Getting started with MQTT (Mosquitto and Paho)

As part of the Eclipse IoT Challange 2016, we shall use as many open source implementations of IoT standards, and Eclipse based technologies as we can. For communication we chose MQTT and its open source broker (Mosquitto) and client (Paho) implementation.


Here is a short description about MQTT from its homepage:

MQTT stands for MQ Telemetry Transport. It is a publish/subscribe, extremely simple and lightweight messaging protocol, designed for constrained devices and low-bandwidth, high-latency or unreliable networks. The design principles are to minimise network bandwidth and device resource requirements whilst also attempting to ensure reliability and some degree of assurance of delivery. These principles also turn out to make the protocol ideal of the emerging “machine-to-machine” (M2M) or “Internet of Things” world of connected devices, and for mobile applications where bandwidth and battery power are at a premium.

As you can find out, MQTT architecture consists of brokers and clients. Brokers interconnect clients through different topics. All clients receive the messages published to the topic they are subscribed for. A message can be anything that is convertible to a byte array. This way an N:N connection cardinality can be easily achieved as depicted on the next figure.

Different open source and proprietary implementations of MQTT brokers and clients exist in most programming languages (C, C++, Java, .NET, Python, JavaScript, etc) . We use Mosquitto as a broker, and Paho as a client implementation.


The Mosquitto broker is the focus of the project and aims to be a lightweight and function MQTT broker that can run on relatively constrained systems, but still be powerful enough for a wide range of applications.

To get started with Mosquitto visit its website at Download and install it on your computer. We use the binary compiled for Ubuntu as it works seamless.

The default address of the running Mosquitto service is tcp://localhost:1883, on localhost over TCP protocol at port 1883.

However, if you would not like to install Mosquitto yourself, there are two Mosquitto brokers publicly available online:

  1. One that is operated by Mosquitto website itself at
  2. One that is operated by Eclipse at tcp://


The Paho project provides open-source client implementations of MQTT and MQTT-SN messaging protocols aimed at new, existing, and emerging applications for Machine‑to‑Machine (M2M) and Internet of Things (IoT). 

To get started with Paho visit its website at and look for the client sample codes. We use Java Client through Maven.

 Demo time

Now we will provide some sample code snippets in Java which demostrate a “Hello World” message exchange between two clients. We use Maven for dependency management so the pom.xml is provided as well.

The code snippets are available at

Publisher (sender) client sample:

Subscriber (receiver) client sample:

Last but not least, the pom.xml that is necessary for Maven:


So far we have been satisfied with Paho and Mosquitto since they provide an open source implementation of the lightweight messaging protocol MQTT.

Happy coding!

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