OPC UA enables Servers, Clients and networks to be redundant. OPC UA provides the data structures and Services by which Redundancy may be achieved in a standardized manner.
Server Redundancy allows Clients to have multiple sources from which to obtain the same data. Server Redundancy can be achieved in multiple manners, some of which require Client interaction, others that require no interaction from a Client. Redundant Servers could exist in systems without redundant networks or Clients. Redundant Servers could also coexist in systems with network and Client Redundancy. Server Redundancy is formally defined in 6.6.2.
Client Redundancy allows identically configured Clients to behave as if they were single Clients, but not all Clients are obtaining data at a given time. Ideally there should be no loss of information when a Client Failover occurs. Redundant Clients could exist in systems without redundant networks or Servers. Redundant Clients could also coexist in systems with network and Server Redundancy. Client Redundancy is formally defined in 6.6.3.
Network Redundancy allows a Client and Server to have multiple communication paths to obtain the same data. Redundant networks could exist in systems without redundant Servers or Clients. Redundant networks could also coexist in systems with Client and Server Redundancy. Network Redundancy is formally defined in 6.6.4.