Many people get confused when they start learning about communication protocols because they don't have an instructor who can make the concept easy to understand. They often get confused by an expert's jargon concerning complex building automation systems, what types of software work with certain types of hardware, and how large systems can become increasingly difficult to manage without understanding the commands that control them.
Get all of the confusing information out of your head and start thinking about communication protocols simply. Communication protocols are nothing more than message formats used between devices. If the protocol doesn't match the devices, then something won't work right. It would be like trying to put together a bike by reading instructions in Chinese. It's the same when you try to use the wrong protocol to operate a building's HVAC system. The system has no idea what kind of gibberish it's being told.
Now that you have a somewhat better understanding of what communication protocols are, you should learn about the three most popular ones used in today's building automation industry.
Modbus is the oldest communications protocol in wide use today. Its designers made their finishing touches in 1979. That might sound young to a human, but it's practically ancient considering how quickly technological trends evolve and die off.
The funny thing about Modbus is that people still use it because everyone uses it. It's kind of like getting paid more money than someone because you already have more money. The fact of the matter is that Modbus took control of the industry a long time ago, and it just hasn't let go. Even though it still uses the same base parameters as it did three decades ago, designers still consider it a standard in the industry.
BACnet is the youngest of the big three communication protocols. In was developed in the early 1990s and became essential to many products released in 1996. The most interesting thing about BACnet, though, is that it wasn't developed by a company looking to make a profit. It's kind of like UNIX in that way.
Another interesting thing about BACnet is that it's almost exclusively used for building automation. Its designers created it to control HVAC systems, air conditioners, heaters, lighting, and fire-detection systems. That makes it one of the best options for people in the building automation industry.
Developed in 1988, LonWorks might have a bit of a middle-child complex that pushes it to overcome boundaries. LonWorks became an ANSI standard in 1999. By 2010, it was installed in more than 90 million devices. As far as popularity goes, the other two don't even come close.
LonWorks gets its popularity, though, from its flexibility. While it's used in many building automation systems, it's also used in subway controls, speaker controls, street lights, and embedded machine controls. With that many uses, it's no wonder such a diverse range of companies use it with their products.
There are plenty of other communication protocols. If you can learn the basics of these three, though, you'll be a master of building automation.