# Switching Coordinator: An SDN Application for Flexible QKD Networks

## TL;DR

This paper introduces an SDN application that enhances the flexibility and efficiency of quantum key distribution networks by enabling real-time monitoring and dynamic resource allocation.

## Contribution

The novel contribution is a framework combining switched QKD with centralized control and global optimization for policy-driven network operation.

## Key findings

- The framework provides real-time visibility into QKD network metrics like key generation and consumption rates.
- SDN applications can dynamically adapt network configurations to prioritize key availability and handle failures.
- The integration of switched QKD and centralized control improves performance and resilience in line with administrator policies.

## Abstract

A monitor and control framework for quantum-key-distribution (QKD) networks equipped with switching capabilities was developed. On the one hand, this framework provides real-time visibility into operational metrics. Specifically, it extracts essential data, such as the switching capabilities of QKD modules, the number of keys stored in buffer queues of the QKD links, and the respective key generation and consumption rates along these links. On the other hand, this framework allows software-defined networking (SDN) applications to operate on the collected information and address the cryptographic needs of the network. The SDN applications dynamically adapt the configuration of the switched network to align with its changing demands, e.g., prioritizing key availability on critical paths, responding to link failures, or reallocating generation capacity to prevent bottlenecks. This contribution demonstrates that the combination of switched QKD, centralized control, and global optimization strategies enables efficient, policy-driven operation of QKD networks. The cryptographic resources are allocated to maximize performance and resilience while remaining aligned with the specific policies set by network administrators.