Dynamic and flexible optical networking combined with virtualization and softwarisation enabled by Network Function Virtualization (NFV) and Software Defined Networking (SDN) are the key technology enablers for supporting the dynamicity, bandwidth and latency requirements of emerging 5G network services. To achieve the end-to-end connectivity objective of 5G, Network Services (NSes) must be often deployed transparently over multiple administrative and technological domains. Such scenario often presents security risks since a typical NS 1 may comprise a chain of network functions, each executed in different remote locations, and tampering within the network infrastructure may compromise their communication.To avoid such threats, Quantum Key Distribution (QKD) has been identified and proposed as a future-proof method immune to any algorithmic cryptanalysis based on fundamental quantumphysics mechanisms to distribute symmetric keys. The maturity of QKD has enabled the research and development of quantum networks with gradual coexistence with classical optical networks using carrier-grade telecom equipment. This makes the QKD technology a suitable candidate for security of distributed and virtualised network services.In this paper, for the first time, we propose a dynamic quantum-secured optical network for supporting network services that are dynamically created by chaining Virtual Network Functions (VNFs 2 ) over multiple network domains. This work includes a new flex-grid quantum-switched Reconfigurable Optical Add Drop Multiplexer (q-ROADM), extensions to SDN-enabled optical control plane, and extensions to NFV orchestration to achieve quantum-aware, on-demand chaining of VNFs. The experimental results verify the capability of routing quantum and classical data channels both individually and dynamically over shared fibre links. Moreover, quantum secured chaining of VNFs in 5G networks is experimentally demonstrated via interconnecting four autonomous 5G islands simultaneously through the q-ROADM with eight optical channels using the 5GUK Exchange orchestration platform. The experimental scenarios and results confirm the benefit of the proposed data plane architecture and control/management plane framework.Index Terms-5G, management and network orchestration, network function virtualization, quantum key distribution, secure network service, q-ROADM.

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First demonstration of quantum-secured end-to-end VNS composition through dynamic chaining of VNFs from multiple-domains. We rely on a novel quantum-switched flexi-grid WDM network and q-ROADM for interconnectivity and on-demand selection of transport functions for quality-of-service.

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5G networks envisage to support a range of vertical industries, circumventing any potential barriers from converging various network technologies and administrative domains. Current solutions focus only on provisioning services within single administrative domains. There is also lack of standards for sustainable end-to-end multi-domain solutions that can use existing Network Function Virtualization (NFV) Management and Orchestration (MANO) systems. This is important to enable operators to collaborate and create innovative end-to-end services in a sustainable environment, where stakeholders can benefit without compromises. In this article, we present the 5GUK Exchange (5GUKEx), a novel hierarchical architecture to enable end-to-end orchestration with minimum overhead in complexity and performance while also allowing operators to maintain full control of their infrastructure. 5GUKEx allows operators to use their existing MANO systems for the single domain orchestration and build a multi-domain API based on standardized models exposed by service catalogues to coordinate the end-to-end service orchestration and interconnection.We built a prototype of the 5GUKEx and evaluated its performance through emulations showing that the 5GUKEx introduces minimum overhead. We also discuss the use-cases and trials using 5GUKEx in addition to the experiments focusing on the flexible nature of architecture, allowing us to use 5GUKEx to