Industrial Ethernet switch selection factors
Industrial Ethernet switches are used to connect Ethernet devices. It first receives data frames sent by a device and then transmits these frames to the appropriate switch port connected to other Ethernet devices. As it transmits these frames, it learns and grasps the location of the Ethernet device and uses that information to decide which ports to use to transmit frames. This helps reduce network usage.
According to an ARC survey – Industrial Ethernet Equipment Market survey involving the global industrial Ethernet switch market, it is forecast to grow at a compound annual growth rate of 49.9% over the next three years. In 2004, the annual industrial Ethernet equipment was 840,000 sets (units), and by 2009 it will reach 6.7 million sets (units).
What industrial Ethernet switch is best suited for your plant’s current application? This can be frustrating because there are many factors to consider, such as the work environment, whether redundancy is required, managed versus unmanaged, future maintenance and scalability, and so on.
Factors to consider before purchasing are:
■ Consideration of working environment: including temperature range, EMC electromagnetic compatibility, protection level, installation method and power supply. Industrial Ethernet switches are designed for use in environments that are not suitable for commercial switches, such as environments with extreme temperatures, high vibration, and strong electromagnetic noise.
■ Choose a managed or unmanaged switch: If the network is simple, you can choose a plug and play unmanaged switch; To facilitate future maintenance, you may need to use the network management type. Only the network management type switch can achieve the ring topology connection.
■ Also need to meet the relevant industry standards: for example, the Marine switch should meet the ship structure standards; If it is used in dangerous situations, it should meet the corresponding certification standards; Transportation industries such as rail transit and roads also have their own standards.
NMS and unNMS
One of the key issues in choosing an industrial Ethernet switch is whether to choose a managed switch or an unmanaged switch. Although a managed switch is generally more expensive, it offers some additional powerful features. Managed switches include the features of unmanaged switches.
Managed switches generally support the Simple Network Management Protocol (SNMP), of course, most managed switches have more than this (SNMP) feature. Basically, a managed switch gives you control over the network, whereas an unmanaged switch usually only allows Ethernet devices to communicate. Managed switches also enable you to monitor the network. Through SNMP, you can view various network status, including the number of bytes received/sent, the number of frames received/sent, the number of errors, and the status of the port. All of these can be viewed port by port.
Managed switches also have some advanced features that improve your network control. Features such as quality of service (QoS), virtual local area network (VLAN), port mirroring, IGMP Snooping, redundancy and SNMP are usually only available on managed switches. Most managed switches have the following advanced features:
QoS is the ability of a switch to apply high priority to specific data frames.
■ vlans allow switches to logically group devices and isolate traffic between device groups even if all devices share a single physical switch.
■ Port mirroring allows one port of the switch to monitor traffic sent or received by one or more ports of the switch. This feature facilitates real-time monitoring of communication data and is a common fault finding method in Ethernet.
■ IGMP Snooping automatically sends multicast frames only to devices that request them. This prevents multicast frames from being sent to devices that do not request them.
■ SNMP is a simple network management protocol, which allows network management applications to communicate with switches in a standard way, request status information and set configuration. Some vendors also offer network management programs that convert SNMP data into OPC data used in the system.
■ Ring network redundancy is a common feature of managed industrial Ethernet switches. Many industrial switch vendors have created their own private ring network redundancy protocols.
In terms of transmission media, most industrial Ethernet communications are carried out over twisted pairs, but optical cables are sometimes required. When the signal transmission distance exceeds the 100 meters supported by the twisted pair, optical cable is required. The communication distance of multi-mode fiber can reach 2 km; The communication distance of single-mode fiber can reach 15 km. Because their communication is not easily affected by electricity or magnetic fields, optical cables are also generally used in high-noise environments.