BACnet MS/TP vs BACnet/IP — what is the difference?

Updated 4 November 2026

Different wires, same BACnet

The objects, properties and services are the same on both; only the lower layers differ. BACnet/IP rides on an Ethernet network, usually a dedicated controls network or VLAN. MS/TP rides on a shielded RS-485 pair (plus a reference conductor) run from controller to controller, with end-of-line termination at each end. Common baud rates are 38400 and 76800; older trunks run 9600 or 19200.

Token passing

MS/TP devices share one pair, so masters take turns: a token passes from one master MAC address to the next, and only the holder may transmit. It works well when the trunk is healthy, but it limits throughput. A heavily loaded trunk (40 to 60 devices), a bad termination or a duplicate MAC address slows every device on it. That is part of why reading a large MS/TP controller from the IP side takes a while. When a trunk misbehaves, work through the MS/TP troubleshooting checklist.

Addressing and how they meet

On MS/TP a device has a one-byte MAC address on its trunk (0–127 for masters), and the trunk has its own BACnet network number. A BACnet router (often built into the JACE or supervisory controller) joins the trunk to BACnet/IP. From the IP side each MS/TP device still has its own Device Instance and answers scans through the router. That is how Easy BACnet, which speaks BACnet IP only, lists and reads MS/TP controllers: through a router on the subnet your phone is on. It cannot connect to an RS-485 trunk directly.

Which am I looking at?

In Easy BACnet's device list, MS/TP devices behind a router show the router's IP address, so a dozen devices sharing one IP are almost certainly on a trunk behind that router. A device with its own IP address is BACnet/IP. If the scan warns that two controllers share one MS/TP address behind a router, that trunk has a duplicate MAC to fix.