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

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.

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.

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.

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.

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).

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.

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.

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.

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.

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.

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.

APIApplication Programming Interface

BNFBackus-Naur Form

CACertificate Authority

CRLCertificate Revocation List

CTLCertificate Trust List

DAData Access

NATNetwork Address Translation

UAUnified Architecture

URIUniform Resource Identifier

URLUniform Resource Locator

OPC UA Services contain parameters that are conveyed between the Client and the Server. The OPC UA Service specifications use tables to describe Service parameters, as shown in Table 1. Parameters are organised in this table into request parameters and response parameters.

Table 1 – Service Definition Table





Defines the request parameters of the Service

Simple Parameter Name

Description of this parameter

Constructed Parameter Name

Description of the constructed parameter

Component Parameter Name

Description of the component parameter


Defines the response parameters of the Service

The Name, Type and Description columns contain the name, data type and description of each parameter. All parameters are mandatory, although some may be unused under certain circumstances. The Description column specifies the value to be supplied when a parameter is unused.

Two types of parameters are defined in these tables, simple and constructed. Simple parameters have a simple data type, such as Boolean or String.

Constructed parameters are composed of two or more component parameters, which can be simple or constructed. Component parameter names are indented below the constructed parameter name.

The data types used in these tables may be base types, common types to multiple Services or Service-specific types. Base data types are defined in OPC 10000-3. The base types used in Services are listed in Table 2. Data types that are common to multiple Services are defined in Clause 7. Data types that are Service-specific are defined in the parameter table of the Service.

Table 2 – Parameter Types defined in OPC 10000-3

Parameter Type

















The parameters of the Request and Indication service primitives are represented in Table 1 as Request parameters. Likewise, the parameters of the Response and Confirmation service primitives are represented in Table 1 as Response parameters. All request and response parameters are conveyed between the sender and receiver without change. Therefore, separate columns for request, indication, response and confirmation parameter values are not needed and have been intentionally omitted to improve readability.