This topic contains the following sections:
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 recognized by WebSphere Event 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's properties to control the way that messages are received: for example, you can indicate that a message is to be processed under transaction control.
When you deploy message flows containing SCADA nodes to a broker, you must deploy them to a single execution group, regardless of the number of message flows.
Because SCADA is primarily publish/subscribe, you typically include a Publication node to terminate the flow. In scenarios where you do not want a Publication node, you can include a SCADAOutput node. If you do so, you must also include a SCADAInput node regardless of the source of the messages, because the SCADAInput node provides the connectivity information 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 start or stop a SCADA listener by publishing messages with a specific topic. This can be done for all ports or for a single port identified in the message.
You cannot use SCADAInput nodes in message flows that are to be deployed on z/OS systems.
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, you can choose one of the supported input nodes.
The SCADAInput node 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 that makes these messages available on a queue serviced by a WebSphere MQ application that analyses and responds to the information received.
When you have put an instance of the SCADAInput node into a message flow, you can configure it. Right-click the node in the editor view and click Properties. The node's basic properties are displayed in the properties dialog.
All mandatory properties for which you must enter a value (those that do not have a default value defined) are marked with an asterisk on the properties dialog.
Configure the SCADAInput node as follows:
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.
If you are using DB2 for your broker database, you must 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 Connecting to the databases for further information.
Use this option only if you expect a large number of clients (greater than 200) to connect.
Click Cancel to close the dialog and discard all the changes that you have made to the properties.
SCADAInput routes each message that it retrieves successfully to the out terminal. If this 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 syncpoint:
(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 on the properties dialog 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 Basic properties are described in the following table.
Property | M | C | Default | Description |
---|---|---|---|---|
Enable listener on startup | Yes | No | Selected | 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 | Whether to use thread pooling. If you select the check box, this action is performed. |
The SCADAInput node Advanced property are described in the following table.
Property | M | C | Default | Description |
---|---|---|---|---|
Transaction Mode | Yes | No | Yes | Whether the incoming message is received under syncpoint. Valid values are Automatic, Yes, and No. |
The Description properties of the SCADAInput node are described in the following table.
Property | M | C | Default | Description |
---|---|---|---|---|
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. |
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