# An Efficient Routing Protocol for Quantum Key Distribution Networks
## 3 Simulation Results and Analysis
### Simulation Results of QOLSR and Analysis  
In this section, we compare our proposed approach with original OLSR and the multi-SPF routing protocol proposed in [22]. The simulation environment in Section 3.2 is the same as in Section 3.1. When the communication level is low, the performance of QOLSR and multi-SPF is close and is higher than that of OLSR, as shown in Figure 9. As communication level increases, the PDRs of OLSR and multi-SPF decrease sharply. However, the PDR of QOLSR still remains high after fluctuation. This is mainly due to link-state awareness and routing based on key recovery capability. Even if the network's communication demand is enormous, it can still route packets in a reasonable manner, and the network will not be paralyzed. It can be seen from the experimental result statistics in Figure 10 that the efficient routing protocol proposed here has very high quantum secure key utilization at any communication level, which is significantly higher than the original, unimproved routing protocol. In particular, it can be seen that when the communication level is 1, the quantum secure key utilization rate of the original OLSR is 38.81%, while the quantum secure key utilization rate of the QOLSR we proposed is 81.84%, which is 2.1 times higher than that of the original OLSR. This is mainly due to improved link-state awareness, which reduces the number of packets lost during path switching, and improved path optimization based on key recovery capability, which reduces the path switching frequency and improves quantum secure key utilization. At low communication levels, the multi-SPF quantum secure key functions effectively. However, its performance decreases rapidly when the communication level rises. This is primarily due to multi-path SPF's selection approach, which is based on the amount of the key pool's remaining keys. When the communication level is low, the key consumption rate is low. Therefore, the key consumption rate has a minimal impact on communication. However, when the amount of communication increases, so does the key consumption rate. For the performance of multi-SPF, which does not take into account key generation, the consumption rate in routing is reduced dramatically. In particular, when the communication level is 0.01 and 0.2, the quantum key utilization of multi-SPF is slightly higher than that of QOLSR. This is mainly due to the low frequency of path switching at extremely low communication levels. The link pre-judgment in the link-state awareness mechanism of QOLSR may cause path switching to occur earlier than multi-SPF. As a result, the switching frequency of QOLSR is higher than that of multi-SPF. Moreover, due to the low key consumption rate, the advantage of choosing a path with a long sustainable working time based on key recovery capability  
Figure 8: Comparison of AODV, DSDV, and OLSR in quantum secure key utilization. cannot be exerted. Consequently, the quantum key utilization rate of QOLSR is slightly lower than that of multi-SPF when the communication level is extremely low. However, with increased communication, the quantum key utilization of QOLSR is significantly higher than that of multi-SPF. The performance of QOLSR, on the other hand, is relatively stable even at high communication levels. This means the quantum secure key utilization of the QKD network with the optimized routing protocol is significantly improved. In addition, since routing packets also need to be encrypted and protected, the routing cost and one-way delay (OWD) time are also compared for a more comprehensive evaluation of the QOLSR protocol's performance. The number of quantum keys consumed by routing packets in communication is referred to as routing cost. The delay of data packets  
Figure 10: Comparison of OLSR, multi-SPF, and QOLSR in quantum secure key utilization. Figure 9: Comparison of OLSR, multi-SPF, and QOLSR in real-time PDR. (**a**) Communication level = 0.2. (**b**) Communication level = 0.4. (**c**) Communication level = 0.6.