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BACnet ( B uilding A utomation and C ontrol Net works) is a network protocol for building automation . It is standardized by ASHRAE , ANSI and as ISO 16484-5. Gateways exist for interoperable and cross-trade communication, which couple communication participants on the BACnet side with other fieldbus systems and protocols (e.g. DALI, KNX or LON).


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


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


The standard defines a number of services that are used for communication between building automation devices. 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 object types :

  • 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 ( trend log , "multiple trend log"),
  • Calendar ( Calendar ),
  • Schedule ( Schedule )
  • others: counter input ( accumulator ), program ("program"), controller ( loop ) etc.

BACnet defines a combined 4-layer communication that offers the following alternatives for layers 1 and 2:

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

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

The standard can be obtained from ASHRAE. Addenda to the current standard can be downloaded from the ASHRAE website. On the website of the BACnet Interest Group Europe there are introductory texts and more detailed information on the standard, definitions of terms, help with the tender, etc.


Web links

supporting documents

  1. News Archive . ASHRAE Standing Standard Project Committee 135.Retrieved June 24, 2009.