Redundancy Protocols in Industrial Ethernet

Industrial Ethernet is a network technology that enables reliable and efficient data communication in industrial environments. Industrial Ethernet networks are often exposed to harsh conditions, such as electromagnetic interference, vibration, temperature fluctuations, and physical damage. Therefore, it is essential to provide redundancy mechanisms that can ensure network availability and performance in case of failures.

Redundancy protocols are network protocols that provide seamless failover against failure of any single network component, such as a cable, a switch, or a node. Redundancy protocols can improve network reliability, safety, and productivity by minimizing downtime and data loss. There are different types of redundancy protocols for industrial ethernet, each with its own advantages and disadvantages. In this article, we will review some of the most common redundancy protocols and compare their features and applications.

Mesh Networks

A mesh network is a network topology where devices or nodes are interconnected, so that multiple paths exist between any two nodes. A mesh network can provide high flexibility and fault tolerance, as it can heal from multiple failures by rerouting traffic through alternative paths. A mesh network can also support load balancing and scalability by distributing traffic across multiple links.

However, a mesh network also has some drawbacks, such as high cabling costs, complex configuration and management, and slow recovery time. A mesh network requires more wiring and ports than other topologies, which increases the installation and maintenance costs. A mesh network also needs sophisticated routing algorithms and protocols to determine the optimal paths and avoid loops, which adds to the network complexity and overhead. Moreover, a mesh network has a slower recovery time than other redundancy protocols, as it needs to re-learn paths and configure ports to work around the failed link.

Link Aggregation

Link aggregation, also known as trunking, is a network technique that combines multiple physical links into a single logical link, increasing the bandwidth and reliability of the connection. Link aggregation can provide fast recovery from a single link failure, as the parallel link can take over the traffic without any reconfiguration. Link aggregation can also enhance network performance and efficiency by utilizing the combined capacity of multiple links.

However, link aggregation has some limitations, such as higher cabling costs, switch dependency, and higher risk of total link failure. Link aggregation requires more cabling than other topologies, which increases the installation and maintenance costs. Link aggregation also depends on the switches that support the link aggregation protocol, such as LACP (Link Aggregation Control Protocol). If a switch fails, the devices connected through it will also lose connectivity. Furthermore, link aggregation has a higher risk of total link failure, as the same event that damages one link may also damage the parallel link, resulting in a more severe disruption.

Redundant Rings

A redundant ring is a network topology where devices are connected in a loop, forming a ring. One link in the ring is disabled until it is needed, creating a backup path. A redundant ring can provide low cabling costs and fast recovery from a single link or switch failure, as the traffic can be redirected to the backup path without any reconfiguration. A redundant ring can also support network segmentation and management by using industrial grade managed switches that can monitor and control the network traffic.

However, a redundant ring has some disadvantages, such as limited scalability, single point of failure, and lower bandwidth. A redundant ring has a limited scalability, as adding more devices to the ring increases the network latency and complexity. A redundant ring also has a single point of failure, as a failure of more than one link or switch at the same time can break the ring and isolate the network segments. Moreover, a redundant ring has a lower bandwidth than other topologies, as one link is always blocked and unused.

High-Availability Seamless Redundancy

High-Availability Seamless Redundancy (HSR) is a network protocol for Ethernet that provides seamless failover against failure of any single network component. HSR nodes have two ports and act as bridges, which allows arranging them into a ring or meshed structure without dedicated switches. HSR nodes send the same frame over both ports to the neighbor nodes, and discard the duplicate frames when they receive them. HSR nodes can also check the redundancy continuously to detect lurking failures.

HSR has some advantages, such as fast recovery, switch independence, and compatibility with PRP (Parallel Redundancy Protocol). HSR can provide fast recovery from a single link or switch failure, as the destination node always receives one frame from either path. HSR does not depend on any switches, as the nodes can forward the frames in cut-through mode. HSR is also compatible with PRP, which is another redundancy protocol that uses two independent networks to provide redundancy. HSR and PRP can be connected without single point of failure and the same nodes can be used in both HSR and PRP networks.

However, HSR also has some drawbacks, such as higher hardware costs, higher network load, and lower bandwidth. HSR requires hardware support, such as FPGA or ASIC, to forward or discard frames within microseconds, which increases the node costs. HSR also generates higher network load, as the nodes send duplicate frames over both ports, which consumes more bandwidth and power. HSR also has a lower bandwidth than other topologies, as one port is always used for sending and receiving frames.

Conclusion

Redundancy protocols are essential for industrial ethernet networks, as they can improve network reliability, safety, and productivity by minimizing downtime and data loss. There are different types of redundancy protocols, each with its own features and applications. The choice of the best redundancy protocol depends on the network requirements, such as the level of redundancy, the recovery time, the network performance, the network complexity, and the network costs. Some of the most common redundancy protocols are mesh networks, link aggregation, redundant rings, and HSR. Each of these protocols has its own advantages and disadvantages, and the comparison of these protocols can help users to select the most suitable protocol for their industrial ethernet network.