Moving forward with BACnet
What is BACnet?

BACnet is a data communication protocol, also known as ANSI/ASHRAE standard 135-2008 and as the international standard ISO 16484-5.
A great article about BACnet was published in 1997 in the journal Heating/Piping/Air Conditioning Engineer. An updated version of that article is available on the BACnet website (http://www.bacnet.org/FAQ/HPAC-3-97.html).
BACnet, like many other protocols, is based on the client/server model. BACnet messages are called service requests. In BACnet, the client sends a service request to the server device, which performs the requested action and reports the result back to the client. BACnet currently includes 35 message types divided into five classes. The various classes of service requests deal with different types of messaging. For example, one class handles alarms and events, while another deals with uploading and downloading files. The BACnet website lists several tutorials (http://www.bacnet.org/Tutorial/index.html) helpful to gaining a deeper understanding of BACnet and its application.