BACnet TSM Timeout
TSM (Transaction State Machine) timeout occurs when a segmented BACnet transaction (e.g., ReadPropertyMultiple of many objects) does not complete within the timeout. One or more segments were lost or never received.
Common Causes
- Network congestion or packet loss on MS/TP trunk
- APDU timeout too short for segmented response
- Device buffer overflow dropping segments
- Router or BBMD segment reassembly timeout
Fix Steps
- Increase APDU timeout (segment timeout) for large transfers; 10–20 s may be needed.
- Reduce ReadPropertyMultiple scope; request fewer objects per transaction.
- Check trunk health: CRC errors, voltage drop, token pass delays.
- Upgrade device or router firmware for improved segmentation handling.
- Use smaller Max_APDU_Length if segments are too large for network.