Relayed vs. Switched QKD: A Comparison in Non-Uniform Ring Networks

The rise of quantum computers threatens public key security and its essential role in distributing symmetric keys. QKD offers a promising solution by leveraging quantum principles for secure key distribution between two points. To enable network-wide key distribution, two candidate architectures have emerged: Relayed QKD which relays neighboring generated keys along a path, and Switched QKD which uses optical switches to dynamically connect QKD devices and create key generation sessions between nodes. Both architectures require algorithmic solutions for effective key management and distribution. In prior work, we derived for uniform ring topologies optimal configurations and analytical formulas for keys consumption and compared the Switched and Relayed architectures. In this study, we extend that work by introducing scheduling and key management algorithms for arbitrary topologies and use them to compare these two architectures in non-uniform rings. Our findings reinforce previous conclusions: Switched QKD is more effective for dense (large number of nodes and short distances) networks, such as metropolitan rings, while Relayed QKD outperforms in larger rings with longer distances.