What UnconfirmedTextMessage Is
UnconfirmedTextMessage is a remote-device-management service in BACnet, defined in Clause 16.6 of ANSI/ASHRAE 135-2024. A client uses it to send a text message to one or more BACnet devices without asking for a reply. It is an unconfirmed service and may be broadcast, multicast, or addressed to a single recipient. Use it when confirmation of receipt is not needed.
It is the fire-and-forget counterpart to ConfirmedTextMessage: the same message content, but with no acknowledgment and the ability to reach many devices at once.
How It Works
The request carries the source device’s identifier, an optional message class, a priority of NORMAL or URGENT, and the message text. The message class, a number or a string, tells receivers how to handle the text, for example which output to print it on; its meaning is a local matter to each receiving device. Because the service is unconfirmed, no response comes back and no device reports whether it acted on the message. Each receiver displays, prints, or files the text according to the class, entirely at its own discretion.
Where You’ll See It
- Broadcast notices. A workstation sending an informational message to every device on a network at once.
- Classified routing. Using the message class to steer a message to a particular output on receiving devices.
- Priority alerts. Marking a message URGENT so receivers handle it ahead of queued NORMAL messages, without waiting for acknowledgments.
UnconfirmedTextMessage Error Codes
UnconfirmedTextMessage is an unconfirmed service, so it has no acknowledgment and returns no application-layer error. A message that produces no visible effect is not a service error; it is a delivery or handling matter. The usual reasons:
- The receiving device does not support text messaging, or the message class named an action it does not recognize, so it silently ignored the text.
- The message was broadcast and did not cross to another IP subnet because there is no BACnet BBMD path, so distant devices never received it.
- What a device does with a received message is a local matter, so there is no way from the wire to confirm any device acted on it.
Profiles That Require It
Text messaging is an optional capability. No standard device profile in Annex L requires UnconfirmedTextMessage; devices support it when a project calls for operator messaging, and declare it in their PICS (Protocol Implementation Conformance Statement). Treat it as a feature to confirm per device, not a baseline.
What Chipkin Provides
The CAS BACnet Stack supports UnconfirmedTextMessage in both directions, as a client sending messages and as a server receiving them. Talk to us about adding BACnet client or server support to your device.