3 BACnet Networking
WHAT IS BACNET?
BACnet is "a data communication protocol for building automation and control networks." This means it
is a set of rules for exchanging BMS information between systems from different manufacturers.
The rules take the form of a written specification that spells out what is required to conform to the
protocol
The key feature of BACnet is that the rules relate specifically to the needs of building automation and
control equipment - for example, how to ask for the value of a temperature, define a fan operating
schedule, or send a pump status alarm.
BACnet provides a standard way of representing the functions of any device - for example analog or
binary inputs or outputs, schedules, control loops and alarms.
The standardized model of a device represents these common functions as collections of related
information called objects
Each object has a set of properties that further describe it. Each analog input, for instance, is
represented by a BACnet "Analog Input object", which has a set of standard properties such as 'Present
Value', 'Sensor Type', 'Location', 'Alarm Limits' etc. Some of these properties are required, while others are
optional.
The only required object in each BACnet controller is the Device object. This object contains the
properties that define the controller’s behavior on the network. Each controller’s Device object has an
associated number called the Device Instance. It is this unique number that allows all other BACnet
devices to unambiguously access the controller.
Here is an illustration of BACnet objects:
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