BACnet APDU Timeout
APDU (Application Protocol Data Unit) timeout occurs when a BACnet client does not receive a response from a device within the configured timeout period. Read/Write or COV requests may fail.
Common Causes
- Device offline, powered down, or disconnected from the trunk
- MS/TP network congestion or token pass delays
- APDU timeout configured too low for network latency
- Router or BBMD dropping or misrouting traffic
Fix Steps
- Verify the target device is online and responding to Who-Is.
- Check MS/TP trunk for congestion; reduce polling frequency if needed.
- Increase APDU timeout (typically 3–20 seconds) in the BACnet client config.
- Inspect router/BBMD logs for packet loss or routing errors.
- Confirm physical layer: RS-485 termination, voltage, and wiring.