OPC UA provides the data structures and services by which Redundancymay be achieved in a standardized manner. Redundancy may be used for high availability, fault tolerance and load balancing. Part 4formally defines Client, Serverand Network Redundancy. Only some Profiles Part 7will require redundancy support, but not the base Profile.

Required client and server behaviours are associated with two distinct modes of Server Redundancy, transparent and non-transparent. The Clientand Serverresponsibilities when using either transparent or non-transparent redundancy are defined in Part 4.

Serversthat support non-transparent redundancy can also support client controlled load balancing. The health of a Serverincluding its ability to Servicerequests is collectively defined as ServiceLevel. See Part 5for a formal definition of ServiceLevel. Part 4defines four distinct ServiceLevelsub-ranges and example usage.