Abstract: This paper introduces some problems in the development of fieldbus, analyzes the problems faced by Ethernet in fieldbus application, and proposes some practical solutions for industrial Ethernet in application based on current domestic and foreign research. It also analyzes the development prospects of industrial Ethernet. Keywords: Industrial Ethernet, control system, fieldbus, communication network 1 Introduction In industrial production, with the expansion of production scale and the increase in complexity, the requirements for control systems in practical applications are becoming increasingly higher. In the 1950s and 1960s, monitoring systems composed of electronic devices and automated instruments with analog signals replaced traditional electromechanical control systems. Subsequently, in the 1970s and 1980s, the emergence of Distributed Control Systems (DCS) centralized and unified the management of a large number of dispersed single-loop measurement and control systems through computers. Various I/O function modules replaced control room instruments, and computers were used to realize multiple functions such as loop regulation, operating condition interlocking, parameter display, and data storage, thus achieving a leap forward in industrial control technology. DCS generally consists of three levels: operator station level, process control level, and field instrument level. Its characteristic is "centralized management and decentralized control." Basic control functions are in the process control level, while the main role of the operator station level is supervision and management. Distributed control (DCS) minimizes the damage to the entire system caused by the unreliability of a single part, and the continuous maturation of various hardware and software technologies has greatly improved the reliability of the entire system, thus rapidly becoming the mainstream of industrial automatic control systems. However, DCS has a multi-level master-slave structure, and information transmission between lower levels must pass through the master unit, resulting in excessive load on the master unit, low efficiency, and the entire system "paralyzing" if the master unit fails. Moreover, DCS is a hybrid digital-analog system, and field instruments still use traditional 4-20mA analog signals, leading to high engineering and management costs and poor flexibility. In addition, each manufacturer's DCS uses its own standards and closed communication protocols, which greatly restricts system integration and application. In the 1990s, Fieldbus technology, characterized by digital communication, a fully distributed system architecture, open interconnected networks, multiple transmission media and topologies, and high environmental adaptability, rapidly emerged and matured. Control functions were fully transferred to field intelligent instruments. Based on this, the new Fieldbus Control System (FCS) integrated digital communication technology, computer technology, automatic control technology, network technology, and intelligent instruments, fundamentally breaking through the limitations of traditional point-to-point analog or digital-to-analog signal control. It constituted a fully distributed, fully digital, intelligent, bidirectional, interconnected, multi-variable, and multi-connector communication and control system. The corresponding control network structure also underwent significant changes. A typical FCS structure consists of a device layer, a control layer, and an information layer. The adoption of Fieldbus technology made it possible to delegate control functions to field devices; the Fieldbus standard is not only a communication standard but also a system standard. FCS is moving towards replacing DCS and driving another leap forward in industrial control technology. 2. Problems in Fieldbus Applications 2.1 Standardization Issues Fieldbus control systems still face several unresolved issues in practical applications, the most prominent being the lack of a unified standard. The IEC 61158 international standard, published in early 2000, resulted in eight subsets of IEC fieldbus international standards: H1 (FF), ControlNet, Profibus, P-Net, HSE (FF), SwiftNet, WorldFIP, and Interbus. The outcome of the IEC fieldbus international standard development indicates that multiple fieldbuses will coexist for a considerable period, leading to difficulties in system and information integration within control networks. End users, engineering integrators, and manufacturers alike are seeking high-performance, low-cost solutions. The eight types of fieldbuses employ different communication protocols, making mutual compatibility and interoperability virtually impossible. Each fieldbus has its own optimal application area. How to combine different levels of fieldbuses according to the application, ensuring that each part of the system selects the most suitable fieldbus, remains a challenging problem for users. 2.2 System Integration Issues In practical applications, a large system may use multiple fieldbuses, especially for China's rapidly growing end users. It is almost impossible to unify the fieldbus technology at different stages of enterprise development and for international multinational manufacturing equipment procurement. How to seamlessly integrate the enterprise's industrial control network with the management data network to achieve integrated management and control of the entire enterprise is crucial. When designing the network layout of the fieldbus system, it is necessary to consider not only the distance between each field node, but also the functional relationship between field nodes and the flow of information on the network. Since intelligent field instruments have strong functions, many instruments will have the same function blocks. When configuring, the selection of function blocks should be carefully considered to minimize the flow of information on the network. At the same time, the configuration of communication parameters is also very important. A balance should be made between the real-time performance of the system and the network efficiency. 2.3 Technical Bottlenecks There are some technical bottlenecks in the application of fieldbus, mainly in the following aspects. (1) When the bus cable is disconnected, the entire system may be paralyzed. Users hope that the system efficiency can be reduced but not crashed. Currently, many fieldbuses cannot guarantee this. (2) Constraints of intrinsically safe explosion-proof theory. Existing explosion-proof regulations limit the length of the bus and the number of loads on the bus. This limits the advantages of fieldbus in saving cables. (3) The system configuration parameters are too complex. There are many configuration parameters for fieldbus, which are not easy to master. However, the quality of the configuration parameters has a great impact on the system performance. Therefore, adopting a unified fieldbus standard is of particular importance to the development of fieldbus technology. In order to accelerate the development and application of the new generation of control systems, major manufacturers have been looking for other ways to solve the problems of scalability and compatibility. Industry insiders have turned their attention to Ethernet technology, which has been very successful in commercial LANs. It has a simple structure, low cost, easy installation, high transmission speed, low power consumption, rich hardware and software resources, good compatibility, high flexibility, easy integration with the Internet, and supports almost all popular network protocols. 3 Ethernet and TCP/IP Ethernet (Ethernet) originated from the network system built by Xerox in 1973. It is a bus-type LAN that uses baseband coaxial cable as the transmission medium and adopts the CSMA/CD protocol. Xerox's Ethernet network was highly successful, and in 1980, Xerox, DEC, and Intel jointly drafted the Ethernet standard. In 1985, the IEEE 802 committee incorporated Ethernet as the IEEE 802.3 standard and modified it. The main difference between the Ethernet standard and the IEEE 802.3 standard is that the Ethernet standard only describes bus LANs using 50-ohm coaxial cable with a data transmission rate of 10 Mbps, and it includes the entirety of the ISO data link layer and physical layer; while the IEEE 802.3 standard describes all LANs using the CSMA/CD protocol running on various media with data transmission rates from 1 Mbps to 10 Mbps. Furthermore, the IEEE 802.3 standard only defines one sublayer of the data link layer (the Media Access Control (MAC) sublayer) and the physical layer in the ISO reference model, while the logical link control (LLC) sublayer of the data link layer is described by IEEE 802.2. This specification stipulates the use of Carrier Sense Multiple Access/Collision Detection (CSMA/CD), with signals transmitted at 10 Mbps over coaxial cable. Following the ISO OSI seven-layer architecture, the Ethernet standard only defines the data link layer and physical layer as a complete communication system. After becoming the protocol for the data link and physical layers, Ethernet became tightly integrated with TCP/IP. Because the international internet later adopted Ethernet and TCP/IP protocols, people even grouped TCP/IP protocol suites such as HTTP together, calling it Ethernet technology. The simplicity and practicality of TCP/IP have been widely accepted by users, not only in office automation but also in the management and monitoring networks of various enterprises, and it is beginning to extend to the field device layer. Today, TCP/IP has become the most popular internet protocol, evolving from a simple TCP/IP protocol into a suite of IP-based TCP/IP protocols. In the TCP protocol, the core protocol of the network layer is IP (Internet Protocol), and it also provides protocols such as ARP (Address Resolution Protocol), RARP (Reverse Address Resolution Protocol), and ICMP (Internet Control Messages Protocol). The main functions of this layer include handling packet transmission requests from the transport layer (i.e., assembling IP datagrams and sending them to the network interface), processing incoming datagrams, forwarding datagrams or extracting packets from datagrams, and handling error and control messages (including routing, flow control, and congestion control). The transport layer provides communication services between applications (end-to-end), offering two protocols: User Datagram Protocol (UDP) and Transmission Control Protocol (TCP). UDP provides high-efficiency service for transmitting small numbers of packets, offering almost no reliability measures; applications using UDP must implement reliability operations themselves. TCP provides highly reliable data transmission service, primarily used for transmitting large numbers of packets and ensuring the reliability of data transmission. Ethernet supports transmission media such as thick coaxial cable, thin coaxial cable, twisted pair, and optical fiber. Its biggest advantage is its simplicity, economy, practicality, and ease of use, which makes it popular among users. Compared with fieldbus, Ethernet has the following advantages: (1) Good compatibility and extensive technical support. Ethernet based on TCP/IP is a standard open network, suitable for solving the compatibility and interoperability problems of different manufacturers' equipment in control systems. Equipment from different manufacturers can be easily interconnected, and seamless integration of information between office automation networks and industrial control networks can be achieved. Ethernet is currently the most widely used computer network technology and is widely supported by technology. Almost all programming languages ​​support Ethernet application development, such as VB, Java, and VC. Using Ethernet as a fieldbus can ensure that a variety of development tools and development environments are available. Using Ethernet in industrial control networks can prevent its development from being outside the mainstream of computer network technology development, thereby promoting mutual development between industrial control networks and information network technologies and ensuring sustainable technological development. (2) Easy to connect to the Internet. Ethernet supports almost all popular network protocols, enabling monitoring of enterprises from anywhere via the Internet, convenient access to remote systems, and sharing/access to multiple databases. (3) Low cost: Using Ethernet can reduce costs, including training costs for technicians, maintenance costs, and initial investment. As Ethernet is the most widely used network, it is widely supported by hardware developers and manufacturers, has abundant software and hardware resources, and offers a variety of hardware products for users to choose from. The hardware price is also relatively low. Currently, the price of Ethernet network cards is only one-tenth of that of fieldbus, and with the development of integrated circuit technology, its price will further decrease. People have a lot of experience in the design and application of Ethernet and are very familiar with its technology. A large amount of software resources and design experience can significantly reduce the development and training costs of the system. No separate research investment is required for technology upgrades, which can significantly reduce the overall cost of the system and greatly accelerate the development and promotion of the system. (4) Great potential for sustainable development: Due to the widespread application of Ethernet, its development has always received widespread attention and attracted a lot of technical investment. Moreover, in the era of rapid information change, the survival and development of enterprises will largely depend on a fast and effective communication management network. The development of information technology and communication technology will be faster and more mature, ensuring the continuous development of Ethernet technology. (5) High communication speed The current communication speed of Ethernet is 10M or 100M. Fast Ethernet of 1000M and 10G has also begun to be used. Ethernet technology is also gradually maturing. Its speed is much faster than the current fieldbus. Ethernet can meet the higher requirements for bandwidth. 4 Problems of Ethernet when applied to control However, traditional Ethernet is a commercial network. There are still some problems when it is applied to industrial control. The main problems are as follows: (1) Poor real-time performance and uncertainty Traditional Ethernet adopts the CSMA/CD media access control mechanism. Each node uses the BEB (Binary Exponential Back-off) algorithm to handle conflicts. It has the defect of queuing delay uncertainty. Each network node has to compete to obtain the right to send information packets. During communication, the node listens to the channel. Only when it finds that the channel is idle can it send information; if the channel is busy, it needs to wait. After the information starts to be sent, it is also necessary to check whether a collision has occurred. If a collision occurs, the information needs to be exited and resent. Therefore, it is impossible to guarantee a definite queuing delay and communication response determinism. It cannot meet the real-time requirements of industrial process control. Even when communication is busy, there is a risk of information loss, which limits its application in industrial control. (2) Industrial reliability problem Ethernet is designed for office automation and does not take into account the adaptability requirements of industrial field environment, such as ultra-high or ultra-low working temperature, strong electromagnetic noise generated by large motors or other high-power equipment that affects the channel transmission characteristics. If Ethernet is used in the workshop floor, the reliability problem must be solved. (3) Ethernet does not provide power and must have an additional power supply cable Industrial field control network can not only transmit communication information, but also provide power for field equipment to transmit work. This is mainly for the convenience of cable laying and maintenance. At the same time, bus power supply can also reduce cables and reduce wiring costs. (4) Ethernet is not an inherently safe system (5) Security problem Because Ethernet uses the TCP/IP protocol, it may be subject to network security threats including viruses, illegal intrusion and illegal operation by hackers. Unauthorized users may enter the network's control or management layers, causing security vulnerabilities. To address this, various security mechanisms such as user passwords, data encryption, and firewalls can be used to strengthen network security management. However, solutions for network security issues in industrial automation control systems still require careful study. (6) Integration issues between existing control networks and newly built Ethernet control networks. Among these issues, real-time performance, determinism, and reliability have long been major obstacles preventing Ethernet from entering the industrial control field. To solve this problem, the solution of Industrial Ethernet has been proposed. 5 Industrial Ethernet Generally speaking, Industrial Ethernet is a standard Ethernet specifically designed for industrial application environments. Industrial Ethernet is technically compatible with commercial Ethernet (i.e., the IEEE 802.3 standard). The differences between Industrial Ethernet and standard Ethernet can be compared to the differences between industrial control computers and commercial computers. To meet the needs of industrial sites, Ethernet needs to meet the following requirements. (1) Adaptability includes mechanical characteristics (vibration resistance, shock resistance), environmental characteristics (operating temperature requirement of -40～+85℃, and corrosion resistance, dustproof, and waterproof), electromagnetic environment adaptability, or electromagnetic compatibility (EMC) should comply with EN50081-2 and EN50082-2 standards. (2) Reliability Due to the harsh environment of industrial control sites, higher requirements are placed on the reliability of industrial Ethernet products. (3) Intrinsic safety and explosion-proof technology For intelligent equipment and communication equipment used in industrial sites with flammable, explosive, and toxic gases, certain explosion-proof measures must be taken to ensure safe production in industrial sites. Explosion-proof technologies for field equipment include two types: flameproof (such as increased safety, airtight, potting, etc.) and intrinsically safe. Compared with flameproof technology, intrinsically safe technology uses the suppression of ignition source energy as an explosion-proof means, which can bring the following technical and economic advantages: simple structure, small size, light weight, and low cost; maintenance and replacement can be carried out under energized conditions; high safety and reliability; and wide applicability. The key technologies for achieving intrinsic safety are low power consumption technology and intrinsically safe explosion-proof technology. Since the power consumption of Ethernet transceivers is relatively high, generally around 60-70 mA (5V operating power), it is difficult to design low power field devices (such as industrial field Ethernet switches, transmission media, and Ethernet-based transmitters and actuators). Therefore, under the current technical conditions, it is more feasible to adopt explosion-proof measures for Ethernet systems. On the other hand, for non-hazardous occasions without strict intrinsic safety requirements, complex explosion-proof measures can be disregarded. (4) Easy to install and adaptable to the installation requirements of industrial environments, such as DIN rail mounting. 6 Methods to improve the practicality of Ethernet With the development of related technologies, the development of Ethernet has also made a fundamental leap. With the help of related technologies, the practicality of Ethernet in industrial control can be improved in general. 6.1 Using switching technology Traditional Ethernet uses a shared hub, whose structure and function are only a multi-port physical layer repeater. All stations connected to the shared hub share a bandwidth and send and receive data in accordance with the CSMA/CD protocol. A switching hub can be considered a controlled multi-port switch matrix where information flows between ports are isolated, providing a direct, fast point-to-point connection between the source and destination ends of the switching equipment. Different ports can form multiple data channels, and data input and output between ports are no longer constrained by CSMA/CD. With the development of modern switching technology, the transmission rate within a switch port is greater than the sum of the transmission rates between all Ethernet ports at the device layer, thus reducing the Ethernet collision rate and providing buffering for conflicting data. Of course, the switch must operate in store-and-forward mode, ensuring only point-to-point connections in the system and preventing collisions. Multiple switches decompose the entire Ethernet into many independent areas; Ethernet data collisions exist only within their respective collision domains, with no collisions between different domains. This significantly increases the bandwidth of each station on the network, thereby improving the network performance and determinism of switched Ethernet. Switched Ethernet does not change the original Ethernet protocol and can directly use ordinary Ethernet cards, greatly reducing networking costs and fundamentally solving the problem of uncertain Ethernet communication transmission delay. Studies show that when the communication load is below 10%, the transmission delay caused by collisions in Ethernet is almost negligible. In industrial control networks, the transmitted information is mostly periodic measurement and control data, with small message sizes, low information volume, and short transmission length. This information includes measured values ​​of production unit operating parameters, control quantities, operating positions of switches and valves, alarm status, equipment resource and maintenance information, system configuration, parameter modifications, zero-point and range calibration information, etc. Its length is generally small, typically only a few to tens of bytes, and the network throughput requirements are not high. Studies show that in a typical industrial control system with 6000 I/Os, the communication load is about 5% of that of 10M Ethernet. Even with operator information transmission (such as changes in setpoints, downloads of user applications, etc.), the load of 10M Ethernet can be kept below 10%. 6.2 Adopting High-Speed ​​Ethernet With the rapid development of network technology, high-speed Ethernet (100M) and gigabit Ethernet products and international standards have emerged, and 10G Ethernet products have also been launched. By increasing communication speed and combining it with switching technology, the overall performance of the communication network can be greatly improved. 6.3 Full-duplex communication mode: In switched Ethernet, each port is a collision domain, and even in half-duplex mode, data cannot be sent and received simultaneously. Full-duplex mode allows two stations on the same data link to send and receive data simultaneously, solving the waiting problem inherent in half-duplex mode and theoretically doubling the transmission rate. Full-duplex communication technology allows simultaneous reception and transmission of message frames on both pairs of twisted-pair cables (or two optical fibers) between device ports, thus eliminating the constraints of CSMA/CD. This prevents collisions when any node sends a message frame, and the collision domain disappears. For urgent information, message priority technology can be applied according to IEEE 802.3p&q, allowing high-priority messages to enter the queuing system first for service. This priority ordering ensures that urgent information in the industrial field can be successfully and promptly transmitted to the central control system for timely processing. 6.4 Virtual LAN technology: The emergence of Virtual LANs (VLANs) has broken many traditional network concepts, making network structures more flexible and convenient. In essence, a VLAN is a broadcast domain, unrestricted by geographical location. It can divide network users in different geographical locations into logical network segments based on factors such as departmental functions, object groups, and applications. Each port of a LAN switch can only be labeled with one VLAN. All stations within the same VLAN share a broadcast domain, and broadcast information between different VLANs is isolated, thus preventing broadcast storms. In industrial process control, control layer units must be distinguished from ordinary units in terms of data transmission real-time performance and security. Using VLANs on the open platform of industrial Ethernet allows for logical segmentation, separating different functional layers and departments, thereby improving overall network security and simplifying network management. Typically, VLANs are divided into three types: static port allocation, dynamic VLANs, and multi-VLAN port configuration. Static port allocation refers to network administrators using network management software or device switches to assign ports directly to a virtual network (VLAN). These ports will maintain this subordination unless the network administrator reconfigures them. Dynamic VLANs (VLANs) refer to ports that support dynamic VLANs, where intelligent management software can automatically determine their subordination. Multi-VLAN port configuration allows a user or a single port to access multiple VLANs simultaneously, enabling a single control layer computer to be configured for simultaneous access by multiple departments or resources within multiple VLANs. 6.5 Introducing Quality of Service (QoS) IP QoS refers to the quality of service of IP, i.e., the performance of IP data streams as they pass through the network. Its purpose is to provide end-to-end quality of service guarantees to users. QoS has a set of metrics, including service availability, latency, variable latency, throughput, and packet loss rate. QoS networks can distinguish between real-time and non-real-time data. In industrial Ethernet, QoS technology can identify higher-priority data from the control layer and prioritize its processing. This ensures that industrial Ethernet meets the real-time control requirements of industrial automation in terms of response latency, transmission latency, throughput, reliability, transmission failure rate, and priority. In addition, QoS networks can prevent unauthorized network use, such as unauthorized access to terminals of control layer field control units and monitoring units. Furthermore, industrial Ethernet application standards and related protocol improvements supported by major companies have emerged. Introducing industrial Ethernet into the underlying network not only facilitates vertical integration of the field layer, control layer, and management layer, but also reduces the horizontal integration costs of equipment from different manufacturers. The extension of Ethernet to the underlying network is inevitable; therefore, well-known manufacturers have supported industrial Ethernet and developed various industrial application standards. For example, companies like Rockwell and OMRON support Ethernet/IP. IP stands for Industrial Protocol, which provides a Producer/Consumer model, porting the application layer of ControlNet and DeviceNet control and information protocols to TCP. FF's high-speed Ethernet protocol HSE provides publisher/orderer and object models, primarily used in engineering control, and has received support from major companies such as Foxboro and Honeywell. The Modbus/TCP protocol released by Schneider Electric bundles the Modbus protocol with the TCP protocol, making it easy to implement and enabling interconnection. To improve real-time performance, the Ethernet protocol has also undergone some improvements. RETHER (Real Time Ethernet), a fully software-based protocol, ensures real-time performance without altering existing Ethernet hardware. It employs a hybrid operating mode to minimize the impact on non-real-time data transmission performance. A non-contention-based permission control mechanism and an efficient token passing scheme prevent token loss due to node failure. Networks adhering to the RETHER protocol operate in both CSMA and RETHER modes. During real-time communication, the network transparently switches to RETHER mode and returns to CSMA mode after the real-time communication ends. Another Ethernet protocol, RTCC (Real Time Communication Control), provides a solid foundation for distributed real-time applications. RTCC is a layer built on top of Ethernet, providing high-speed, reliable, and real-time communication. It does not require changes to existing hardware and uses two novel mechanisms—command/response multiplexing and bus tables—to allocate channels. In the RTCC protocol, all nodes are classified into two categories: Bus Controller (BC) and Remote Terminal (RT). There is only one BC, and the rest are RTs. The BC (Block Controller) handles both the initiation and management of information transmission, and implements both the access arbitration process and the transmission control process. Through the integration and synchronization of these two processes, not only is the node's transmission time deterministic, but the node's bus usage time is also controllable. Experiments on 10Mbps Ethernet demonstrate that RTCC has satisfactory determinism. A third method to improve real-time performance is flow balancing, which involves adding a flow balancer between UDP or TCP/IP and Ethernet MAC. This flow balancer serves as the interface between them and is installed on each network node. At the local node, it prioritizes real-time packets to eliminate competition between real-time and non-real-time information, while balancing non-real-time information to reduce conflicts with real-time information from other nodes. To ensure the throughput of non-real-time information, the flow balancer can also adjust the data flow generation rate according to the network load. This method does not require any modifications to the existing standard Ethernet MAC protocol and TCP or UDP/IP. Therefore, by addressing the uncertainty of Ethernet queuing delays through appropriate flow control, switching techniques, full-duplex communication, and information prioritization, and by improving fault tolerance, system design, and redundancy structures, Ethernet can be fully utilized in industrial control networks. In fact, in the mid-to-late 1990s, major domestic and international industrial control companies adopted Ethernet in their control systems, launching Ethernet-based DCS, PLCs, data acquisition units, and Ethernet-based field instruments and display instruments. With the increasing maturity of network and information technology, the adoption of Ethernet and TCP/IP protocols as the primary communication interfaces and means in industrial communication and automation systems, and the development towards networking, standardization, and openness, will be the main trend in the development of various control system technologies. Ethernet, as the most widely used and fastest-growing local area network (LAN) technology, has achieved extraordinary development in industrial automation and process control. At the same time, IP-based end-to-end addressing, providing a standardized, shared, and high-speed information channel solution for industrial production, will inevitably have a profound impact on control systems.