Disabling ReadPropertyMultiple Requests in CAS BACnet Explorer
In BACnet networks, the ReadPropertyMultiple (RPM) service allows a client to request multiple properties from a BACnet object using a single protocol transaction. While this can improve efficiency, there are scenarios where RPM requests are not supported, not expected, or cause interoperability issues with certain devices.
When using CAS BACnet Explorer, RPM requests are enabled by default. However, some BACnet devices only support individual ReadProperty requests or exhibit unreliable behavior when handling ReadPropertyMultiple services. In these cases, disabling RPM can improve compatibility and simplify troubleshooting.
This article explains when and why you may want to disable ReadPropertyMultiple requests and provides step-by-step instructions for configuring CAS BACnet Explorer to use individual ReadProperty requests instead.
Understanding ReadPropertyMultiple in BACnet
ReadPropertyMultiple is a standard BACnet service that allows a client to read multiple properties from one or more objects in a single request. This reduces network traffic and improves polling efficiency, particularly in large systems with many objects.
Despite being part of the BACnet standard, not all BACnet devices fully or correctly implement ReadPropertyMultiple. Some devices may only support basic ReadProperty services, while others may respond inconsistently or return errors when RPM requests are issued.
For diagnostic tools such as CAS BACnet Explorer, having the ability to disable RPM is important. It allows engineers and integrators to match the behavior of simpler BACnet clients, isolate communication problems, and confirm whether a device properly supports the RPM service.
Step-by-Step: Disabling Read Property Multiple Requests
Follow the steps below to disable ReadPropertyMultiple requests in CAS BACnet Explorer. Once disabled, the tool will use individual ReadProperty requests when reading object properties.
Step 1: Open CAS BACnet Explorer.
Step 2: Open the Settings dialog from the main menu.
Step 3: From the menu on the left-hand side of the Settings dialog, select Preferences.
Step 4: Uncheck the option labeled Read property multiple.
Step 5: Click the OK button to apply the change.
Once this setting is disabled, CAS BACnet Explorer will no longer issue ReadPropertyMultiple requests and will instead read properties individually. This change applies immediately and does not require restarting the application.
When Disabling ReadPropertyMultiple Is Useful
Disabling RPM is commonly used during interoperability testing, commissioning, and troubleshooting. If a BACnet device fails to respond correctly to property reads, switching to individual ReadProperty requests can help determine whether the issue is related to RPM support.
This setting is also useful when working with older BACnet devices, proprietary implementations, or devices with limited protocol stacks. In these cases, simplifying the communication pattern can lead to more predictable behavior.
It is important to note that disabling RPM may increase the total number of BACnet requests on the network, since each property is read individually. This tradeoff is generally acceptable during testing and diagnostics, but should be considered when working on large systems.
CAS BACnet Explorer
CAS BACnet Explorer is a BACnet diagnostic and commissioning tool used to discover devices, browse objects, and test BACnet services. It provides configurable options that allow engineers to adapt communication behavior to match the capabilities of the devices being tested.
For more information about CAS BACnet Explorer, including downloads and product details, visit:
https://store.chipkin.com/products/tools/cas-bacnet-explorer
Frequently Asked Questions (FAQ)
What is ReadPropertyMultiple in BACnet?
ReadPropertyMultiple is a BACnet service that allows a client to request multiple object properties in a
single message, reducing network traffic compared to individual ReadProperty requests.
Why would I disable ReadPropertyMultiple?
Some BACnet devices do not fully support RPM or respond incorrectly. Disabling RPM allows CAS BACnet
Explorer to use simpler ReadProperty requests for improved compatibility.
Does disabling RPM affect device discovery?
No. This setting only affects how properties are read after devices and objects are discovered. Discovery
services such as Who-Is and I-Am are not impacted.
Will disabling RPM increase network traffic?
Yes. Individual ReadProperty requests generate more messages than RPM. This is usually acceptable for
troubleshooting and testing but should be considered on large or busy networks.
Do I need to restart CAS BACnet Explorer after changing this setting?
No. The setting takes effect immediately once you click OK in the Preferences dialog.