Chapter 8 introduced protocols such as TCP, HTTP, UDP, and CoAP, which can facilitate local control. In addition, they can also be used for remote control.
MQTT is an application protocol based on the TCP protocol. Both can be used for remote data communication. For socket programming, TCP requires users to develop their own application protocols, which have limited usability in the current environment of IoT interconnection. On the other hand, MQTT is a standardized lightweight protocol for IoT and is widely used by most cloud servers, such as Alibaba Cloud and Amazon Cloud, making it advantageous for product integration.
Both are client-server application protocols based on TCP. However, compared to MQTT, HTTP has a much larger overhead in message size, and it is generally difficult for an HTTP server to initiate data push to clients, which may not meet the requirements of remote control in IoT. In cases where only one-way transmission from clients to the server is needed, HTTP protocol can be used.
Similar to HTTP, CoAP adopts the REST model where the server creates resources in URI format and clients access these resources using GET, PUT, POST, and DELETE methods. Besides, CoAP also has a similar protocol style to HTTP, but it requires fewer device resources and network overheads, making it suitable for IoT. However, CoAP may not be a good choice for remote control. If smartphones send control commands for remote control, the architecture may require CoAP + Web + Database + App. When CoAP protocol is used, control commands must pass through the Database before reaching the device, because CoAP is connectionless. When smartphones send control commands, the server will first store the control commands in the Database, and the device will request the server via GET method to check if there are any control commands, and then decide whether to operate. On the other hand, MQTT is connection-oriented, and the server will forward the control commands from smartphones to all subscribed devices without storing them. Only MQTT client + MQTT server + App is needed to implement remote control, making MQTT more advantageous in terms of deployment.