WebSphere Message Brokers
File: ac04620_
Writer: Terry Cowling

Reference topic

This build: July 31, 2007 21:17:27

SCADAInput node

This topic contains the following sections:

Purpose

Use the SCADAInput node to receive messages from clients that connect to the broker across the WebSphere MQ Telemetry Transport. SCADA device clients use the MQIsdp protocol to send messages, which 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 that are received from SCADA devices must always start with a SCADAInput node. Set the SCADAInput node's 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.

SCADA is primarily publish/subscribe, so you typically include a Publication node to terminate 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 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
  • JMSMap
  • JMSStream
  • MIME
  • BLOB
  • IDOC

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 like the ResetContentDescriptor node, and set its properties to force the bit stream to be re-parsed 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 instance of the 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 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 using the Database node, and enriched using a Compute node to create an XML message, which is published using a Publication node.

XML messages are expensive to send (because satellite transmission has a high cost for each byte), so 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 it. To display its properties, 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.

Configure the SCADAInput node as follows:

  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:
    1. The Enable listener on startup check box is initially selected, which means that the listener for MQIsdp clients is initialized when the message flow is deployed.

      You can 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.

    2. 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.
    3. 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. See Enabling connections to the databases for further information.

    4. 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, and the default topic that is associated with the message.
    • If the incoming message has an MQRFH2 header, you do not need to set values for the Input Message Parsing properties because the values can be derived from the <mcd> folder in the MQRFH2 header; for example:
      <mcd><Msd>MRM</Msd><Set>DHM4UO906S001</Set><Type>receiptmsg1</Type>
      <Fmt>XML</Fmt></mcd>

      If you set values, and those values differ from those in the MQRFH2 header, the MQRFH2 header values take precedence.

    • In Message Domain, select the name of the parser that you are using from the drop-down list. You can choose from the following names:
      • MRM
      • XML
      • XMLNS
      • XMLNSC
      • JMSMap
      • JMSStream
      • MIME
      • BLOB
      • IDOC
    • If you are using the MRM or IDOC parser, select the correct message set from the drop-down list in Message Set. This list is populated with available message sets when you select MRM or IDOC as the domain.

      Leave Message Set blank for XML, XMLNS, XMLNSC, JMS, MIME, and BLOB parsers.

    • If you are using the MRM parser, select the correct message from the drop-down 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, JMS, MIME, BLOB, and IDOC parsers.

    • If you are using the MRM or IDOC parser, select the format of the message from the drop-down 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, JMS, MIME, 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 syncpoint if it is marked as persistent; otherwise, it is not. 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 syncpoint. 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 syncpoint. 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 should be put under syncpoint.
  6. On the Validation tab, set the validation properties if you want the MRM parser to validate the body of messages against the dictionary that is generated from the message set. (If a message is propagated to the Failure terminal of the node, it is not validated.)

    For more details, refer to 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 syncpoint:

  • If you set this property to Yes (the default), the message is received under syncpoint (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 syncpoint, unless the output node has overridden this explicitly.
  • If you set this property to Automatic, the message is received under syncpoint if the incoming message is marked as persistent; otherwise, it is not. Any message that is sent subsequently by an output node is put under syncpoint, 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 syncpoint. Any messages that are sent subsequently by an output node in the message flow are not put under syncpoint, unless an individual output node has specified that the message should be put under syncpoint.

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 Description properties of the SCADAInput node 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 properties of the Parser Options for the SCADAInput node are described in the following table.

Property M C Default Description
Parse timing Yes No On Demand This property controls when an input message is parsed. Valid values are On Demand, Immediate, and Complete.

Refer to Parsing on demand for a full description of this property.

Use XMLNSC Compact Parser for XMLNS Domain Yes 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 RFH2 header or Input Message Parsing properties Domain is XMLNS.
Retain Mixed Content Yes 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 Yes 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 Yes 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 are 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 syncpoint. Valid values are Automatic, Yes, and No.

The Validation properties of the SCADAInput node are described in the following table.

Refer to Validation properties for a full description of these properties.

Property M C Default Description
Validate Yes Yes None This property controls whether validation takes place. Valid values are None, Content and Value, and Content.
Failure Action Yes 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 Yes 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 Yes No None You cannot edit his property.
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This build: July 31, 2007 21:17:27

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