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MQTT.Cool - MQTT Throttling Demo - HTML Client

The MQTT Throttling Demo is a demonstration of MQTT.Cool data throttling using simulated sensors by MIMIC MQTT Simulator.

Live Demo

Live Demo

View live demo


The MQTT Throttling Demo uses the MQTT.Cool Web Client API to show how MQTT.Cool can be used to send real-time telemetry data through the Web and, very important, how incoming update flow can be further manipulated in terms of bandwidth and frequency. You can read more details in the article "Throttling MQTT Data".

The demo leverages the flexibility and power offered by MIMIC MQTT Simulator, by which it is extremely easy to generate an unlimited range of simulated scenarios.

In this case, we simulate a set of sensors that:

  • Continuously detect the distance between themselves and fictitious moving objects.
  • Publish real-time data to a specific topic of the MQTT broker listening at tcp://

To keep things simple, distances vary as sine waves. Furthermore, waves are generated with different frequencies to show different traffic patterns.

The web application submits an MQTT subscription for each sensor/topic to receive real-time data and displays them on the relative chart.

For each chart, a frequency selector can be handled to dynamically change the maximum update rate of incoming messages of the related sensor.

A max bandwidth selector allows you to change the bandwidth globally used by subscriptions.

To make you appreciate the difference between throttled and not-throttled data, two kinds of connection are employed:

  • A shared connection, whose MQTT subscriptions change the update rate according to the frequency slider. Messages are displayed as red points on the charts.
  • A dedicated connection, whose MQTT subscriptions receive data as they come, which means that any change on the sliders does not affect how data flow from the MQTT broker to the web page. Messages are displayed as continuous orange lines.

You can see how the bandwidth and frequency constraints act on different levels. The bandwidth constraint globally applied to the shared connection. On the other hand, the frequency constraint is applied to each MQTT subscription individually. Both the constraints set an upper bound, which is dynamically managed by MQTT.Cool. Note that the updates are not queued and delayed, but resampled and conflated. In other words, when a subscription has a chance to be updated (based on a round-robin algorithm), it will receive the very latest available message, not an old one.

Overall Architecture

Here the overall architecture of the demo:


If you want to install a version of this demo pointing to your local MQTT.Cool, follows these steps.

  • Download MQTT.Cool from the web site download page and unpack it (see the Quick Start section of Getting Started Guide for more details).
  • Launch the MQTT.Cool server.
  • Download this project.
  • As the latest version of the MQTT.Cool JavaScript library is always available through unpkg, it is hot-linked in the html page.
  • Deploy this demo on MQTT.Cool (used as Web server) or in any external Web server. If you choose the former, create a folder with name such as mqtt-throttling under the <MQTT.COOL_HOME>/pages folder, and copy there the contents of src/web of this project.


The demo assumes that the MQTT.Cool server is launched from localhost, but if you need to target a different server, search in src/web/js/app.js this line:

const MQTT_COOL_URL = 'http://localhost:8080';

and change it accordingly.


Open your browser and point it to http://localhost:8080/mqtt-throttling, or to the address according to the host and/or the name of the folder where you deployed the project.

Immediately, the gauges in the web page reflect updates according to the received real-time metrics.

See Also

MQTT.Cool Compatibility Notes

  • Compatible with MQTT.Cool SDK for Web Clients version 1.2.1 or newer.
  • Compatible with MQTT.Cool since version 1.2.0 or newer.


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