BACnet is based on a model of objects and services independent of the physical medium. This model travels either over BACnet/IP (Ethernet) or BACnet MS/TP (Master-Slave/Token-Passing over RS485). The objects (analog value, binary input…) are the same; only the network differs.
BACnet/IP vs BACnet MS/TP
Two media for the same BMS protocol — how to choose.
Two media for BACnet
Side by side
| BACnet/IP | BACnet MS/TP | |
|---|---|---|
| Medium | Ethernet | RS485 |
| Speed | 10/100 Mbit/s | 9.6–115.2 kbaud |
| Access | IP | Token passing |
| Distance | IP network | ~1200 m over RS485 |
| Wiring | existing Ethernet | 2-wire twisted pair |
| Inter-network | BBMD | BACnet router |
| Best for | backbone, supervision | field, HVAC devices |
Which to choose, or mix them
BACnet/IP acts as the backbone and carries supervision; MS/TP serves the HVAC field at low wiring cost. In practice you combine them: MS/TP segments connected to an IP backbone through BACnet routers. The WBox gateway speaks both with the BACnet driver, and can route BACnet to MQTT or integrate Modbus and KNX.
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