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 that is recognized by WebSphere Event 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 can be done for all ports or for 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.
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:
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.
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:
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 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.
Use this option only if you expect a large number of clients (greater than 200) to connect.
The SCADAInput node 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 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, e.g. Input | 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 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. |
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