Kazuma Tsuda

We considered research and development aimed at improving the operability and scalability of large-scale QKD net-works (QKDNs) by introducing hierarchical control architecture. This paper focus on a distributed-control QKDN within such a hierarchical large scale QKDN and presents the design and implementation of a QKDN controller (QKDN-C) that selects appropriate key relay routes in response to control instructions from an orchestrator (QKDN-O). In particular, it describes a method for distributed key relay and routing table management, in which the routing tables of individual key managers (KMs) are dynamically updated on instructions from the QKDN-O. It also shows that, in a hierarchically structured QKDN, coordinated operation between the QKDN-O and distributed QKDNs enable key re-laying to be realized over optimal routes.

In quantum key distribution (QKD) networks, key resources are limited, and efficient key relay is essential for stable multi-site operation. However, evaluating how effective the key relay paths are requires large-scale and iterative verification using real networks, which entails substantial costs and practical constraints. This paper reports on a simulator that was developed to evaluate the performance and effectiveness of key relay path computation models in large-scale QKD networks. The simulator takes as input the results of key relay path selection obtained from various routing models and simulates fluctuations in the amount of key across the entire QKD network. Using this simulator, we confirmed that it is possible to systematically verify whether the key relay paths are suitable for efficient and stable operation of QKD networks under various network scales and operational conditions. The results provide a useful foundation for the design and evaluation of future QKD networks.