Compared with civil Ethernet switches, industrial Ethernet switch products can meet the needs of industrial sites in terms of design and selection of components, as well as product strength and applicability. Next, we will introduce some common professional terms of industrial Ethernet switches in detail, let's take a look!
1. Topology The
topology is the arrangement of cables in the network. As we all know, EIA-485 or CAN adopts bus topology. However, in industrial Ethernet, due to the widespread use of hubs or switches, the topological structure is star or scattered star.
2. Wiring
Industrial Ethernet Topics"> The cables used in Industrial Ethernet include shielded twisted pair (STP), unshielded twisted pair (UTP), multi-mode or single-mode optical cables. The rate of 10Mbps is not too high for twisted-pair cables. At 100Mbps, it is recommended to use Category 5 or Super Category 5 cables.
A pair of optical fiber links are required. The commonly used multimode optical fiber has a wavelength of 62.5/125μm or 50/125μm. Compared with the inner core of a multimode fiber, the inner core of a single-mode fiber is very thin, only about 10μm. Generally, multi-mode fiber is used for 10Mbps, and both single-mode and multi-mode fiber are suitable for 100Mbps.
Three, joints and connections
RJ-45 is more common in twisted-pair connectors. There are two pairs of wires, one pair is used for sending and the other pair is used for receiving. In the definition of the media-related interface (MDI), these four signals are respectively identified as RD+, RD-, TD+, TD-.
A communication link consists of DTE (data terminal equipment, such as workstations) and DCE (data communication equipment, such as repeaters or switches). The hub port marked as MDI-X port indicates that DTE and DCE can be connected using a straight-through cable. What if two DTEs or two DCEs are connected? You can use the cable cross method or directly use the uplink port provided by the hub (the cable should not be crossed).
There are two types of optical fiber connectors, ST connector is used for 10Mbps or 100Mbps; SC connector is dedicated for 100Mbps. Single-mode fibers usually use SC connectors. The connection between DTE and DCE only needs to follow the TX and RX marks of the port.
4. Industrial Ethernet and ordinary commercial Ethernet products.
What is industrial Ethernet? Technically, it is compatible with IEEE802.3, but the design and packaging take into account the requirements of industrial and commercial applications. The designer of the industrial scene hopes to adopt the Ethernet chip and medium that can be found on the market, taking into account the special requirements of the industrial scene. The first consideration is high temperature, humidity, and vibration. Second, see if it can be easily installed in the industrial field control cabinet. The third is power requirements. The power supply provided in many control cabinets is low-voltage AC or DC. Wall-mounted power supply devices sometimes cannot be adapted. The requirements for electromagnetic compatibility (EMC) vary with the requirements of industrial environments for EMI (industrial anti-interference) and ESD (industrial anti-seismic). The safety standards on site are completely different from those in the office. Sometimes what is needed is a rating for harsh environments. The factory may adopt the industrial control cabinet standard and the building system often adopts the smoke standard. Obviously, low-cost commercial Ethernet hubs and switches cannot meet these requirements.
5. Speed and distance When
discussing the distance of shared Ethernet, the concept of collision domain cannot be ignored.
The media access of shared Ethernet or half-duplex Ethernet is determined by carrier sense multiple access/collision detection (CSMA/CD). In the half-duplex communication mode, sending and receiving cannot be carried out at the same time, otherwise the data will collide. Before the station sends, it must first check whether there is a free channel. When sending, the station will also listen for a period of time to ensure that no other stations are performing synchronous transmission during this time, and finally the station is successfully sent. On the contrary, if a collision occurs, the source site sends a blocking signal to strengthen the collision. Retry after the contending site is delayed (the delay time is determined by the algorithm and is random). Under this mechanism, all stations and all hubs must be in the same collision domain.
For industrial Ethernet, 10Mbps and 100Mbps are the most commonly used. In a 10Mbps, all twisted pair Ethernet network, there are two concepts related to distance, namely segment and network diameter. The former refers to the distance between two devices (hub, switch or host), and the latter refers to the distance between the two most remote devices in the network. Regardless of the 10Mbps or 100Mbps network, the longest distance of the network segment cannot exceed 100 meters. Considering network extension, the most useful rule is the 5-4-3 rule (only for 10Mbps repeaters). The content of the rules is as follows: a network has up to five network segments, four repeaters, and no more than three mixed network segments. The mixed network segment refers to the coaxial bus network segment (obsolete). Since the longest distance of the twisted pair network segment is 100 meters, the maximum network (network range) is 500 meters. The maximum distance of the optical fiber network segment can be up to 2 kilometers, but the IEEE802.3 standard stipulates that the use of optical fiber, the number of cascades cannot exceed 3, and the end of the network needs to use twisted pair cables, and the middle two are optical fiber network segments. Each network segment does not exceed 1 km. In this way, the length of the entire optical fiber network segment is limited to 2 kilometers. The 5-4-3 rule does not apply to 100Mbps. It is recommended to use a 100Mbps switch.
6. Hubs and switches
Relay-type hubs (hubs) are the basic equipment that constitutes the Ethernet topology. The hub is a multi-port device with four, eight, or twelve ports, etc., which can be cascaded to form a decentralized star topology. The hubs are in compliance with IEEE802.3 relay unit requirements. These requirements include preamble generation, symmetry, and amplitude compensation. The repeater must retiming the signal so that the signal jitter caused by the transceiver and cable will not accumulate during multi-segment propagation. These devices can detect incomplete data packets and collisions, and generate a blocking signal to act. They will also automatically isolate problematic ports to maintain normal network operation.
Another series of interface adapters is interface adapters, sometimes called transceivers. They transform one medium into another. The most important conversion is the conversion from twisted pair to optical fiber. Since many hubs do not have fiber ports, interface adapters are used to support fiber optic applications in the network. These devices are transparent in the network. The port does not store frames or detect collisions, but converts one medium to a compatible signal on the other end.
Switching hubs (switches) Switching hubs can replace relay hubs and improve network performance. Different from the physical layer equipment-relay hub, the switching hub is actually a bridge connecting two data links, that is to say, the collision domain is terminated at each switch port. Therefore, the addition of switches expands the geographical scope of the network, and cascaded switches can achieve network expansion on a large scale. Switches are more complex than trunking hubs. The twisted-pair port automatically negotiates the rate with the auxiliary port (10Mbps or 100Mbps). The flow control function is also carried out through negotiation. The full-duplex network segment adopts the PAUSE scheme, and the half-duplex network segment usually adopts the backpressure scheme. After the switch reads a complete frame and looks at its source address, it can find out the port location of the connected Ethernet device. The switch then generates a port address table and maintains the contents of the table. From then on, network communication is limited to ports related to this transmission. Since synchronous transmission can be realized on these ports without any operation, the throughput of the network is improved. The content of the table will be automatically refreshed according to the change of the connection information.
If the information received by a certain port needs to be broadcasted, sent in a group, or the sending address is unknown, the switch will automatically send the information to all ports. Unlike the relay hub, there are multiple collision domains, and each collision domain must comply with the above-mentioned rules.
The relay hub can be connected to the switch port. If there are all switches in the network, the twisted pair network segment remains 100 meters, but there is no restriction on cascading. Before using the optical fiber, you must first indicate whether it is half or full duplex. The comparison between the relay hub and the switching hub is obviously that the performance of the switch is better than that of the hub, but the advantage of the hub is that it is easy to understand, and data communication can be observed through a network analyzer at any port. The switch must implement broadcast transmission on a certain port to be able to measure. As a bridge, the switch stores and forwards the entire data frame and causes data delay. The hub receives the network signal without data delay. The switch cascade also increases the delay. Therefore, hubs and switches have their own applications in the "Industrial Ethernet topic">Industrial Ethernet.
Seven, half-duplex, full
- duplex half-duplex means that the transmission and reception of the same media are performed asynchronously. The opposite is true for full-duplex, where there are separate transmit and receive channels. The full-duplex link is the key to expanding Fast Ethernet (100Mbps). The full-duplex link network segment cannot exceed two devices, which can be network cards or switch ports. Note: It is not a trunked hub port, the hub does not have a full-duplex mode. This is because the hub is part of the collision domain, and it enhances the collisions received by other ports. When there are only two network cards, full-duplex communication can be implemented. For full-duplex communication with more than two network cards, switches must be considered.
10BASE-T and 10BASE-FL have separate transmission and reception paths, and can perform full duplex according to the complexity of the network card or switch port. If these interfaces are configured in half-duplex mode, synchronous detection of receiving and sending will trigger collision detection. The same interface is set to full-duplex, because full-duplex does not comply with the shared CSMA/CD rules, collision detection will be prohibited.
The configuration of the full-duplex link must be correct. When the station is configured in full-duplex mode, the port of the station or switching hub sends frames in a way that ignores the CSMA/CD protocol. If the other end is set in half-duplex mode, it will detect collisions and cause other problems, such as CRC errors, the speed of the network drops, and the advantages of Fast Ethernet disappear.
As mentioned earlier, due to collisions, the network range at 100Mbps has been reduced. For twisted pair network segments and switch ports, the longest distance of the network segment is 100 meters (within the collision domain). The problem is that on the fiber port, for multimode fiber, the length of the network segment is 2 kilometers; for single-mode fiber, it is 15 kilometers. In half-duplex mode, limited by the collision domain, the network segment distance is 412 meters. Therefore, only in full-duplex mode (CSMA/CA is ignored), the extension of the optical fiber network segment can reach the limit. In Fast Ethernet mode, switch technology is recommended. For fiber ports under Fast Ethernet, full duplex is recommended.
8. Auto-negotiation
With the widespread use of Fast Ethernet and wiring rules similar to traditional Ethernet, IEEE802.3u recommends automatic configuration of Fast Ethernet so that traditional Ethernet ports can work with other Fast Ethernet ports. The configuration protocol is based on National Semiconductor's NWay standard. The twisted pair link automatically performs speed matching to facilitate data communication. This scheme is suitable for twisted pair links. The situation with optical fiber is different. Although optical fiber has a very important position in the development history of Ethernet. However, the speed of the two fiber optic devices cannot be automatically negotiated because the 10BASE-FL device works at 850nm and the 100BASE-FX works at 1300nm. The two cannot interoperate. However, for the auto-negotiation protocol, auto-negotiation between two fiber optic devices is feasible (if there is no problem with the communication). Aware of this, the newly introduced 100BASE-SX standard can make 850nm fiber work at 10Mbps or 100Mbps. The distance of the network segment under 100Mbps is 300 meters. Therefore, please pay attention when installing. The speed of the optical fiber is usually fixed and no negotiation is implemented. The auto-negotiation protocol is successful on the twisted pair link. The advantage of auto-negotiation is that it eliminates the need for users to make manual settings, and the equipment itself determines their technical level. The levels from high to low are as follows:
1000BASE-T full-duplex highest
1000BASE-T
100BASE-T2 full duplex
100BASE-TX full duplex
100BASE-T2
100BASE-T4
100BASE-TX
10BASE-T full duplex
10BASE-T minimum
The lowest level is 10BASE-T (half-duplex, shared Ethernet), and the highest is 1000BASE-T full-duplex. This is a complete priority scheme, but it does not mean that a certain network card can handle all of these technologies. In fact, there are some technologies that have not been implemented commercially, but they are all consistent with the IEEE802.3 standard. Each port checks its technical performance and determines the final rate (lower rate). For example: if the network card supports 10BASE-T and the switch port capability is 10BASE-T or 10BASE-TX, then the final choice is 10BASE-T. If one network card is 10BASE-T and the other is 100BASE-TX, the two cannot communicate because of incompatibility.
Nine, the transmission protocol The
original design did not involve a reliable end-to-end information transmission. The obligation of network interconnection (two networks communicate with each other) lies in the third layer-the network layer. Transmission and interconnection become part of the protocol stack, and TCP/IP and SPX/IPX are two commonly used protocols. These two protocols are not interoperable, so Ethernet nodes must use compatible protocols. Due to the application of TCP/IP in the Internet, it has become the main protocol, as well as in industrial networks. In fact, TCP/IP is a set of RFC-defined protocols (request for comments) for many years. In addition to Ethernet, TCP/IP also works with other data link technologies. It is located above the physical layer/data link layer. At the transport layer, there are two important protocols: TCP and UDP. The former confirms the received information. Both are very useful. In the upper layer of the protocol stack, there are a number of useful application layer protocols used in "Industrial Ethernet Topics">Industrial Ethernet. For users, addressing is an important topic. The IP protocol is responsible for data packets that may be located between sites in different networks Each site has a unique 32-bit address (representing network address and host address respectively). The address is represented by four bytes in dotted decimal notation. 128.8.120.5 is a valid address but it is impossible to determine what is a host and what is a network. The address is divided into five categories, and the addresses are divided into categories A to E. The classification can be done by observing the first byte.
The allocation of IP is not simple, it is usually allocated by the network manager. Once allocated, it must be applied to each station in the network. There are two types of IP addresses: static and dynamic allocation. Dynamic allocation is performed by the server. Static allocation is performed by configuration. The following addresses are private addresses and cannot be assigned on the router. Therefore, they have no application on the Internet.
10.0.0.0 ~ 10.255.255.255
172.16.0.0~172.31.255.255
192.168.0.0~192.168.255.255
The IP address and the Ethernet MAC address are different and should not be confused. The MAC address is assigned by the equipment manufacturer, so it is unique in the world. The IP address is allocated during installation and reallocated as needed.
X. Application layer protocol
Determine the connector and cable used, whether it is a hub or a switch, and assign an IP, and then you can communicate between sites. Now need to consider the compatibility of OSI high-level. The recommended industrial automation protocols here are Ethernet/IP, iDA, PROFInet and Modbus/TCP. This does not include traditional Internet applications-FTP, SNMP, SMTP and TELNET. The device in the user's hands may not support these protocols, so you need to understand the compatibility of your own system.
Well, the above content is the detailed introduction of Feichang Technology's technical terminology of industrial Ethernet switches, I hope it can be helpful to everyone! Feichang Technology has been engaged in the R&D, production and sales of industrial communication equipment such as optical transceivers, industrial-grade switches, optical fiber transceivers, and protocol converters for 20 years. Welcome to come to understand and exchange ideas.