For the purposes of this document, the terms and definitions given in OPC 10000-1, OPC 10000-2, and OPC 10000-3, as well as the following apply.

Server which is currently sourcing information

Note 1to entry: In OPC UA redundant systems, an active Serveris the Serverthat a Clientis using as the source of data.

permitted range for value changes that will not trigger a data change Notification

Note 1to entry: Deadbandcan be applied as a filter when subscribing to Variablesand is used to keep noisy signals from updating the Clientunnecessarily. This standard defines AbsoluteDeadbandas a common filter. OPC 10000-8defines an additionalDeadband filter.

Endpointthat allows Clientsaccess to Discovery Serviceswithout security

Note 1to entry: A DiscoveryEndpointallows access to Discovery Serviceswithout a Sessionand without message security.

physical address available on a network that allows Clientsto access one or more Servicesprovided by a Server

Note 1to entry: Each Servermay have multiple Endpoints. The address of an Endpointmust include a HostName.

Server that is not operational.

Note 1to entry: In OPC UA redundant system, a failed Server is a Serverthat is unavailable or is not able to serve data.

act of switching the source or target of information.

Note 1to entry: In OPC UA redundant systems, a failover is the act of a Client switching away from a failed or degraded Server to another Server in the redundant set (Server failover). In some cases a Client may have no knowledge of a failover action occurring (transparent redundancy). The act of an alternate Client replacing an existing failed or degraded Client connection to a Server(Client failover).

Serverthat acts as an intermediary for one or more Servers

Note 1to entry: Gateway Serversmay be deployed to limit external access, provide protocol conversion or to provide features that the underlying Serversdo not support.

unique identifier for a machine on a network

Note 1to entry: This identifier shall be unique within a local network; however, it may also be globally unique. The identifier can be an IP address.

identifier for a cryptographic key set

Note 1to entry: All Security Tokensbelong to a security context. For OPC UA the security context is the SecureChannel.

digital certificate for a software product that can be installed on several hosts to describe the capabilities of the software product

Note 1to entry: Different installations of one software product could have the same software certificate. Software certificates are not relevant for security. They are used to identify a software product and its supported features. SoftwareCertificates are described in 6.4.

the presence of duplicate components enabling the continued operation after a failure of an OPC UA component

Note 1This may apply to Servers, Clients or networks.

two or more Serversthat are redundant with each other

Note 1A redundant server set is a group of Serversthat are configured to provide Redundancy. These Servershave requirements related to the address space and provide failovers.