What's the difference between BACnet/IP and BACnet MS/TP?

BACnet/IP and BACnet MS/TP are two distinct physical layer implementations of the BACnet communication protocol, primarily differing in their underlying network technology, speed, and typical application.

BACnet/IP
BACnet/IP utilises standard Ethernet (IEEE 802.3) as its physical and data link layer, leveraging the Internet Protocol (IP) for routing and communication. It operates over conventional network infrastructure like CAT5/6 cabling, switches, and routers, making it suitable for high-speed, enterprise-wide networks. BACnet/IP devices communicate by sending UDP/IP packets, allowing for rapid data exchange and seamless integration with existing IT networks. It is typically employed for connecting supervisory controllers, workstations, and high-level building systems where bandwidth and network reach are critical.

BACnet MS/TP (Master-Slave/Token-Passing)
BACnet MS/TP operates over a serial RS-485 physical layer, using a multi-drop bus topology. Communication is slower compared to BACnet/IP, typically ranging from 9.6 kbps to 76.8 kbps. MS/TP networks use a token-passing scheme to manage access to the bus, ensuring that only one device transmits at a time. This makes it a robust and cost-effective solution for connecting field devices such as unitary controllers, sensors, and actuators at the equipment or plant level. MS/TP networks are limited in cable length and the number of devices per segment, often requiring a BACnet router to connect to a BACnet/IP backbone.

Key Differences:

• Physical Layer: BACnet/IP uses Ethernet (CAT5/6), while MS/TP uses RS-485 (shielded twisted pair).
• Speed: BACnet/IP offers high speeds (10/100 Mbps, 1 Gbps), whereas MS/TP is slower (9.6-76.8 kbps).
• Network Topology: BACnet/IP typically uses star or mesh topologies; MS/TP uses a multi-drop bus.
• Addressing: BACnet/IP uses IP addresses; MS/TP uses MAC addresses on the RS-485 segment.
• Application: BACnet/IP is ideal for high-level integration and backbone networks. MS/TP is suited for connecting field devices and smaller, localised control networks.
• Routing: A BACnet router is often required to bridge MS/TP networks to BACnet/IP networks.

Related Topics

• What is BMS integration? — how a BMS connects with VFDs, energy meters, BACnet/Modbus devices and other building systems
• How to design a BMS system step by step — the complete BMS design methodology covering site survey, IO list, controller selection, sequence of operations
• What is a Building Management System (BMS)? — fundamentals of BMS controls and architecture for HVAC, lighting, energy and access
• What is BMS commissioning? — the disciplined commissioning process that turns a BMS install into a working building brain
• Browse all General topics — more from this section of the EnSmart BMS Library