Hit Me Up On TCP - Part 2 Using TCP/IP for transferring data, MQTT is lightweight and simple-to-use

This is the second in a two-part series where Pedro highlights network communication using ESP32 SOC and the ESP-IDF framework. Part two shows how to establish a multiple-end communication through MQTT, with an ESP32 SOC on one end to another end that can be anything capable of communicating through MQTT. Transport fundamentals are covered through a practical example showing how an ESP32-S2 SoC communicates using MQTT.

- Pedro Bertoleti

Embedded systems are nearly ubiquitous in our lives, affecting both developers and everyday users. Almost every electronic and electrical device around us relies on embedded systems, from smartwatches and phones to modern vehicles like electric cars, electric buses and rental bikes.

The widespread presence of these systems introduces a critical requirement: network communication capability. Many of these devices, integral to our daily routines, need to communicate with other devices or even cloud services to enhance our comfort and efficiency in daily tasks. Consequently, network communication capability - whether local or over the Internet has become a fundamental requirement for embedded systems solutions.

This article explores one of the most popular and scalable methods to allow embedded systems' communication over the network: MQTT. It covers from TCP sockets fundamentals to a practical example on how to communicate to an ESP32-S2 SoC using MQTT communication protocol.

MQTT OVERVIEW

A good start point is to define what MQTT is. MQTT stands for Message Queuing Telemetry Transport, and it was created by IBM in the late 90s. MQTT uses TCP/IP as a layer for transferring data, and has been designed to be a lightweight and simpleto-use network protocol, working with the publish-subscribe paradigm, as seen in the MQTT simplified diagram shown in Figure 1.

Every node in a MQTT communication (usually called MQTT client) is connected to a central MQTT server called an MQTT broker and sends and receives messages to other nodes addressed by MQTT topics. When a node publishes a message, it sends the desired payload addressed to a specific MQTT topic, and each node that subscribes to this referred MQTT topic will receive this message. In terms of communication possibilities, any MQTT client can be subscribed to N topics and publish to N topics simultaneously, making MQTT a very versatile communication protocol.