Communication of a BMS

Buses and protocols

Most building automation networks consist of primary and secondary buses which connect high-level controllers with lower-level controllers, input/output devices and a user interface devices. ASHRAE's open protocol BACnet or the open protocols LonTalk specify how most such devices interoperate. Modern systems use SNMP to track events, building on decades of history with SNMP (Simple Network Management Protocol)-based protocols in the computer networking world.

Physical connectivity between devices was historically provided by dedicated optical fiber, ethernet, ARCNET, RS-232, RS-485 or a low-bandwidth special purpose wireless network. Modern systems rely on standards-based multi-protocol heterogeneous networking. These accommodate typically only IP-based networking but can make use of any existing wiring, and also integrate power line networking over AC circuits, power over Ethernet low power DC circuits; high-bandwidth wireless networks such as LTE and IEEE 802.11n and IEEE 802.11ac and often integrate these using the building-specific wireless mesh open standards.

Current systems provide interoperability at the application level, allowing users to mix-and-match devices from different manufacturers, and to provide integration with other compatible building control systems. These typically rely on SNMP, long used for this same purpose to integrate diverse computer networking devices into one coherent network.