Abstract: This paper analyzes the characteristics of industrial Ethernet and real-time Ethernet technologies and introduces the industrial Ethernet protocol in the IEC international standard system. Keywords: Industrial Ethernet, Real-time Ethernet, International Standard 1 Introduction With the development of information technologies such as computers, communications, and networks, the field of information exchange has covered factories, enterprises, and even markets around the world. Therefore, it is necessary to establish a comprehensive automation network platform that includes all levels from industrial field devices to control and management layers, and to establish an enterprise information system based on industrial control network technology. As a special type of network, the industrial control network directly faces the production process, shouldering the special task of transmitting measurement and control information at the front line of industrial production operation, and generating or triggering the movement and conversion of matter or energy. Therefore, it should usually meet special requirements and characteristics such as strong real-time performance, high reliability, adaptability to harsh industrial field environments, and bus power supply. Against this background, fieldbus technology, which emerged and developed in the 1980s, replaced the analog transmission method of 4-20mA current with fully digital communication, enabling the control system and field instruments to transmit not only production process measurement and control information, but also a large amount of non-control information from the field instruments, making the integrated management and control of industrial enterprises possible. This has led to significant changes in the architecture and functional structure of current automation instruments, DCS, and programmable logic controllers (PLCs). Fieldbus technology has several shortcomings in its development: (1) There are too many existing fieldbus standards; the international standard IEC61158 alone includes eight types, failing to unify into a single standard; (2) Different buses are incompatible, unable to truly achieve transparent information exchange, and unable to achieve seamless information integration; (3) Fieldbus is a dedicated real-time communication network, resulting in higher costs; (4) Fieldbus has lower speeds, supports limited applications, and is not convenient for integration with Internet information. 2 Industrial Ethernet What is Industrial Ethernet? Generally speaking, Industrial Ethernet is technically compatible with commercial Ethernet (i.e., the IEEE 802.3 standard), but in product design, it must meet the needs of industrial sites in terms of material selection, product strength, and applicability. That is, it must meet the following requirements: (1) Environmental adaptability, including mechanical environmental adaptability (such as vibration resistance and shock resistance), climatic environmental adaptability (working temperature requirement is -40～+85℃, at least -20～+70℃, and it must be corrosion resistant, dustproof and waterproof), electromagnetic environmental adaptability or electromagnetic compatibility (EMC) should comply with EN 50081-2 and EN 50082-2 standards. (2) Reliability, industrial Ethernet products must be able to adapt to the harsh environment of industrial control sites. (3) Safety, in explosive or flammable environments, industrial Ethernet products also need to have explosion-proof requirements, including explosion-proof and intrinsically safe methods. (4) Easy installation, adapting to the installation requirements of industrial environments. In order to solve the problem of stable network operation under extreme conditions in uninterrupted industrial applications, some companies have specially developed and produced a series of DIN rail transceivers, hubs and switches, which are installed on standard DIN rails and have redundant power supply. The connectors adopt a robust DB-9 structure. Other companies have also developed and produced ruggedized connectors specifically for industrial control fields (such as ruggedized RJ45 connectors, industrial Ethernet switches with ruggedized RJ45 connectors, ruggedized fiber optic converters/repeaters, etc.), which can be used in industrial Ethernet transmitters, actuators, etc. The differences between industrial Ethernet equipment and commercial Ethernet equipment are shown in the attached table. 3 Real-Time Ethernet As is well known, Ethernet, due to its CSMA/CD media access control mechanism, has the characteristic of communication uncertainty, which was once a major obstacle to its application in fieldbus. Therefore, simply taking some measures to improve the reliability and environmental adaptability of Ethernet equipment applications has not yet solved the real-time communication problem for industrial Ethernet. To this end, major companies worldwide began to study the deterministic and real-time communication problems based on Ethernet and achieved some important results, some of which have been verified through practical applications in industrial fields. In May 2003, IEC/SC65C established WG11 working group to meet the application needs of the real-time Ethernet market and to develop international standards for real-time Ethernet applications. According to the definition of IEC/SC65C/WG11, Real-time Ethernet (RTE) refers to Ethernet that does not change the communication characteristics, related network components, or overall behavior of ISO/IEC 8802-3 or IEC 1588, but can be modified to a certain extent to meet real-time behavior: real-time performance, i.e., deterministic communication; time synchronization behavior between field devices; and sufficient and frequent exchange of short data. Therefore, the Real-time Ethernet standard first needs to solve the real-time communication problem. Simultaneously, it needs to define application-layer service and protocol specifications to address the interoperability issues between open systems. During the standard development process, IEC/SC65C/WG11 received six new Real-time Ethernet proposals, including those from the Chinese EPA, each with its own unique characteristics. Finally, after several serious discussions, and based on the IEC/SC65C's 2002 decision that "no new types will be added to the IEC 61158 standard before 2007," the working group unanimously agreed to release the new real-time Ethernet protocol as a Publicly Available Specification (PAS). These PAS will be considered for inclusion in IEC 61158 during its 2007 revision. 4. Introduction to Industrial Ethernet Protocols Currently, in the fieldbus architecture, in addition to HSE, Ethernet/IP, and Profinet included in the international fieldbus application standard IEC 61784-1, Ethernet-based communication protocols also include EPA, EtherCAT, Ethernet PowerLink, Vnet/IP, TCnet, and Modbus/IDA—six new proposals. 4.1 HSE (High Speed ​​Ethernet) HSE is a new work by the Fieldbus Foundation after abandoning the original high-speed bus H2. The Fieldbus Foundation explicitly positions HSE as enabling the integration of control networks with the Internet. HSE linking devices transmit H1 network segment information to the Ethernet backbone and further to the enterprise's ERP and management systems. Operators in the control room can directly view the field operation status using a web browser. Field devices can also obtain control information from the network. HSE directly adopts Ethernet + TCP/IP at the lower four layers, and directly adopts the FF H1 application layer services and function block application process specifications at the application and user layers. Linking devices connect the FF H1 network to the HSE network segment. HSE linking devices also function as bridges and gateways; their bridging function can connect multiple H1 bus segments, enabling peer-to-peer communication between H1 devices on different H1 segments without host system intervention. The HSE host can communicate with all linking devices and the H1 devices connected to them, enabling the transmission of operational data to remote field devices and the receipt of data from field devices, achieving monitoring and reporting functions. Monitoring and control parameters can be directly mapped to standard function blocks or "flexible function blocks" (FFBs). 4.2 Profinet Developed by Siemens and supported by Profibus International, Profinet currently has three versions. The first version defined automation components based on TCP/UDP/IP. It uses standard TCP/IP + Ethernet as the connection medium, employing standard TCP/IP protocols plus application-layer RPC/DCOM to complete communication and network addressing between nodes. It can simultaneously connect to traditional Profibus systems and new intelligent field devices. Existing Profibus network segments can be connected to the Profinet network through a proxy device, allowing the entire Profibus device and protocol to be used seamlessly within Profinet. Traditional Profibus devices can communicate with COM objects on Profinet through the proxy, and COM object calls are implemented through the OLE automation interface. It applies Ethernet to non-time-critical communication between higher-level devices and Profibus-DP field device technology, integrating the real-time control domain to a higher level through the proxy. In its second version, Profinet opened two channels over Ethernet: a standard non-real-time communication channel using the TCP/IP protocol, and a real-time channel that bypassed Layer 3 and Layer 4, providing precise communication capabilities. This protocol reduced data length to decrease the throughput of the communication stack. To optimize communication, Profinet defined message priorities according to IEEE 802.p. A maximum of seven priorities were available. Profinet version 3 adopted a hardware solution to shrink the software-based channel, further reducing the processing time of the communication stack software. For connection to integrated Ethernet switches, Profinet version 3 also began to address motion control solutions based on IEEE 1588 synchronous data transmission. 4.3 Ethernet/IP Ethernet/IP (Ethernet/Industrial Protocol) was defined by Rockwell and supported by ODVA and ControlNet International. Ethernet/IP networks utilize commercial Ethernet communication chips, physical media, and a star topology. They employ Ethernet switches to achieve point-to-point connections between devices, simultaneously supporting 10Mbps and 100Mbps commercial Ethernet products. The Ethernet/IP protocol consists of three parts: the IEEE 802.3 physical and data link layer standards, the TCP/IP protocol suite, and the Control and Information Protocol (CIP). The first two parts are standard Ethernet technologies, while the distinctive feature is the CIP component. To improve interoperability, Ethernet/IP uses the same CIP found in ControlNet and DeviceNet control networks. CIP provides both real-time I/O communication and peer-to-peer information transmission. Its control portion handles real-time I/O communication, while its information portion handles non-real-time information exchange. 4.4 EPA The EPA standard was drafted by a standard drafting working group led by Professor Jin Jianxiang, President of Zhejiang Supcon Technology Co., Ltd., jointly established by Zhejiang University, Zhejiang Supcon, Shenyang Institute of Automation of the Chinese Academy of Sciences, Chongqing University of Posts and Telecommunications, Dalian University of Technology, and Tsinghua University, with the support of the National High Technology Research and Development Program of China (863 Program). In the EPA system, the control network is divided into several control areas, each of which is a micro-segment. Each micro-segment is separated from other network segments by an EPA bridge. Communication between EPA devices within a micro-segment is restricted to its own control area and does not consume bandwidth resources of other network segments. Communication between EPA devices in different micro-segments requires forwarding control by the corresponding EPA bridge. An EPA bridge has at least two EPA interfaces. When it needs to forward a packet, it first checks the source IP address, destination IP address, EPA service identifier, and other information in the packet to determine whether forwarding is necessary and to determine the packet forwarding path. Therefore, the forwarding of any broadcast packets will also be controlled, preventing the broadcast bursts that occur with general switches. The EPA devices connected to each micro-segment send messages to the network in a time-division multiplexing manner through their built-in communication stack software. This avoids two devices sending data to the network simultaneously, preventing message collisions. Users can predict when their sent information will arrive at the destination station within a predictable timeframe. The EPA system supports IEEE 1588 time synchronization and also supports parallel transmission of standard Ethernet frames and EPA real-time Ethernet frames. 4.5 EtherCAT EtherCAT (Ethernet for Control Automation Technology) was developed by Beckhoff GmbH in Germany and supported by the EtherCAT Technology Group (ETG). It uses Ethernet frames and sends data in a specific ring topology. Each station on the network takes data relevant to that station from the Ethernet frame or inserts its own specific input/output data. The last module in the network sends a frame to the first module to form and create a physical and logical ring. EtherCAT also uses an internal priority system to give real-time Ethernet frames higher priority than other data (such as configuration or diagnostic data). Configuration data is transmitted only during gaps in the transmission of real-time data (if the gap time is sufficient for transmission) or through specific channels. EtherCAT also retains standard Ethernet functionality and is compatible with traditional IP protocols. To implement such a device, a dedicated ASIC chip is required to integrate at least two Ethernet ports and employ an IEEE 1588-based time synchronization mechanism to support real-time applications in motion control. 4.6 Powerlink Powerlink was developed by B&R and supported by the Ethernet Powerlink Standardisation Group (EPSG). The Powerlink protocol extends the TCP (UDP)/IP stack at layers 3 and 4. It uses Slot Communication Network Management (SCNM) middleware to control data flow on a shared Ethernet segment. SCNM uses a master-slave scheduling method, where each station can only send real-time data when it receives a request from the master station. Therefore, only one station can access the bus at a given time, so there are no conflicts, thus ensuring real-time communication. For this purpose, Powerlink requires IEEE 1588-based time synchronization. In its extended second version, communication and device protocols based on CANopen were included. 4.7 VNET/IP VNET/IP, developed by Yokogawa of Japan, is a real-time extension of the Real-time & Reliable Datagram Protocol (RTP). It uses UDP at the transport layer but is optimized at the IP stack protocol layer for redundant network connections. 4.8 TCnet TCnet, developed by Toshiba of Japan, features a real-time extension to MAC and establishes two redundant channel connections based on standard Ethernet. 4.9 Modbus-IDA Modbus/TCP, defined by Schneider Electric and supported by Modbus-IDA, applies the Modbus protocol over TCP/IP networks. Its real-time extension uses Real-time Publisher Subscriber (RTPS) over UDP. Modbus/TCP is an extension of Modbus, based on Ethernet and the standard TCP/IP protocol, directly applying Layer 4. It defines a simple, open, and widely used transport protocol for master-slave communication. The IDA architecture can be used for both real-time and non-real-time applications. Its deterministic communication can be achieved through IDA middleware. The middleware includes the standard Modbus/TCP protocol. IDA also employs web-based communication applications, providing horizontal and vertical integration and extending the application of web servers. 5. Conclusion From the perspective of the development trend of industrial Ethernet technology, although various industrial Ethernet technologies may coexist, similar to the international competition in fieldbus technology, a basic consensus has been reached internationally: the development of industrial automation technology cannot be separated from the development of mainstream international information technology, and the application of Ethernet in industrial control systems will inevitably become increasingly widespread. Based on real-time Ethernet technology, many mainstream technologies in the IT field will undoubtedly play a driving role in the development of industrial control technology.