Integrating quantum and classical networks

Amelia Jensen

Classical network infrastructure -- spanning enterprise TCP/IP backbones, metropolitan optical networks, and wide-area internet exchange points -- was designed without native provisions for quantum cryptographic channels. Integrating Quantum Key Distribution (QKD) and post-quantum cryptographic (PQC) algorithms into this existing fabric requires addressing four engineering challenges: photon transport over existing fibre plants, protocol encapsulation within classical network stacks, key management interoperability between quantum and classical systems, and hybrid quantum-classical cryptographic negotiation. This paper proposes the Quantum-Classical Integration Architecture (QCIA) framework, a systematic methodology for deploying quantum cryptography within operational classical networks without infrastructure replacement. QCIA is evaluated across 12 enterprise and metropolitan network scenarios encompassing fibre-based QKD co-deployment on DWDM infrastructure, QKD-over-SDN controller integration, and hybrid TLS-QKD handshake protocol design. Results demonstrate that QCIA achieves quantum-secured key exchange with 94.8% channel compatibility on standard SMF-28 fibre, hybrid TLS-QKD handshake latency overhead of 24.6 ms, and a Quantum Integration Readiness Score (QIRS) of 0.882 across evaluated scenarios. The framework provides a practical migration roadmap and open-source tooling for network operators transitioning to quantum-secured infrastructure.

M. Caruso

Günter Mahler A, Volker A. Weberruß

Vicente Martín, Alejandro Aguado, Juan P. Brito +7 more

QKD technology is mature enough to be used beyond the usual single, point to point, link by creating networks. Quantum ad hoc networks, where a separate, quantum-only network, is running in parallel to a classical network have been demonstrated in several occasions. Having to, essentially, duplicate the network to introduce quantum communications is very expensive and, beyond niche use-cases, fully integrated quantum-classical networks is what the industry demands to accept quantum technologies as a serious networking technology, ready for a broad market uptake.Recently we have reported on the successful deployment of the Madrid Quantum Network. This network is novel because it has been the first installed in production sites of a Telecommunications operator and moreover it is managed through a Software Defined Networking (SDN) structure that integrates classical and quantum channels. The network was operating for four months and we could demonstrate several technologies utilizing the integration of quantum and classical networks. Here we report on some implementation aspects and its usage in several use cases, in particular to secure the management of the SDN control plane as a critical infrastructure.

Günter Mahler A, Volker A. Weberruß

Siddharth Das, Riccardo Bassoli, Frank H. P. Fitzek

In the context of integrating quantum principles into the Internet of Things (IoT) network to enhance capacity, security, and resilience, we present a classical-quantum (CQ) protocol stack that can be systematically integrated into a classical network. The CQ architecture explicitly defines the physical and link layer behavior to accommodate quantum functionalities. We demonstrate how the use of classical error correction codes (ECC) is practical within a quantum communication protocol integrated into a classical network setup. Furthermore, we have modeled a method to calculate the classical capacity of quantum-assisted transmission over a noisy quantum channel that employs classical ECC. As a proof of concept, we have emulated classical packet transmission through various layers of the proposed protocol stack, and the behavior has been analyzed.