BACnet Gateway Kit for Central Air Conditioners
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Appendix B BACnet Protocol
1 Brief Introduction to the BACnet Protocol
1.1 What is BACnet
BACnet - A Data Communication Protocol for Building Automation and Control Networks - see
bacnet.org. BACnet is a standard data communication protocol for Building Automation and Control
Networks. BACnet is an open protocol, which means anyone can contribute to the standard, and
anyone may use it. The only caveat is that the BACnet standard document itself is copyrighted
by ASHRAE, and they sell the document to help defray costs of developing and maintaining the
standard (just like IEEE or ANSI or ISO).
1.2 BACnet Collapsed Architecture
BACnet is based on a four-layer collapsed architecture that corresponds to the physical, data
link, network, and applicationlayers of the OSI model.
BACnet Layers Equivalent OSI Layers
BACnet Application Layer
BACnet Network Layer
ISO 8802-2(IEEE 802.2)
Type 1
MS/TP
PTP
LonTalk
BVLL
ISO 8802-
3(IEEE 802.3)
ARCNET
EIA-485
EIA-232
UDP/IP
BACnet is defined for several physical layers.
BACnet/IP has only later been added to the original group.
1.3 BACnet device profiles
Today 6 device profiles are defined with BACnet:
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-SA)
BACnet Smart Sensor (B-SS)
Any device that implements all the required BACnet capabilities for a particular device type
and interoperability area may claim to be a device of that particular type.Devices may also provide
additional capabilities and shall indicate these capabilities in their PICS.
Application
Network
Data Link
Physical
