Qu'est-ce que le protocole BACnet ?

BACnet protocol, a communication protocol designed for intelligent buildings. It not only defines the data formats and transmission methods, but also allow the different devices to communicate in the same network. It is easy to install and low maintenance. It can be found in many management systems such as HVAC systems, lighting control, access control systems, fire detection systems, and so on.

What are the components of the BACnet protocol?

Peer-to-peer network architecture

All the network devices except those based on the MS/TP protocol are fully peer-to-peer in a BACnet network.

Object Model

Each device in BACnet is abstracted to consist of multiple objects. Each object has attributes that define the state and behavior of the object. For example, a temperature sensor object may contain attributes such as current temperature, maximum temperature threshold, and minimum temperature threshold.


BACnet defines a set of services. These services are used to read and write the properties of an object, as well as perform other operations. Such as subscribing to event notifications, sending alarms, and so on.

Conformance category

The perfection of a device is represented by its conformance category, which guarantees that the device can perform basic operations according to the BACnet standard.

The BACnet protocol data link layer and physical layer options

Protocol Hierarchy of BACnet

BACnet provides us with a variety of data link layer and physical layer options, so it can be adapted to different network environments and application requirements.

1. The first option utilizes the Logical Link Control (LLC) protocol of ISO 8802-2 type 1 in conjunction with the Media Access Control (MAC) protocol and the physical layer protocol of ISO 8802-3. ISO 8802-2 type 1 provides a connectionless unacknowledged service. And ISO 8802-3 is the international standardized version of the widely known Ethernet protocol.

2. The second option is also based on the ISO 8802-2 Type 1 Logical Link Control (LLC) protocol. But it partnered with the ARCNET (ATA/ANSI 878.1) protocol.

3. The third option is a combination of the Master-Slave/Token-Passing (MS/TP) protocol and the EIA-485 protocol. The MS/TP protocol is designed for building automation equipment. It is similar to the ISO 8802-2 Type 1 protocol and provides an interface to the network layer by controlling the physical layer of EIA-485.

4. The fourth option is a combination of the Point-to-Point (PTP) protocol and the EIA-232 protocol, which provides a communication mechanism for dial-up serial asynchronous communication.

5. The fifth option is the LonTalk protocol, which is a comprehensive communications protocol stack that can be used to support LonWorks technology. It is often used in a variety of physical and data link layers.

These options provide flexibility in the implementation of the BACnet protocol. It allows the designer to select the most appropriate communication scheme for the specific network environment and device requirements.

What are the objects and services of BACnet?

The Role of IoT in Smart Cities

Firstly, let’s talk about the BACnet object. A BACnet object is an abstraction of a feature in a real device, and its properties represent the state and behavior of the object. There are 28 BACnet objects, including analog inputs, analog outputs, binary inputs, and so on.

Next, BACnet’s services allow devices to read and write properties of objects, subscribe to event notifications, and perform other functions. These services include read attributes, write attributes, subscribe and 35 other services.

These objects and services provide a standardized way for building automation systems to communicate. Allows devices from different vendors to work together seamlessly in the same network. Greatly improves the interoperability and flexibility of building automation systems.

What are the application scenarios for the BACnet protocol?

In the HVAC control systems it can control the temperature to comfortable environment.  In the energy management system, it can help to monitor the energy consumption of the building to achieve energy optimization. Of course, it does a lot more. You can see it in access control, video surveillance, environmental monitoring and other scenarios.

Anyway we hope that through this article, readers can understand the concept of BACnet and some basic knowledge. EG8200 is an passerelle informatique périphérique focusing on data acquisition and protocol conversion. Besides, it also provides the interface to BACnet protocol and can help to monitor the building. Please visit iotrouter to learn more about it.


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