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Add IP Network Listener tags to your application if you want to be able to accept inbound TCP or (rarely) UDP connections. This tag is for use with the DNP3 and Modbus Compatible Devices, but may also be used by custom drivers.
In addition to use with drivers, an IP Network Listener can also be used with services, such as the SNMP Agent.
The IP Network Listener may be useful for enhanced security when you are employing a Modbus Compatible driver configured for virtual I/O. This will allow you to limit the traffic to or from the driver to approved addresses. Note that when used in this situation, the TCP/IP tag to which the driver is attached must be configured for address 127.0.0.1 and not a blank address, as is common. This will prevent conflicts on the common port.
The IP Network Listener will not be required in most situations. It may be useful if your TCP connections will close between polling intervals and you need to allow the RTU to connect to the driver before the next cycle, perhaps to report a fault condition. It is required by the SNMP Agent in order to provide access to the system. Otherwise, use with caution.
Note that most support calls involving the IP Network Listener tag are solved by determining that the tag was unnecessary and removing it.
While this tag will work with both TCP and UDP, it is intended primarily for TCP connections. Drivers using the UDP protocol may not need a Network Listener unless the RTU is connecting to VTScada using a different IP address each time. If using an IP Network Listener tag with a UDP connection, use care to ensure the port number is set correctly and is compatible with the corresponding UDP/IP port tag configuration.
The IP Network Listener uses a socket server to accept incoming connections. Improper configuration can result in communications failure for UDP/IP Port tags that make use of the same local port number. Refer to UDP/IP Port Tags for more information and further warnings.
Use of an IP Network Listener Tag is generally not recommended for UDP/IP communications. The VTScada engine will listen for UDP/IP datagram packets and place them into existing UDP streams if the remote IP address matches that of the UDP stream.
Multiple Modbus and DNP3 driver tags can share the same IP Network Listener.
Modbus Compatible Device: Serial tab - Modbus Compatible Device configuration
DNP3 Driver properties Communications tab - DNP3 driver configuration
SNMP Agent Configuration - Details for enabling an SNMP client to connect and access tag data.
IP Network Listener properties ID tab
The ID tab of every tag includes the same common elements: Name, Area, Description, and Help ID.
Name:
Uniquely identifies each tag in the application. If the tag is a child of another, the parent names will be displayed in a separate area before the name field.
You may right-click on the tag's name to add or remove a conditional start expression.
Area
The area field is used to group similar tags together. By defining an area, you make it possible to:
- Filter for particular tag groups when searching in the tag browser
- Link dial-out alarm rosters to Alarm tags having a particular area
- Limit the number of tags loaded upon startup.
- Filter the alarm display to show only certain areas.
- Filter tag selection by area when building reports
When working with Parent-Child tag structures, the area property of all child tags will automatically match the configured area of a parent. Naturally, you can change any tag's area as required. In the case of a child tag, the field background will turn yellow to indicate that you have applied an override. (Orange in the case of user-defined types. Refer to Configuration Field Colors)
To use the area field effectively, you might consider setting the same Area for each I/O driver and its related I/O tags to group all the tags representing the equipment processes installed at each I/O device. You might also consider naming the Area property for the physical location of the tag (i.e. a station or name of a landmark near the location of the I/O device). For serial port or Roster tags, you might configure the Area property according to the purpose of each tag, such as System or Communications.
You may define as many areas as you wish and you may leave the area blank for some tags (note that for Modem tags that are to be used with the Alarm Notification System, it is actually required that the area field be left blank).
To define a new area, type the name in the field. It will immediately be added. To use an existing area, use the drop-down list feature. Re-typing an existing area name is not recommended since a typo or misspelling will result in a second area being created.
There is no tool to remove an area name from VTScada since such a tool is unnecessary. An area definition will exist as long as any tag uses it and will stop existing when no tag uses it (following the next re-start).
Description
Tag names tend to be brief. The description field provides a way to give each tag a human-friendly note describing its purpose. While not mandatory, the description is highly recommended.
Tag descriptions are displayed in the tag browser, in the list of tags to be selected for a report and also on-screen when the operator holds the pointer over the tag’s widget. For installations that use the Alarm Notification System, the description will be spoken when identifying the tag that caused the alarm.
The description field will store up to 65,500 characters, but this will exceed the practical limits of what can be displayed on-screen.
This note is relevant only to those with a multilingual user interface:
When editing any textual parameter (description, area, engineering units...) always work in the phrase editor. Any changes made directly to the textual parameter will result in a new phrase being created rather than the existing phrase being changed.
In a unilingual application this makes no difference, but in a multilingual application it is regarded as poor practice.
Help Search Key
Used only by those who have created their own CHM-format context sensitive help files to accompany their application.
IP Network Listener properties Options tab
Enable
Accepts a 1 to enable or a 0 to disable inbound connections. The options Expression or Tag allow you to enable or disable connections based on user control of your choice, or based on current operating conditions. Set to 1 (online) by default for all workstations.
Protocol
Select either TCP/IP and UDP/IP, as appropriate for the device your drivers will be communicating with.
Port Number
Define the port that be used for inbound connections. Ensure that your firewall has been configured to allow connections to this port.
Remote Port Number
Enabled only for UDP/IP. UDP responses from VTScada will be sent to this port number. Leave this option Invalid to send responses back to the source port on the RTU.
Review the warnings in the introduction of the UDP/IP Port tag description.
IP Allow List
Optional. As a security measure, this listener may be configured to accept connections only from the IP addresses you add to this list. A range of allowed addresses may be defined by leaving portions empty.
Support is provided for CIDR Classless Inter-Domain Routing ranges. For example, 192.168.1.0/24 or 192.0.0.0/8
Discriminator Options - Idle Time and Sample Limit
These two values control how incoming data is sampled. Sample Limit specifies the number of bytes to be received before the stream is sampled. In the event that the stream is not changing, the passage of Idle Time seconds will trigger a sample. The default values were selected to work in most cases, but you may find that Sample Limit need only be set to 10 bytes when this tag is used by a DNP3 driver.
IP Network Listener Tag Widgets
The following widgets are available to display information about your application’s IP Network Listener tags:
