A great way to quickly take notes on massive amounts of industrial protocols

When it comes to Industrial Internet of Things (IIoT) communication protocols, most people can easily name a few, such as RS-232, RS-485, DeviceNet, Modbus RTU, Modbus TCP, Ethernet/IP, PROFINET, or even TCP, UDP, OPC UA, and MQTT. But what are the differences and connections between them? It's a confusing mess! Below, we'll clear up the fog and bring clarity. This article is recommended for your reference!

To quickly grasp the differences and connections between numerous protocols, beginners first need to understand one thing: the "OSI model."

The OSI (Open Systems Interconnection) model is a standardized reference model for communication protocols, published by the International Organization for Standardization (ISO) in 1984. It aims to provide a common reference framework for computers and communication equipment to achieve interoperability between different manufacturers. This model divides computer network communication into seven layers, each providing different functions and services. Data is progressively abstracted and encapsulated from the lower layers to the upper layers, and standardized protocols and services are defined between each layer through interfaces, enabling devices from different manufacturers to communicate with each other. The OSI model plays a crucial role in the Industrial Internet of Things (IIoT). In IIoT applications, devices need to exchange data and communicate, and the selection and implementation of communication protocols must adhere to the principles of the OSI reference model. For example, fieldbus communication protocols such as PROFIBUS and Foundation Fieldbus are designed based on the OSI reference model. They perform different functions at different OSI layers and possess a degree of interoperability.

Furthermore, IIoT applications also involve standardized protocols such as Ethernet, TCP/IP, HTTP, and MQTT. These protocols are also designed based on the OSI reference model, and their different layers and functions are closely related to it. Therefore, the OSI model is a very important standardized reference model in the IIoT, providing guidance and support for the communication and interaction of IIoT devices.

The seven layers are:

1. Physical Layer: Responsible for transmitting the raw bit stream, defining the characteristics of electrical appliances, physical devices, and transmission media, such as voltage, current, encoding, and physical interfaces.

2. Data Link Layer: Responsible for frame synchronization, flow control, and error checking. Its main task is to convert raw bitstreams into logically meaningful data frames.

3. Network Layer: Responsible for selecting appropriate paths between source and destination hosts and for packet forwarding and addressing via routers, enabling interconnection between different networks.

4. Transport Layer: Provides reliable end-to-end data transmission, including data segmentation, transmission control, error recovery, and flow control.

5. Session Layer: Responsible for establishing, managing, and maintaining sessions and connections between applications, including session establishment, maintenance, and termination.

6. Presentation Layer: Responsible for data format conversion, encryption/decryption, compression/decompression, and data description, enabling different systems to correctly interpret data.

7. Application Layer: Provides users with various network application services, such as email, file transfer, remote login, and web browsing. Now, let's get to the main point! Pay attention! In the field of industrial automation, communication protocols are typically divided into multiple layers, some of which correspond to the layers of the OSI reference model, as follows:

1. Physical Layer: Responsible for transmitting data signals. Commonly used industrial physical layer protocols include RS-232, RS-485, PROFIBUS PA, Foundation Fieldbus, etc.

2. Data Link Layer: Responsible for data framing, error detection and correction, flow control, etc. Commonly used industrial data link layer protocols include PROFIBUS DP, DeviceNet, Modbus RTU, etc.

3. Network Layer: Responsible for transmitting data packets from source address to destination address, forwarding packets and addressing them through routers, etc. Commonly used industrial network layer protocols include Modbus TCP, Ethernet/IP, PROFINET, etc.

4. Transport Layer: Provides reliable end-to-end data transmission. Common industrial transport layer protocols include TCP, UDP, and ISO Transport Service on top of TCP (ISO over TCP).

5. Session Layer: Responsible for establishing, managing, and maintaining sessions and connections between applications. Common industrial session layer protocols include OPC UA and MQTT.

6. Presentation Layer: Responsible for data format conversion, encryption/decryption, compression/decompression, etc. Common industrial presentation layer protocols include OPC UA and DDS.

7. Application Layer: Provides users with various network application services. Common industrial application layer protocols include OPC UA, Modbus TCP, PROFINET IO, and Ethernet/IP.

It should be noted that the classification and layering of industrial protocols are not entirely uniform, and different manufacturers and organizations may use different classification methods and layers. The above is only one common classification method.