###### Abstract  
This paper demonstrates the use of software-defined networking (SDN) orchestration to integrate regionally separated networks in which different network parts use incompatible key management systems (KMSs) managed by different SDN controllers to ensure end-to-end QKD service provisioning to deliver the QKD keys between geographically different QKD networks. The study focuses on scenarios in which different parts of the network are managed separately by different SDN controllers, requiring an SDN orchestrator to coordinate and manage these controllers. In practical network deployments, operators often utilize multiple vendors for their network equipment. This practice also enables the expansion of the QKD network's coverage by interconnecting various QKD networks equipped with devices from different vendors. However, as coordinating different parts of the QKD network is a complex task, this paper proposes the implementation of an SDN orchestrator which acts as a central entity to manage multiple SDN controllers, ensuring end-to-end QKD service provisioning to address this challenge. For instance, when there are multiple border nodes to interconnect different networks, the SDN orchestrator calculates the path in advance for the end-to-end delivery of keys between initiating and target applications belonging to different networks. This path selection requires the SDN orchestrator to gather information from each SDN controller managing the respective parts of the QKD network. This work shows the practical implementation of SDN orchestration for interoperable KMS in commercial QKD networks in South Korea. By employing an SDN orchestrator, it becomes possible to coordinate multiple SDN controllers and ensure the efficient and secure delivery of QKD keys between different QKD networks with varying vendor equipment. QKD; SDN; SDN orchestrator; SDN controller; interoperable KMS; interworking 2023 IEEEexample:BSTcontrolcontrol, machine learning, distributed  
In [3; 4], a QKD network enabled by SDN by elaborating on its overall architecture, related interfaces, and protocols is presented. Further, the previous works in [2; 5] demonstrated SDN services utilizing QKD technologies that were fully integrated with standard telecommunication networks. However, there is a lack of studies addressing orchestration with SDN functionality between different QKD networks to deliver the keys. This can be particularly challenging in large-scale communication networks where the QKD network is made up of parts from several different vendors. This challenge must also be solved when connecting the QKD networks of different operators. The objective of this work is to demonstrate, for the first time, SDN orchestration for interoperable key management systems (KMSs) to deliver QKD keys to cryptographic applications in which different parts of a network use KMSs that are incompatible as the network is composed of different QKD devices and KMSs from different vendors. The use case is the delivery of QKD keys when different parts of a network use KMSs that are managed separately by different SDN controllers which require an SDN orchestrator to manage. It is assumed to have common trusted nodes, which are border nodes, to interconnect different parts of networks. This is common practice, and it is sometimes mandatory for operators to have multiple vendors for deploying network equipment in their own network. This practice also facilitates the extension of the coverage of the QKD network, allowing for the interconnection of different QKD networks equipped with QKD devices from various vendors. Given that the development of an extensive and global QKD network is still in an early stage, it is crucial to interconnect different QKD networks equipped with various QKD devices. This facilitates the expansion of QKD network coverage for key delivery, but it requires the operator to coordinate the SDN controllers that manage each QKD network individually.