Redundant networks can be used with OPC UA in either transparent or non-transparent Redundancy.
Network Redundancy can be combined with Server and Client Redundancy.
In the transparent network use-case a single Server Endpoint can be reached through different network paths. This case is completely handled by the network infrastructure. The selected network path and Failover are transparent to the Client and the Server.
Figure 34 – Transparent Network Redundancy
- A physical appliance/device such as a router or gateway which automatically changes the network routing to maintain communications.
- A virtual adapter which automatically changes the network adapter to maintain communications.
In the non-transparent network use-case the Server provides different Endpoints for the different network paths. This requires both the Server and the Client to support multiple network connections. In this case the Client is responsible for selecting the Endpoint and for Failover. For Failover the normal reconnect scenario described in 6.7 can be used. Only the SecureChannel is created with another Endpoint. Sessions and Subscriptions can be reused.
Figure 35 – Non-Transparent Network Redundancy
The information about the different network paths is specified in NonTransparentRedundancyType ObjectType defined in OPC 10000-5.