# How to Isolate Non-Public Networks in B5G: A Review
## 1 Introduction  
With the development of wireless communication technologies [1; 2; 3; 4; 5], one main target of Beyond 5G (B5G) is to serve various vertical industries, which are developing rapidly in the era of the Internet of Things [6]. With the capacities of the network-as-a-service, multiple logical networks will be able to be deployed with the same resources and infrastructures in the B5G era [7]. Thus, it has been proposed for non-public networks (NPNs) to share the B5G system in part or totally to provide customized communication services. Although NPNs are flexible and efficient, there are two problems. The first is how to configure the network parameters to achieve customized service, and the other is that the dynamic factors of one NPN may deteriorate the performance metrics of other NPNs due to the sharing of resources and infrastructures [8]. Therefore, isolation among NPNs has become a big challenge for the establishment of customized NPNs without mutual influence among To achieve this, isolation needs to guarantee that each NPN can be configured with its own attributes and stable performance, where \"stable performance\" means that any change in the network state of one NPN does not violate the qualities of service (QoS) of other NPNs [8]. Since the QoS performance metrics are mainly determined by the resources one NPN can use, isolation of the computing resources and of the spectrum are significant. The own attributes can then be configured with parameters and schemes. Related researchon isolation mainly focuses on computing resources isolation, spectrum isolation and customized configuration of protocol parameters, as shown in Figure 1.  
For computing resources isolation, virtualization technology has been designed, which divides and maps physical resources into logical resources to realize resources isolation [9; 10; 11]. This virtualization technology can be summarized with two concepts: the platform of virtualization and the object of virtualization. There are two main types of platforms of virtualization in the computer field, which are hypervisors and containers. The main difference between them is the level of abstraction in terms of virtualization and isolation. A hypervisor, called a virtual machine monitor (VMM), provides the abstraction of physical hardware, while a container implements isolation of processes at the operating system (OS) level [12; 13; 14]. The container enables applications to run on the same OS kernel so that the guest OS is not required. Therefore, the container acts as a lightweight alternative to the hypervisor by excluding the execution of the guest OS, hardware virtualization, etc. However, the hypervisor has better performances in isolation, security and supporting different guest OS because each virtual machine is standalone and independent of the host kernel. Common hypervisors include VMware's ESX, Microsoft's Hyper-V, the open source Xen, KVM, etc. Representatives of containers are Docker and LXC. With regard to the objects of virtualization technology, these include general computing resources, such as CPU, and accelerated computing resources, such as FPGA and DSP. The virtualization of general computing resources is undertaken by the hypervisor and container platforms, while the virtualization of accelerated computing resources is usually undertaken at the task level. Differently from hypervisors and containers, accelerated computing resources can be scheduled directly without the interruption of operating systems in task-level virtualization [15]; thus, the processing delay brought by virtualization is minimized to guarantee real-time performance metrics [12], but the scheduling scheme has to be designed case by case. For NPNs, the proposed virtualization technologies can be used to achieve computing resources isolation. However, more aspects of the spectrum and the protocol configuration still need to be considered to achieve isolation among NPNs. Previous work on slicing technology has discussed spectrum isolation and protocol configuration [16].