MQTT Protocol and Brokers: A Comprehensive Guide to IoT Communication using PUB SUB Mechanism

What is MQTT?

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.




Who invented MQTT?
MQTT was invented by Dr Andy Stanford-Clark of IBM, and Arlen Nipper of Arcom (now Eurotech), in 1999.


Where is MQTT in use?
MQTT has been widely implemented across a variety of industries since 1999. 

Is MQTT a standard?

v5.0 and v3.1.1 are now OASIS standards (v3.1.1 has also been ratified by ISO).

How does MQTT relate to SCADA protocol and MQIsdp?

The “SCADA protocol” and the “MQ Integrator SCADA Device Protocol” (MQIsdp) are both old names for what is now known as the MQ Telemetry Transport (MQTT). The protocol has also been known as “WebSphere MQTT” (WMQTT), though that name is also no longer used.

Are there standard ports for MQTT to use?

Yes. TCP/IP port 1883 is reserved with IANA for use with MQTT. TCP/IP port 8883 is also registered, for using MQTT over SSL.

Does MQTT support security?

You can pass a username and password with an MQTT packet in V3.1 of the protocol. Encryption across the network can be handled with SSL, independently of the MQTT protocol itself (it is worth noting that SSL is not the lightest of protocols, and does add significant network overhead). Additional security can be added by an application encrypting data that it sends and receives, but this is not something built-in to the protocol, in order to keep it simple and lightweight.


How does it works?

Like any other internet protocol, MQTT is based on clients and a server. Likewise, the server is the guy who is responsible for handling the client’s requests of receiving or sending data between each other.
MQTT server is called a broker and the clients are simply the connected devices.

• When a device (a client) wants to send data to the broker, we call this operation a “publish”.
• When a device (a client) wants to receive data from the broker, we call this operation a “subscribe”.

In addition, These clients are publishing and subscribing to topics. So, the broker here is the one that handles the publishing/subscribing actions to the target topics.
Example:

Let’s say there is a device that has a temperature sensor. Certainly, it wants to send his readings to the broker. On the other side, a phone/desktop application wants to receive this temperature value. Therefore, 2 things will happen:

The device defines the topic it wants to publish on, ex: “temp”. Then, it publishes the message “temperature value”.

The phone/desktop application subscribes to the topic “temp”. Then, it receives the message that the device has published, which is the temperature value.

Again, the broker role here is to take the message “temperature value” and deliver it to phone/desktop application.MQTT Components:

That takes us to the MQTT components, which are 5 as follows:

Broker, which is the server that handles the data transmission between the clients.

A topic, which is the place a device want to put or retrieve a message to/from.

The message, which is the data that a device receives “when subscribing” from a topic or send “when publishing” to a topic.

• Publish, is the process a device does to send its message to the broker.
• Subscribe, where a device does to retrieve a message from the broker.

How many devices you can connect to a broker?

The number of connected devices “clients” to the broker depends on the broker service provider.

In fact, it can reach a massive number of clients those are publishing and subscribing all the time. But the amazing part of this isn’t only the huge number of these connected devices but also any the fact that any device can get any other device’s data at any time. As a result, the applications based on these quickly shared data are limitless.

But one question here, what if you used HTTP protocol to share these data between devices? I would say that’s really a bad idea  

Why not HTTP?

HTTP is slower, more overhead and power consuming protocol than MQTT. So, let’s get into each one separately:

Slower: because it uses bigger data packets to communicate with the server.

Overhead: HTTP request opens and closes the connection at each request, while MQTT stays online to make the channel always open between the broker “server” and clients.

Power consuming: since it takes a longer time and more data packets, therefore it uses much power.

Broker in the IoT system components

In the previous IoT blog, we discussed the IoT system in details and its 4 components. I would recommend you go through it if this is your first time reading about IoT.

One of these components was the IoT platform. It’s responsible for connecting the devices together, indeed.

Though, the IoT platform is just a cloud-based software that implements a broker server and some software with GUI to allow user control and monitor his connected devices.

Therefore, MQTT broker is included implicitly inside the IoT platform.

But we won’t use an IoT platform in our upcoming IoT blogs and tutorials.

That’s because we will only connect a few devices for small projects. So, IoT platform isn’t needed here. But it was necessary to get you a bit knowledge about it.

Which broker to use?

There are many brokers that implement the MQTT protocol. One of the most popular and commonly used is the mosquito broker.

Mosquitto broker

But rather than using the Mosquitto on a local PC, you will need to use a cloud-based server that implements the Mosquitto broker. That’s necessary to make your IoT projects controllable over the internet.

Mosquitto is an open source message broker that implements the MQTT protocol. It’s lightweight and suitable for use on all devices from a low power single board like Arduino, ESP8266 to full computers and servers.

HiveMQ:HiveMQ is a MQTT broker. A broker is basically the server part in the MQTT communication. Beside the common broker functionality HiveMQ provides some extended functionality like building (high availability) clusters, deep integration to your application- and IT infrastructure and enhanced security.

Pre-Installation requirements

Windows, Linux and Mac OS X are supported environments. Java 11 or newer is required.

1. Installation
2. Download the latest HiveMQ archive
3. Unpack
4. Run

Windows

1. Unpack: Extract the Zip-archive using your file browser into a directory of your choice
2. Run: Change to the folder bin and run the run.bat file by double clicking on it.

Linux/Mac OS X

Unpack:

1	unzip hivemq-.zip

Run:

1 2 3

cd <hivemq_install_directory>/bin chmod 755 run.sh ./run.sh

MQTT Public Brokers

Field	Value
Address	mqtt.flespi.io
Port	1883 (TCP), 80 (WebSocket), 8883 (SSL), 443 (Secure WebSockets)
Type	flespi
Info	Requires signup/username, information page, REST API, MQTT 5.0 compliant

Field	Value
Address	iot.eclipse.org
Port	1883, 80 (WebSockets), 443(WebSockets+SSL)
Type	mosquitto
Info	Web page, Xively statistics, topics and HTTP bridge

Field	Value
Address	test.mosquitto.org
Port	1883, 8883 (SSL), 8884 (SSL), 80 (WebSockets)
Type	mosquitto
Info	Web page, Xively statistics, topics and HTTP bridge

Field	Value
Address	broker.hivemq.com
Port	1883, 8000 (WebSockets)
Type	HiveMQ
Info	Information page, statistics and dashboard

Field	Value
Address	www.cloudmqtt.com (Note: actual host varies, see dashboard)
Port	18443, 28443 (SSL)
Type	mosquitto
Info	Requires signup/username and password, pricing (free plan available), documentation

Field	Value
Address	mqtt.dioty.co
Port	1883 (MQTT), 8883 (MQTT+SSL), 8080 (WebSockets), 8880 (WebSockets+SSL)
Type	mosca
Info	Free – requires signup/username and password, documentation, includes mobile IoT app (iOS and Android)

Field	Value
Address	mqtt.swifitch.cz
Port	1883 (MQTT)
Type	mosquitto
Info	Free, it is mostly running for Swifitch project, but you can use it too for testing your IoT or whatever ;), it is running on Raspberry Pi professional VPS

Field	Value
Address	broker.bevywise.com
Port	1883 (TCP), 8443 (WebSockets)
Type	Bevywise
Info	Web page. Secure. Need to sign up to view your devices. Use MQTT Authentication in your devices to connect securely. Free trial with unsecure ports (see https://devicemanager.bevywise.com/help)

Field	Value
Address	mqtt.fluux.io
Port	1883 (TCP), 8883 (TLS)
Type	ejabberd
Info	Free – no registration required, MQTT 5.0 compliant

Field	Value
Address	console.solace.cloud (MQTT hostname varies, see dashboard)
Port	TCP, TLS, WS, WSS: varies per instance
Type	solace
Info	Requires sign-up, free plan available (50 connections), getting started, docs

Field	Value
Address	node02.myqtthub.com
Port	1883 (TCP), 8883 (SSL), 443 (Web, REST and API interface)
Type	MyQtthub
Info	Requires signup/username, information page, REST API

Sources:  

 https://www.hivemq.com/developers/getting-started/

https://www.hivemq.com/developers/getting-started/

https://image.slidesharecdn.com/introductionmqtten-140327003613-phpapp01/95/introduction-mqtt-in-english-9-638.jpg?cb=1395880666

http://www.steves-internet-guide.com/mosquitto-broker/

https://www.google.com/

http://mqtt.org/projects