3 Terms, definitions, abbreviated terms 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 OPC 10000-1, OPC 10000-2, OPC 10000-3, and 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 document 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. Each Endpoint includes a HostName.

3.1.5 EphemeralKey

public-private key pair generated for each execution of a key establishment process.

Note 1 to entry: EphemeralKeys are necessary when using ECC based SecurityPolicies.

3.1.6 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.

3.1.7 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). A Client failover is the act of an alternate Client replacing an existing failed or degraded Client connection to a Server.

3.1.8 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.

3.1.9 HostName

unique identifier for a machine on a network

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

3.1.10 Redundancy

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

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

3.1.11 Redundant Server Set

two or more Servers that are redundant with each other

Note 1 to entry: 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.

3.1.12 SecurityToken

identifier for a cryptographic key set

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

3.1.13 ServerUri

ApplicationUri for a Server

3.1.14 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.

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