Redundancy in industrial networks

Network redundancy is the backbone of 800xA's network technology. ABB's Redundant Network Routing Protocol (RNRP) enables a network architecture with two physically separate networks.

Network redundancy adds an extra instance within the network infrastructure to ensure network availability. This serves as a backup for shifting network communications onto the other network in case of a disturbance in the first one, and therefore avoiding single point of failure.

Redundancy is of special importance in industrial process applications and in safety-critical systems where network downtime could cause serious problems and production stop. In a redundant network, a disturbance in one of the networks automatically leads to a shift over to the other network.

All RNRP versions used in previous system versions of System 800xA are compatible with each other.

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Redundancy - typical RNRP use cases

Connect a control network to the system client server network

  • The Control Network is used for communication between controllers and between controllers and Connectivity Servers.
  • The Client/Server network is used for communication between servers and between client workplaces and servers.
  • The Client/Server Network supports network redundancy using the RNRP protocol and redundant Ethernet switches. Server and client PCs need additional network cards to adapt to redundant networks.
  • Client/server and control networks use RNRP to achieve redundancy through two physically separated networks. There is therefore a limited need for additional redundancy concepts such as rings. A simple star topology is recommended since the number of “switch-hops” traffic needs to take is reduced. 

Connect two separate controller areas

Controllers on Control Network areas can communicate with each other if the Connectivity servers work as routers. If it is desired that controller-to-controller communication is independent from the operation of the Connectivity servers and/or from the Client Server network it is possible to build a network where control networks are directly connected via dedicated routers.

Connect multiple controller networks to a controller "backbone"

A Backbone Network Area is similar to the Local Area with the difference that routing information can be received from neighbor areas but no routing information is sent out to standard neighbor areas. A node connected in the Backbone area receives all network information from all network areas (except local areas).

Create a secure "tunnel" between controller areas

It is possible to connect RNRP Network Areas using standard IP routers and/or firewalls that do not run the RNRP protocol. This is done by configuring so-called RNRP Tunnel Areas. A Tunnel Area is a specification of IP routes and addresses in a path between two Network Areas. Both static network routes in the routers and explicit addresses to the routers in the Area border nodes need to be configured.

Connect to a DMZ

By using a firewall with more than two network interfaces it is possible to build a solution where one interface is connected to the 800xA System Network, one interface is connected to the external network and at least one port is connected to a separate network, called “Demilitarized Zone” (DMZ).

The idea with a Demilitarized zone is that the traffic between the external network and the 800xA System needs to go via nodes on the demilitarized zone. Connections should not be made directly between an external node and a node on the 800xA System network. All connections must be terminated in the demilitarized zone. External nodes must only be allowed to connect to nodes in the demilitarized zone.

Ring redundancy using FRNT for field networks

Field networks do not use RNRP to create redundancy using two physically separate networks. It makes sense to create network rings for some level of redundancy. The NE800 equipment uses the Fast Recovery of Network Topology (FRNT) protocol to create rings. Offering 20ms failover, it is one of the fastest ring protocols available.

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