## 2 Background
### 5G Non-Public Networks for Industrial Communication  
In order to offer customized 5G solutions for serving the needs of particular enterprise customers (e.g., factories), 3 GPP introduces the non-public networks (NPN) architecture concept that enables 5 GS deployments for private use. According to the 3 GPP TS23.501, an NPN could be categorized as:  
* Standalone NPN (SNPN), which is deployed in an isolated way from the public network and operated by an NPN operator;
* Public network integrated NPN (PNI-NPN), which is deployed with the support of a public land mobile network (PLMN), e.g., by allocating one (or more) network slice instances for the NPN.  
In [4], 5G-ACIA describes four variants of NPN deployment options. The first one is the standalone NPN, while the other three belong to the PNI-NPN and differ in the degree of interaction and infrastructure sharing with the public network.  
In the case of a standalone NPN, all of the 5G network functions are located in a certain enterprise (e.g., factory) premises, and the complete 5G infrastructure is totally separated from the public network. The industrial party or a third-party integrator is responsible for operating and maintaining the SNPN as the NPN operator. However, it is possible to establish a roaming agreement with a mobile network operator (MNO), so the public network can also be reached in this case.  
The second deployment option is the PNI-NPN with a shared radio access network (RAN), in which case all 5G core network functions (including user and control plane) remain isolated. Thus, the traffic is handled on-premises, however, the RAN is shared with the public network. In order to fulfill the required communication service requirements, proper local radio planning and dimensioning are required for the NPN.  
The third deployment option is the PNI-NPN with a shared RAN and control plane, where the 5G control plane is also shared. The segregation between the private and public networks can be ensured by using network slicing. Since the User Equipment (UE) is also PLMN subscriber, seamless mobility between the NPN and the public network is guaranteed. In order to enable the proper management of this deployment option, the interaction between the MNO's management system and the industrial party's management system is required.  
The fourth deployment option is when the NPN is hosted by the public network, where NPN is provided by an MNO. All user and control plane network functions are deployed in the public network and can be used for both public and private network purposes. It should be considered that in this case, all of the traffic is routed via the public network, so the separation of the public network and NPN segments can be ensured by using network slicing. Since all NPN subscribers are also subscribers of the public network, roaming is enabled between the PLMN and the NPN.  
In 3 GPP, the 5G-TSN support and the non-public networks currently are on separate tracks; however, the evolution towards an integrated solution is expected. In [5], the 5G integration with TSN for different NPN deployment options is discussed. SNPN enables the most flexible and tight integration of legacy industrial TSN and 5G NPN network deployment, considering the user plane design and the network management. In the dedicated user plane and shared control plane option, it is proposed to deploy the dedicated control plane function for TSN traffic handling on-premises. In the NPN hosted by the public network scenario, a dedicated slice is required for the TSN services.