The Internet of Things is an extension and expansion of the traditional Internet. The user terminal extends from a traditional computer to any device that collects information through various sensors and then collects, exchanges, and communicates network information through the computing device.The reason for the emergence of MQTT protocol is that mobile Internet is still in its infancy and can not provide reliable network guarantee.

  First, MQTT has many advantages

  1.The unique feature of MQTT is that each header can be shortened to 2 bytes. For HTTP, reestablishing the HTTP connection for each new request message incurs considerable overhead. The persistent connections used by MQ and MQTT can greatly reduce this overhead.

  2. To accommodate unstable networks, MQTT and MQ can recover from failures such as disconnection without further code requirements. However, HTTP cannot achieve this goal by itself, and the client must retry the encoding, which adds to the identity problem.

  3. The low-power MQTT is designed for low-power targets. HTTP is not designed with this in mind, which increases power consumption.

  4. With millions of clients connected, maintaining millions of concurrent connections in the HTTP stack requires a lot of work to support. Although this support is possible, most commercial products are optimized to handle persistent connections on this order.IBM offers IBM Message Sight, a single-rack-mount server that has been tested to handle up to one million concurrent devices via MQTT. Conversely, MQ is not designed for many simultaneous customers.

  5. Push notifications. You need to be able to send notifications to customers in a timely manner. To do this, you should use the regular polling or push method. Push is the best solution in terms of battery, system load, and bandwidth.

  6. Differences in client platforms. Both HTTP and MQTT clients are implemented on many platforms. The simplicity of MQTT helps you implement MQTT on other clients with minimal effort.

  7. Firewall fault tolerance. Some corporate firewalls restrict outbound connections to certain predefined ports, which are usually limited to HTTP (port 80), HTTPS (port 443), etc. HTTP obviously works in this case. MQTT is encapsulated in a Web Sockets connection and appears as an HTTP upgrade request, so it can be run in this case.

  2. Disadvantages of MQTT

  In fact, MQTT is widely used and can be found in almost any large hardware and Internet company, such as Facebook, BP, Alibaba and Baidu.

  Because of the technical advantages of MQTT, more and more companies choose MQTT as the standard protocol for the communication of Internet of Things products. As a result, engineers have come to realize that the functionality of the MQTT protocol needs to be improved for large-scale commercialization. For example

  1. Without a complete SDK, software SDK packages for different heterogeneous devices are required to communicate with MQTT servers (e.g. MCU, Linux, Android, IOS, WEB) for interconnection and interoperability.

  2. File and AV are not supported. In some application scenarios, the information that needs to be transmitted may not be limited to instructions that need to be communicated with the file via AV, such as voice and video signals.

  3. Integration with third-party HTTP is not supported. The MQTT protocol is superior to the conventional HTTP protocol, but WEB servers based on the conventional HTTP protocol still dominate the mainstream market. These servers should be interconnected with the MQTT protocol to reduce upgrade costs.

  4. Load sharing is not supported. Load distribution servers are also essential for high concurrency and protection against malicious attacks.

  5. The user management interface is not supported. This is especially important when users are analyzing device behavior data. In the era of industrial 4.0 and big data, this is an inevitable demand.

  6. Offline messages are not supported to compensate for the loss of control information from the MQTT server to the device when the device goes offline.

  7. Point-to-point communication is not supported and the standard MQTT protocol is used. In theory, peer-to-peer communication can be achieved by subscribing to each other, but the logic is relatively complex and involves device security.When device B and device C are the same-in the case of the subject, device A has no way of knowing whether the message came from device B or from device C, and the message is likely to have been eavesdropped by device D.

  8. It does not support group communication or group management, but implements the management of group members. Group members can exchange messages, which is particularly useful if one device is controlled by more than one person or multiple devices are controlled by one person.