15 Frequently Asked MQTT Questions

Written by The HiveMQ Team

Category: FAQ MQTT

Published: October 22, 2019


We at HiveMQ are experts in the field of MQTT. This is why we collected 15 frequently asked questions about MQTT for you:

What is MQTT in IoT?

MQTT is the standard protocol for messaging and data exchange for the Internet of Things. The protocol uses a publish/subscribe architecture. The technology provides a scalable and cost-effective way to connect devices over the Internet. It is able to deliver data over the Internet in near real-time and with guarantees of delivery. MQTT is designed for IoT devices - lightweight, which enables low-cost device communication.

Who uses MQTT?

MQTT is used by many major companies, especially in the automotive, industry 4.0, transport, and entertainment sectors. MQTT is used for data exchange between constrained devices and server applications. It keeps bandwidth requirements to an absolute minimum, handles unreliable networks, requires little implementation effort for developers, and is, therefore, ideal for machine-to-machine (M2M) communication.

How does MQTT work?

MQTT follows the Publish/Subscribe paradigm. The sender (Publisher) and receiver (Subscribers) of messages communicate via so-called topics and are decoupled from each other. The connection between them is handled by the broker. The task of the broker is to filter all incoming messages and distribute them correctly to the subscribers. A client doesn’t have to pull the information it needs, the broker pushes the information to the client whenever something new is available.

What is an MQTT client?

An MQTT client is any device (from a microcontroller to a full-fledged server) that operates an MQTT library and connects to an MQTT broker over a network. Each MQTT client can be both publisher and/or subscriber.

What does an MQTT broker do?

An MQTT broker is at the heart of any MQTT deployment. Depending on the implementation, a broker can handle up to millions of concurrently connected MQTT clients. The broker is responsible for receiving all messages, filtering the messages, determining who is interested in each message, and sending the message to these subscribed clients.

What is an MQTT topic?

Communication in MQTT is based on the topic principle. An MQTT topic is a UTF-8 string that the broker uses to filter messages for each connected client. To receive messages, the client must subscribe to the topic. A topic can have one or more topic levels. Each topic level is separated by a slash (Topic Level Separator).

Is MQTT secure?

MQTT is designed to allow very secure communication. As an application layer protocol it introduces extensive device authentication and authorization possibilities. The underlying TCP/IP transport protocol can add additional security via TLS encryption.

Is MQTT open source?

MQTT is an open protocol that is standardized by OASIS and ISO (ISO/IEC 20922:2016).

What is the difference between HTTP and MQTT?

MQTT is a data-centric, extremely lightweight, binary protocol. Due to its minimal packet overhead, MQTT excels when transferring data over the wire in comparison to document-centric protocols such as HTTP. Unlike HTTP, which is based on a request/response pattern, MQTT provides push-based communication. This push is made possible via standing TCP connections.

What is the difference between AMQP and MQTT?

AMQP is bi-directional, synchronous peer-to-peer messaging protocol that has high demands for implementation complexity and a larger network overhead. It is a binary wire protocol, build as replacement for message middleware with main focus on interoperability between different vendors via rich featuring and several exchange patterns.

MQTT is a binary protocol with strength in simplicity to be ideal for mobile IoT app and M2M. It provides the pub/sub messaging pattern and is designed for resource-constrained devices, low bandwidth and high latency networks. MQTT is specified by the official OASIS Standard.

Does MQTT use WebSockets?

With the right broker implementation that supports native WebSockets, MQTT with 100% of its features set can be used via WebSockets. As they provide a bi-directional, ordered, and lossless communication channel via TCP.

Does MQTT use TCP or UDP?

MQTT uses TCP. Due to ordering requirements MQTT over UDP is not possible.

Does MQTT require internet?

Yes, to send or receive messages, the MQTT client must establish a TCP connection to the broker. However, MQTT comes with features specifically designed to cope with unstable network connections, like the broker buffering incoming messages for disconnected clients.

Does MQTT work with Apache Kafka?

Yes, MQTT and Kafka can be integrated with one another. The most efficient way to do so is to use the HiveMQ Enterprise Kafka Extension.

Is MQTT restful?

No. MQTT is not stateless and does not provide a request/response pattern. It is a publish/subscribe application layer messaging protocol that requires a standing TCP connection and transmit messages in an instantaneous, push way.

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