MQTT (Message Queuing Telemetry Transport)

MQTT (Message Queuing Telemetry Transport) is a lightweight, stateful publish/subscribe messaging protocol for the efficient transmission of telemetry and event data in distributed systems. It was developed for low-bandwidth, latency-critical, or unstable networks and is today a central communication protocol in the Internet of Things (IoT) and in industrial IT architectures.

In the context of production and quality environments, MQTT enables the standardized, decoupled transmission of process, machine, and quality data between sensors, controllers, manufacturing systems, and higher-level platforms.

Basic Principle and Communication Model

MQTT is based on a broker-centered publish/subscribe model. In contrast to classic request/response protocols, communication does not take place directly between two endpoints, but via an intermediary instance (broker).

Roles in an MQTT System

• Publisher: sends messages on defined subjects (topics).
• Subscriber: subscribes to topics and receives the corresponding messages.
• Broker: mediates messages between publishers and subscribers.

This decoupling of sender and receiver increases scalability, flexibility, and system robustness in distributed architectures.

Technical Characteristics

Topic-Based Addressing

Messages are assigned to hierarchically structured topics. This structure allows fine-grained filtering and segmentation of data streams, for example by plant, line, machine, or process step.

Quality of Service Levels (QoS)

MQTT defines three levels of transmission quality:

• QoS 0: “at most once” – no delivery guarantee.
• QoS 1: “at least once” – at least one delivery.
• QoS 2: “exactly once” – exactly one delivery.

The choice of QoS level influences network load, latency, and delivery reliability.

State Information and Retained Messages

The broker can store the last valid message state of a topic (retained message). New subscribers thus immediately receive the current state without having to wait for a new event.

MQTT in Industrial Production

In manufacturing, MQTT is frequently used as an integration protocol between:

• sensors and edge devices,
• machine controllers,
• manufacturing execution systems (MES),
• enterprise resource planning (ERP),
• quality management and CAQ systems.

In the context of Industry 4.0, MQTT supports horizontal and vertical data integration as well as the real-time transmission of process and quality information.

Relationship with Quality Management

For quality management, MQTT enables the continuous provision of measurement and status data. This allows mechanisms of quality assurance and statistical process control to be supplied with production data in near real time.

The immediate availability of process data supports:

• early detection of deviations,
• automated escalation mechanisms,
• transparent traceability of quality events,
• data-based decision-making processes.

Security and Governance Aspects

MQTT itself is a transport protocol and does not define a complete security architecture. Security mechanisms are typically implemented through:

• TLS encryption,
• authentication and authorization procedures,
• network segmentation,
• broker-side access control.

In regulated environments, these measures must be aligned with the requirements of a quality management system based on ISO 9001 with regard to documented information, integrity, and traceability.

Distinction from Other Protocols

MQTT differs from classic industrial protocols such as OPC UA or HTTP-based interfaces in its low protocol complexity and its strictly event-driven publish/subscribe model. It is not a fieldbus and does not replace real-time control protocols, but serves primarily for the efficient distribution of data at IT and platform level.

FAQ – Frequently Asked Questions About MQTT

What is MQTT in an industrial context?

MQTT is a lightweight publish/subscribe protocol for the efficient transmission of machine, process, and quality data in distributed production and IT systems.

What role does an MQTT broker play?

The broker mediates messages between publishers and subscribers, manages topics, and can store state information.

Why is MQTT relevant for quality data?

MQTT enables the continuous transmission of measurement and status data that can be used in real time for quality assurance and statistical process control.

Is MQTT a quality management system?

No. MQTT is a technical communication protocol. However, it supports data integration within a quality management system.

Standards and Norms

• ISO 9001 – quality management systems
• ISO/IEC 20922 – MQTT version 3.1.1 as an international standard
• OASIS MQTT version 5.0 – current protocol specification

Further Internal Content

• Machine data acquisition as a data source for MQTT-based integration
• Statistical process control (SPC)
• Machine data acquisition in the CAQ system

AI-assisted · Editing and publication: Christian Sedlag · Last updated: 28 October 2026