Common Terms and Analysis of Industrial Ethernet Switch

As the most efficient data communication equipment at present, industrial ethernet switch itself is a high-tech product. There are many parameters and indicators. However, many purchasers may only choose the corresponding industrial ethernet switch according to the company's requirements. They do not have a deep understanding of industrial ethernet switches, and even have little understanding of some common terms of ethernet switches. The following is a summary of some terms most mentioned by industrial ethernet switches. I hope you can have a better understanding of industrial ethernet switches. Let's have a look!

1. Classification of industrial ethernet switches

The most common categories of industrial ethernet switches are managed and unmanaged, rack and rail, layer 2 switches, layer 3 and layer 4 switches. For the detailed classification of industrial ethernet switches, there will be no more complaints here.

2. Industrial Switch backplane bandwidth?

The backplane bandwidth of an industrial switch is the maximum amount of data that can be handled between the switch interface processor or interface card and the data bus. Backplane bandwidth indicates the total data exchange capacity of industrial switches. The unit is Gbps, also known as switching bandwidth. The backplane bandwidth of general switches ranges from a few Gbps to hundreds of Gbps. The higher the backplane bandwidth of a ehernet switch, the stronger the data processing capacity it can handle, but at the same time, the higher the design cost.

3. Packet forwarding rate of industrial switch?

The packet forwarding rate of an industrial switch indicates the capacity of the switch to forward packets. The unit is generally PPS (packet per second). The packet forwarding rate of general switches ranges from tens of kpps to hundreds of MPPs. Packet forwarding rate refers to the number of millions of data packets (MPPs) that the switch can forward per second, that is, the number of data packets that the industrial switch can forward at the same time. Packet forwarding rate reflects the switching capacity of industrial switches in the unit of data packets.

4. Connectors and connections

RJ-45 is common in twisted pair connectors. There are two pairs of wires, one for sending and the other for receiving. In the definition of media related interface (MDI), these four signals are identified as rd+, rd-, td+, td-. One communication link consists of DTE (data terminal equipment, such as workstation) and DCE (data communication equipment, such as repeater or switch). The hub port is identified as an mdi-x port, indicating that DTE and DCE can be connected using a straight through cable. If two DTEs or two DCEs are connected? You can use the method of cable crossing or directly use the uplink port provided by the hub (do not cross the cables). There are two types of optical fiber connectors. St connectors are used for 10Mbps or 100Mbps; The SC connector is dedicated to 100Mbps. Single mode fibers usually use SC connectors. The connection between DTE and DCE only needs to follow the TX and Rx identification of the port.

5. Half duplex, full duplex

Half duplex means that the sending and receiving of the same media are asynchronous. Full duplex, on the contrary, has separate transmit and receive paths. Full duplex link is the key to the expansion of Fast Ethernet (100Mbps). The full duplex link network segment cannot exceed two devices. It can be a network card or a switch port. Note: it is not a relay hub port, and the hub does not have full duplex mode. This is because the hub is part of the collision domain, which will enhance the collision received by other ports. When there are only two network cards, full duplex communication can be implemented. When there are more than two network cards, the switch must be considered.

10Base-T and 10base-fl have separate transmit and receive channels, and can perform full duplex according to the complexity of network card or industrial switch port. If these interfaces are configured in half duplex mode, the synchronous detection of reception and transmission will trigger collision detection. The same interface is set to full duplex. Since full duplex does not comply with shared csma/cd rules, collision detection will be prohibited.

The configuration of full duplex link should 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, network speed drops, and the advantage of Fast Ethernet disappears.

As mentioned above, the network range at 100Mbps is reduced due to collision. For twisted pair network segments and switching ports, the maximum distance of the network segment is 100 meters (within the collision domain). The problem is that for multimode fiber, the length of the network segment is 2km; For single-mode fiber, it is 15 kilometers. In the half duplex mode, the network segment distance is 412m due to the collision domain. Therefore, only in full duplex mode (csma/ca is ignored) can the extension of optical network segment reach the limit. Under Fast Ethernet mode, switch technology is recommended. It is recommended to use full duplex for fiber ports under Fast Ethernet.

6. Auto negotiation

With the extensive use of Fast Ethernet and the wiring rules similar to the traditional Ethernet, ieee802.3u recommends that fast Ethernet be automatically configured so that the traditional Ethernet port can work with other fast Ethernet ports. The configuration protocol is based on the nationalsemiconductor'snway standard. The levels are as follows:

1000BASE-T full duplex maximum

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 network card can handle all these technologies. In fact, some technologies are not implemented commercially, but they are consistent with the IEEE802.3 standard. Each port checks its own technical performance and determines the final rate (lower rate). For example, if the network card supports 10Base-T and the switch port capacity is 10Base-T or 10base-tx, 10Base-T is the final choice. If one network card is 10Base-T and the other is 100base-tx, they cannot communicate because they are incompatible.

7. Transmission protocol

The original design did not involve a reliable end-to-end transfer of information. The obligation of network interconnection (the two networks communicate with each other) is at the third layer - the network layer. Transmission and interconnection become a part of the protocol stack. Tcp/ip and spx/ipx are two commonly used protocols. The two protocols cannot operate with each other, so the Ethernet node must use a compatible protocol. 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 (requestforcomments) 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. On the transport layer, there are two important protocols: TCP and UDP. The former confirms the received information. Both are useful. On the upper layer of the protocol stack, there are several useful application layer protocols used in industrial Ethernet. Addressing is an important topic for users. The IP protocol is responsible for routing packets between sites that may be located in different networks. Each site has a unique 32-bit address (representing network address and host address respectively). The address is expressed in dotted decimal four bytes. 128.8.120.5 is a valid address, but it is impossible to determine what is the host and what is the network. The addresses are divided into five categories, and the addresses are divided into a~e categories. Classification can be made by observing the first byte.

IP allocation is not simple. It is usually allocated by the network management. Once allocated, it must be applied to each station in the network. IP addresses are divided into static and dynamic allocation. Dynamic allocation is done by the server. Static allocation is done by configuration. The following addresses are private 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

IP address and Ethernet MAC address are different and cannot be confused. The MAC address is assigned by the equipment manufacturer, so it is unique in the world. IP addresses are assigned during installation and reassigned as needed.

8. Application layer protocol

Determine the connectors and cables to be used, whether the hub or switch is used, and allocate IP to enable communication between sites. Now we need to consider the compatibility of the OSI upper layer. The industrial automation protocols recommended 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.