I. Introduction Industrial Ethernet is an Ethernet technology applied in the field of industrial control. It is technically compatible with commercial Ethernet (i.e., the IEEE 802.3 standard). When designing products, the selection of materials, product strength, applicability, real-time performance, interoperability, reliability, anti-interference performance, and intrinsic safety should meet the needs of industrial sites. Ethernet was once considered a "non-deterministic" network. As the foundation of information technology, it was developed for IT applications and could only be used in a limited way in the field of industrial control. This is because: (1) Ethernet's Media Access Control (MAC) layer protocol uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD). When the network load is heavy, the determinism of the network cannot meet the real-time requirements of industrial control; (2) The connectors, hubs, switches, and cables used by Ethernet are designed for office applications and do not meet the requirements of harsh industrial environments; (3) In factory environments, Ethernet has poor anti-interference (EMI) performance. If used in hazardous situations, Ethernet does not have intrinsic safety performance; (4) Ethernet cannot supply power to field devices through signal lines. With the development and popularization of Internet technology, the improvement of Ethernet transmission speed, and the development of Ethernet switching technology, the above problems are being rapidly solved in industrial Ethernet. II. Key Technologies for Ethernet Application in Industrial Fields (I) Communication Determinism and Real-Time Performance The biggest difference between industrial control networks and ordinary data networks is that they must meet the real-time requirements of control operations, that is, signal transmission must be fast enough and the determinism of signals must be satisfied. Real-time control often requires accurate and timely updates of data for certain variables. Because Ethernet uses the CSMA/CD method, when the network load is large, the uncertainty of network transmission cannot meet the real-time requirements of industrial control. Therefore, traditional Ethernet technology is difficult to meet the real-time requirements of accurate and timely communication for control systems and has always been considered a "non-deterministic" network. Industrial Ethernet has taken the following measures to basically solve this problem: 1. Adopting Fast Ethernet to increase network bandwidth. The communication speed of Ethernet has increased from 10, 100 Mb/s to the current 1, 10 Gb/s. Under the same data throughput, the increase in communication speed means a reduction in network load and a reduction in network transmission latency, that is, a significant decrease in the probability of network collisions, thereby improving its real-time performance. 2. Full-duplex switched Ethernet is adopted. Switching technology replaces the original bus-type CSMA/CD technology, avoiding collisions caused by multiple stations sharing and competing for the channel, reducing channel bandwidth waste, and enabling full-duplex communication, thus improving channel utilization. 3. Reduce network load. Industrial control networks differ from commercial control networks. Each node transmits very little real-time data, typically a few bits or bytes, and sudden large-scale data transmissions are rare. Therefore, limiting the number of network segment stations can reduce network traffic and further improve the real-time performance of network transmission. 4. Apply message prioritization technology. In intelligent switches or hubs, message prioritization is designed to improve transmission real-time performance. (II) Stability and Reliability Traditional Ethernet was not designed for industrial applications and did not consider the adaptability requirements of industrial environments. Due to the harsh conditions of machinery, climate, and dust in industrial environments, higher requirements are placed on the industrial reliability of equipment. In factory environments, industrial networks must possess good reliability, recoverability, and maintainability. To address the challenge of stable network operation under extreme conditions in uninterrupted industrial applications, companies such as Synergetic Microsystems (USA) and Hirschmann & Jetter AG (Germany) have developed and manufactured DIN rail hubs and switches. These products are mounted on standard DIN rails, feature redundant power supplies, and utilize robust DB-9 connectors. Furthermore, in practical applications, fiber optic transmission can be used for the backbone network, while shielded twisted-pair cables can be used for field device connections. Redundant network technology can be employed for critical network segments to enhance network anti-interference capabilities and reliability. (III) Safety In industrial production processes, many sites inevitably contain flammable, explosive, or toxic gases. For intelligent devices and communication equipment used in these industrial environments, explosion-proof measures must be implemented to ensure safe production. Under current technological conditions, explosion-proof measures are feasible for Ethernet systems. These measures include safety enhancement, airtightness, and potting to prevent the leakage of ignition energy generated by equipment malfunctions, thus ensuring system safety. For non-hazardous environments without strict intrinsic safety requirements, complex explosion-proof measures can be disregarded. Network security is another security issue that must be considered for industrial Ethernet applications. Industrial Ethernet can integrate a company's traditional three-layer network system—information management layer, process monitoring layer, and field device layer—into a single entity, enabling faster data transmission rates, higher real-time performance, and seamless integration with the Internet to achieve data sharing and improve factory operational efficiency. However, it also introduces a series of network security issues. Industrial networks may be subject to network security threats, including virus infections, illegal intrusions by hackers, and unauthorized operations. Generally, gateways or firewalls can be used to isolate industrial networks from external networks, and network security management can be strengthened through various security mechanisms such as access control and data encryption. (IV) Bus Power Supply Issues Bus power supply (or bus feeding) refers to the fact that cables connected to field devices not only transmit data signals but also provide operating power to the field devices. The following methods can be used for power supply to field devices: 1. Based on the current Ethernet standard, appropriately modify the physical layer technical specifications to modulate the Manchester signal of Ethernet onto a DC or low-frequency AC power supply, and then separate these two signals at the field device end. 2. Without changing the current physical layer structure, power is supplied to field devices through idle cables in the connection cable. III. Industrial Ethernet Protocols When Ethernet is used for information technology, the application layer includes commonly used protocols such as HT-TP, FTP, and SNMP. However, when it is used for industrial control, the application layer is reflected in real-time communication, objects used for system configuration, and application protocols for engineering models. Currently, there is no unified application layer protocol, but the following main protocols have received widespread support and corresponding products have been developed: (I) Modbus TCP/IP. This protocol, introduced by Schneider Electric, embeds Modbus frames into TCP frames in a very simple way, combining Modbus with Ethernet and TCP/IP to become Modbus TCP/IP. This is a connection-oriented approach; each call requires an answer. This call/answer mechanism works in conjunction with the Modbus master/slave mechanism, giving switched Ethernet high determinism. Using the TCP/IP protocol, a webpage format makes the user interface more user-friendly. A web browser can be used to view the operating status of devices within the enterprise network. Schneider Electric has registered port 502 for Mod-bus, which allows real-time data to be embedded into web pages. By embedding a web server in the device, a web browser can be used as the device's operating terminal. (II) ProfiNet In response to industrial application needs, Siemens of Germany released this protocol in 2001. It combines the original Profibus with Internet technology to form the ProfiNet network solution, which mainly includes: (1) a distributed automation system based on the Component Object Model (COM); (2) specifying open and transparent communication between ProfiNet fieldbus and standard Ethernet; (3) providing a system model that is independent of the manufacturer, including the device layer and the system layer. ProfiNet uses standard TCP/IP + Ethernet as the connection medium and uses standard TCP/IP protocol plus application layer RPC/DCOM to complete the communication and network addressing between nodes. It can connect traditional Profibus systems and new intelligent field devices at the same time. Existing Profibus network segments can be connected to the ProfiNet network through a proxy device, so that the entire Profibus device and protocol can be used in Pet without any changes. Traditional ProFibus devices can communicate with COM objects on ProFiNET through a proxy and implement calls between COM objects through the OLE automation interface. (III) The FF Fieldbus Foundation released the Ethernet specification, called HSE (High Speed ​​Ethernet), in 2000. HSE is a combination of the Ethernet protocol IEEE 802.3, the TCP/IP protocol suite, and FF Ill. The FF Fieldbus Foundation clearly positions HSE as the integration of control networks and the Internet. A core part of HSE technology is the linking device, which is a key component of the HSE architecture that connects H1 (31.25 kb/s) devices to the 100 Mb/s HSE backbone network, and also has the functions of a bridge and gateway. The bridging function can be used to connect multiple H1 bus segments, enabling peer-to-peer communication between H1 devices on the same H1 segment without interference from the host system; the gateway function allows the HSE network to be connected to other factory control networks and information networks. HSE link devices do not need to interpret messages for the H1 subsystem, but instead aggregate message data from the H1 bus segment and translate H1 addresses into IP addresses. (IV) Ethernet/IP Ethernet/IP is a protocol system suitable for industrial environments. It is the latest member launched by two major industry organizations, ODVA (Open Devicenet Vendors Association) and ControlNet International. Like DeviceNet and ControlNet, they are networks based on the CIP (Control and Information Protocol). It is an object-oriented protocol that can guarantee the effective transmission of implicit (control) real-time I/O information and explicit information (including information used for configuration, parameter setting, diagnostics, etc.) on the network. Ethernet/IP uses the same application layer protocol CIP as DeviceNet and ControlNet. Therefore, they use the same object library and consistent industry standards, and have good consistency. Ethernet/IP uses standard Ethernet and TCP/IP technologies to transmit CIP communication packets. This combination of the universal and open application layer protocol CIP and the widely used Ethernet and TCP/IP protocols constitutes the Ethernet/IP protocol architecture. IV. Advantages of Industrial Ethernet (I) Wide Application Ethernet is the most widely used computer network technology. Almost all programming languages, such as Visual C++, Java, and Visual Basic, support Ethernet application development. (II) High Communication Speed ​​Currently, 10 and 100 Mb/s Fast Ethernet are widely used, and 1Gb/s Ethernet technology is gradually maturing, while the highest speed of traditional fieldbuses is only 12Mb/s (such as Siemens Profibus-DP). Obviously, Ethernet speed is much faster than traditional fieldbuses, fully meeting the ever-increasing bandwidth requirements of industrial control networks. (III) Low Cost Ethernet network cards are much cheaper than fieldbus network cards (approximately 1/10); in addition, Ethernet has been used for many years, and people have a lot of experience in Ethernet design and application, possessing quite mature technology. A wealth of software resources and design experience can significantly reduce system development and training costs, lower the overall system cost, and greatly accelerate system development and promotion. (IV) Strong resource sharing capability With the development of the Internet/Intranet, Ethernet has penetrated every corner. Users on the network have been freed from the constraints of geographical location of resources. Data from the industrial control field can be viewed on any computer connected to the Internet, realizing "integrated control and management," which is unmatched by any other fieldbus. (V) Great potential for sustainable development The introduction of Ethernet will provide possibilities for the subsequent development of control systems. Users do not need to invest in independent research in terms of technology upgrades. In this respect, no existing fieldbus technology can match it. At the same time, the development of robotics and intelligent technology requires communication networks to have higher bandwidth and performance, and communication protocols to have higher flexibility. Ethernet can meet these requirements very well. V. Current Status of Industrial Ethernet Applications in the Control Field Compared with fieldbus, industrial Ethernet provides an open standard, enabling enterprises to achieve comprehensive and seamless information integration from field control to management, solving the problem of "automation islands" caused by different protocols. However, from the current development, the application of industrial Ethernet in the control field is mainly reflected in the following forms. (I) Hybrid Ethernet/Fieldbus Network Structure This structure is actually a typical integrated form of information network and control network. Ethernet is gradually developing towards the field device level and is trying to integrate with other network forms as much as possible. However, Ethernet and TCP/IP were not originally designed for the control field and are not mature in many aspects such as architecture, protocol rules, physical media, data, software, and experimental environment. Fieldbus can fully meet the basic requirements of modern enterprises for the underlying control network and realize a truly fully distributed system. Therefore, Ethernet is used at the enterprise information layer and Fieldbus is used at the underlying device level, and information exchange between the two is realized through a communication controller. (II) Dedicated Industrial Ethernet Control Network How to use industrial Ethernet as a separate control network is one of the development directions of industrial Ethernet and also one of the research hotspots in the field of industrial control. For example, JetWeb, the new generation control system of Jetter AG in Germany, is an industrial automation control system that integrates fieldbus technology, 100Mb/s Ethernet technology, CNC technology, PLC technology, visual human-machine interface technology and global production management technology. It also has wide compatibility and can be compatible with third-party automation control products. It proposes the concept that "the network is the controller" and is an industrial network structure that replaces all underlying fieldbuses. This type of industrial control network integrates Ethernet throughout all layers of the network, making it a transparent application entity covering the entire enterprise. It achieves a seamless integration of office automation and industrial automation, essentially a single-layer, flat structure. Its excellent scalability and interconnectivity make it a truly unified, fully open network architecture. (III) Web-based Network Monitoring Platform Embedded Ethernet is a recent hot topic in network applications. It enables all network-connected devices to communicate with each other via the Internet, from computers, PDAs, and communication equipment to instruments and home appliances. Within an enterprise, the enterprise information network can be used to publish and display real-time factory operation data. Managers can use a web browser to remotely monitor on-site conditions, remotely debug equipment, and remotely diagnose and handle equipment faults. The simplest way to achieve this is to use an independent Ethernet controller, connecting a control host with a TCP/IP interface and field devices with RS-232 or RS-4.85 interfaces. The Ethernet controller acts as a bridge between the general computer network and various field devices, such as the I-7188EX/EN series embedded controller from Taiwan's ICP DAY. VI. Conclusion Ethernet is renowned for its "E-networking all the way," meaning it extends all the way to the control layer of enterprise field devices, and is considered the best solution for future control networks. While currently, Industrial Ethernet is not suitable for all industrial automation equipment and cannot be fully applied to the industrial control field, and the different application layer protocols of various manufacturers have some impact on its comprehensive application, Ethernet will gradually mature in the process of entering the industrial control field, possessing enormous development potential and a very broad prospect. Its application areas will continue to expand, and its breadth and depth of application will continue to increase.