves network service quality. As depicted in Figure 9, the success rate of CPSR-HQKDN, APR-QKDN, and KL-SPRA requests varies with the request interval, with CPSR-HQKDN exhibiting better performance than the other schemes as the request interval increases. Compared to APR-QKDN, CPSR-HQKDN has an approximately 3% higher success rate, while a 7% improvement is observed compared to KL-SPRA.