# Service for Deploying Digital Twins of QKD Networks
## 2 Background
### Service Orchestration  
The advent of the fifth generation of mobile networks, 5G, has brought profound advancements in delivering value-added services to end-users. Beyond defining a new radio access network architecture, aimed at enhancing the overall performance of end-user communications, 5G has introduced novel technological paradigms and business models to meet the stringent performance requirements demanded by 5G services. In particular, softwarization and virtualization [40] play a pivotal role in 5G, facilitating the swift deployment of complex services as a composition of individual software components. These may be executed in virtual machines or lightweight virtualization containers [41], which may strategically be deployed close to end users leveraging cloud and edge infrastructures of service providers. This way, service delivery can be enhanced from an end-user perspective, e.g., in terms of perceived latency and content transmission rates, while reducing capital and operating expenditures. Still, it is important to note that this approach for service delivery requires specific control procedures, which are able to manage and orchestrate the deployment and the proper configuration of the software components of every service at their respective locations.  
Service management and orchestration has received intense attention from the research community and standards-developing organizations. In this respect, the ETSI has led the definition of the NFV technology [42]. ETSI NFV provides a reference framework to support the automated deployment of telecommunication and industry-specific services on cloud and edge facilities, referred to as NFV infrastructures. These research and standardization efforts have resulted in numerous open-source solutions that have been used in different contexts to provide an operational implementation of the ETSI NFV reference architecture. Well-known examples of these solutions are Open Source MANO (OSM) [43], Cloudify [44], and OpenStack [45]. More recently, the open-source community has started to consider the integration of cloud-native solutions, such as Kubernetes [46], into the ETSI NFV framework. The cloud-native paradigm enables novel approaches for service development and deployment, decomposing a service into smaller units that inter-operate, known as microservices [47], and executing microservices in portable, lightweight virtualization containers.  
The design of our solution is inspired on ETSI NFV management and orchestration principles. The user describes a QKD network as an NFV service, that is, as a composition of interconnected QKD nodes. Our digital twin solution incorporates, as will be covered in the following sections, state-of-the-art technologies and open-source NFV tools, in order to support the automatic deployments of QKD network digital twins.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Simulator** & **Publicly Available** & **Distributed Nodes** & **Modularity** & **Simulation Environment** \\ \hline SeQueNCe & Yes (open source) & Not allowed & High & Python \\ \hline QuNetSim & Yes (open source) & Not allowed & Low & Python \\ \hline NetSquid & Yes (upon registration) & Not allowed & High & Python \\ \hline Parallel Simulation Framework & No & Not allowed & Low & N/A \\ \hline SimulaQron & Yes (open source) & Allowed & High & Python \\ \hline \end{tabular}
\end{table}
Table 1: Comparison of the different quantum network simulators considered [34].