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Oleksandr Zdir


Introduction to communication protocols in Building Management Systems

5 Minutes

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1. What is the BMS protocol?


A communication protocol is a set of rules that defines how different entities of a communication system should transmit information. In the case of Building Management Systems, it is set for rules that define how different BMS devices communicate with each other.  It is a commonly used practice to think of BMS communication protocols as of languages. As two people speaking different languages cannot understand each other, so do BMS devices.

You might ask “Why we have different languages in BMS environment in the first place? Can’t we have one? Why to complicate life?”. In a perfect world that would be the case. We would have one protocol, perfectly fitted for every use in BMS, widely available for free everywhere for everyone. While different manufacturers of the BMS devices  were creating their controllers so they created the way they “speak” with each other. As long as all the devices are using the same language we have no problem with sending/receiving information. But it is not the case now in our globalized world. Designers of Building Management Systems know very well the problem of interconnecting the whole building where thousands of devices are from different manufacturers. The goal is to build a system where every alien language would be translated in commonly used language so the data may be understood and used for building automation purposes. Devices which are “bilingual” or “multilingual” and can support two or more communication protocols have obvious advantage on the BMS market just because they can be integrated without translation into a larger number of BMS systems. For example, iSMA-B-MIX38 support both BACnet and Modbus – widely used communication protocols.


iSMA-B-MIX38-IP supports BACnet and Modbus


2. What communication protocols are commonly used in BMS worldwide?


There are dozens of communication protocols used in BMS Systems. Some are open and available for free for every manufacturer. Some are restricted for one specific manufacturer and patented. Some are designed for use with a specific area of the building. Some are universal and can be used everywhere in the building.


The most popular open building automation network protocol is BACnet. BACnet stands for Building Automation and Control Network, it was designed specifically for Building Automation. It is updated and supported by ASHRAE and quickly winning the market of Building automation.


One we should mention after BACnet is LonWorks. It is a very popular technology worldwide created by Echelon Corporation in 1988. This protocol proved to be a cost-effective solution and was implemented by numerous manufacturers.


The third kind of Building Management Systems Communication protocols is Modbus. It was developed during the 1970s by Modicon Inc and was primarily designed for industrial automation. Its simplicity made this protocol popular in building automation applications.


Other well-known names of BMS communication protocols are KNX, DALI and EnOcean. KNX is standard for building control. DALI (Digital Addressable Lighting Interface) designed specifically for lighting control. EnOcean is a low power wireless protocol widely used in wireless sensors and switches.


Every manufacturer of Building Automation Devices is choosing which of those protocols are best suitable for his devices. Global Control 5 implemented BACnet and Modbus into each device in its portfolio. Let's dig in deeper into these two protocols.



3. What advantages does the BACnet protocol offer?


BACnet is winning the market of BMS communication and not without solid reasons for that.

First of all, BACnet is an open communication protocol. Open means that every manufacturer in the world can use codes for this communication protocol for free and implement them in its own devices. That makes this protocol potentially widely used. So if you decide to learn a language it is better to be commonly used language, otherwise, there would be no one to speak with. BACnet’s open nature has led to more partnerships between manufacturers, which leads to greater innovation in the industry.


Secondly, it is flexible. This communication protocol can be used for all building automation and control applications. This includes HVAC, lighting, security, safety, fire and life safety. That’s what you need if you want to have one protocol for all the levels of communication in your building.


One additional benefit is that BACnet is scalable. This standard of communication can be used from tiny, single device applications to global networks with thousands of devices.
The simplicity of integration. If you are from the Building Management System field you know that there is nothing easier than integrate BACnet device into the system. Discover the connected device, search for available points and choose what you are interested in. That’s it. With correct configuration, it is as easy as pie.


BACnet also has a proven record of working in real Building Automation Applications. It has been applied in thousands of buildings all over the world. ASHRAE has also done a great job in controlling the quality of implementation of the protocol among the different manufacturers by providing BACnet communication certifications. If you want to be sure that the device was checked by BACnet laboratory just search for manufacturer on their website. For example, the list of certified devices by Global Control 5 can be found here.



4. What advantages does the Modbus protocol offer?


Modbus, same as BACnet, is openly published and free of charge communication protocol. The specification is available free of charge and there are no licensing fees. That’s a good start. What else? One of the greatest advantages of Modbus is its simplicity. Modbus if often characterized as easy to install, configure and use. It has been on the market since 1979 and during its long period of life, it proved to be an excellent solution not only for industrial automation but also for commercial buildings.


It provides reliable communication between automation devices. Every message contains CRC (Cyclic Redundancy Check) code which proves that the message we get is complete and correct.
Versatility. There are different versions of Modbus protocol which can be used for Serial Port communication and Ethernet.


Its popularity is also a significant advantage. Modbus networks are still widely used in Industrial Automation and Building Automation in multiple client-server applications to monitor and program devices.
Security. In 2018 Modbus Organization, Inc. released Modbus Security – a new version of the protocol which provides robust protection through TLS (Transport Layer Security). Cybersecurity becoming a crucial part of BMS communication and it is nice to see that Modbus working on keeping up with the industry trends.

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