What are the key differences between BACnet MS/TP and BACnet/IP?

BACnet MS/TP (Master-Slave/Token-Passing) runs over RS-485 at 9,600–76,800 bps with a token-passing MAC layer that supports up to 127 devices per segment (typically 30–50 in practice for reliable throughput) and is the dominant wiring protocol for VAV controllers and terminal unit-level devices. BACnet/IP encapsulates BACnet messages in UDP/IP packets at Ethernet speeds (100 Mbps–1 Gbps), uses BBMD (BACnet Broadcast Management Device) servers to forward broadcasts across IP subnets, and is now the preferred backbone protocol for connecting supervisory controllers, routers, and operator workstations. BACnet/IP supports much higher device counts and data throughput, making it suitable for large campuses with thousands of devices, while MS/TP remains cost-effective for floor-level controllers where a dedicated RS-485 daisy-chain avoids IT network dependencies. The key architectural rule is that BACnet MS/TP segments should be limited to devices that communicate primarily with a single supervisory controller, while all inter-controller and enterprise-level traffic should use BACnet/IP.