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For this demonstration of the MQTT protocol.
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We need a broker and at least one publisher and one subscriber.
For the broker,
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there are many choices:
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First, we could set up our own.
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That's possible.
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But I won't be the choice for this demonstration because we want to keep things very simple,
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so we'll use a public broker.
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A public broker is a broker available in an Internet to test the MQTT protocol.
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They are maintained by companies or foundation and are sometimes open source.
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The most famous is probably mosquitto, but there are also others like HiveMq that we might also use
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later.
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Right.
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So for the broker, that will be very easy.
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Now, we also need to set up an MQTT client for the subscriber and the publisher.
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There are also many clients available.
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Some clients can be directly controlled with a Command Line Interface in the terminal.
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Another option is to set up an MQTT using node-red.
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...
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And finally, some other clients have a standalone user interface.
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I don't really have a favorite choice among all these methods, so I will show you two possibilities.
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The first one is using node-red,
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because, we'll use Node-red anyway later in this course.
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And the second one is the MQTT Explorer Client that we find very useful in some situation and often
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a bit quicker to set up than node-red.
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...
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But whatever MQTT client we're using, the configuration is always the same.
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We need to specify:
- whichever we want to connect to,
- the login and password for the connection,
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- the topic we want to target:  if we are a subscriber, the topic refers to the topic we want to read and
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if we are a publisher, then it refers to the topic we want to write.
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- And one last thing, only for the publisher.
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It needs to provide a message to send to the topic.
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So let's try that first with the node-red MQTT client.
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Then after I will also make a demonstration with the MQTT Explorer client.
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In both cases, we're going to use the public broker called Mosquitto.
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Right.
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Let's start with node-red.
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I'm not going to explain how to install it.
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We've done it before,
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and I just remind you that you can find all the useful explanation at the beginning of this course in
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the HOW TO section.
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For this demonstration, I assume that you're already logged on the node-red user interface.
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Great.
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We need to find 2 nodes, one for the publisher and one for the subscriber.
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We can look for the MQTT node in the filter field here.
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"MQTT out" is our publisher and "MQTT in" is our subscriber.
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So I place them in the center and I will just change their names because right now it's a little bit
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confusing.
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And we need to imagine here, that there is the Mosquitto broker in the middle.
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That is just a comment.
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The node
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configuration is pretty easy.
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As we said earlier, we need to configure the publisher and subscriber with the broker address, the
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credential for the connection, and the topic.
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Great.
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Let's start with the publisher. In the server section,
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I need to add a new MQTT broker.
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I give it a name.
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And I specify the address which is "test.mosquitto.org" on port 1883.
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For this public broker there is no credentials, so we don't have to fill any of these fields.
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So now the new mosquito broker is configured and we just have to specify the topic here.
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I will use the topic LoRaWAN.
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Okay.
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This publisher is ready.
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The only thing missing is to feed this node with the message we would like to send.
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For that we take a new node called "Inject Node".
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We could leave it like this. By default,
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it will send a timestamp, so the actual time.
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But in my case I will change it to send a string instead.
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Let's say "hello".
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Okay, We are done with the publisher part.
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Now, for the subscriber, I also need to configure the broker.
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We simply reuse the Mosquitto broker that we registered previously and I specify the topic.
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In my case, it's LoRaWAN.
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Great.
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The subscriber is ready as well.
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And the last thing is to direct the output of the subscriber to the debug node.
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Thanks to the debug node, anything coming out of this node will be written in the debug message window
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and right when the flow will be deployed.
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So I deploy my flow.
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I can see that both my publisher and subscriber are connected to the broker.
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That's a good news.
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I click on the debug window here and I can try to publish a message.
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Yes, I can see here that as soon as I've published the message on the LoRaWAN topic, then it's sent
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to all subscribers.
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So this one, in that case, great.
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We are done with this MQTT demonstration with node-red.
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This is saved already, so I don't need to do anything else.
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But I'm going to change the tab name in case we need it later.
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I call it MQTT Mosquitto.
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Okay, so that's the node-red client demonstration.
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I'm also going to show you how it works a more user friendly MQTT application.
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There are a lot available so we could use any of them.
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But MQTT Explorer is free, open source, and supports many platforms.
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We can download the installation file from their website and it's very easy to set up.
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Once we've launched the User Interface, we end up on the connection tab.
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This is where we enter the broker address and the credential.
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There is already two brokers registers and the second one is the test mosquitto broker.
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Everything is already configured properly.
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If not, then we just add a new connection at the top and fill in this field with the same information.
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To define the topic we want to subscribe to,
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we need to go on the advanced section.
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There we can see that the default configuration subscribes to all topic of the mosquitto public broker.
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While it would be a good idea when we only use our own broker, using the # wild card on a public broker
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is complicated because we receive thousands of messages on our clients.
Actually we'll receive all mixed
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messages sent by all publishers around the world.
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That's huge.
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Let's try anyway.
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I go back on the connections section and I connect the client to the broker.
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Great.
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I can see all topics and messages used.
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Now I will disconnect and go back on the advanced section to subscribe only on a topic called LoRaWAN.
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First, I delete the # topic and I can also delete the $SYS topic.
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SYS is a specific topic to subscribe to some information on the broker itself, like the number
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of client connected, the number of topic available and so on.
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You can leave it if you want, but for this demonstration we don't need it, so I will delete it.
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Now I can add the LoRaWAN topic.
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Go back and save my configuration.
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On the left there is my subscribe section.
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So if anything arrives on the topic LoRaWAN, it should be here.
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And on the right, I've got the publisher section.
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I enter a value in the topic LoRaWAN.
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Let's say hello.
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And there we go.
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We receive it on the subscriber.
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The nice thing with MQTT Explorer is that we can even plot these values if we send numbers.
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For example, if I send several data is like 2, then 5,
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and 4.
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I can click on the history and have a quick overview of the previous data received on this topic.
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We are done with the basic functionalities of both MQTT clients.
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Now, what we would like to do is exactly the same demonstration, but this time we're going to connect
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the client to our LoRaWAN server.
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Thanks to that, we'll get the uplink messages of our devices and we'll also be able to send downlink
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messages.