SCADAInput node

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:

Purpose

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.

The SCADAInput node handles messages in the following message domains:
  • MRM
  • XML
  • XMLNS
  • XMLNSC
  • BLOB

z/OS platform 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:

SCADAInput node icon

Using this node in a message flow

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.

Configuring the SCADAInput node

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.

  1. Optional: On the Description tab, enter a Short description, a Long description, or both. You can also rename the node on this tab.
  2. On the Basic tab, set the following properties:
    • Update the status of the listener by publishing on the control topic $SYS/SCADA/MQIsdpListener/<port_number> with the Payload part of the message set to ON or OFF. Enable listener on startup is initially selected, which means that the listener for MQIsdp clients is initialized when the message flow is deployed.
    • Specify the Port number on which the MQIsdp server listens. This value must be a unique port number, and must not conflict with other listeners (for example, those set up for WebSphere MQ or WebSphere MQ Everyplace®). The default number is 1883.
    • Set the Max threads value to indicate the maximum number of threads available to the MQIsdp server to support clients. The default value is 500.

      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.

    • Select Use thread pooling if you want the node to use a pool of threads to service clients. If you select this option, the number of threads that are available to the MQIsdp server is limited by Max threads, which is most effective when set to a value between 20 and 40. If you do not select this option, a new thread is created for each client that connects. The check box is cleared initially.

      Use this option only if you expect a large number of clients (greater than 200) to connect.

  3. On the Input Message Parsing tab, set values for the properties that describe the message domain, message set, message type, and message format that the node uses to determine how to parse the incoming message.
    • In Message domain, select the name of the parser that you are using from the list. You can choose from the following options:
      • MRM
      • XML
      • XMLNS
      • XMLNSC
      • BLOB
    • If you are using the MRM parser, select the Message set that you want to use. This list is populated with available message sets when you select MRM or XMLNSC as the domain.

      Leave Message set blank for XML, XMLNS, XMLNSC, and BLOB parsers.

    • If you are using the MRM parser, select the correct message from the list in Message type. This list is populated with messages that are defined in the Message set that you have selected.

      Leave Message type blank for XML, XMLNS, XMLNSC, and BLOB parsers.

    • If you are using the MRM parser, select the format of the message from the list in Message format. This list includes all the physical formats that you have defined for this Message set.

      Leave Message format blank for XML, XMLNS, XMLNSC,, and BLOB parsers.

  4. On the Parser Options tab, Parse timing is, by default, set to On Demand. This value causes validation to be delayed until it is parsed by partial parsing. If you change this value to Immediate, partial parsing is overridden and everything in the message is parsed and validated, except for those complex types with a composition of Choice or Message that cannot be resolved at the time. If you change this value to Complete, partial parsing is overridden and everything in the message is parsed and validated; complex types with a composition of Choice or Message that cannot be resolved at the time cause a validation failure.
  5. On the Advanced tab, set the required value for Transaction mode to define the transactional characteristics of how this message is handled:
    • If you select Automatic, the incoming message is received under sync point if it is marked as persistent; otherwise, it is not received under sync point. The transactionality of any derived messages that are sent subsequently by an output node is determined by the incoming persistence property, unless the output node has overridden transactionality explicitly.
    • If you select Yes, the incoming message is received under sync point. Any derived messages that are sent subsequently by an output node in the same instance of the message flow are sent transactionally, unless the output node has overridden transactionality explicitly.
    • If you select No, the incoming message is not received under sync point. Any derived messages that are sent subsequently by an output node in the flow are sent non-transactionally, unless the output node has specified that the message must be put under sync point.
  6. On the Validation tab, set the validation properties if you want the parser to validate the body of messages from the Message set. If a message is propagated to the Failure terminal of the node, it is not validated.

    For more details, see Validating messages and Validation properties.

Connecting the terminals

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.

Configuring for coordinated transactions

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:

  • If you set this property to Yes (the default), the message is received under sync point; that is, within a WebSphere MQ unit of work. Any messages that are sent subsequently by an output node in the same instance of the message flow are put under sync point, unless the output node has overridden this explicitly.
  • If you set this property to Automatic, the message is received under sync point if the incoming message is marked as persistent; otherwise, it is not received under sync point. Any message that is sent subsequently by an output node is put under sync point, as determined by the incoming persistence property, unless the output node has overridden this explicitly.
  • If you set this property to No, the message is not received under sync point. Any messages that are sent subsequently by an output node in the message flow are not put under sync point, unless an individual output node has specified that the message must be put under sync point.

The MQOutput node is the only output node that you can configure to override this option.

Terminals and properties

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.
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Copyright IBM Corporation 1999, 2009Copyright IBM Corporation 1999, 2009.
Last updated : 2009-01-07 15:20:06

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