Optimizing IoT with MQTT: Efficiency and Low Power

given by Bala mahendran

Introduction to MQTT

Message Queuing Telemetry Transport (MQTT) is a lightweight, publish-subscribe network protocol used to transport messages between devices. It’s specifically designed for low-bandwidth, high-latency, or unreliable networks, making it ideal for Internet of Things (IoT) applications, where devices often operate under constrained resources.

?In this blog post, we’ll dive into the MQTT architecture, explore a real-world use case, discuss its advantages and disadvantages compared to other IoT protocols, and review available benchmark data.

?MQTT Architecture

At the core of MQTT is the broker, which acts as an intermediary between devices, allowing them to communicate without being directly connected. Clients can either publish messages on a topic or subscribe to topics to receive messages.

?Key Components of MQTT Architecture

• Broker: The central hub that routes messages between clients. It handles all incoming messages and determines who gets what based on TOPIC based subscriptions.
• Clients: Devices or applications that either publish messages or subscribe to topics (or both).
• Topics: Hierarchical labels used to categorize messages (e.g., "sensors/temperature/living-room").
• QoS (Quality of Service): Ensures the reliability of message delivery, with three levels:

• QoS 0: "At most once" delivery - Low Overhead
• QoS 1: "At least once" delivery - Medium Overhead
• QoS 2: "Exactly once" delivery - High Overhead

?MQTT Architecture Diagram

The following diagram illustrates a typical MQTT architecture

Description

1. Devices (sensors, applications, etc.) act as MQTT clients.
2. MQTT broker acts as a brain for MQTT protocol as if it's dead nothing works.
3. The device / clients either publish messages to the broker on a specific topic (IOT, ALL_IOT) or subscribe to a topic to receive relevant messages.
4. The MQTT broker forwards messages to clients subscribed to the corresponding topics.
5. A MQTT client can acts both as a Publisher and Subscriber. This dual role is useful in many IoT (Internet of Things) applications where devices need to both send and receive data.

?Real-World Example: Smart Home HVAC System using MQTT

Imagine a smart home setup where MQTT is used to control the heating, ventilation, and air conditioning (HVAC) system.

Scenario Overview

• Temperature Sensor: Publishes the current room temperature to the MQTT broker.
• Thermostat: Subscribes to the temperature topic and, based on predefined thresholds, decides whether to activate the air conditioning (AC) or the heating system.
• MQTT Broker: Acts as the central communication hub between the sensor and the thermostat.
• HVAC System: Thermostat directly communicates with HVAC to notify temperature data and it decides what needs to be done using Zigbee or any other wireless protocols.
• Air Conditioner: Subscribes to the control topic from the thermostat to adjust cooling based on the room’s current temperature.

?Flow of Message in MQTT

1. Temperature Sensor regularly publishes the room temperature (e.g., 30°C) to the MQTT broker on a topic like home/room1/temperature.
2. Thermostat subscribes to this topic and receives the temperature data from the broker and sends it to HVAC.
3. HVAC System logic processes this information. If the temperature exceeds 25°C, it decides to activate the Air Conditioner.
4. HVAC then publishes a message on the control topic (e.g., home/room1/AC/control) via the MQTT broker.
5. Air Conditioner which subscribes to the control topic(home/room1/AC/control) receiving the signal, turns on to cool the room.
6. The temperature decreases, and the sensor sends the updated temperature again, continuing the cycle until the desired room temperature is maintained.

?Advantages of MQTT Over Other IoT Protocols

1. Low Bandwidth Usage

MQTT is light weighted protocol, with minimal overhead (just a 2-byte header), makes it much more efficient than HTTP-based protocols such as REST.

2. Optimized for High Latency/Unreliable Networks

MQTT can withstand poor network conditions. The Quality of Service (QoS) levels allow flexibility in how reliably messages are delivered:

• QoS 0: Ensures minimal overhead and latency but sacrifices guaranteed delivery.
• QoS 2: Provides the highest reliability for mission-critical messages.

3. Efficient Power Consumption

MQTT is a perfect fit for power efficiency IoT devices. Though it allows devices to maintain long-lived connections with minimal bandwidth usage, it consumes less power by its ability to deliver messages efficiently with very minimal overhead.

4. Easy Scalability

Since MQTT is a lightweight publish/subscribe protocol, it supports many clients with minimal server load. MQTT brokers like Mosquitto can handle hundreds of thousands of clients and millions of messages with the proper configuration.

5. Support for Persistent Connections

MQTT allows devices to maintain long-lived connections with minimal bandwidth usage, suitable for environments where devices need to stay connected for extended periods, such as industrial monitoring systems.

?Disadvantages of MQTT

1. Not Suited for Large Data Transfers

MQTT is best for small messages. When large payloads (such as images or video streams) need to be transferred, protocols like HTTP or WebSocket may be more efficient.

2. Limited Security

Although MQTT supports secure communication via TLS/SSL, it doesn’t have built-in mechanisms for authentication or encryption. Security must be implemented at a higher layer or through a custom broker configuration.

3. Broker Dependency

The MQTT broker is a single point of failure. If the broker goes down, communication between clients is interrupted. To mitigate this, redundant broker architectures can be used, but that adds complexity to the system.

?MQTT vs. Other IoT Protocols

MQTT vs. CoAP (Constrained Application Protocol)

• Data Size: CoAP is also lightweight but operates over UDP, while MQTT uses TCP. This makes MQTT slightly more reliable but possibly slower than CoAP.
• Message Delivery: CoAP has a simpler design and may be better for use cases where extremely low overhead is critical, but it lacks MQTT’s built-in reliability mechanisms like QoS.

?Benchmark Data: MQTT Performance

Multiple studies have shown that MQTT can transmit messages more than 90% faster than HTTP in bandwidth-constrained environments. Benchmark data shows, MQTT was able to deliver messages in under 30ms in scenarios where HTTP took over 300ms to complete the same transaction. ?

On comparing MQTT and CoAP under scenarios with frequent message exchanges revealed that MQTT consistently used 10-15% less power and achieved lower latency in similar network conditions due to its use of TCP and persistent connections.

?Conclusion

MQTT has established itself as the go-to protocol for IoT applications due to its lightweight nature, efficient bandwidth usage, and ability to work in unreliable networks for telemetry and real-time data monitoring applications.