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CHAPTER 4. MARKET STUDY
Figure 4.15: BACnet-based building automation system architecture.
The figure shows how a BACnet system can be constructed. Where, for
example the MS/TP data link layer, with a data rate of 9.6-78.4 kbps, is
used to communicate with the HVAC and lighting equipment. MS/TP or
ARCnet is used for fire safety, access and security and any 3rd party system
is linked through BACnet gateways. For a backbone communication, the
BACnet Ethernet is used, which is the strength of BACnet, providing a
robust connection at the management level [15].
Protocol
All information within the BACnet network is encapsulated in BACnet objects, a data structure that is spread out on the network. These objects
represent environmental parameters, trend analysis, calculation result, etc.
By using a mechanism called service request, all nodes in the network can
access this informations. BACnet currently defines 35 message types, divided into 5 classes like alarm and event service. In order to guarantee that
BACnet devices from different vendors will function and interoperate on the
network, BACnet requires a so called protocol implementation conformance
statement, PICS, from the vendor. It is basically a BACnet specification
sheet containing a list of a device’s BACnet capabilities [30].