Use of MQTT in Linux Embedded
MQTT is a lightweight messaging protocol suitable for Linux embedded systems. It is based on the publish-subscribe model to achieve efficient communication between devices.
It is widely used in the fields of Internet of Things, smart home, etc. to promote data interaction and remote control between devices.
MQTT protocol for smart home – WIFI Bluetooth serial port transparent transmission wireless module – IoT remote control smart home MQTT protocol
MQTT (Message Queuing Telemetry Transport) is a lightweight communication protocol based on the publish/subscribe model. It is built on the TCP/IP protocol and was released by IBM in 1999. The latest version is v5.0 (at the time of writing, although v3.1.1 is still the widely used version, v5.0 introduces more features and improvements, which is worth noting).
Internet of Things Linux Embedded Development Board
The design goal of MQTT is to provide real-time and reliable message services to remote devices with very little code and limited bandwidth, so it has a wide range of applications in the Internet of Things (IoT), small devices, mobile applications, etc.
The following is a detailed introduction to the use of MQTT in Linux Embedded by the Internet of Things Cloud Platform (blog.iotcloudplatform.com).
MQTT Protocol Overview
1. Definition and Background
MQTT is a message transmission protocol based on the publish/subscribe model of the client-server architecture. It was originally designed for remote devices with low hardware performance and poor network conditions, so it is particularly suitable for scenarios such as the Internet of Things and machine-to-machine (M2M) communication.
2. Main features
- Lightweight: The MQTT protocol is simple and easy to implement, with low overhead and low bandwidth, and is suitable for running on embedded devices with low computing power and few resources.
- Publish/Subscribe mode: This mode provides one-to-many message publishing, decoupling applications and allowing message publishers and subscribers to work independently.
- Based on TCP/IP: MQTT is built on the TCP/IP protocol, so MQTT can be used wherever the TCP/IP protocol stack is supported.
- Support for QoS: MQTT supports three levels of quality of service (QoS), from at most once delivery to ensuring once and only once delivery, to meet the needs of different applications for message delivery reliability.
- Small transmission: The fixed header of MQTT is only 2 bytes, and the protocol exchange is minimized to reduce network traffic.
- Will mechanism: A mechanism that uses the Last Will and Testament features to notify relevant parties of abnormal client interruptions.
3. Application scenarios
MQTT is widely used in the fields of Internet of Things, mobile Internet, smart hardware, Internet of Vehicles, electric power and energy. Specific application scenarios include IoT M2M communication, Android message push, mobile instant messaging, smart hardware control, Internet of Vehicles communication, smart city, telemedicine, distance education, etc.
Use of MQTT in Linux Embedded
1. Environment Preparation
To use MQTT in Linux embedded systems, you first need to ensure that the system supports the TCP/IP protocol stack. In addition, you also need to install the MQTT client library or related tools to implement the publishing and subscription of MQTT messages on embedded devices.
2. Client Library Selection
There are many MQTT client libraries available under Linux, such as Paho MQTT C Client, Eclipse Mosquitto, etc. These libraries provide rich APIs to facilitate developers to implement MQTT functions on embedded devices.
3. Connection and Disconnection
When using the MQTT client library, you first need to establish a connection with the MQTT server. During the connection process, you need to specify the server address, port number, client ID and other information. After the connection is successful, the client can publish messages to the specified topic, or subscribe to the topic of interest to receive messages. When the MQTT service is no longer needed, the client can disconnect from the server.
4. Message publishing and subscription
- Message publishing: The client sends messages to the specified topic by calling the publishing API. Messages can contain information such as payload data, QoS level, retention flag, etc.
- Message subscription: The client subscribes to one or more topics by calling the subscription API. When new messages are published on these topics, the server pushes the messages to the clients that have subscribed to the topic.
5. Heartbeat mechanism and QoS
- Heartbeat mechanism: The MQTT protocol maintains the connection between the client and the server through the heartbeat mechanism. When the connection is established, the client and the server will agree on a heartbeat interval. During this interval, if the client does not send any messages, it needs to send a PINGREQ message to the server. After receiving it, the server will reply with a PINGREESP message. In this way, it can be ensured that the connection is not considered disconnected by the server.
- QoS level: MQTT supports three QoS levels, namely QoS 0 (at most once delivery), QoS 1 (at least once delivery), and QoS 2 (only once delivery). Developers can choose the appropriate QoS level according to application requirements to optimize bandwidth usage and message delivery reliability.
6. Error handling and reconnection mechanism
When using MQTT, you may encounter various error situations, such as network disconnection, server unavailability, etc. In order to deal with these error situations, developers need to implement error handling logic and reconnection mechanism. When an error is detected, the client can try to reconnect to the server and restore the previous session state (such as subscriptions and undelivered messages).
7. Security considerations
The MQTT protocol itself does not provide security guarantees, so security issues need to be considered during use. Common security measures include using TLS/SSL encrypted communication, setting passwords and usernames for authentication, etc. In addition, you can also consider using technologies such as MQTT over WebSocket to improve security.
Actual application of MQTT in Linux embedded systems
1. Smart home
MQTT has a wide range of applications in the field of smart home. Through the MQTT protocol, smart home devices (such as smart bulbs, smart sockets, smart cameras, etc.) can communicate with the server to achieve remote control, status monitoring and other functions. For example, users can send MQTT messages through mobile phone APP to control the switch and brightness adjustment of smart bulbs.
2. Industrial Automation
In the field of industrial automation, MQTT can be used to achieve communication and data exchange between machines. Through the MQTT protocol, various sensors, controllers and actuators can communicate with the central server to achieve real-time monitoring, fault diagnosis and remote control. This helps to improve production efficiency, reduce maintenance costs and enhance system reliability.
3. Internet of Vehicles
MQTT also has important applications in the field of Internet of Vehicles. Through the MQTT protocol, vehicles can communicate with the cloud platform to achieve vehicle status monitoring, remote control, fault diagnosis and other functions. In addition, MQTT can also be used to achieve communication and data exchange between vehicles, providing support for applications such as intelligent transportation and autonomous driving.
4. Telemedicine
In the field of telemedicine, MQTT can be used to achieve remote monitoring and data collection of medical equipment. Through the MQTT protocol, medical equipment can send information such as patients’ physiological parameters and equipment status to remote servers or doctors’ handheld devices. Doctors can view patients’ health status in real time and give corresponding diagnosis and treatment suggestions. This helps to improve the quality and efficiency of medical services and reduce medical costs.
5. Smart City
In the construction of smart cities, MQTT can be used to achieve intelligent management and monitoring of urban infrastructure. Through the MQTT protocol, various sensors (such as environmental monitoring sensors, traffic flow sensors, etc.) can send real-time data to the cloud platform for analysis and processing. These data can be used to optimize urban traffic, improve environmental quality, and improve the level of public services.
Comparison of MQTT with other communication protocols
When choosing a communication protocol, it is necessary to weigh it according to the specific application scenario and requirements. The following is a comparison of MQTT with other common communication protocols:
1. HTTP
HTTP is one of the most commonly used network protocols on the Internet, with a wide application base and good compatibility. However, the HTTP protocol is a request/response mode, and the client needs to actively initiate a request to obtain data on the server. This makes HTTP perform poorly in scenarios with high real-time requirements or frequent communication. In contrast, the MQTT protocol adopts a publish/subscribe mode, which can realize the function of the server actively pushing messages to the client, and is more suitable for scenarios such as the Internet of Things that require real-time data transmission.
2. CoAP
CoAP (Constrained Application Protocol) is a low-power, narrow-bandwidth, unreliable binary protocol based on UDP, designed for constrained devices and constrained networks. CoAP uses a REST architecture similar to HTTP, which is easy to understand and implement. However, since CoAP is an unreliable transmission protocol based on UDP, it may not perform well in scenarios that require high reliability and real-time performance. In contrast, the MQTT protocol supports TCP connections and QoS level settings, which can provide more reliable message transmission services.
3. WebSocket
WebSocket provides a way to communicate in full duplex on a single TCP connection, allowing the server to actively send information to the client. This makes WebSocket perform well in scenarios with high real-time requirements. However, the WebSocket protocol is relatively complex and has a large overhead, which may not be suitable for resource-constrained embedded devices. In contrast, the MQTT protocol is more lightweight and easy to implement, and is more suitable for scenarios such as the Internet of Things.
WiFi Bluetooth module MQTT for Linux embedded development
Conclusion and Prospects
As a lightweight and easy-to-implement communication protocol, MQTT has broad application prospects in Linux embedded systems. Through the MQTT protocol, embedded devices can communicate and exchange data with servers efficiently and reliably, providing strong support for the Internet of Things, industrial automation, and Internet of Vehicles.
With the continuous development and popularization of Internet of Things technology, the application scope of the MQTT protocol will become more and more extensive.
In the future, we can expect the MQTT protocol to play an important role in more fields and bring more convenience and intelligent experience to people’s lives.
The above content is a detailed introduction of the use of MQTT in Linux embedded by the Internet of Things Cloud Platform (blog.iotcloudplatform.com), including an overview of the MQTT protocol, the use of MQTT in Linux embedded, the practical application of MQTT in Linux embedded systems, the comparison of MQTT with other communication protocols, and conclusions and prospects.
I hope these contents can help readers better understand and apply the relevant knowledge of the MQTT protocol in Linux embedded systems.
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IoT Cloud Platform (blog.iotcloudplatform.com) focuses on cutting-edge technology, IOT embedded development, IoT technology solutions, IoT programming knowledge, sensor module selection, WiFi module procurement, and Bluetooth chip supply support.
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FAQs
The following are FAQs about the use of MQTT in Linux embedded and the Internet of Things:
MQTT (Message Queuing Telemetry Transport) is a lightweight communication protocol based on the publish/subscribe model. The protocol is built on the TCP/IP protocol and was released by IBM in 1999. The latest version is v3.1.1. The biggest advantage of MQTT is that it can provide real-time and reliable message services to remote devices with very little code and limited bandwidth.
The advantages of MQTT in Linux embedded systems mainly include lightweight design, efficient transmission, reliable transmission, and a wide range of application scenarios. It is designed for low-bandwidth and resource-constrained devices, and uses a binary-encoded message format to reduce the use of network bandwidth and resources. At the same time, it supports three levels of quality of service (QoS) to meet the needs of different applications for message delivery reliability.
Deploying an MQTT server in a Linux system usually involves installing MQTT broker software such as Mosquitto. You can install Mosquitto through a package manager (such as apt or yum), and then configure its configuration file (such as mosquitto.conf) to set options such as port, log, and persistence. Finally, start the Mosquitto service.
To modify the port number of the MQTT server, you need to edit the configuration file of Mosquitto (usually mosquitto.conf), find or add the “port” directive in the file, and set it to the port number you want. Then, restart the Mosquitto service for the changes to take effect. Note that if the port number is already occupied by another service, you may need to stop the service first or select an unoccupied port.
MQTT supports three quality of service (QoS) levels:
QoS 0: At most once delivery. Messages may be lost during transmission, but message arrival is not guaranteed.
QoS 1: At least once delivery. Ensure that messages arrive at least once, but may be duplicated.
QoS 2: Ensure once and only once delivery. This is the most reliable way to deliver messages, but it also consumes the most resources.
The heartbeat packet mechanism is an important feature of the MQTT protocol, which is used to maintain the connection between the client and the server. When the MQTT connection is established, the client and the server agree on a time interval (called the Keep Alive time interval). During this time interval, if the client does not send any messages to the server, it must send a PINGREQ (heartbeat request) message. After receiving the PINGREQ, the server sends back a response (PINGRESP) to the client to confirm that the connection is normal. This helps ensure that devices that are idle for a long time but need to remain connected (such as IoT devices) are not disconnected.
The application scenarios of MQTT in Linux embedded systems are very wide, including but not limited to scenarios that require real-time data transmission and low bandwidth, such as smart home, industrial automation, and agricultural monitoring. In these scenarios, MQTT, as the core protocol for communication between devices, realizes the interconnection between devices and the real-time transmission of data.
Under Linux system, you can use the package manager to install Mosquitto or other MQTT server software. After the installation is complete, edit the configuration file of the MQTT server, set the listening port, authentication method, TLS/SSL encryption, etc. Finally, start the MQTT server service and ensure that it continues to run.
MQTT has a wide range of application scenarios in the Internet of Things, including but not limited to smart home, industrial automation, smart city, and remote monitoring and maintenance. As the core protocol for communication between devices, it realizes the interconnection between devices and the efficient transmission of data.
The Linux system provides the application of MQTT with rich development resources, efficient resource management, powerful network functions and extensive hardware support. These advantages make the application of MQTT under the Linux system more stable, efficient and flexible.
The MQTT protocol provides three QoS levels, namely 0 (at most once), 1 (at least once) and 2 (only once). When selecting the QoS level, it is necessary to balance the reliability and transmission delay of the message according to the specific application scenario. Critical data such as commands and alarm information should use a higher QoS, while real-time but non-critical data can use a lower QoS.
MQTT supports TLS/SSL encryption to protect the security of data transmission and prevent man-in-the-middle attacks. At the same time, an authentication mechanism based on certificates or OAuth can be implemented to enhance the security authentication of devices and users. Configure permission management (such as ACL) on the Broker side to limit the access rights of different clients to Topics.
When the IoT device encounters the problem of MQTT service unavailability when applying for dynamic registration, you can troubleshoot and solve it from the following aspects: verify whether the MQTT service of the IoT platform is running normally; ensure that the network environment in which the device is located can correctly access the MQTT server; verify that the MQTT service area that the device is trying to connect to is consistent with the area selected when the product is created; ensure that the information used for pre-registration is valid and within the validity period; the device-side SDK version used should be synchronized with the latest documentation and API specifications provided by the IoT platform.
To start the MQTT service on a Linux system, you usually need to use MQTT agent software such as Mosquitto. You can use the system service manager (such as systemctl) to start the Mosquitto service and ensure that it starts automatically after the system restarts. In addition, you can also run Mosquitto in foreground mode directly in the command line for debugging or testing purposes.
The reasons for MQTT message loss may include network problems, server problems, client problems, and subscription relationship problems. To solve these problems, the following measures can be taken: ensure that the network connection is stable and reliable; test the performance and stability of the MQTT server; add exception handling logic in the client code; ensure the correct setting and management of subscription relationships; use a reliable messaging mechanism with QoS level set to 1 or 2.
The lightweight of MQTT in the Linux environment is mainly reflected in its concise message format and small payload, which is suitable for resource-constrained devices. At the same time, the Linux system is known for its efficient resource management and multi-tasking capabilities, which is essential for running MQTT services.
Install MQTT server software: Select suitable MQTT server software, such as Mosquitto, EMQ X, HiveMQ, etc., and download and install it from the official website.
Configure the server: Open the server configuration file, set the server’s listening port, connection authentication and other parameters, and save the configuration file.
Start the server: Execute the start command to start the MQTT server. The specific command depends on the selected server software.
Verify the server: Use the MQTT client tool to connect to the server, publish and subscribe to messages to verify that the server is working properly.
Advantages:
Low protocol overhead: The MQTT message header is short, which reduces the network bandwidth usage.
Tolerance to unstable networks: MQTT can recover from failures such as disconnection and is suitable for unstable network environments.
Low power consumption: Designed for low-power devices and suitable for IoT applications.
Support for a large number of connections: Can effectively manage millions of concurrent connections.
Push notification: Supports push messages, suitable for scenarios that require timely notifications.
Firewall fault tolerance: MQTT is encapsulated in a WebSockets connection and can be restricted by a firewall.
Disadvantages:
Incomplete SDK: May lack a complete software development kit (SDK) to support different devices.
No support for files and AV: Cannot directly transfer files or audio/video signals.
No support for third-party HTTP integration: Interconnection with mainstream HTTP servers may be challenging.
No support for load distribution: Additional load distribution mechanisms may be required in high-concurrency environments.
Lack of user management interface: Analysis and management of device behavior data may not be intuitive enough.
Offline messages are not supported: Devices may not receive missed messages after being offline.
Smart home: Connect smart lights, temperature sensors and other devices to realize device status publishing and user subscription.
Industrial automation: Real-time communication monitoring and control of various sensors and devices on the production line.
Logistics and transportation: Monitor vehicle location and cargo status, and provide accurate logistics tracking services.
Agricultural monitoring: Connect sensors and controllers to monitor crop status and realize irrigation control.
