10 Keywords Help You Fully Understand Industrial Switch

Industrial Switches are also called industrial Ethernet switches. Because of the selected Internet specifications, they are open, widely used, high-quality and low-cost, and use the fully transparent and unified TCP/IP protocol. The Ethernet interface has already become a key wireless communication module for industrial manipulation.

Industrial switches are mainly used in electric power, factory automation, coal mining automation technology, urban rail, wind and wind power generation and other industries, followed by metallurgical industry, crude oil petrochemical industry, highway traffic control automation technology, house automatic control system, oil and gas field control Automation technology, hydropower plant manipulation automation technology, computer room monitoring system software, water conservancy project supervision, environmental protection supervision and other industrial automation automatic sites.

Industrial switches are different from civilian and commercial switches. They are not substantially different from other switches in the fields of transmission layer, data link layer, protocol, etc., but because of their unique office environment and work regulations, industrial switches solve technical problems such as communication practicability, Internet security factor, security system and safety explosion-proof technology, and selects some countermeasures suitable for industrial natural environment, such as moisture-proof, anti-vibration.

In general, industrial switches are quite different from ordinary Ethernet switches, not only in appearance design, but also in the layout of components, applicable scenarios and adaptability of products, all have stricter requirements.Today, we introduce the following 10 keywords, which are necessary knowledge for mastering industrial switches. Before deciding to use industrial switches, they will help us to fully understand industrial switches.

1. Topological structure

Topology is the arrangement of cables in a network.As we all know, EIA-485 or CAN adopts bus topology.But in industrial Ethernet, due to the common use of hubs or industrial switches, the topology is star or distributed star.

2. Wiring

Similar to most Ethernet products, the cables used include shielded twisted pair, unshielded twisted pair, multimode or single mode, etc.The rate of 10Mbps does not have high requirements for twisted pair cables, while at 100Mbps rate, it is recommended to use Category 5 or Category 5e cables.A pair is required for fiber link, and the commonly used multimode fiber wavelengths are 62.5/125μm or 50/125μm.Compared with the inner core of multimode fiber, the inner core of single mode fiber is very thin, only about 10μm.Usually, 10Mbps uses multi-mode fiber, and under 100Mbps, both single-mode and multi-mode fibers are applicable.

3. Connector box wiring

The twisted pair connector RJ-45 is the most common.In the definition of Media Dependent 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).Hub ports identified as MDI-X ports indicate 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 crossover or directly use the uplink port provided by the hub (the cable should not be crossed).

There are two types of fiber optic connectors, ST connectors are used for 10Mbps or 100Mbps; SC connectors are dedicated to 100Mbps.Singlemode fibers usually use SC connectors.The connection between DTE and DCE only needs to follow the TX and RX marks of the port.

4. The product characteristics of industrial Ethernet

(1) The special requirements of the industrial environment need to be considered, such as adapting to high temperature, humidity, vibration and other environments; (2) The elements of industrial interference need to be considered; (3) The power supply requirements generally require low-voltage AC or DC.

Generally speaking, industrial switches are more demanding, and it is difficult for general commercial Ethernet switches to meet these requirements.

5. Speed and distance

In terms of speed, 10Mbps and 100Mbps are more commonly used.

The longest distance of the twisted pair network segment is 100 meters, and the maximum network (network range) is 500 meters.The longest distance of an optical fiber network segment can reach 2 kilometers, but the IEEE802.3 standard stipulates that when using optical fiber, the maximum number of cascades cannot exceed 3, and the end of the network needs to use twisted pair cables, and the two middle ones are optical fiber network segments and ensure that Each network segment does not exceed 1 km.In this way, the length of the entire fiber network segment is limited to 2 kilometers.

6. Hubs and switches

Relay type hub (hub) is the basic device that constitutes the Ethernet topology. It is a multi-port device with four, eight, twelve ports, etc., which can be cascaded to form a decentralized star topology.The hubs all meet the requirements of IEEE802.3 relay units.These requirements include preamble generation, symmetry, and amplitude compensation.

Switching Hubs (Switches) can replace trunking hubs and improve network performance.Unlike physical layer devices - trunking hubs, switching hubs are actually bridges connecting two data links, which means that the collision domain is terminated at each switch port.

Trunk hubs can be connected to switch ports.If there are switches in the network, the twisted-pair network segment is kept 100 meters, but there is no limit for cascading.

7. Half duplex and full duplex

Half-duplex means that the transmission and reception of the same media are performed asynchronously, while full-duplex is the opposite, with separate transmission and reception paths.The full-duplex link segment cannot exceed two devices, which can be network cards or switch ports.

It should be noted that in half-duplex mode, the network segment distance is 412 meters due to the limitation of the collision domain.Therefore, only in full-duplex mode (CSMA/CA is ignored) can fiber segments be stretched to their limit.In Fast Ethernet mode, switch technology is recommended.For fiber ports under Fast Ethernet, it is recommended to use full duplex.

8.Automatic negotiation

What needs to be understood in advance is that the twisted pair link automatically performs speed matching, and the speed of the two fiber optic devices cannot be automatically negotiated.

However, for the auto-negotiation protocol, auto-negotiation between two optical fiber devices is feasible, provided that there is no problem in communication.The subsequent 100BASE-SX standard enables 850nm fiber to work at 10Mbps or 100Mbps.The distance of the network segment under 100Mbps is 300 meters.Therefore, please be careful when installing.The speed of fiber is usually fixed and no negotiation is performed.The auto-negotiation protocol is successful on twisted-pair links.

9. Transmission Protocol

TCP/IP and SPX/IPX are two commonly used protocols.The two protocols are not interoperable, so Ethernet nodes must use compatible protocols.For users, addressing is very important.The IP protocol is responsible for the routing of packets between sites that may be located in different networks.Each site has a unique 32-bit address (representing the network address and host address, respectively).The address is expressed in dotted decimal four bytes.

10. Application layer protocol

Taking into account the compatibility of the OSI layer, industrial automation protocols include Ethernet/IP, iDA, PROFInet and Modbus/TCP.It does not include traditional Internet applications such as SNMP, SMTP and TELNET.The products in use may not all support these protocols, so it is necessary to understand and communicate in advance to find an industrial switch that meets the requirements.