# A Virtualization Infrastructure Cost Model for 5G Network Slice Provisioning in a Smart Factory
## 4 Results and Discussion
### Dimensioning  
The different slice types have different hardware requirements from the virtualization infrastructure. The slice type requirements can be presented in terms of the number of VMs required by a VNF for the UP and the CP. The smart factory vertical requires high availability and a guaranteed level of service; thus, a worst-case scenario with all services running all the time is considered. Alternatively, some other scenarios are also possible when not all services are running all the time, allowing the overbooking of resources, as studied in the sensitivity analysis section. Different configurations for VMs and servers can be used in the model, and for evaluation purposes--up to eight VMs the size of two cores, with a 16 GB RAM, 500 GB storage, and 10 Gbps throughput capacity are assumed to be running on a server with 16 cores, 128 GB RAM, 4000 GB storage, and 80 Gbps throughput capacity. The UP requirements are based on the traffic model for industrial use cases described in [36], which utilizes 3 GPP requirements [25]. These requirements are then divided by the throughput capacity of a VM. For the CP requirements, it is assumed that 10,000 devices can be supported per server core (20,000 devices are supported per VM for any CP VNF). It should be noted that the requirements are only representative examples and real input values as well as costs will be case-dependent and will vary per customer segment and from provider to provider. It can also be assumed that resource requirements per device type or slice type are known to operators and slice providers, as they apply such information to build their service portfolios. The assumed input VM requirements for UP and CP are listed in Table 4.  
A partial isolation case is first considered, where some VNFs are dedicated to each slice type and some VNFs are common between slice types. For evaluation, the UPF and the CP functions of SMF and AMF are assumed to be dedicated functions, while other CP functions such as NSSF, PCF, UDM, and AUSF are assumed to be common to multiple slices. The VMs for a dedicated VNF and for a common VNF are then calculated. With  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Number of VMs per Device** & **UP** & **CP** \\ \hline eMBB & \(8\times 10^{-4}\) & \(5\times 10^{-5}\) \\ mIoT & \(10^{-5}\) & \(5\times 10^{-5}\) \\ URLLC & \(9.6\times 10^{-4}\) & \(5\times 10^{-5}\) \\ V2X & \(9.6\times 10^{-4}\) & \(5\times 10^{-5}\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Input VM requirements for UP and CP VNFs, per device and for different slice types.  
Figure 4: Slice Type Forecast for 2021–2030.  
regard to sensitivity, full and no isolation cases that encompass all the possible distributions of VNFs per slice are also considered later in the sensitivity analysis section.  
The calculated number of VMs for UPFs, dedicated CP VNFs, and common CP VNFs is shown in Figures 5-7 respectively. The number of common CP VNFs is depicted with a black line measured along the secondary y-axis on the right, while the percentage of this common dimensioning for different slice types is shown using the primary y-axis. Due to a small annual growth rate of 6% and only ten-slice customer factories, the VMs required do not increase dramatically. However, the sensitivity analysis for different growth rates and the number of factories will be performed later in the paper. After calculating the total VMs per slice, the total servers per slice are calculated.  
Figure 5: VMs dimensioning for UPFs.  
Figure 6: VMs dimensioning for dedicated CP VNFs.