# How to Isolate Non-Public Networks in B5G: A Review
## 4 RAN Isolation  
RAN isolation means that different NPNs sharing the infrastructures have customized access schemes and run the software of their RANs with logical-isolation computing resources. With RAN isolation, customized performance metrics for an air interface can be provided economically. In spite of this, there are two big challenges: mapping the customized performance metrics of the air interface to the parameters of the RAN and sharing computing resources with latency requirements. To achieve this, when deploying one NPN, the RAN protocol is first configured diversely, and then the RAN software where the computing resource needs to be virtualized at the task level is set up and run. For customized configuration of the RAN protocol, network slicing is an important technology used to set the parameters of RAN slices flexibly [24]. For the radio resource \begin{table}
\begin{tabular}{p{71.1 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Items** & **Advantages** & **Challenges** & **Solutions** \\ \hline Spectrum isolation & \begin{tabular}{c} High-efficiency and flexibility \\ for the \\ spectrum resources \\ \end{tabular} & \begin{tabular}{c} Expressing isolation \\ performance of NPNs \\ quantitatively \\ Meeting the corresponding \\ isolation requirements \\ \end{tabular} & \begin{tabular}{c} Formulating the performance and \\ requirements for spectrum isolation \\ quantitatively \\ \end{tabular} \\  & \begin{tabular}{c} Introducing quantitative spectrum isolation \\ when assigning spectrum resources among \\ NPNs to meet the isolation requirements \\ \end{tabular} \\ \hline RAN isolation & \begin{tabular}{c} Customized performance \\ metrics for air interface in one \\ economical way \\ \end{tabular} & \begin{tabular}{c} Mapping the customized \\ performance metrics of the air \\ interface to the parameters of \\ the RAN \\ Sharing computing resources \\ with latency requirements \\ \end{tabular} & \begin{tabular}{c} Configuring the RAN protocol diversely \\ Adopting task-level virtualization and \\ designing a RAN task scheduling scheme \\ \end{tabular} \\ \hline CN isolation & \begin{tabular}{c} Multiple logical standalone \\ links for CNs in one \\ economical way \\ \end{tabular} & \
\begin{tabular}{c} Distinguishing data from \\ different NPNS and their \\ terminals \\ Assigning the minimum \\ computing resources to meet \\ the QoS requirements of CNs \\ \end{tabular} &
\begin{tabular}{c} Identifying the NPN and its subscribers \\ Calculating the minimum resource \\ demand of one CN, considering the \\ coupled QoS requirements jointly, then \\ assigning the minimum computing resources using virtualization technologies, \\ such as KVM, VMware and Docker \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Advantages, challenges and solutions for spectrum isolation, RAN isolation and CN isolation. control (RRC) protocol of radio protocol layer 3, attention must be paid to the usage of the resource assigned to guaranteed QoS services (GSs). For a particular NPN, part of these resources need to be reserved for the GSs being served by the NPN. Thus, various resource reservation ratios [19] can be set for the NPNs. In two NPNs with the same assigned and occupied GSs resources, one new GS can be forbidden in one NPN and can be allowed in the other NPN, since the reservation ratios of the GSs in the two NPNs are different. The medium access control (MAC) sub-layer of radio protocol layer 2 focuses on the amounts of resources assigned to GSs and non-guaranteed QoS services (non-GSs), which can be set in the admission control methods according to the resource demand of the NPNs [23]. For radio protocol layer 1, the parameters in the NPNs can also be configured differentially; for example, the uplink and the downlink subframe ratios can be configured based on the corresponding data rate requirements of NPNs.