# A Virtualization Infrastructure Cost Model for 5G Network Slice Provisioning in a Smart Factory
## 2 Background
### Virtualization Infrastructure  
In this paper, virtualization infrastructure refers to the major cost components of a data center required for the operation of the VNFs for slice provisioning by the virtualized 5G core network. The 3 GPP release 16 includes enhancements for the RAN for higher reliability as required by industrial use cases through the duplication of data packets and the addition of corresponding redundant resources [18]. While the RAN and transport dimensioning are not included in this paper, and the focus is limited to virtualization infrastructure for the core network, a similar concept of redundant resources also typical in the factory environment is applied to data center resources. The VNFs can be deployed on different virtualization technologies such as Virtual Machines (VMs), containers, or unikernels with the required network, storage, and computing capacities [1]. A VM is a virtually simulated hardware with required capacities as well as a guest operating system, running in isolation from other VMs in the same physical machine. VMs are a popular approach for provisioning VNFs in the cloud and are suitable for long-running services. On the other hand, containers do not have a guest operating system and allow the applications to directly interact with the underlying system kernel, having faster startup times while still being capable of isolated capacities. Unikernels provide the static linking of applications to small library operating systems and provide similar isolation to that in VMs, but unikernels are less flexible as a recompilation of the entire unikernel image is required for the addition and removal of functionality [1; 19]. Thus, different approaches and granularities can be defined for the dimensioning of virtual resources and can be suitably applied in the cost model. Additionally, different levels of isolation between the virtual resources can be defined. For example, in the no-isolation approach, multiple VNFs can run on the same virtual resources; in the partial-isolation approach, some VNFs run on dedicated resources, while some run on shared virtual resources; finally, in the full-isolation approach, each VNF runs on its own dedicated virtual resources. In the cost model, a VM is selected as the virtual resource to be dimensioned. With the increasing dependence on the cloud for networking services, new virtualization technologies and supporting business models are emerging. For example, microservices can be used to create reusable and independently deployable cloud components and serverless computing with function as a service platforms can then be utilized so that the application developer does not need to maintain virtualization infrastructure, and the resources are invoked only when required by the functions [19; 20; 21]. Several large cloud providers such as Microsoft, Google, and Amazon can act as virtualization infrastructure providers and offer such different options for virtualized resources and can also provide high scalability and lower costs due to centralization [19]. The VNFs can be deployed in centralized or distributed virtualization infrastructures that can be dedicated to one actor or may be common for multiple actors. Edge clouds have generated sufficient interest to enable low latency and the faster processing of data closer to customers [22]. Likewise, micro data centers can be considered for local data processing in urban environments [23]. Various business actors need to strategize between centralized and distributed deployments of virtualization infrastructure, considering technical constraints such as data security, latency, and reliability as well as economic costs and benefits. The infrastructure can be owned either by a single actor (network operator, virtualization infrastructure provider, network slice provider, network slice customer) or by a neutral host in order to enable sharing between different actors or even as a joint venture. Furthermore, the  
Figure 1: Isolation in network slice provisioning.