BACnet ( Building Automation and Control Networks) is a network protocol for building automation.


BACnet has been and is being developed under the auspices of the American Society of Heating, Refrigerating and Air - Conditioning Engineers ( ASHRAE ). Development began in June 1987 to provide a uniform company -neutral standard for data communication and building automation systems. BACnet was in the 1995 ANSI / ASHRAE Standard 135 In January 2003, BACnet standard ISO 16484-5 was.


BACnet ensures interoperability between devices from different manufacturers, provided that all partners involved in the project on certain defined by the standard BIBBs. A BIBB (BACnet Interoperability Building Block ) defines which must be supported services and procedures at the server and client side in order to realize a specific requirement of the system. Belonging to a device document PICS ( Protocol Implementation Conformance Statement ) lists all supported BIBBs, object types, character sets and options of communication.


The standard defines a set of services ( Services) that are used for communication between devices in building automation. These services are divided into different groups:

  • Data Sharing,
  • Alarm and event processing,
  • Processing of changes in value,
  • Device and network management etc.

The standard defines different types of objects:

  • Device ( Device Object )
  • Analog input (Analog Input), Digital Input (Digital Input), Multi-level input ( multi-state input)
  • Analog output (Analog Output ), digital output ( digital output), Multi-level output (Multi- State Output )
  • Analog value ( analog value ), Digital value (digital value ), Multi-level value ( Multi-State Value)
  • Notification ( Notification Class )
  • Trend recording ( trendlog, "Multiple trend log ")
  • Calendar (Calendar )
  • Schedule (Schedule )
  • More: counter input ( Accumulator ), program ( "Program" ), controller ( Loop), etc.

BACnet defines a combined four -layer communication that has the following alternatives for the layer 1 and 2:

  • PTP (Point- To- Point) via RS -232, data rate 9.6 kbit / s to 56.0 kbit / s
  • MS / TP ( Master-Slave/Token-Passing ) via RS- 485 to twisted-pair cables with 9.6 kbit / s to 115.200 kbit / s
  • Ethernet
  • BACnet / IP
  • LonTalk ANSI/EIA709.1
  • ZigBee

Here is an example of the OSI model of BACnet / IP:

  • BACnet Application Layer (Layer 7, application)
  • BACnet Network Layer ( layer 6, 5, 4, 3, mediation )
  • BACnet Virtual MAC Layer ( VMAC ) ( Layer 2 Security for BACnet MAC addresses with more than 6 bytes: ZigBee, IPv6)
  • BACnet Virtual Link Layer ( BVLL ) ( layer 2, 1, backup and Physical Layer )

The standard can be purchased from ASHRAE. Addenda to the current standard can be downloaded from the website of ASHRAE. On the website of the BACnet Interest Group Europe, there are introductory texts and more advanced information for standard definitions of terms, helps to tender etc.

Pictures of BACnet