# Key Issues on Integrating 5G into Industrial Systems
## 2 Composition and Communication Networks of Industrial Systems
### Hierarchy and Characteristics of Communication Networks  
According to the business and communication requirements supported, communication networks in industrial systems can be divided into four network levels (from top to bottom) [25; 26; 27].  
1. Outside-enterprise communication network: When connected to the Internet, the communication network outside enterprises' industrial firewalls would act as a bridge between the public Internet and the communication network inside enterprises. It can easily and efficiently realize business applications, e.g., to provide services for customers and enterprise cooperation through the Web. The amount of data transmitted at this level is not limited, so a large bandwidth for communication is required, but with no real-time requirements. As a result, consumer communication technologies, such as Ethernet and Internet, can be adopted. Application of wireless technologies (including 5G) at this level is natural, so this study would not focus on this level;
2. Enterprise communication network: All communication networks within enterprise industrial firewalls, except the control network and control-layer communication network. Internal communication networks within enterprises are office networks used by enterprises for efficient information resource sharing, communication, and management, generally adopting the client/server structure. Enterprise communication networks require large bandwidth and basically have no control and real-time requirements, so they also use consumer-level communication technologies, such as Ethernet and general-purpose computers. The application of wireless technologies, such as 5G, at this level is also natural so it is not the focus of this study;
3. Control network: The control network is used for automated control management and users can interact with controllers used for field control through control networks on computers. The interaction is mainly for field data, device status information, and user control information. The bandwidth requirement of control networks' data transmission is relatively low but with certain real-time requirements. Ethernet can be used as their communication protocol but needs to be improved to enhance security by such methods as using switches instead of hubs, limiting communication network usage, etc. This study will discuss how to apply 5G successfully at this level;  
Figure 1: A production case in the process-oriented industry.  
4 Control-layer communication network: The control-layer communication network connects industrial control system equipment for controlling automated field production. It shall obtain the real-time device working status information, support network status monitoring, and facilitate analysis and statistics by network management personnel or intelligent network management software. It can also manage device configuration through wired network interfaces for functions such as basic device information management, diagnosing scope and alarm threshold management, device firmware upgrades, etc. The control-layer communication network transmits the least amount of data but requires low latency and high reliability, so industrial-grade field buses are often used, such as the foundation field bus, Profibus, Modbus, industrial Ethernet, etc. Applying 5G at this level shall be the focus of this study.