3 Terms, definitions and conventions ToC Previous Next

3.1 Terms and definitions ToC Previous Next

For the purposes of this document, the terms and definitions given in The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments and errata) applies.

OPC 10000-1, OPC 10000-2, and OPC 10000-3, as well as the following apply.

3.1.1 Active Server

Server which is currently sourcing information

Note 1 to entry: In OPC UA redundant systems, an active Server is the Server that a Client is using as the source of data.

3.1.2 Deadband

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

Note 1 to entry: Deadband can be applied as a filter when subscribing to Variables and is used to keep noisy signals from updating the Client unnecessarily. This standard defines AbsoluteDeadband as a common filter. OPC 10000-8 defines an additional Deadband filter.

3.1.3 DiscoveryEndpoint

Endpoint that allows Clients access to Discovery Services without security

Note 1 to entry: A DiscoveryEndpoint allows access to Discovery Services without a Session and without message security.

3.1.4 Endpoint

physical address available on a network that allows Clients to access one or more Services provided by a Server

Note 1 to entry: Each Server may have multiple Endpoints. The address of an Endpoint must include a HostName.

3.1.5 Failed Server

Server that is not operational.

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

3.1.6 Failover

act of switching the source or target of information.

Note 1 to 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).

3.1.7 Gateway Server

Server that acts as an intermediary for one or more Servers

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

3.1.8 Hostname

unique identifier for a machine on a network

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

3.1.9 Security Token

identifier for a cryptographic key set

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

3.1.10 SoftwareCertificate

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

Note 1 to 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.

3.1.11 Redundancy

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

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

3.1.12 Redundant Server Set

two or more Servers that are redundant with each other

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

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