MQTT | What is MQTT | MQTT in Depth | QoS | FAQs | MQTT Introduction

What is MQTT?

MQTT, originally standing for MQ Telemetry Transport, is now simply referred to as MQTT and is no longer considered an acronym. It is a lightweight, publish/subscribe messaging protocol designed for constrained devices and low-bandwidth, high-latency, or unreliable networks. It was developed by IBM and Arcom (now Eurotech) to facilitate communication in such environments.

Why MQTT?

MQTT was initially designed for scenarios where sensor nodes communicate over unreliable or high-latency networks. A classic example is oil and gas pipeline monitoring, where pipelines pass through remote areas with poor connectivity. Sensor nodes, often battery-powered with limited resources, need an efficient protocol to send data over satellite or low-bandwidth links.

However, MQTT is no longer limited to industrial use cases. It is widely used in IoT, mobile applications, and M2M (Machine-to-Machine) communications. Even Facebook Messenger uses MQTT due to its efficiency in managing connectivity changes and conserving battery life on mobile devices.

Key Features of MQTT

1. Quality of Service (QoS)

MQTT provides three levels of QoS to ensure reliable message delivery based on network conditions:

• QoS 0 (Fire and Forget): No acknowledgment from the broker; fastest but prone to message loss.
• QoS 1 (At Least Once): Message is acknowledged by the broker, ensuring delivery at least once.
• QoS 2 (Exactly Once): Ensures the message is delivered once and only once, avoiding duplication.

2. Last Will and Testament (LWT)

This unique feature allows a client to provide a “last will” message upon connection. If the client disconnects unexpectedly, the broker sends this message to other clients, helping monitor device status.

3. Clean Session

MQTT sessions store state information, allowing clients to reconnect without losing messages. If “clean session” is disabled, the broker retains subscriptions and pending messages for disconnected clients.

4. Retained Messages

A retained message is the last known good message stored by the broker for new subscribers. This is useful for scenarios where new clients need the latest sensor data upon subscription.

5. Message Queue

MQTT uses a queue-based system to store and forward messages, ensuring decoupled communication between publishers and subscribers.

6. Publish/Subscribe Model

The publish/subscribe architecture enables efficient data distribution:

• Decouples senders (publishers) and receivers (subscribers)
• Supports multiple subscribers for a single topic
• Scales well for large IoT applications

FAQs on MQTT

What is MQTT?

MQTT is a lightweight, publish/subscribe messaging protocol for M2M and IoT communication over low-bandwidth networks.

What is an MQTT broker?

An MQTT broker is a server that handles message routing between publishers and subscribers.

Why is MQTT used in IoT?

MQTT is efficient, minimizes battery and bandwidth usage, supports QoS, and works well in poor network conditions.

Does MQTT require the internet?

No, if all devices are on the same local network. However, for remote access, an internet-connected MQTT broker is required.

Is MQTT secure?

Yes, MQTT supports TLS/SSL encryption and authentication mechanisms.

Does MQTT use TCP or UDP?

MQTT primarily uses TCP/IP, but MQTT-SN (Sensor Networks) enables UDP communication.

What port does MQTT use?

• 1883: Default MQTT TCP port
• 8883: Secure MQTT over TLS/SSL

Can MQTT be hosted in Docker containers?

Yes, MQTT brokers like Mosquitto can be deployed in Docker environments.

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