Connecting to the OPC UA server

The probe uses an exchange of SOAP messages that encapsulate various OPC Unified Architecture (UA) services to establish a connection with the EMS.

The process of connecting to the OPC UA server has the following stages:

  1. Creating a secure channel.
  2. Creating a OPC UA session.
  3. Activating the OPC UA session.

The following sections summarize the actions in each stage and highlight the properties that the probe uses in each stage.

Creating a secure channel

The probe uses secure transport layer (SSL) to enable a secured HTTPS transmission. You can choose to use HTTP (non-secured) or HTTPS by configuring EnableSSL and setting the keystore/truststore.

Creating a OPC UA session

Once the secure channel is established the probe creates an OPC UA session with the OPC UA server using the OPC UA CreateSession service. This service has a number of parameters that define the characteristics of the session. The probe maintains values for some of the parameters as properties.

Table 1. Properties used in the CreateSession service

Properties

Usage

EndpointHttpHost
EndpointHttpPort
EndpointSessionServiceName

The probe uses these properties to construct the URL of the OPC UA server as follows:

http://host:port/service

Where:

  • host is the value of the EndpointHttpHost property. This value can either be a hostname or an IP (IPv4/IPv6) address.

    If you specify an IPv6 address, ensure that the address is enclosed in [] (square brackets). For example, as a value in the properties file:

    EndpointHttpHost:
'[2001:15f8:106:195:250:56ff:
fe9c:5183]'
    For example, in the command line:
    -httphost 
[2001:15f8:106:195:250:56ff:fe9c:5183]
  • port is the value of the EndpointHttpPort property.
  • service is the value of the EndpointSessionServiceName property.

In addition, if the EndpointWsdlLocation property is empty (by default), the probe will use the formed URL to reach the WSDL location. The formed URL is http://host:port/server?wsdl http://<EndpointHttpHost>:<EndpointHttpPort>/<EndpointSessionServiceName>.

OPCSessionName

The name for the OPC UA session.

RequestedSessionTimeout

The maximum amount of time (in milliseconds) that the session can remain in use without communications activity taking place. If the probe fails to issue a Service request within this interval, then the OPC UA server automatically terminates the session.

Make sure that the value of this property is greater than the value of the ResynchInterval property.

MaxResponseMessageSize

The maximum size (in bytes) of the body of any message that the OPC UA server sends to the probe.

Ensure that all these properties have values that are suitable for the needs of your site.

Activating the OPC UA session

Having created the OPC UA session, the probe uses the OPC UA ActivateSession service to bring it into use.