OPC UA does not provide redundancy but defines specific services and data structures by which redundancy can be achieved in a standardized manner. Vendors can create redundant client and servers with a consistent behaviour.
Generally we can distinguish redundancy of: servers/clients, communication paths and signals. Although the specification provides support only for client/server redundancy, product vendors can incorporate all kinds of redundancy into the framework proposed by the specification. For example, a server can establish wireless connection as the means of recovery from cable connection failure or a server can use many data sources bound to a variable to provide continuous updating of the variable value even if one of the sensors has been damaged.
Note – Redundancy is defined in UA Part 4, the Information Model is specified in OPC UA Part 05