May 2017

Eliminate System Downtime in Your Mission-Critical Applications

The data packets that are sent in Ethernet-based communication can be categorized into unicast, broadcast, and multicast. There are numerous redundancy protocols available that can help network operators build a reliable network for unicast and broadcast communication. A good indicator of the reliability of a network is how fast it can recover from an error when transmitting data. For many years, RSTP (Rapid Spanning Tree Protocol) has been widely used across the networking industry to prevent loops on Ethernet networks. When an error occurs on the network, RSTP may require around 10 seconds to rectify the cause of disruption. In comparison, Moxa’s network recovery technologies, Turbo Ring and Turbo Chain, can redirect to the backup path in less than 50 ms. For mission-critical applications, Moxa’s technologies are extremely beneficial because they help avoid downtime and allow data to be continually passed along the network even when there is an interruption. Posing a more difficult challenge to network operators is how to ensure reliable communication on multicast networks.

Multicast communication primarily relies on IGMP (Internet Group Management Protocol) to ensure smooth communication across networks. However, when an error occurs on a network, even in a RSTP or Turbo Ring/Chain network, IGMP requires up to 125 seconds to update the multicast transmission path. A recovery time in excess of two minutes is not acceptable for mission-criticial applications. A common example is when a network error causes disruption to a PLC that is controlling processes in a factory. A malfunctioning PLC will cause devices to experience downtime, which stops production and causes financial losses for the company that is managing the factory.

Packet type
Protocol
Recovery time*
Unicast/Broadcast
RSTP
Around 10 seconds
Turbo Ring/Chain (Moxa)
Less than 50 ms
Multicast with IGMP snooping
RSTP
Up to 125 seconds
Multicast fast recovery (Moxa)
Less than 50 ms

*The above data is based on internal testing conducted by Moxa. We can guarantee the above recovery times for your network.

The diagram below illustrates the type of network that is often deployed for factory automation. The robotic arms have to communicate reliably with a conveyor belt in order to ensure continuous and stable production. To determine system availability between the PLC and other devices requires implicit communication to be used, which allows information to be provided in real time. However, when the transmission path is broken, the implicit multicast messages cannot be delivered to the recipient. If the link is unable to recover within a short period such as 100 ms, a safety mechanism will often be triggered that causes the PLC to shut down the whole system to prevent damage to facilities, equipment, or even personnel.

In order to avoid disruption to networks where downtime is unacceptable, Moxa developed a fast recovery multicast technology. Moxa built this technology on top of traditional packet communication technology and then enhanced it to ensure that multicast transmissions can be recovered in less than 50 ms. When this technology is combined with either Turbo Ring or Turbo Chain, the network operator can build a network with strong redundancy. For factory automation applications, similar to the example above, the PLC is not likely to experience downtime even when there is disruption to the network.

Moxa has developed V-ON, which is an innovative technology that ensures fast recovery times for layer 2/3 multicast communication. This multicast fast recovery technology is a part of V-ON, and it can guarantee layer 2 multicast recovery in less than 50 ms. For network operators who want to take advantage of Moxa’s fast recovery technologies, our EDS-500E Series, IKS, and ICS switches all support V-ON. The software is very easy to use and can be enabled by selecting “multicast fast forwarding” in the web interface. It is currently available for free by downloading the latest firmware.

To learn more about Moxa’s V-ON technology, visit our website here.

 
 
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