Customizing BACnet Communication Settings

The channel configuration provides a number of tuning parameters to optimize and control BACnet communications. Although the default values work well with most standard installations, customizing some of the settings can help to adjust to the performance and functionality limitations of many different vendor devices. ​

These settings apply to the communications of all devices in the network(s) associated with the channel.

To set the communication parameters on the channel:

  1. Open Workbench and in the Project Explorer pane, expand your project > Data Connectivity > BACnet > Channels.

  2. On the Communication tab, adjust the default values of the parameters in the Communication Settings section as needed. View the Available Communication Settings table for the parameters' descriptions and available ranges of values.

    Available Communication Settings:

    Communication Parameter

    Description

    Range

    APDU Timeout,
    APDU Segment Timeout

    Specifies how long the application protocol data unit (APDU) waits for the response from a device after sending a message.

    500 - 300,000 ms

    APDU Retries

    Specifies the number of attempts to send an APDU request to a device.

    0 - 10

    Expiry Time

    Specifies the time to store an expired data point in the cache.

    0 - 1,000,000 s

    Consecutive Errors

    Specifies how many Bad responses can be received from a device before it is considered offline.

    0 - 1,000,000

    Offline Device Polling

    Specifies the period after which the BACnet point manager repeats an attempt to establish communication with an offline device.

    0 - 1,000,000 s

    Poll Before Subscribing

    Specifies if data should be retrieved by Read Property or Read Property Multiple before the SubscribeCOV is performed.

    0 = False

    1 = True

    Max Parallel Requests

    Specifies the maximum number of simultaneous requests for reading the property values on a device.

    1 - 128

    Max Properties Per Request

    Specifies the maximum number of properties that can be included in one Read Property Multiple request (the devices might have their limits).

    1 - 50

    Who-Is Period

    Specifies the frequency for sending Who-Is messages to undiscovered devices in the network.

    0 - 4,194,303 s

    Time Between Sending Who-Is

    Specifies the delay between each individual Who-Is message.

    0 - 4,194,303 ms

    Max TSM Per Device

    Specifies the maximum number of BACnet transactions such as Read or WriteProperty, SubscribeCOV, ReadRange, or AddListElement that can be simultaneously opened on a device. When this number is reached, no further transactions are processed until one or more transactions are closed.

    1 - 16

    Max TSM Per Router

    Specifies the maximum number of BACnet transactions such as Read or WriteProperty, SubscribeCOV, ReadRange, or AddListElement that can be simultaneously sent through a specific BACnet router. When this number is reached, no further transactions are sent through that router until one or more transactions are closed.

    1 - 16
  3. Select Enable Routing to set up the channel as a router. When both IP and SC ports are enabled, the router resends incoming messages such as Who-Is broadcasts from one port to the other.
  4. Click Apply and continue with notification class settings.