Use the SCADAInput node to receive messages from clients that connect to the broker across the WebSphere® MQ Telemetry Transport.
This topic contains the following sections:
SCADA device clients use the MQIsdp protocol to send messages that are converted by the SCADAInput node into a format that is recognized by WebSphere Message Broker. The node also establishes the processing environment for these messages.
Message flows that handle messages received from SCADA devices must always start with a SCADAInput node. Set the SCADAInput node properties to control the way in which messages are received; for example, you can indicate that a message is to be processed under transaction control.
When you deploy message flows that contain SCADA nodes to a broker, deploy them to a single execution group, regardless of the number of message flows.
The execution group to which the SCADA flows are deployed must be the default execution group. The default execution group can be identified by inspecting the defaultExecutionGroup field in the BIP2201 message at the execution group startup. A value of true denotes the default execution group.
SCADA is primarily a publish/subscribe protocol; therefore, you typically include a Publication node to end the flow. In scenarios where you do not want to use a Publication node, include a SCADAOutput node. If you include a SCADAOutput node, you must also include a SCADAInput node, regardless of the source of the messages, because the SCADAInput node provides the connectivity information that is required by the SCADAOutput node.
If you include an output node in a message flow that starts with a SCADAInput node, it can be any of the supported output nodes, including user-defined output nodes. You can create a message flow that receives messages from SCADA devices, and generates messages for clients that use all of the supported transports to connect to the broker, because you can configure the message flow to request the broker to provide any necessary conversion.
You can request that the broker starts or stops a SCADA listener by publishing messages with a specific topic. This request can apply to all ports or to a single port that is identified in the message.
You cannot use SCADAInput nodes in message
flows that are to be deployed on z/OS® systems.
To process the data in an incoming SCADA message, include a node such as the ResetContentDescriptor node, and set its properties to force the bit stream to be reparsed by a subsequent node.
If you create a message flow to use as a subflow, you cannot use a standard input node; you must use an Input node as the first node to create an In terminal for the subflow.
If your message flow does not receive messages across SCADA connections, choose one of the supported input nodes.
The SCADAInput node is contained in the Additional Protocols drawer of the palette, and is represented in the workbench by the following icon:
For an example of how to use this node, assume that you create a message flow with a SCADAInput node that receives messages from a remote sensor when it detects a change in its operating environment (for example, a drop in outside temperature). You connect the node to an MQOutput node, which makes these messages available on a queue that is serviced by a WebSphere MQ application that analyses and responds to the information that is received.
In another example, you create a message flow with a SCADAInput node that receives messages every minute from a remote system. The messages contain details of the system's switch settings. The data that is received is fed into a ResetContentDescriptor node to cast the data from binary (BLOB) to MRM message format. The information about the system is stored in a database by using the Database node, and is enriched by using a Compute node to create an XML message, which is published by using a Publication node.
XML messages are expensive to send (because satellite transmission has a high cost for each byte); therefore, it is advantageous to use this method because data is enriched by the broker.
When you have put an instance of the SCADAInput node into a message flow, you can configure the node. For more information, see Configuring a message flow node. The properties of the node are displayed in the Properties view. To display the properties of the node in the Properties dialog, either double-click the node, or right-click the node and click Properties.
All mandatory properties for which you must enter a value (those that do not have a default value defined) are marked with an asterisk.
If you are using DB2® as your broker database, specify a value that is less than or equal to the value that you have set for the DB2 configuration parameters maxappls and maxagents. For further information, see Enabling ODBC connections to the databases.
Use this option only if you expect a large number of clients (greater than 200) to connect.
Leave Message set blank for XML, XMLNS, XMLNSC, and BLOB parsers.
Leave Message type blank for XML, XMLNS, XMLNSC, and BLOB parsers.
Leave Message format blank for XML, XMLNS, XMLNSC,, and BLOB parsers.
For more details, see Validating messages and Validation properties.
The SCADAInput node routes each message that it retrieves successfully to the Out terminal. If this action fails, the message is propagated to the Failure terminal; you can connect nodes to this terminal to handle this condition. If you have not connected the Failure terminal, the message loops continually through the node until the problem is resolved.
If the message is caught by this node after an exception has been thrown further on in the message flow, the message is routed to the Catch terminal. If you have not connected the Catch terminal, the message loops continually through the node until the problem is resolved. Ensure that a node is always connected to this terminal if there is the possibility of the message rolling back within a message flow.
When you include a SCADAInput node in a message flow, the value that you set for Transaction mode defines whether messages are received under sync point:
The MQOutput node is the only output node that you can configure to override this option.
The SCADAInput node terminals are described in the following table.
Terminal | Description |
---|---|
Failure | The output terminal to which the message is routed if an error occurs. |
Out | The output terminal to which the message is routed if it is successfully retrieved from the queue. |
Catch | The output terminal to which the message is routed if an exception is thrown downstream and caught by this node. |
The following tables describe the node properties. The column headed M indicates whether the property is mandatory (marked with an asterisk if you must enter a value when no default is defined); the column headed C indicates whether the property is configurable (you can change the value when you add the message flow to the BAR file to deploy it).
The SCADAInput node Description properties are described in the following table.
Property | M | C | Default | Description |
---|---|---|---|---|
Node name | No | No | The node type, SCADAInput | The name of the node. |
Short description | No | No | A brief description of the node. | |
Long description | No | No | Text that describes the purpose of the node in the message flow. |
The SCADAInput node Basic properties are described in the following table.
Property | M | C | Default | Description |
---|---|---|---|---|
Enable listener on startup | Yes | No | Selected | This property controls when the listener is started. If you select the check box, the listener starts when the message flow is started by the broker. If you clear the check box, the listener starts on the arrival of a message on the specified port. |
Port | Yes | Yes | 1883 | The port on which the SCADA protocol is listening. |
Max threads | Yes | Yes | 500 | The maximum number of threads to be started to support SCADA devices. |
Use thread pooling | Yes | Yes | Cleared | If you select the check box, thread pooling is used. |
The SCADAInput node Input Message Parsing properties are described in the following table.
Property | M | C | Default | Description |
---|---|---|---|---|
Message domain | No | No | The domain that is used to parse the incoming message. | |
Message set | No | No | The name or identifier of the message set in which the incoming message is defined. | |
Message type | No | No | The name of the incoming message. | |
Message format | No | No | The name of the physical format of the incoming message. |
The SCADAInput node Parser Options properties are described in the following table.
Property | M | C | Default | Description |
---|---|---|---|---|
Parse timing | No | No | On Demand | This property controls when an input message
is parsed. Valid values are On
Demand, Immediate,
and Complete. For a full description of this property, see Parsing on demand. |
Use XMLNSC compact parser for XMLNS domain | No | No | Cleared | This property controls whether the XMLNSC Compact Parser is used for messages in the XMLNS Domain. If you set this property, the message data appears under XMLNSC in nodes that are connected to the output terminal when the Input Message Parsing properties Message domain is XMLNS. |
Retain mixed content | No | No | Cleared | This property controls whether the XMLNSC parser creates elements in the message tree when it encounters mixed text in an input message. If you select the check box, elements are created for mixed text. If you clear the check box, mixed text is ignored and no elements are created. |
Retain comments | No | No | Cleared | This property controls whether the XMLNSC parser creates elements in the message tree when it encounters comments in an input message. If you select the check box, elements are created for comments. If you clear the check box, comments are ignored and no elements are created. |
Retain processing instructions | No | No | Cleared | This property controls whether the XMLNSC parser creates elements in the message tree when it encounters processing instructions in an input message. If you select the check box, elements are created for processing instructions. If you clear the check box, processing instructions are ignored and no elements are created. |
The SCADAInput node Advanced property is described in the following table.
Property | M | C | Default | Description |
---|---|---|---|---|
Transaction mode | Yes | No | Yes | This property controls whether the incoming message is received under sync point. Valid values are Automatic, Yes, and No. |
The SCADAInput node Validation properties are described in the following table.
For a full description of these properties, see Validation properties.
Property | M | C | Default | Description |
---|---|---|---|---|
Validate | No | Yes | None | This property controls whether validation takes place. Valid values are None, Content and Value, and Content. |
Failure action | No | No | Exception | This property controls what happens if validation fails. You can set this property only if you set Validate to Content or Content and Value. Valid values are User Trace, Local Error Log, Exception, and Exception List. |
Include all value constraints | No | No | Selected | You cannot edit this property. If you select the check box, basic value constraint checks are included in Content and Value validation. |
Fix | No | No | None | You cannot edit his property. |