Knowledge Drop for when to use a managed or an unmanaged switch

Dan French, with Anixter's Industrial Communication and Control marketing team, helps you choose what network redundancy techniques are right for you.

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Redundant Networks Video Transcript

Hello, I’m Dan French with the industrial communication and control marketing team with Anixter.


The use of Ethernet in mission-critical and industrial environments has added more stress on network reliability and robustness. Even with purpose-built, more robust networking equipment and cabling, over 70 percent of network failures occur in the network media and hardware. This means that the majority of network failures occur in cables, connectors and switches. For this reason, having a redundant network is paramount. The purpose of this video is to help you choose what network redundancy techniques are right for you by selecting between implementation costs, complexity and speed of recovery.


There are dozens of recovery techniques available. Many of them have been developed as proprietary systems. These are costly to implement and difficult to expand. At Anixter, we focus on standard-based technologies because they grant users the freedom to choose best-in-class manufacturers as well as improved network growth and troubleshooting abilities.


The most common redundancy techniques being implemented now are Rapid Spanning Tree, or RSTP, Media Redundancy Protocol and Fast-Media Redundancy Protocol or Fast-MRP, Parallel Redundancy Protocol or PRP and High Available Seamless Ring HSR.


The recovery times and implementation techniques of these network technologies can vary greatly. Rapid Spanning Tree, or RSTP, is one of the most common redundancy methods available. This is because it is very flexible to implement and can be used in a mesh network. RSTP networks can also be used to defeat multiple network failures. The main drawbacks are limitations on network size and recovery speed. The recovery speeds can last into the realm of 2 seconds to re-establish all network connections, while the networks are limited to 40 hops.


Media Redundancy Protocol or MRP and Fast-MRP are standards developed by Hirschmann and are for ring networks. They are useful when faster, more reliable recovery times are needed. MRP can only be used in ring topologies, with up to 200 switches in a network. The standard recovery times are 30 ms for a network of 50 switches, and 80ms for a network of 200 switches.


RSTP and Ring methods are commonly used because they already have a wide installation base and most applications can tolerate a short network interruption of less than a second. They can also be used to vastly improve a network resiliency at a minimal cost – oftentimes only requiring one extra cable to be installed. In applications where high speed control is done locally, oftentimes these relatively short network recovery times can be tolerated.


Parallel Redundancy Protocol and High Available Seamless Ring are both zero recovery time protocols. They both are predicated on sending duplicate packets from the transmitting device over separate paths to the receiving devices. PRP will send the duplicate packets over two independent networks. Packet delivery is ensured because, in the case of one network having a catastrophic failure, the other network should continue to operate.


HSR is used in a ring topology with packets sent in two opposing directions over the ring network. The drawbacks of these network technologies are the added complexity, hardware costs and more network traffic being generated. These technologies are in demand for applications where even a short delay in the flow of data can be costly, such as track and trace, high-speed data acquisition or critical control.


Parallel Redundancy Protocol also has the option to be used wirelessly. This can be useful with mobile applications where cables are subject to more wear and tear from flexing operations or are at a high risk of being damaged.


This concludes this video in the Knowledge Drop series. I hope that it was helpful in helping you select a technology that works for your application. If you have any further questions, please don’t hesitate to ask an expert or contact your Anixter representative. Thanks for watching!