Abstract: This article discusses the current status and prospects of Ethernet applications in the field of automation, and hot topics such as Ethernet and fieldbus technologies. Starting from a technical comparison, it presents personal views. This article argues that Ethernet will become the mainstream technology in factory management and workshop monitoring layers, and its combination with Internet technology will form the foundation for future eManufactory technology. It will also see some development at the device layer without strict time requirements. However, for general industrial networks requiring real-time and deterministic communication, fieldbus technology will remain dominant. We must learn to face a real world where multiple network technologies coexist. Keywords: Ethernet, Fieldbus, PLC Introduction: Ethernet and TCP/IP communication technologies have achieved great success in the IT industry, becoming the preferred network communication technology in IT applications. In recent years, due to the lack of ideal results in international fieldbus technology standardization, Ethernet and TCP/IP technologies have gradually been applied in the automation industry and developed into a technological trend. The application of Ethernet in the automation industry should be divided into two aspects, or two levels. One is the combination of factory automation technology with IT technology and Internet technology, becoming the prototype of future manufacturing e-commerce technology and network manufacturing technology. Most experts give a positive evaluation to this development trend of automation technology. On the other hand, can Ethernet be widely used at the bottom layer of industrial process control, that is, the device layer or the field layer? Can it become or even replace the existing fieldbus technology as a unified industrial network standard? These questions are currently hot topics of debate among automation industry experts. This article will only discuss this issue, starting from the technical comparison between Ethernet and fieldbus, and talk about personal views. 1. What does Ethernet mean? What is "Ethernet"? And related IEEE 802.3 and TCP/IP technologies? This may be basic common sense for computer network engineers, but we automation engineers may not be clear about it. Before discussing Ethernet and automation technology and fieldbus technology, it is necessary to clarify the meaning of these basic terms. I have consulted relevant materials and now summarize the technical background of "Ethernet", IEEE 802.3 and TCP/IP as follows: (1) Ethernet: ►1975: The Palo Alto Research Center of Xerox Corporation in the United States successfully developed [METC76]. This network uses passive cables as buses to transmit data frames, hence the name "Ether" which propagates electromagnetic waves. ►1981: Xerox, Digital Equipment Corporation, and Intel jointly launched the Ethernet protocol [ETHE80]. ►1982: Revised to the second version, DIX Ethernet V2. Therefore, "Ethernet" should specifically refer to the technology described by "DIX Ethernet V2". (2) IEEE 802.3 ►Early 1980s: The IEEE 802 Committee of the Institute of Electrical and Electronics Engineers (IEEE) developed the local area network architecture, namely the IEEE 802 reference model. The IEEE 802 reference model is equivalent to the lowest two layers of the OSI model: ►1983: Based on DIX Ethernet V2 submitted by Xerox, Digital Equipment Corporation, and Intel, the IEEE 802 Committee launched IEEE 802.3. ►IEEE 802.3 is also called a network with CSMA/CD (Carrier Sense Multiple Access/Collision Detection). CSMA/CD is the media access control technology adopted by IEEE 802.3. Therefore, IEEE 802.3 is based on Ethernet, and its essential characteristic is the use of CSMA/CD media access control technology. Ethernet differs slightly from IEEE 802.3, but when ignoring network protocol details, people commonly refer to IEEE 802.3 as "Ethernet." Other network protocols related to IEEE 802 include: IEEE 802.1—Overview, architecture, and network interconnection, as well as network management and performance measurement; IEEE 802.2—Logical Link Control (LLC)—the highest-level protocol and interface with any LAN MAC sublayer; IEEE 802.3—CSMA/CD network—defining the specifications for the MAC sublayer and physical layer of a CSMA/CD bus network; IEEE 802.4—Token Bus network—defining the specifications for the MAC sublayer and physical layer of a token passing bus network; and IEEE 802.5—Token Ring network. Define the specifications for the MAC sublayer and physical layer of a token-passing ring network. IEEE 802.6—Metropolitan Area Network. IEEE 802.7—Broadband Technology. IEEE 802.8—Fiber Optic Technology. IEEE 802.9—Integrated Voice and Data LAN. IEEE 802.10—Security of Interoperable LANs. IEEE 802.11—Wireless LAN. IEEE 802.12—Preferred High-Speed ​​LAN (100Mb/s). IEEE 802.13—Cable TV. (3) TCP/IP Protocol ► TCP/IP is a set of communication protocols for exchanging information between multiple computers of the same or different types. The accurate name of the TCP/IP protocol suite should be the Internet Protocol Family, of which TCP and IP are two protocols. The Internet Protocol Family TCP/IP also includes other protocols and network applications related to these two protocols, such as User Datagram Protocol (UDP), Address Translation Protocol (ARP), and Internet Control Message Protocol (ICMP). Because TCP/IP is the protocol suite used by the Internet, the TCP/IP architecture is called the Internet architecture. ►Ethernet is the most widely used physical network for TCP/IP. In fact, TCP/IP technology supports various local area network protocols, including: Token Bus, Token Ring, FDDI (Fiber Distributed Data Interface), SLIP (Serial Line IP), PPP (Point-to-Point Protocol), X2.5 data network, etc. Since TCP/IP is the protocol suite used by the world's largest Internet, and the underlying physical network of TCP/IP mostly uses the Ethernet protocol, Ethernet + TCP/IP has become the most widely used technology in the IT industry. The "Ethernet" mentioned in this article mainly refers to the IEEE 802.3 protocol. If the TCP/IP protocol suite is further adopted, it is represented as "Ethernet + TCP/IP". 2. Why Has Ethernet Entered the Automation Industry? Ethernet + TCP/IP dominates the IT industry as an office and business network, and its technical characteristics are mainly suitable for information management and information processing systems. But why has it gradually developed into the automation industry in recent years, creating a situation of competition with fieldbus technology? Looking back at the development of automation technology in recent years, we can understand the reasons behind it. (1) Automation technology has developed from single machine control to factory automation (FA) and then to system automation. In recent years, the development of automation technology has made people realize that simply improving the automation level of single machines in production equipment may not necessarily bring good benefits to the whole enterprise. Therefore, the further requirement that enterprises put forward for automation technology is to realize the automation of the whole factory as a system, with the goal of achieving the best economic benefits for the enterprise. Therefore, the modern manufacturing automation model has emerged, so it can be said that automation technology has developed from single machine automation to system automation. Automation technology has developed from single machine control to factory automation (FA) and system automation. The manufacturing industry has put forward the requirements of digital communication and information integration technology for automation technology; that is, it requires the application of digital communication technology to realize the vertical transparent communication of factory information. (2) The integration of equipment status and production information at the bottom level of the factory and the digital communication network at the bottom level of the workshop are the foundation of the information integration system. In order to meet the requirements of the upper management of the factory for the information of the bottom equipment, the integration of equipment status and production information at the bottom level of the factory workshop is the foundation for realizing the whole factory FA/CIMS. The hierarchical structure of the factory automation information network: factory management level, workshop monitoring level, field device level (3) The emergence of fieldbus technology Fieldbus is a communication network between the bottom devices of the factory. It is the application of computer digital communication technology in the field of automation, and provides a communication technology platform for the integration of information of the bottom devices of the workshop and production process information. Figure 4 shows the transparent communication of vertical integration of information of the whole factory through the application of fieldbus technology at the bottom of the factory, that is, data access from the management level to the bottom of automation. (4) One of the international standards of fieldbus ROBIBUS technology ROBIBUS technology was jointly developed by 13 companies including Siemens and 5 research institutions in 1987; it was approved as the German industrial standard DIN 19245 (PROFINUS-FMS/-DP) in 1989; it was approved as the European standard EN 50170 V.2 (PROFIBUS-FMS/-DP) in 1996; and in 1999, PROFIBUS became a component of the international standard IEC 61158 (Type III). PROFIBUS technology provides PROFIBUS-DP and -PA technologies for the device layer and PROFIBUS-FMS technology for the shop floor layer. ►PROFIBUS-DP is a device-level fieldbus used for communication between controllers (such as PLCs, PCs, and NCs) and field control devices (such as drives, detection devices, and HMIs). ► Device-level fieldbus technology features high speed (12M), real-time operation, determinism, and reliability (e.g., -DPV2 can be used for motion control), while transmitting relatively small amounts of data. ►PROFIBUS-PA is also a device-level bus with an IEC61158-2 physical layer, enabling bus power supply and intrinsically safe technology. ►PROFIBUS-FMS is a shop floor-level fieldbus primarily used for shop floor-level equipment monitoring. It mainly performs shop floor production equipment status and process monitoring, shop floor-level production management, and integration of shop floor-level equipment and production information. Shop floor-level fieldbus features large data transmission capacity, complete application layer information specifications, and low requirements for network real-time performance. (5) International Fieldbus Technology Standard IEC 61158 Based on the concept of fieldbus technology, given the ever-changing field instrumentation equipment in the automation industry, standardization of fieldbus technology is crucial for achieving interconnection between different manufacturers and product types. Therefore, the International IEC Committee proposed the development of the fieldbus technology standard IEC 1158 (i.e., IEC 61158) in 1984. A. Objectives of IEC 61158: The objective of IEC 61158 is to develop a fieldbus standard for the entire industrial automation sector. To this end, based on the different needs of various industries for automation technology, automation technology is divided into five different sectors; see Figure 6: Objectives of IEC 1158. IEC 61158 aims to develop a fieldbus technology standard that meets the different application needs of the five major industrial automation sectors. B. The Result of Compromise After more than a decade of effort, a vote was held on IEC 61158 (TS) in 1998. Since IEC 61158 (TS) only included the Process Control part, it failed to pass the vote, and the automation industry's efforts to achieve a unified fieldbus technology standard, which had been anticipated for over a decade, failed. In December 1999, IEC 61158 abandoned its original concept and adopted a compromise solution: IEC 61158 (TS) + Add. Protocols as the IEC 61158 technical standard; where Add. Protocols include Control Net, PROFIBUS, P-Net, FF HSE, Swift Net, WorldFIP, and Interbus buses. The automation industry will face a reality of multiple bus technology standards coexisting. C. Lessons from the Development of IEC 61158 Facing the current trend of Ethernet application in the automation field, the development history of IEC 61158 offers at least two lessons, which are helpful for us to face reality clearly: I. Industrial automation technology is applied to various industries, and it is impossible to meet the technical requirements of all industries using a single fieldbus technology; fieldbus is different from computer networks, and people will face a reality of multiple bus technology standards coexisting. II. Technological development is largely constrained by market forces and commercial interests; technical standards are not only technical specifications but also products of compromise for commercial interests. (6) Ethernet enters the field of automation. The failure of IEC61158 to formulate a unified fieldbus technology standard has led some people to turn to Ethernet technology, which has already achieved success in the IT industry. Therefore, the fieldbus standard dispute has given Ethernet a rare opportunity to enter the field of automation. Companies that actively promote this technology concept, such as Schneider Electric of France, have proposed a solution based on Ethernet + TCP/IP for factory automation, which is called "Transparent Factory". It can be understood as: "Unified protocol specifications and transparent access to information". Schneider Electric is an active advocate and practitioner of introducing Ethernet technology into the bottom layer of factory equipment and widely replacing the existing fieldbus technology. A number of industrial-grade products have been launched and applied. 3. Current status of Ethernet application in the field of automation . At present, there are many successful application examples of Ethernet in the field of automation, mainly concentrated in the following aspects: (1) Workshop-level production information integration: mainly composed of dedicated production equipment, dedicated testing equipment, barcode scanners, PCs and Ethernet network equipment; the main function is to complete the management of workshop-level production information and product quality information. Management information network: that is, the computer network that supports the factory management MIS system. It mainly completes information systems such as ERP. SCADA systems: Especially those covering a wide area and incorporating computer wide area network (WAN) and wireless communication technologies, such as SCADA systems for urban water supply or sewage pipe networks, and SCADA systems for water conservancy and hydrological information monitoring. Individual control system networks: Some distributed control systems requiring high reliability and a certain degree of real-time performance have also adopted Ethernet + TCP/IP technology with excellent results; such as computer monitoring systems in hydropower plants. Since Ethernet has been successfully applied to many aspects of industrial automation, and since IEC 61158 has not provided a unified fieldbus technology standard, why can't Ethernet technology be introduced into the lower layer of industrial process control, i.e., the device layer, becoming or even replacing existing fieldbus technologies as a unified industrial network standard? This brings us back to the topic at the beginning of this article. On this issue, aside from the commercial propaganda driven by the interests of various companies, even automation industry experts have differing opinions. As someone engaged in fieldbus technology R&D, I am accustomed to comparing Ethernet and fieldbus technologies from a technical perspective, and have thus drawn several observations. 4. Comparison of Ethernet and Fieldbus Technologies (1) Physical Layer Fieldbus A. Transmission Media: Mostly uses shielded twisted-pair cable (RS-485), optical fiber, coaxial cable to solve problems such as long-distance transmission, data transmission rate and electromagnetic interference. There are also wireless transmission solutions to adapt to different occasions. B. Connectors: Industrial-grade connectors with various protection levels. C. Line power supply and intrinsic safety: such as IEC61158-2, used for process control and occasions requiring explosion-proof functions. D. Encoding: Asynchronous NRZ, bit synchronous Manchester encoding, etc. E. Transmission Rate: 9.6k～12M Ethernet A. Transmission Media: UTP Category 3 cable, UTP Category 5 cable, shielded twisted-pair cable, optical fiber, coaxial cable, wireless transmission solutions. B. Connectors: RJ45, AUI, BNC C. Bus power supply and intrinsic safety: None. D. Encoding: Synchronous, Manchester encoding. E. Transmission rate: 10M, 100M ( （2） Media access control mode Fieldbus: The media access control mode of the fieldbus must meet the requirements of industrial control networks, namely the real-time and deterministic nature of communication. Determinism means that the interval and time at which a station receives network services are determined each time; real-time means that the service time and interval allocated to the station by the network can guarantee that the station completes its determined task. Currently, the media access control modes used in fieldbus technology are mainly: token, master-slave, producer/consumer. Ethernet CSMA/CD (Carrier Sense Multiple Access/Collision Detection) is the media access control mode used by Ethernet (or IEEE 802.3). If it is not like this, it is not Ethernet (or IEEE 802.3); for example, if the token scheduling mode is used, it should be based on the IEEE 802.4 token bus network. According to the CSMA/CD (Carrier Sense Multiple Access/Collision Detection) mechanism, it cannot meet the real-time and deterministic requirements of industrial network communication. Since Ethernet and CSMA/CD have equivalent technical connotations, it can be said that Ethernet is not the real-time and deterministic network required by traditional industrial networks. (3) Transmission efficiency: Different networks have a limit on message length. In addition to the valid data, network messages also contain additional fields for synchronization, address, checksum, etc. The ratio of valid data fields to additional fields reflects the efficiency of valid data transmission in the network, or the cost of a single valid data transmission. Transmission efficiency = Valid data length / [Total additional field length + Valid data length] Ethernet Total additional field length = 26 bytes Maximum valid data length = 1500 bytes Minimum valid data length = 1 byte (fill in 0 if less than 46) Maximum transmission efficiency = 1500 / (1500 + 26) = 98.3% Minimum transmission efficiency = 1 / (1 + 26 + 45) = 1.39% PROFIBUS Fieldbus Total additional field length = 11 bytes Maximum valid data length = 244 bytes Minimum valid data length = 1 byte Maximum transmission efficiency = 244 / (244 + 11) = 95.69% Minimum transmission efficiency = 1 / (1 + 11) = 8.33% Typical data transmission volume of industrial networks (bytes) Transmission efficiency Typical data transmission volume (bytes) of industrial network Transmission efficiency 8 11.11% 8 42.11% 16 22.22% 16 59.26% 24 33.33% 24 68.57% 32 44.44% 32 74.42% 40 55.55/5 40 78.43% 48 64.86% 48 81.36% 56 68.29% 56 83.58% 64 71.11% 64 85.33% 128 83.11% 128 92.09% (4) Field equipment information specifications and functional specifications The format and functional description specifications of field equipment information are called "profiles". Profiles can effectively realize the interconnection of various field equipment application layers. Example: PROFIBUS profile: ▼NC/RC industry standards (robot, CNC industry standards) ▼Industry standards for various speed drives ▼Operator control and process monitoring (HMI) industry standards ▼Industry standards for encoders ▼Industry standards for inter-controller communication ▼Industry standards for building automation ▼Industry standards for low-voltage switchgear ▼Industry standards for temperature, pressure, level, flow transmitters and positioners, etc. 5. How far can Ethernet go in the field of automation ? Ethernet has been widely used and recognized by users in the factory automation management layer and workshop monitoring layer. It also has many applications in the equipment layer where real-time performance is not strictly required. If Ethernet wants to go further and fully enter the bottom layer of the factory to become the main network technology for equipment connection, then Ethernet must make technical improvements. (1) Improve the physical layer A. The transmission medium should be able to provide a variety of industrial-grade sheathed and armored cables, optical fibers, etc. B. Various protection levels of industrial-grade connectors. C. It should have bus power supply and intrinsic safety solutions for process control and explosion-proof applications. (2) How to meet the requirements of real-time performance and determinism? Increasing bandwidth and reducing collisions are the most direct methods and have a certain effect; however, “as fast as possible” and “definitely fast” are different. In recent years, Ethernet has also made some improvements based on CSMA/CD technology, such as the application of intelligent hubs and switch technologies, but it has not guaranteed the real-time and deterministic nature of communication from a mechanistic perspective. How to further solve this problem? There are only two approaches: software-based and hardware-based. The hardware solution is to design new intelligent network switching equipment, hoping not to blindly follow the old path of increasing bandwidth; the software solution is to achieve real-time and deterministic communication functions by software scheduling based on a certain bandwidth resource. It should be pointed out that the above-mentioned shortcomings of Ethernet technology do not mean that Ethernet cannot be applied in the field layer. In fact, Ethernet has many successful application examples in many field layers where time requirements are not very strict. (3) Cost: When Ethernet enters the field layer, the cost per site is a necessary factor to consider; it competes with current fieldbus (PROFIBUS, DeviceNet, ControlNet) products. 6. Can Ethernet replace fieldbus technology to become a unified industrial network standard? (1) Predicting the future is the most difficult thing; fieldbus is designed specifically for communication of industrial field devices and is a technology tailored to automation. Ethernet was originally designed as an office network for data processing. It seems easy to draw conclusions from a technical comparison. However, technological development is influenced by social, political, and economic factors, and market factors largely determine the direction of technology. Looking back at the history of computer development, there are countless precedents for this. Therefore, Ethernet will become the main application technology in the monitoring and management layers of factory automation workshops, especially since it can be connected to the Internet using the TCP/IP protocol, which is the technical foundation of the future eManufactory. At the device layer, Ethernet can also have a market share under conditions without strict time requirements. Before Ethernet can truly solve the problems of real-time performance and determinism, most field layers will still prefer fieldbus technology. (2) Faced with the coexistence of multiple industrial bus technologies, we should have an open-minded attitude. Philosophers tell us that integration and diversification are a pair of interdependent contradictions that will coexist and compete for a long time. Ethernet reflects people's desire for standardized and integrated technology, but in reality, it is impossible to cover all the different needs of various industries with one technology. The development history of IEC61158 has given us a profound insight. We must learn to face a real world where multiple industrial bus technologies compete and coexist. 7. Possible solutions How to make a choice when facing specific problems? I think it is wise to deal with the matter at hand. Simply put, use the technology that is most suitable for your project. (1) Ethernet is more suitable for workshop-level production information integration for the following reasons: A. Most processing equipment has RS-232 interface: such as barcode machine, special equipment; B. Real-time, deterministic, and reliability requirements are not high; C. It is compatible with the information specifications and software interfaces of the upper-level network. (2) Fieldbus technology is preferred for equipment-level control for the following reasons: A. Real-time, deterministic, and reliability requirements; B. Specialization: For motion control requiring strict synchronization, Sercos or PROFIBUS-DPV2 are used; C. Reliability: Industrial-grade transmission layers enhance system reliability; D. A wide variety of fieldbus technologies and products are available, providing solutions at various cost levels.