## 5 Conclusions and Outlook  
This paper primarily introduces a routing scheme based on the classification of packet security requirements in a hybrid Quantum Key Distribution (QKD) network within the Software-Defined Networking (SDN) framework. In existing QKD routing schemes,  
Figure 11: Change in Key Utilization with Simulation Time. Figure 10: Change in request success rate with simulation time. typically, only one type of QKD link is utilized for the network design, or the routing algorithm solely considers the length of the path or the quality of service, overlooking the distinct characteristics of different packet security levels. In contrast, the proposed scheme employs a hybrid QKD network model composed of two types of links: the BB84 protocol and the MDI-QKD protocol. Additionally, this scheme establishes a unique linear programming mathematical model based on the key bit generation features of BB84 and MDI-QKD, and proposes a routing scheme based on the classification of packet security requirements. Furthermore, it incorporates a new theory of queuing encrypted packets to alleviate congestion, reduce the packet loss rate, and enhance quantum key utilization in the overall quantum network. Firstly, the data packets are classified into different security levels according to their sensitivity and confidentiality requirements. The level information is then added to the request header of the packet. Subsequently, the packets are classified based on the request header of the encryption request during the routing process. During routing, the packets are forwarded through paths corresponding to the appropriate security levels, ensuring the security of the packet transmission. At the same time, the slow generation speed, high cost, and precious nature of the keys generated by QKD technology are taken into account to improve the key utilization rate and the overall quality of service in the network environment. The experimental results demonstrate that the routing scheme based on the classification of packet security requirements effectively reduces the consumption of quantum keys and improves the overall network service quality. It can select suitable paths for transmission based on the demands of packets with different security levels, thereby reducing the risks of eavesdropping, tampering, or delayed packet loss. However, there are still potential areas for improvement in this routing scheme. On one hand, further research can be conducted on how to conceal request header information in the design of routing protocols, and consider introducing traditional keys to confound the security levels, optimizing the overall network security. On the other hand, although this routing scheme is based on emerging architectures such as Software-Defined Networking (SDN), insufficient integration has been made to enhance the overall network service quality and security. Future exploration can be conducted on the integration of packet security requirement classification with novel network architectures. In conclusion, the routing scheme based on the classification of packet security requirements holds potential and promising applications in enhancing the security of network packets. With further research and improvements, this scheme can be made more effective and feasible in practical network environments. [PERSON] and [PERSON] played a key role in the initial conception of the ideas. [PERSON] and [PERSON] further developed and refined these ideas. [PERSON] and [PERSON] were responsible for writing the source code and conducting the simulations. [PERSON] and [PERSON] provided valuable input during the editing process. All authors actively contributed to writing the manuscript. All authors have read and agreed to the published version of the manuscript. This research was supported by the Natural Science Foundation of the Jilin Province (Grant No. 20210101417)C.  
Not applicable. The data presented in this study are available on request from the corresponding author.