RSTP vs. Ring redundancy network. Which one provides better performance?

While Industrial Ethernet networking has gained more popularity, stability of network has become more and more important. With the industrial environment there are many different requirements needed, fast network recovery, higher temperature range, DC power, fiber-built-in media, robust enclose, and easy configuration.

Today, high availability, achieved through redundancy and fault tolerance, is a critical component of many industrial network deployments. Where loss of an enterprise network for a few minutes is inconvenient, loss of an industrial network can have disastrous consequences. In substations, transportation systems, video surveillance, access control and production environments, processes are highly integrated; a fault at one location can travel rapidly upstream and downstream. Interruptions to factory operations can cost tens of thousands of dollars per hour, easily justifying the extra expense for hardened and highly reliable control and information systems.

Types of Redundancy network available

STP (Spanning Tree Protocol) and RSTP (Rapid Spanning Tree Protocol)

The IEEE 802.1d standard Spanning Tree Protocol (STP), adopted in 1990, was the original standard for Ethernet fault recovery. It provides a mechanism for resolving redundant physical connections to maintain the operation of standard Ethernet LANs but does not allow more than one path for a packet to be in use at a given time. STP has been deemed too slow for most modern industrial applications. The recovery time is somewhere from 30 to 50 seconds. Some vendors offer proprietary alternatives, however Rapid Spanning Tree Protocol (RSTP), adopted in 1998 and described in IEEE 802.1w, was up to 50 times faster than STP and is widely accepted today. The recovery time is 1 to 2 seconds.

IEEE 802.1D-2004 further revised the standard and now offers a higher-speed implementation of RSTP that can also support larger networks. Redundant LAN configurations can be constructed in a variety of ways. While mesh configurations are a more general topological case, ring configurations for redundancy are especially useful and cost-effective in industrial LAN systems, and will be treated in this paper in more detail. In addition to RSTP, which requires a managed switch or router at each node.

RSTP


Ring Redundancy

Ring redundancy is a physical ring structure, it is well suited for a distributed network application, as it allows different participants in communication systems to be allocated over a large physical diameter with low cabling effort,compared to other physical topologies like star or tree topologies. Instead of connecting each participant to a central distribution device and creating a star network,all participants are interlinked, with the last device in the list connecting to the first device, closing the ring.

Currently there are 3 major types of ring redundancy, HiPER Ring from Hirschmann, Turbo Ring from Moxa, S-Ring from Garrettcom, all of them offer fast recovery time, easy setup, monitoring tools, and some even offer dip switch configuration.

Redundant_RingTopology

The Ring redundancy is ususlly used in Industrial environments which have a very limit tolerance in data and connection lost. For most of the industrial applications, 30 ms or less recovery time is required. The ring redundancy offers a quick and easy way to configure many ring devices at once with only a few configuration steps necessary. This aids administrators by saving time in configuration processesand enables the possibility of ring redundancyconfiguration for application specialists who want to useredundant Ethernet network structures, but don’t want tobe burdened with an elaborate configuration process.

The automatic ring configuration has the ability to detect whether it will work in a certain network layout, but, like with a manually configured network, precautions in the deployment of actual physical network devices have to be made in order not to mix devices not supporting network protocols with devices supporting it. The ring redundancy configuration is especially useful in application scenarios where the installation follows frames that are additionally. The mechanism works the same way for the frame from MRM ring port 2, just the other way around.

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