I. Ethernet Transmission Media
The transmission medium for 10G Ethernet is as follows:
10G high-speed Ethernet can meet new capacity requirements, solve the bottleneck problem of low bandwidth access and high bandwidth, expand the scope of application, and is compatible with all previous Ethernet networks.
Generally, full-duplex Ethernet protocols have no distance limitation. In practical applications, the physical layer technology limits the maximum transmission distance, but the Ethernet link length can be extended by using high-performance transceivers or link extenders. Therefore, Ethernet technology can also be applied to MANs and WANs, and the cost of MANs and WANs built using Ethernet technology is about 25% lower than similar systems built using ATM/SONET technology. These factors have driven the expansion of Ethernet from LANs to MANs and WANs, establishing reliable, high-speed data networks with operating rates of 10Gb/s. This allows the network to be based on a single core technology, making it easy to manage and inexpensive. At high data rates of 10Gb/s, Ethernet as a WAN technology avoids protocol conversion, enabling seamless connection between WANs and LANs/MANs, and seamless compatibility with DWDM optical networks.
Therefore, 10G high-speed Ethernet typically uses optical fiber as the physical transmission medium. When using single-mode optical fiber, the transmission distance can reach 300KM, and when using multimode optical fiber, it can reach 40KM.
Single-mode fiber: This fiber has a very thin central glass core (typically 9 or 10 μm in diameter) and can only transmit one mode. Its intermodal dispersion is very small, making it suitable for long-distance communication. However, material dispersion and waveguide dispersion still exist, thus single-mode fiber places high demands on the spectral width and stability of the light source; that is, the spectral width must be narrow and the stability high. Compared to multimode fiber, single-mode fiber can support much longer transmission distances. In 100 Mbps Ethernet and even 1 Gigabit Ethernet, single-mode fiber can support transmission distances exceeding 5000 m.
Single-mode transmission has a long transmission distance, while multi-mode transmission has a large bandwidth. Single-mode does not experience dispersion and is reliable. Single-mode typically uses lasers as the light source, which is expensive, while multi-mode typically uses inexpensive LEDs. Single-mode is relatively expensive, while multi-mode is cheaper and can handle short-distance transmission.
When physical layer technology limits the maximum transmission distance, we can also extend Ethernet links by purchasing high-performance imagers or link extenders.
A transceiver is a device for signal conversion, typically referring to a fiber optic transceiver. The advent of fiber optic transceivers enables the conversion between twisted-pair electrical signals and optical signals, ensuring smooth transmission of data packets between two networks. It also extends the network's transmission distance limit from 100 meters for copper wires to 100 kilometers for single-mode fiber.
Fiber optic transceivers break the 100-meter limitation of Ethernet cables in data transmission. Relying on high-performance switching chips and large-capacity buffers, they not only achieve truly non-blocking transmission and switching performance, but also provide functions such as traffic balancing, collision isolation, and error detection, ensuring high security and stability during data transmission.
II. Problems with the Application of Ethernet in Industrial Control
Traditional Ethernet is a commercial network, and there are still some problems in applying it to industrial control, mainly in the following aspects.
(1) It suffers from poor real-time performance and uncertainty.
Traditional Ethernet employs the CSMA/CD media access control mechanism, with each node using the BEB (Binary Exponential Back-off) algorithm to handle collisions. This mechanism suffers from uncertain queuing delays, requiring each network node to compete for the right to send packets. During communication, nodes listen to the channel and can only send information when it is idle; if the channel is busy, they must wait. After transmission begins, collision checks are performed; if a collision occurs, transmission must be abandoned and retransmitted. Therefore, deterministic queuing delays and communication response cannot be guaranteed, failing to meet the real-time requirements of industrial process control. Furthermore, during periods of high traffic, there is a risk of data loss, thus limiting its application in industrial control.
(2) Industrial reliability issues
Ethernet was designed for office automation and did not consider the adaptability requirements of industrial environments, such as extremely high or low operating temperatures, and strong electromagnetic noise from large motors or other high-power equipment that affects channel transmission characteristics. If Ethernet is to be used in the lower levels of a factory floor, reliability issues must be addressed.
(3) Ethernet does not provide power and requires an additional power cable.
Industrial field control networks must not only transmit communication information but also provide power to field devices for operation. This is primarily for ease of cabling and maintenance, and bus power supply also reduces cabling costs.
(4) Ethernet is not an intrinsically safe system.
(5) Security issues
Ethernet, due to its use of the TCP/IP protocol, is susceptible to network security threats, including viruses, unauthorized intrusions by hackers, and unauthorized operations. Unauthorized users may gain access to the network's control or management layers, creating security vulnerabilities. While various security mechanisms such as user passwords, data encryption, and firewalls can be used to strengthen network security management, solutions specifically for industrial automation control network security require further investigation.
(6) Integration issues between the existing control network and the newly built Ethernet control network
Among these problems, real-time performance, determinism, and reliability have long been major obstacles preventing Ethernet from entering the field of industrial control. To address these issues, industrial Ethernet solutions have been proposed.
