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　　 1, using exchange technology
Traditional Ethernet uses a shared hub. Its structure and function are just a multi-port physical layer repeater. All stations connected to the shared hub share a bandwidth and send and receive data according to the CSMA/CD protocol. The switched hub can be thought of as a controlled multi-port switch matrix. The flow of information between the ports is isolated, providing a direct and fast point-to-point connection between the source and the target of the switching device. Different ports can form multiple data channels, and the data input and output between ports are no longer constrained by CSMA/CD. With the development of modern switch technology, the transfer rate between switch ports is larger than the transfer rate between the entire device layer Ethernet ports, thus reducing the collision rate of Ethernet and providing caching for conflict data. Of course, the working mode of the switch must be the store-and-forward mode, so that there is only a point-to-point connection in the system, and no collision occurs. Multiple exchanges decompose the entire Ethernet into many independent areas. Ethernet data collisions exist only in their respective collision domains. There is no conflict between different domains, which can greatly increase the bandwidth of each site on the network, thus improving the exchange. Network performance and determinism.
Switched Ethernet does not change the original Ethernet protocol, and can directly use a common Ethernet card, which greatly reduces the cost of networking, and fundamentally solves the problem of uncertainty in Ethernet communication transmission delay. Studies have shown that when the communication load is below 10%, the transmission delay caused by Ethernet collision is almost negligible. In the industrial control network, the information transmitted is mostly periodic measurement and control data, the message is small, the amount of information is small, and the length of information transmitted is small. The information includes the measured values ​​of the operating parameters of the production equipment, the control amount, the working position of the switch and the valve, the alarm status, the resource and maintenance information of the equipment, the system configuration, the parameter modification, the zero point and the range adjustment information. The length is generally small, usually only a few to tens of bytes, and the throughput of network transmission is not high. Studies have shown that in a typical industrial control system with 6000 I / O, the communication load is about 5% of 10M Ethernet, even if there is operator information transmission (such as changes in set values, download of user applications, etc.), The load of 10M Ethernet can also be kept below 10%.
　　 2, using high-speed Ethernet
With the rapid development of network technology, high-speed Ethernet (100M) and Gigabit Ethernet products and international standards have been produced, and 10G Ethernet products have also been available. By improving the communication speed and combining the switching technology, the overall performance of the communication network can be greatly improved.
　　 3, using full duplex communication mode
One port in switched Ethernet is a collision domain, and it is still not possible to send and receive data simultaneously in the case of half-duplex. If full-duplex mode is adopted, two stations in the same data link can receive data while transmitting data, which solves the problem that half-duplex needs to wait in this case, and theoretically can double the transmission rate. . Full-duplex communication technology allows two pairs of twisted pairs (or two fibers) to receive and transmit message frames simultaneously between device ports, so that they are no longer constrained by CSMA/CD, so that any node sends a message frame. There will be no more collisions and the conflict domain will cease to exist. For emergency transaction information, the packet priority technology can be applied according to IEEE802.3p&q, so that packets with higher priority are first entered into the queuing system to receive services first. Through this prioritization, emergency information in the industrial field can be successfully and timely transmitted to the central control system for timely processing.
　 4, using virtual LAN technology
The emergence of virtual local area networks (VLANs) has broken many of the inherent concepts of traditional networks, making the network structure more flexible and convenient. In fact, a VLAN is a broadcast domain. It is not restricted by geographical location. Network users in different geographical locations can be divided into logical network segments according to factors such as department functions, object groups, and applications. Each port of a LAN switch can only mark one VLAN. All stations in the same VLAN have one broadcast domain. The broadcast information between different VLANs is isolated from each other, thus avoiding broadcast storms. In the process control of industrial process, the control layer unit should be distinguished from the common unit in terms of real-time data transmission and security. The virtual local area network is used for logical division on the open platform of Industrial Ethernet to distinguish different functional layers and different departments. Open, thereby achieving the goal of improving the overall security of the network and simplifying network management. Generally, virtual LANs are classified into three types: static port allocation, dynamic virtual network, and multiple virtual network port configurations. Static port allocation refers to the network management personnel using the port of the network management software or device switch to directly subordinate to a virtual network. These ports will maintain such dependencies unless the network administrator resets them; dynamic virtual network refers to support dynamics. The ports of the virtual network can automatically determine their dependencies by means of intelligent management software; the multiple virtual network port configuration supports one user or one port to access multiple virtual networks at the same time, so that one control layer computer can be configured to be accessed by multiple departments at the same time. It is also possible to access resources of multiple virtual networks at the same time.
　　 5. Introducing quality service (QoS)
IP QoS refers to the quality of service of IP, that is, the performance of IP data streams when they pass through the network. Its purpose is to provide end-to-end service quality assurance 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. QoS technology is used in industrial Ethernet to identify higher priority data from the control layer and prioritize them in response delay, transmission delay, throughput, and reliability. Sex, transmission failure rate, priority, etc., make Industrial Ethernet meet the requirements of industrial automation real-time control. In addition, the QoS network can also prevent illegal use of the network, such as illegal access control layer field control unit and monitoring unit terminals.
In addition, there have been improvements in industrial Ethernet application standards and related protocols supported by large companies. Introducing Industrial Ethernet into the underlying network not only facilitates the integration of the field layer, the control layer and the management layer at the vertical level, but also reduces the integration cost of devices of different manufacturers at the horizontal level. The extension of Ethernet to the underlying network is inevitable. Therefore, famous manufacturers have supported industrial Ethernet and formulated different industrial application standards. For example, Rockwell, OMRON and other companies support Ethernet/IP. IP refers to the industrial protocol, which provides the Producer/Consumer model to port the application layer of ControlNet and Devicenet control and information protocols to TCP. The high-speed Ethernet protocol HSE developed by FF provides models for publishers/orderers, objects, etc., mainly used in the field of engineering control, and is supported by some large companies such as Foxboro and Honeywell. The Modbus/TCP protocol released by Schneider bundles the Modbus protocol on the TCP protocol, which is easy to implement and enables interconnection.
In order to improve real-time performance, the Ethernet protocol has also made some improvements. A completely software-based protocol, RETHER (Real Time Ethernet), ensures real-time performance without changing the existing hardware of Ethernet. It uses a hybrid operation mode to reduce the impact on non-real-time data transmission performance in the network. A non-competitive admission control mechanism and an efficient token delivery scheme can prevent token loss due to node failure. Networks that adhere to the RETHER protocol operate in both CSMA and RETHER modes. During the live conversation, the network will transparently transition to RETHER mode, returning to CSMA mode after the real-time conversation is over. There is also an Ethernet protocol called RTCC (Real Time Communication Control), which provides a good foundation for distributed real-time applications. RTCC is a layer of protocol over Ethernet that provides high-speed, reliable, real-time communication. It does not require changes to existing hardware devices, and uses a novel mechanism of command/response multiplexing and bus tables to allocate channels. All nodes are divided into bus controller (BC) and remote terminal (RT) in the RTCC protocol. There is only one BC, and the rest are RT. The initiation and management of information transmission are undertaken by the BC. The access arbitration process and the transmission control process are all implemented by BC. Through the integration and synchronization of the two processes, not only the transmission time of the node is determined, but also the time when the node uses the bus. Also controllable. Experiments on 10 Mbps Ethernet show that the RTCC has satisfactory certainty. A third way to improve real-time performance is traffic balancing, which is to add a traffic balancer between UDP or TCP/IP and Ethernet MAC. As an interface between them, it is installed on each network node. At the local node, it gives priority to real-time data packets to eliminate competition between real-time information and non-real-time information, while balancing non-real-time information to reduce collisions with real-time information of other nodes. To ensure the throughput of non-real-time information, the traffic balancer can also adjust the data stream generation rate according to the load of the network. This method does not require any changes to the existing standard Ethernet MAC protocol and TCP or UDP/IP.
Therefore, in response to the uncertainty of Ethernet queuing delay, real-time performance is improved by adopting appropriate flow control, switching technology, full-duplex communication technology, information priority, etc., and fault-tolerant technology, system design technology, and redundant structure are improved. Ethernet can be used in industrial control networks. In fact, in the mid-to-late 1990s, major industrial and commercial companies at home and abroad adopted Ethernet in their control systems, and launched Ethernet-based DCS , PLC , data collectors, and Ethernet-based field instruments and display instruments. And other products.
With the maturity of network and information technology, Ethernet and TCP/IP protocols are adopted as the main communication interfaces and means in industrial communication and automation systems. The development of network, standardization and openness will be various control systems. The main trend of technology development. As the most widely used and fastest growing LAN technology, Ethernet has achieved extraordinary development in the fields of industrial automation and process control. At the same time, IP-based integrated addressing, standard, shared, high-speed information channel solutions for industrial production will also have a profound impact on the control system.
Ways to improve the usability of Ethernet
With the development of related technologies, the development of Ethernet has also made an essential leap, and with the help of related technologies, the practicality of Ethernet in industrial control can be improved as a whole.