Due to the extremely high requirements of the industrial environment for the reliable performance of the industrial control network, the redundancy function of the industrial Ethernet emerges as the times require. From Rapid Spanning Tree Redundancy (RSTP), Ring Redundancy (RapidRing) to trunk redundancy (Trunking), they have their own different advantages and characteristics, and control engineers can choose according to their own requirements. In order to better help you understand and learn the characteristics of industrial Ethernet redundancy technology, let us first review the development process of the following Ethernet equipment.
I believe that the vast majority of people are familiar with hubs. Many people use this simple device to connect various Ethernet-based devices such as personal computers, programmable controllers, etc. A hub receives a message from one port and broadcasts the message to all other ports.
For every message from any port, the hub passes it on to every other port. In terms of message passing, hubs are slow and inefficient, and message collisions can occur. However, the hub is very simple to use – it’s practically plug and play. The hub doesn’t have any bells and whistles, nor does it have redundancy.
2. Unmanaged switches
The development of hubs gave rise to a device called an unmanaged switch. It can realize the routing function of messages from one port to another port, which is more intelligent than the hub. Unmanaged switches can automatically detect the network speed of each network device. In addition, it has a feature called “MAC address table” that can identify and remember devices on the network.
In other words, if port 2 receives a message with a particular identifier, the switch will then send all messages with that particular identifier to port 2. This intelligence avoids message collisions and improves transmission performance, a huge improvement over hubs. However, unmanaged switches cannot implement any form of communication detection and redundant configuration.
3. Managed switch
The next generation in the evolution of Ethernet connectivity equipment is the managed switch. Relative to hubs and unmanaged switches, managed switches have more and more complex functions, and the price is much higher—usually 3 to 4 times that of an unmanaged switch. Managed switches offer more functionality and are usually fully configurable through a network-based interface. It can automatically interact with network devices, and users can also manually configure network speed and flow control for each port. Some older devices may not be able to use the automatic interaction function, so manual configuration is essential.
Most managed switches also typically offer some advanced features, such as SNMP (Simple Network Management Protocol) for remote monitoring and configuration, port mapping for diagnostics, VLAN (Virtual Local Area Network) for A prioritization function to ensure that priority messages pass through, etc. With managed switches, redundant networks can be built. Using a ring topology, managed switches can form a ring network. Each managed switch can automatically determine the optimal 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 optimized for redundant systems with strict requirements in terms of stability and security. The main ways to build a redundant network are as follows, STP, RSTP; Ring redundant RapidRing
STP and RSTP
STP (Spanning Tree Protocol, IEEE 802.1D), is a link layer protocol that provides path redundancy and prevents network loops from occurring. It forces the alternate data path to a blocked state. If a path fails, the topology can be reconfigured and links reconfigured by activating alternate paths. The network interruption recovery time is between 30 and 60 seconds. RSTP (Rapid Spanning Tree Algorithm, IEEE 802.1w), as an upgrade of STP, shortens the network interruption recovery time to 1~2s. The spanning tree algorithm has a flexible network structure, but it also has the disadvantage of slow recovery.
Ring redundancy RapidRing
In order to meet the real-time characteristics of industrial control networks, RapidRing was born. This is a technique that uses a ring network to provide high-speed redundancy in an Ethernet network. This technology enables the network to recover itself within 300ms after an interruption. And can remind users of the disconnection phenomenon through the switch’s fault relay connection, status Display lights and SNMP settings. These can all help diagnose where the ring is broken.
RapidRing also supports two connected rings, making the network topology more flexible and diverse. The two rings are connected via dual channels, and these connections can be redundant to avoid problems caused by single cable errors.
Backbone redundant trunking
Set multiple ports of different switches as trunking trunk ports and establish a connection, then a high-speed backbone link can be formed between these switches. It not only doubles the network bandwidth of the backbone link and enhances the network throughput, but also provides another function, that is, the redundancy function.
If the backbone link in the network has problems such as disconnection, the data in the network will be transmitted through the remaining links to ensure normal network communication. The trunk network of trunking adopts the bus type and star network structure, and the theoretical communication distance can be extended indefinitely. This technology adopts the method of hardware detection and data balance, so the network interruption recovery time has reached a new height, and the general recovery time is less than 10ms.
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