To establish Connections defined in a ConnectionConfigurationSet, the ConnectionManager shall use the sequence of Calls illustrated in Figure 36 to the EstablishConnections Method on the involved AutomationComponents.

See Figure 35 for an illustration of the configuration information contained in the ConnectionConfigurationSet. The figure illustrates a single Connection. For further examples, please refer to Annex E.

Figure 35 – ConnectionConfigurationSet example

The EstablishConnections Method (see 6.2.4) is used to establish ConnectionEndpoints on an AutomationComponent.

The Method allows establishing multiple Connections with a single Call. The number of Connections to be established with a single Call may be restricted by the addressed AutomationComponent as indicated by MaxConnectionsPerCall (see 6.2.6).

The Method provides several commands (see 10.21) to verify and create the individual Information Model Objects related to a Connection.

Figure 36 illustrates the sequence of commands to a single AutomationComponent when calling the EstablishConnections Method.

Figure 36 – Command sequence illustration

A ConnectionManager shall call the EstablishConnections Method on the AutomationComponents, passing in one or several commands to be executed together with their required arguments. A ConnectionManager may use one or multiple EstablishConnections Calls (see 6.2.4).

The ConnectionManager shall use the following commands in the following sequence: CreateConnectionEndpointCmd, EstablishControlCmd, SetConfigurationDataCmd, ReassignControlCmd, and SetCommunicationConfigurationCmd. The sequence may be built by having one EstablishConnections Call with the required commands (in this case, the mandated sequence is maintained by the AutomationComponent) or multiple subsequent EstablishConnections Calls by keeping the sequence of commands across the Calls (in this case, the mandated sequence is maintained by the ConnectionManager).

The ConnectionManager may use the following commands at any time and in any order: VerifyAssetCmd, VerifyFunctionalEntityCmd, ReserveCommunicationIdsCmd, and EnableCommunicationCmd.

A Client using the Methods exposed in the Information Model (e.g., VerifyAsset, ReassignControl) can invoke them in any order or at any time. The sequence is only mandated for the commands within the EstablishConnections Method.

The following applies to the usage of commands:

• Commands may be omitted if not needed, e.g., if no ControlGroups are exposed by the AutomationComponent or used by the configuration in the ConnectionConfigurationSet, the commands EstablishControlCmd and ReassignControlCmd can be omitted.
• Method Calls are subject to certain limits defined by OPC UA and provided by a Server (e.g., MaxMessageSize, MaxByteStringLength, etc.). Therefore, it might be necessary to issue commands in consecutive EstablishConnections Calls, e.g., to apply large configuration data, multiple Calls with SetConfigurationDataCmd can be required.
• If AutomationComponentConfiguration CommandBundleRequired is set to TRUE, the ConnectionManager shall issue all required bundled commands in a single Call (see 6.2.4.3.1).
• It is recommended that the ConnectionManager issue all required commands in a single Call.
• It is recommended that a ConnectionManager establishing multiple Connections between multiple AutomationComponents performs these operations in parallel.

If Auditing is supported, the ConnectionManager shall generate an Event of AuditClientUpdateMethodResultEventType for all calls of the EstablishConnections Method and shall pass the AuditEventId as part of the Method invocation.

It is recommended that the ConnectionManager has the well-known Role ConnectionAdmin as defined in Clause 5.9.

NOTE   The specified configuration sequence applies to the establishment of a single Connection (on an AutomationComponent). It is implementation-specific in which sequence (and to which extent in parallel) a ConnectionManager establishes multiple Connections.

Table 75 lists the commands and their required configuration information in the ConnectionConfigurationSetType Information Model.

Table 75 – Commands and their required configuration information

Command	Description	Relevant types from configuration model
VerifyAssetCmd	Verify that the Assets are the ones expected by system engineering.	The argument AssetVerifications that is passed for this command is constructed out of the AssetVerificationType instances in the AutomationComponentConfiguration.
VerifyFunctionalEntityCmd	Verify that the FunctionalEntity is the one expected by system engineering.	The argument ConnectionEndpointConfigurations ExpectedVerificationVariables that is passed for this command is constructed out of the ExpectedVerificationVariables contained in Endpoint1 or Endpoint2 Object in the instances of ConnectionConfigurationType.
ReserveCommunicationIdsCmd	Reserves identifier for the communication configuration.	The argument ReserveCommunicationIds that is passed for this command is constructed out of the instance of CommunicationModelConfigurationType.
CreateConnectionEndpointCmd	Create a ConnectionEndpoint on the FunctionalEntity. Alternatively, use a preconfigured ConnectionEndpoint.	The argument ConnectionEndpointConfigurations ConnectionEndpoint that is passed for this command is constructed out of the Parameter Object in the ConnectionEndpoint Object in Endpoint1 or Endpoint2 Object in the instances of ConnectionConfigurationType.
EstablishControlCmd	Establish control of specific ControlGroups of the FunctionalEntity.	The argument ConnectionEndpointConfigurations ControlGroups that is passed for this command is constructed out of the ControlGroups Variable in Endpoint1 or Endpoint2 Object in the instances of ConnectionConfigurationType.
SetConfigurationDataCmd	Set ConfigurationData on the FunctionalEntity to adapt its behaviour as required (e.g., setting engineering units).	The argument ConnectionEndpointConfigurations ConfigurationData that is passed for this command is constructed out of the ConfigurationData Variable in Endpoint1 or Endpoint2 Object in the instances of ConnectionConfigurationType.
ReassignControlCmd	Reassigns the ControlGroups to be associated with a Connection.	The argument ConnectionEndpointConfigurations ControlGroups that is passed for this command is constructed out of the ControlGroups Variable in Endpoint1 or Endpoint2 Object in the instances of ConnectionConfigurationType.
SetCommunicationConfigurationCmd	Set communication configuration specific for the communication model utilized for data exchange (e.g., PubSub).	The argument CommunicationConfigurations that is passed for this command is constructed out of the instance of CommunicationModelConfigurationType. The argument ConnectionEndpointConfigurations CommunicationLinks is constructed out of CommunicationLinks Variable in Endpoint1 or Endpoint2 Object in the instances of ConnectionConfigurationType.
EnableCommunicationCmd	Enable the communication model.	The argument ConnectionEndpointConfigurations ConnectionEndpoint that is passed for this command is constructed out of the ConnectionEndpoint Object in Endpoint1 or Endpoint2 Object in the instances of ConnectionConfigurationType.

The ConnectionManager shall resolve identifier information contained in the ConnectionConfigurationSets to the arguments required for the EstablishConnections Call (see 13).

If any of the ConnectionEndpoints require SKS configuration, the ConnectionManager shall also call the SKS and add the appropriate configuration (SecurityGroups and/or PushTargets; see E.5 for examples).

If a configuration entry is null or empty, the corresponding command shall be skipped.

If EstablishConnections returns Uncertain, indicating an Abort of the Method (see 6.2.4.3.11) or if a fatal OPC UA communication error occurs, the ConnectionManager shall stop the establishing sequence and initiate a ProcessingToError transition in the ConnectionConfigurationSetStateMachine (see 6.9). If RollbackOnError is TRUE, the ConnectionManager shall call the Method CloseConnections for all ConnectionEndpoints established so far with Remove set to TRUE. If RollbackOnError is FALSE, no additional actions are performed by the ConnectionManager.