How does the redundancy function of Industrial Ethernet ensure the stability of the network?

Due to the extremely high requirements of industrial control network reliability in industrial environments, the redundancy function of industrial Ethernet came into being. From Rapid Spanning Tree Redundancy (RSTP), Ring Network Redundancy (RapidRing) to Trunk Redundancy (Trunking), each has its own advantages and characteristics, and control engineers can choose according to their own requirements. In order to better help everyone understand and learn the characteristics of industrial Ethernet redundancy technology, let us first review the development process of the following Ethernet equipment.

1. Hub

I believe most people are familiar with hubs. Many people use this simple device to connect various Ethernet-based devices, such as personal computers, programmable controllers, etc. The hub receives a message from a port and broadcasts the message to all other ports.

For every message from any port, a hub passes it on to every other port. Hubs are slow and inefficient at passing messages, and message collisions can occur. However, hubs are very simple to use—virtually plug-and-play. Hubs have no bells and whistles, and no redundant features.

2. Unmanaged switches

The development of hubs has led to a device called an unmanaged switch. It can route messages from one port to another and is more intelligent than a hub. An unmanaged switch can automatically detect the network speed of each network device. In addition, it has a function called a "MAC address table" that can identify and remember devices on the network.

In other words, if port 2 receives a message with a specific identifier, the switch will then send all future messages with that identifier to port 2. This intelligence avoids message collisions and improves transmission performance, which is a huge improvement over hubs. However, unmanaged switches cannot implement any form of communication detection and redundant configuration functions.

3. Managed Switches

The next generation of Ethernet connection devices is managed switches. Compared with hubs and unmanaged switches, managed switches have more complex functions and are much more expensive - usually 3 to 4 times the price of an unmanaged switch. Managed switches provide more functions and are usually fully configured through a web-based interface. It can automatically interact with network devices, and users can also manually configure the network speed and flow control of each port. Some older devices may not be able to use the automatic interaction function, so manual configuration function is indispensable.

Most managed switches also usually provide some advanced functions, such as SNMP (Simple Network Management Protocol) for remote monitoring and configuration, port mapping for diagnosis, VLAN (Virtual Local Area Network) for grouping network devices, and priority sorting function for ensuring priority messages pass through. Managed switches can be used to build redundant networks. Using a ring topology, managed switches can form a ring network. Each managed switch can automatically determine the best transmission path and the backup path, and automatically block the backup path when the priority path is interrupted.

4. Managed redundant switches

Advanced managed redundant switches provide some special functions, especially for redundant systems with strict requirements on stability and security. The main ways to build redundant networks are as follows: STP, RSTP; ring network redundancy RapidRing

(1) STP and RSTP

STP (Spanning Tree Protocol, IEEE 802.1D) is a link layer protocol that provides path redundancy and prevents network loops. It forces the backup data path to be blocked. If a path fails, the topology can be reconfigured and the link reconstructed by activating the backup path. The network interruption recovery time is between 30 and 60 seconds. RSTP (Rapid Spanning Tree Algorithm, IEEE 802.1w) is an upgrade of STP, which shortens the network interruption recovery time to 1 to 2 seconds. The spanning tree algorithm has a flexible network structure, but it also has the disadvantage of slow recovery speed.

(2) RapidRing redundancy

RapidRing was born to meet the real-time requirements of industrial control networks. It is a technology that uses ring networks to provide high-speed redundancy in Ethernet networks. This technology can enable the network to recover within 300ms after an interruption. It can also remind users of network disconnection through the switch's error relay connection, status display lights, and SNMP settings. These can help diagnose where the ring network is disconnected.

RapidRing also supports two connected rings, making the network topology more flexible. The two rings are connected via dual channels, and these connections can be redundant to avoid problems caused by a single cable error.

(3) Trunk redundancy

By setting multiple ports of different switches as trunk ports and establishing connections, a high-speed backbone link can be formed between these switches. This not only doubles the network bandwidth of the backbone link and enhances network throughput, but also provides another function, namely redundancy.

If the backbone link in the network is disconnected, the data in the network will be transmitted through the remaining links to ensure normal network communication. The trunking backbone network adopts bus and star network structures, and the theoretical communication distance can be greatly extended. This technology uses hardware detection and data balancing methods, so the network interruption recovery time has reached a new height, and the general recovery time is less than 10ms.