Status Quo and Development of Industrial Ethernet

I Current Status and Development of Industrial Ethernet Technology

The so-called industrial Ethernet is technically compatible with commercial Ethernet (that is, the 802.3 standard), but in product design, it can meet the needs of industrial sites in terms of material selection, product strength, applicability and real-time performance.
With the development and popularization of Internet technology, Ethernet technology has also developed rapidly, with the improvement of Ethernet transmission rate and the Development of Ethernet exchange technology, it brings hope to solve the non-deterministic problem of Ethernet communication and makes it possible for Ethernet to be fully applied in the field of industrial control.
The current development of industrial Ethernet technology will be reflected in the following aspects:

1. Communication certainty and timeliness

Unlike ordinary data networks, industrial control networks must meet real-time requirements for control functions. Real-time Control usually requires that the data of certain variables be refreshed accurately and regularly. Because Ethernet adopts a Media Access Control Mode with burst detection, multiple nodes attached to a bus compete for the bus in equal competition mode, when the node requests to send data, it first monitors whether the bus is idle. If it is idle, it sends data. If the bus is busy, it can only continue to listen and send data after the bus is idle. Even so, several nodes may conflict with each other at the same time. Therefore, the Traditional Ethernet technology is difficult to meet the real-time requirement of accurate and scheduled communication in the control system, always regarded as a non-deterministic network.
However, due to the rapid development of Ethernet and switched Ethernet technology, it has brought a new opportunity to solve the non-deterministic problem of Ethernet, making this application possible.
First, the Ethernet communication rate ranges from 10 m, 1000 m to m and 10g today. When the data throughput is the same, the increase in communication rate means the reduction of network load and the reduction of network transmission latency, that is, the probability of network collision is greatly reduced.
Second, a star network topology is used to divide the network into several CIDR blocks. Due to the data storage and forwarding functions of the Ethernet switch, the input and output data frames between ports can be buffered and the collision will not occur; at the same time, the switch can also filter packets for data transmitted over the network, so that data transmission between nodes in each network segment can only be performed within the primary network segment, without going through the backbone network, it also does not occupy the bandwidth of other network segments, thus reducing the network load of all network segments and backbone networks.
Thirdly, full-duplex communication ensures that the two pairs of twisted pair wires (or two optical fibers) between ports receive and send packets at the same time without conflict.
Therefore, the use of exchange hub and full duplex communication can make the conflict domain no longer exist on the Network (Full Duplex Communication), or greatly reduce the collision probability (Half Duplex ), this greatly improves the certainty and real-time performance of Ethernet communication.

2. stability and reliability

Another major problem for Ethernet to enter the industrial control field is that the connectors, hubs, switches, and cables used by Ethernet are designed for OA, with poor anti-interference performance, it does not meet the requirements of the harsh environment on the industrial site, nor does it have the safety characteristics and the performance of supplying power to the on-site instrumentation.
With the development of network technology, the above problems are quickly solved. To solve the problem that the network can work stably under extreme conditions in the uninterrupted industrial application field, synergetic Microsystems in the United States and German companies such as Hirschmann and jetter Ag specifically developed and produced rail hub and switch products, installed on Standard DIN rail, with redundant power supply, connectors use a solid DB-9 structure. The price of each industrial Ethernet communication interface chip developed by netsilicon has dropped to 10 ~ $15, which has a great price advantage over various fieldbus interface chips. The Ethernet Bus Power Supply specification is also defined in the IEEE 802.3af standard recently released.
In addition, in practical applications, optical fiber transmission can be used for the backbone network, while shielding twisted pair wires can be used for the connection of field equipment. redundant network technology can also be used for important network segments, this improves the anti-interference capability and reliability of the network.

3. Industrial Ethernet protocol

Because the industrial automation network control system is not only a communication system that completes data transmission, but also an automatic control system that uses the network to complete control functions. In addition to data transmission, it usually needs to execute some control computing and operation functions based on the transmitted data and commands. Multiple network nodes can coordinate and complete automatic control tasks. Therefore, it must meet the requirements of open systems in terms of application, user, and other high-level protocols and specifications, and meet the interoperability conditions.
As mentioned above, for the ISO/OSI Layer-7 communication model, the Ethernet technical specification is mapped only to the physical layer and data link layer, currently, it is mainly based on TCP/IP agreement (it has become the "de facto" standard for the transmission layer and network layer over Ethernet ). There are no technical regulations on higher layers, such as the Session Layer, presentation layer, and application layer. Currently, commercial computer devices use FTP (file transfer protocol), telnet (Remote logon protocol), SMTP (Simple Mail Transfer Protocol), and HTTP (WWW protocol) SNMP (Simple Network Management Protocol) and other application-layer protocols for transparent mutual information access, they are now playing a very important role on the Internet. However, the data structures defined by these protocols are not suitable for real-time communication between equipment in the industrial process control field.
In order to meet the application requirements of industrial field control systems, a complete and effective communication service model must be established based on Ethernet + TCP/IP protocol, and an effective real-time communication service mechanism should be developed, coordinates the real-time and non-real-time information transmission services in the industrial field control system to form the application layer and user layer protocols received by the majority of industrial control manufacturers and users, thus forming open standards.
To this end, bus organizations have introduced ethernet into the high-speed part of their fieldbus system, using Ethernet, TCP/IP technology, and the original low-speed fieldbus application layer protocol, this constitutes a so-called industrial Ethernet protocol, such as HSE, profinet, and Ethernet/IP.
(1) HSE (high speed Ethernet, high speed Ethernet)
HSE is a new work of the Fieldbus Foundation after abandoning the original high-speed bus H2. The FF Fieldbus Foundation clearly positions HSE in the integration of control networks and the Internet. The HSE Link Device transmits the H1 network segment information to the Ethernet trunk and further delivers the information to the enterprise's ERP and management systems. In the main control room, the operator can directly use a web browser to view the on-site operation status. On-site setup and backup can also obtain control information from the network.
HSE uses Ethernet + TCP/IP at the lower layer, uses FF H1 application layer service and functional block application process specifications at the application layer and user layer, and uses linking Device) connect the FF H1 network to the hse cidr block. The HSE connection device also has the functions of bridging and gateway. The bridge function can be used to connect multiple H1 CIDR blocks, enables peer-to-peer communication between H1 devices in different H1 network segments without the intervention of the host system. The HSE host can communicate with all connected devices and H1 devices attached to the connected devices, so that the operation data can be transmitted to remote on-site devices and receive data from on-site devices, monitors and reports. Monitoring and control parameters can be directly mapped to standard functional blocks or flexible functional blocks (FFB.
(2) profinet
According to the industrial control requirements and the characteristics of PROFIBUS technology, PROFIBUS International puts forward the Ethernet-based profinet, which mainly includes three technologies: (1) based on the universal Object Model (COM) (2) Provision of open and transparent communication between Profibus and standard Ethernet; (3) provides a system model that consists of the device layer and system layer and is independent of the manufacturer.
Profinet uses standard TCP/IP + Ethernet as the connection medium, and uses standard TCP/IP protocol and application-layer rpc/DCOM to complete communication and network address retrieval between nodes. It can be mounted to a traditional PROFIBUS system and a new smart field device. The existing PROFIBUS network segment can be connected to the profinet network through a proxy, so that the entire PROFIBUS device and protocol can be used in profinet intact. Traditional PROFIBUS devices can communicate with COM objects on profinet through proxy, and call COM objects through Ole automated interfaces.
(3) Ethernet/IP
Ethernet/IP (Ethernet industrial Protocol) is a positive response from Rockwell, which promotes controlnet fieldbus, to Ethernet entry automation. Ethernet/IP networks use commercial Ethernet communication chips, physical media, and star topologies. Ethernet switches are used to achieve point-to-point connections between devices, supports 10 Mbit/s and 100 Mbit/s Ethernet commercial products at the same time, the Ethernet/IP protocol consists of three parts: the IEEE 802.3 physical layer and the data link layer standard, the TCP/IP protocol group, and the Control and Information Protocol CIP (Control Information Protocol, the first two parts are the standard Ethernet technology, which features the CIP part called Control and Information Protocol. To improve the interoperability between devices, Ethernet/IP adopts the same CIP in controlnet and DeviceNet control networks. CIP provides real-time I/O communication and implements peer-to-peer information transmission, the control part is used for real-time I/O communication, and the information part is used for non-real-time information exchange.

Development Trend and prospects of the Second Industrial Ethernet Technology

Ethernet has many advantages, such as wide application, low price, high communication rate, rich software and hardware products, and mature application support technologies, at present, it has been widely used in the resource management layer and execution layer in the integrated automation system of industrial enterprises, and shows the trend of direct application in the field of industrial control. According to the development of international and domestic industrial Ethernet technologies, industrial Ethernet has been widely used in the manufacturing Implementation Layer and has become a de facto standard. In the future, industrial Ethernet will play an increasingly important role in the interconnection and information integration between field equipment in the integrated automation system of industrial enterprises.
In general, the development trend of Industrial Ethernet technology will be reflected in the following aspects:

1. Combination of Industrial Ethernet and Field Bus

The Research on Industrial Ethernet technology has only attracted the attention of industrial control experts at home and abroad in recent years. After more than 10 years of development, the Field Bus is becoming more and more mature in technology, and has been fully promoted in the market, and has formed a certain market. At present, there are still some problems in replacing the Fieldbus. We need to make further research on the new control system architecture based on industrial Ethernet and develop a series of products based on industrial Ethernet. Therefore, in the recent period, the development of industrial Ethernet technology will be combined with the field bus, as shown in:
(1) standard Ethernet connections are used for physical media, such as twisted pair wires and optical fibers;
(2) Use standard Ethernet connection devices (such as switches) to use industrial Ethernet switches at industrial sites;
(3) Adopt IEEE 802.3 physical layer and data link layer standards and TCP/IP protocol groups;
(4) The application layer (or even the user layer) adopts the application layer and user layer protocols of the Fieldbus;
(5) compatible with existing mature traditional control systems, such as DCS and PLC;
Typical applications in this area include the application of Ethernet, embedded web, and other commercial Internet technologies in the "transparent factory" system based on embedded web introduced by Schneider Corporation in France to the information management layer, monitoring layer, and field equipment layer.. For example, the webfield ECs series control system of central control of Zhejiang University in China.

2. The direct application of industrial Ethernet technology to communication between industrial devices has become a trend of the times

With the improvement of Ethernet communication speed, full-duplex communication, and exchange technology, it provides a technical basis for the deterministic solution of Ethernet communication, this eliminates the main obstacle for the direct application of Ethernet to inter-industrial field equipment communication, and provides technical possibilities for the direct application of Ethernet to inter-industrial field equipment communication.
To this end, the International Electrotechnical Commission IEC is working on drafting real-time Ethernet (RTE) standards to promote the full application of Ethernet technology in the field of industrial control.
In response to this situation, with the support of the national "863" plan, Zhejiang University central control, Shenyang Institute of automation of the Chinese Emy of sciences, Tsinghua University, Dalian University of Technology, and Chongqing Institute of Posts and Telecommunications, the EPA (Ethernet for Plant Automation) technology has been studied. The focus is on the key technologies that apply Ethernet technology to inter-device communication in industrial control field. through research and research, the following achievements have been made:
(1) major breakthroughs in key technologies used for communication between on-site devices over Ethernet
In view of the characteristics and requirements of industrial field equipment communication, such as strong real-time performance, short data information, and strong periodicity, after careful research and analysis, the following technologies are basically used to solve the key technologies of Ethernet Used for field communication between devices:
(A) Real-Time Communication Technology
Ethernet Switching Technology, full-duplex communication, traffic control, and other technologies are used, the real-time communication measures for industrial process control, such as deterministic Data Communication scheduling control policies, simplified communication stack software layers, and on-site equipment layer network micro-network segmentation, solve the real-time Ethernet communication.
(B) bus power supply technology
Using technologies such as DC power supply coupling and power supply redundancy management, an Ethernet Hub is designed for network power supply or bus power supply, which solves the power supply problem of Ethernet bus.
(C) Remote Transmission Technology
Network Tiering, control area micro-network segmentation, network ultra-small time-delay Relay, optical fiber and other technologies are used to solve the problem of long-distance Ethernet transmission.
(D) network security technology
Control Area micro-network segmentation is adopted. Each control area is connected to the system trunk through an on-site controller with network isolation and Security filtering, thus implementing Logical Network isolation between control areas and other areas.
(E) Reliability Technology
The use of distributed structured design, EMC design, redundancy, self-diagnosis, and other reliability design technologies to improve the reliability of Ethernet-based field equipment. By EMC testing in the laboratory, the equipment reliability meets the requirements of industrial field control.
(2) Draft National EPA standards
Based on Ethernet, wireless LAN, Bluetooth Technology + TCP/IP protocol, industrial control engineers (including development and application) are used for communication between industrial field equipment, the EPA (Ethernet for Plant Automation) system structure and communication standards for industrial measurement and control systems were drafted and passed the technical review organized by tc124.
(3) Develop an Ethernet-based Fieldbus Control Device and prototype of related software, and successfully apply the device to chemical production devices.
In view of the characteristics of industrial field control applications, through the adoption of software, hardware anti-interference, EMC design measures, developed based on Ethernet technology field control equipment, mainly including: ethernet-based field equipment communication modules, transmitters, implementing agencies, data collectors, Soft PLC and other achievements.
On this basis, the distributed network control system developed based on EPA has been successfully applied to the alkali carbide unit of a chemical plant in Hangzhou. The system has been running stably since it was put into operation in April 2003.

3. Development Prospects

According to a report by the US authority's arc (auto-mation Research Company), in the future, Ethernet will not only continue to monopolize the upper-layer network communication market of commercial computer networks and industrial control systems, it will also lead the development of the field bus in the future. Ethernet and TCP/IP will become the basic protocols of the device bus and the Field Bus. United States VDC (venture Development Corp .) the survey report also pointed out that Ethernet will be widely used in the industrial control field and its market share will grow faster and faster, increasing from 2000 in 11% to 2005 in 23%.

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Source: World instrument and automation

Status Quo and Development of Industrial Ethernet