This plugin is based on the S2OPC open source library.

OPC UA server protocol stack configuration

Connection configuration

This section provides the connection-level configuration details of an OPC UA server. 

Attributes definition

Configuration JSON structure

{
   "transport_layer":{
      "url":"opc.tcp://localhost:4841/OPCUA/s2opc",
      "appUri":"urn:S2OPC:localhost",
      "productUri":"urn:S2OPC:localhost",
      "appDescription":"Application description",
      "localeId":"en-US",
      "namespaces":[ "urn:S2OPC:localhost" ],
      "policies":[
         {
            "securityMode":"None",
            "securityPolicy":"None",
            "userPolicies":[
               "anonymous"
            ]
         },
         {
            "securityMode":"SignAndEncrypt",
            "securityPolicy":"Basic256Sha256",
            "userPolicies":[
               "username_Basic256Sha256",
               "username_None"
            ]
         }
      ],
      "users":{ "user":"password", "user2":"xGt4sdE3Z+" },
      "certificates":{
         "serverCertPath":"server_2k_cert.der",
         "serverKeyPath":"server_2k_key.pem",
         "trusted_root":[ "cacert.der" ],
         "trusted_intermediate":[],
         "revoked":["cacrl.der"],
         "untrusted_root":[],
         "untrusted_intermediate":[],
         "issued":[]
      }
   }
}

OPC UA server endpoint interface

Connection

A client requires knowledge of parameters provided in previous section to establish a secured channel with the server:

• Endpoint URL
• Server certificate (It is the responsibility of the client to ensure that it is connecting to the expected server)
• User login/password, if applicable.

Endpoint

This section provides the user-level configuration details of an OPC UA server, once a client-server secured connection is established.

The endpoint (see "transport_layer.url") is an OPC UA interface and provides several means of use by a client (Browse, Read, Write, Subscribe). The following items allow any connected client to access directly all server data without prior use of browsing, provided that it has knowledge of the PIVOT object it needs and there related types.

Interface specification:

All PIVOT objects are split on OPC UA server in one variable for each field. The variables are organized as follow:

• There is a folder-type node for each PIVOT data. This folder is defined by:
  • NodeId ns=1;s=<PIVOT_ID>
  • BrowseName/DisplayName <PIVOT_ID>
  • IsOrganizedBy "Root.Objects" (= "i=85")

• There is one Variable for each exposed filed of the PIVOT data:
  • NodeId ns=1;s=<PIVOT_ID>/<FieldName>
  • BrowseName/DisplayName <FieldName>
  • IsOrganizedBy ns=1;s=<PIVOT_ID>

TeleMeasure /TeleSignal

Both TeleMeasure and TeleSignal use exactly the same OPC variables organization. They both represent data received from a south plugin and therefore only expose Read-Only Nodes.

Common notes

• With <PIVOT_ID> as provided in exchanged_data.datapoints[].pivot_id section configuration.
• All read-only variables have a OpcUa_BadWaitingForInitialData quality (0x80320000) initial value until a valid value is received from FledgePower.
• All non-mandatory values will be set automatically by the server if not received from a south device.
• If a mandatory value is missing, then the whole PIVOT object is not updated.
• As a standard OPC UA server, all functional data are organized under the Root.Objects  node of namespace 0 ( nodeId = i=85).
• All data are stored under the namespace 1. Its URI is configured in protocol "namespaces" parameter.

Value content and metadata

PIVOT timestamp

The ns=1;s=<PIVOT_ID>/Value variable contains the pivot timestamp value (t.FractionOfSecond + t.SecondSinceEpoch) is converted to OPC-UA timestamp (Unit=  number of 100 nanosecond since Jan 1st,1600).

The timestamp is not optional in OPCUA. Thus, in case the timestamp were not provided by south layers, the OPC UA north plugin will set the timestamp to 0.

PIVOT value validity

The ns=1;s=<PIVOT_ID>/Value variable contains the pivot value <Root>.<type>.q.validity field. It is represented as the OPC UA Quality of the variable, using the following conversion:

TeleControl

The TeleControls represent commands received from an OPC UA client -connected to the North plugin- that must be sent to a south service. Therefore, they expose Read/Write variables that will be written by a client, except for the feedback of operation, which is Read-Only (Variable Reply).

As a single PIVOT TC contains the information provided in several OPC variables, the following procedure has been defined to ensure atomicity of the operation. An OPC UA client must:

• first write all relevant parameters in the TC variables. This can be done in a single OPC UA 'write' operation, The plugin will not check that all fields have been updated. This is under the responsibility of the OPC UA client.
• then activate the command Trigger. This must be executed after the previous write command was successfully completed.

PIVOT variant value

The base type of the value itself is static and depends on the configuration provide in  "exchanged_data" section.