# Cellular and Virtualization Technologies for UAVs:
## 2 Related Work and Background
### Virtualization and UAVs
In our previous work [30], we analyzed the different issues that NFV Management and Orchestration (MANO) platforms might face in resource-constrained aerial networks, showcasing that popular solutions like Openstack (Open Source Cloud Computing Infrastructure: [[https://www.openstack.org/](https://www.openstack.org/)]([https://www.openstack.org/](https://www.openstack.org/)) (accessed on 27 April 2020)) might not be an optimal solution for these networks due to its high technical requirements, transport-layer limitations and its centralized approach for the management communications. Openstack is an Open Source cloud operating system in charge of managing the computational, networking and storage resources from an NFV infrastructure for the deployment of VNFs, i.e., it is a Virtualized Infrastructure Manager (VIM). In order to perform this resource control, it uses a set of services for each one of its functionalities (i.e., one service is in charge of the networking resources, other for allocating computational resources, etc. ), controlling them from a central node, the controller. However, all these services are generally resource demanding, which is not suitable for resource-constrained environments or intermittently-available nodes, and due to its a cloud-oriented approach it focuses on supporting Virtual Machines, and such environments with limited computational resources might not be able to efficiently use this type of virtualization for its higher resource cost. In consequence, there has been an effort on proposing more lightweight alternatives that could both be applied in systems with lower resources or cloud environments to increase their performance without compromising their functionalities: container technology. This approach does not isolate the Operating System (OS) of the host through hypervisor technology, but rather modifies the underlaying host OS in order to separate the instances through kernel namespaces and control groups. In consequence, containers provide better performance when compared with VMs, as they require a lower amount of resources to perform the same functions [31; 32]. In this context, we can find the open-source solution Kubernetes [33], also known as K8s, as one of the most popular platforms in both industry and academia. K8s is an open-source solution to deploy and manage applications based on Docker (Docker: [[https://www.docker.com/](https://www.docker.com/)]([https://www.docker.com/](https://www.docker.com/)) (accessed on 27 April 2020)) containers allowing the managing of workloads and services, as well as their automatic configuration and deployment. Thanks to its ever-growing support due to its large community of users and developers, some researchers have already proposed solutions combining K8s with UAV technologies, as can be seen in works like [34], where authors propose a cloud-based platform for a control system architecture in order to allow controlling several UAVs despite their physical location, Ref. [35] where authors propose a cloud-native NFV-driven Intrusion Detection System using Kubernetes, and Ref. [36], where authors present an architecture to support reconfigurable multimedia services for a practical emergency environment use case of rescue operations using UAVs. Unfortunately, K8s is a resource-demanding solution since it is still cloud-oriented (i.e., its application in large data centers with full connectivity where connectivity drops are infrequent), which limits its application in further resource-constrained environments such as IoT environments. Hence, a lightweight version of Kubernetes called K3s (Lightweight Kubernetes: [[https://k3s.io/](https://k3s.io/)]([https://k3s.io/](https://k3s.io/)) (accessed on 27 April 2020)) is currently being developed as well, reducing the K8s footprint and size for its suitability in resource-constrained environments, as authors in [37] propose using this platform to incorporate IoT devices into a smart city.