protocol based on XML that communicates via the Internet. Like XML, SOAP is
independent of hardware platforms, programming languages, and operating sys-
tems, and is important in facilitating the exchange of information between applica-
tions and systems.
BACnet
BACnet is an acronym for building automation and control networks. An
international data communication protocol, BACnet was first published in
1996, and was developed and is maintained by the American Society of Heat-
ing, Refrigerating and Air-Conditioning Engineers (ASHRAE).
BACnet provides a standard for representing the functions and operations
of building automation and control devices. For example, the protocol covers
how to request a value from a humidity sensor or send a pump status alarm.
For each type of building automation and control device, a standard software
object is created that contains the identifier and properties of such a device ref-
lecting the functions and operation of the device. Some of these properties may
be inherent or required properties of the device, while other properties may be
optional features of the device. The essence of BACnet is to move away from
proprietary communications to similar devices by different manufacturers and
treat communications and control of like-devices in a standard common way.
This approach and structure allow BACnet to be used in HVAC, lighting
systems, fire alarm systems, and other building automation systems.
In addition to standardization of the device objects, BACnet also defines the
message types between a server and a client. These messages are called “service
requests,” and the BACnet standard defines 35 message types that are divided
into five groups or classes. The latter involve messages for the following:
- Accessing and manipulating the properties of the objects
- Alarms and events
- File uploading and downloading
- Managing the operation of remote devices
- Virtual terminal functions
BACnet can communicate over several types of networks, including Ether-
net, ARCNET, MS/TP (master-slave/token-passing), and PTP (point-to-
point) for use over phone lines or hardwired EIA-232 connections.
ARCNET is an archaic network topology and PTP is not widely deployed.
ASHRAE has recognized the importance of the IP protocol in
22 Smart Building Systems for Architects, Owners, and Builders