Introduction to the BACnet Communication
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INTRODUCTION TO THE BACNET COMMUNICATION
BACnet, acronym for "Building Automation Control Network", is a protocol defined by the ANSI/ASHRAE/ISO
Standard 135-2004. The protocol defines a model for building-automation, describing the interaction between
devices and systems. The protocol defines:
Data and commands structured in an object-oriented model;
Services that describe the access to data;
A flexible network architecture.
The BACnet standard defines six types of communication networks for transporting BACnet messages, as
showed in the Figure 3.1. The type of network defines the physical and data link layers. The six types of
networks are:
BACnet ARCnet;
BACnet Ethernet;
BACnet Lontalk;
BACnet MS/TP;
BACnet Point-to-Point;
BACnet IP;
Figure 3.1:
BACnet protocol architecture
A BACnet equipment contains an information collection defined as objects and properties.
A BACnet object represents physical or virtual information of the equipment, as a digital or analog input, control
variables and parameters. The BACnet standard defines 25 types of objects. Each object is identified by a
propriety called Object Identifier, which codifies the object instance type in a 32-bit binary number.
A BACnet property represents characteristics or information of a BACnet object. It is through the properties that
other elements can access the equipment information. The property access can be defined as read-only or
writing/reading. The BACnet specification defines services that are grouped in five categories:
Object access
Device Management
Alarm and event
File transfer
Virtual terminal
BACnet equipments can be classified in six different profiles according to the set of services made available:
BACnet Operator Workstation (B-OWS)
BACnet Building Controller (B-BC)
BACnet Advanced Application Controller (B-AAC)
BACnet Application Specific Controller (B-ASC)
BACnet Smart Actuator (B-AS)
BACnet Smart Sensor (B-SS)
