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First, if you want to know more about the MQTT protocol, I advise you to go back to the previous chapter
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where we explain everything about the protocol itself.
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I'm going to use exactly the same diagram for this explanation about the liquidity integration with
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ChirpStack, because it works exactly in the same way.
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So, if you were comfortable with the previous demonstration, this one should be easy.
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What we want to do is to connect two clients, one subscriber for the uplink stream and one publisher
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for the downlink stream.
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And these two clients will be connected to the embedded broker in ChirpStack.
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This broker is already available and enabled because this service was part of the ChirpStack installation
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process.
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Now let's recap what we need to configure for the connection of the subscriber and the publisher.
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First, we need to know the broker address on ChirpStack to reach the broker.
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We need to use the IP address of the LoRaWAN server colon 1883.
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In our case it will be chirpstack.univ-lorawan.fr:1883
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Fine.
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Secondly, we said that we will need credentials to connect to this broker.
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However, the default ChirpStack installation remove these needs of credentials.
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This is absolutely not secure.
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So of course, except for this demonstration, we will never leave it like this.
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If we want to apply some credentials, then before the installation we need to configure the MQTT broker
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called Mosquitto.
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We can do this configuration thanks to the configuration folder from the ChirpStack installation files.
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In this folder we will find a folder for each service.
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In the folder called Mosquitto, which is the name of the broker used in ChirpStack, there is a configuration
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file.
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This file is called mosquitto.conf, and that's in this file that we will need to set the credentials.
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We just have to follow the steps explained in the documentation.
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Third, we need a topic.
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And again, we'll make it easy for the subscriber because we're going to use the #.
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What happens if I do that?
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I will receive all events from all sensors of all applications.
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Of course, if we want the data from a specific device of a specific application, then we need the
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exact topic.
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And again, we'll find this information in the documentation.
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So, let's have a look.
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We go on the ChirpStack website?
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Then in the ChirpStack section, we go on Integrations.
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Then MQTT.
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Here we have the default event topic.
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That is the generic topic we need to subscribe if we want information on an event.
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Application/APPLICATION_ID.
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device/DEV_EUI.
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event/
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EVENT
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APPLICATION_ID needs to be replaced by our application identifier.
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DEV_EUI needs to be replaced by the device EUI in lower case and EVENT needs to be replaced by the type
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of event we are interested in.
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Let's see what we can have: all these ones.
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But of course the most important will probably be the up event.
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Anyway, if you want all of them then we just need to use the wildcard + instead of the keyword EVENT.
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Okay.
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And now for the publisher,
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so to send downlink messages, the information we need is just at the bottom of that page.
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The topic is this one.
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Again, we need to replace the APPLICATION_ID and DEV_EUI with the right values.
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Okay, we're almost done.
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We need one last information for the publisher.
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That's the format of the downlink message.
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The payload of the message has to respect a specific JSON format.
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It's represented here in the documentation.
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Basically, we will specify once again the devEui, whether it's a confirmed or unconfirmed value and obviously
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the data we want to send.
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Great.
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We are now ready. For this demonstration
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my device is going to send a temperature each time I press the user button. On the left, I've got my
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end-device logs and on the right I've got my application and I can check that everything works well.
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Now I want to connect my subscriber and publisher.
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Let's start with Node-red and after I will show you the same demonstration with MQTT Explorer.
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We will need all the information gathered previously so I saved everything here.
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First, let's start with the uplink.
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I come back on my node-red user interface.
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I will keep the previous demonstration so I open a new tab.
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But the flow I'm going to use is very similar, so I copy all nodes of the demonstration we made already
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and I paste them on my new flow.
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I change the name of the tab.
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This demonstration is about an MQTT connection with ChirpStack, so the name will be MQTT ChirpStack.
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The broker is now ChirpStack.
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Again, this is just a comment, so don't worry about that.
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But I think it's clearer if we keep in mind that there is a ChirpStack broker here.
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Okay, so now let's configure the Subscriber.
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So let's click on the subscriber node and I'm going to add a new broker.
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I fill in the server name.
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So chirpstack.univ-lorawan.fr on port 1883.
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This time in the security tab.
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There is nothing to enter because, as we said, ChirpStack doesn't use credentials for its default
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configuration.
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So I just add the broker to the list available when the configuration is done.
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Now I've got the new ChirpStack broker available in the list.
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Great.
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So, now the topic.
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I said I would use the #, but if you want you can specify one.
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And there we go.
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We are done with the Subscriber.
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So we can retry that part and it should work.
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I click on deploy.
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For this test.
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I'm only interested on the subscriber part, so don't look at the publisher because this is just the
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one I copied from our previous demonstration.
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And if I hit the push button of my end device, then I receive the message on my application.
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This message has traveled all the way from my device, my gateway, the Network Server, the Application
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Server, the ChirpStack broker, and finally has been pushed on my Subscriber here.
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If we want the exact topic of our device, then we can find it here in the debug.
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We just need to copy that and change the topic of our subscriber with this one if we wish.
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Okay.
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So the right part of this flow is working for the uplink traffic.
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Now on the left, I'm going to take care of the Publisher part for the downlink traffic.
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So I click on the Publisher here, I choose the ChirpStack broket I've just added.
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And for the topic I just paste, the topic I took from the documentation.
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All right.
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We are done with the Publisher configuration.
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Now I need to select the content of the JSON object to send the downlink message.
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This is what I picked up from the documentation, so I just opened the JSON editor here.
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I erase the content because this is the one used for the other Network Server and I paste it here.
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In this example, I'm just going to send the command 1, which is this payload in base 64.
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On the application port 15 that will turn on the LED on  my end-device.
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Great.
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So let's deploy and test this application.
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Both Publisher and Subscriber are now connected.
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If there were any problems, I would have them reported here.
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So now everything seems fine. For the moment,
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nothing happened.
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And then I press the button to publish the downlink message on the broker. On my debug window,
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I've got a message from the LoRaWAN server telling me that the message has been queued.
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It has not been sent yet because I remind you that this device is a class A end-device, so I need to
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send a message before sending a downlink.
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And for that I need to press my end-device push button. On my application,
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I received two messages, one telling me that an uplink data has been received.
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And another message telling me that my downlink message has been transmitted.
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So, let's go on the device.
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And yes, indeed, I've received 01 and
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I can check that the LED is turned on.
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If I now want to turn it off, then I just need to modify the downlink frame payload in the other injection
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node.
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This time, I want to send the payload "AA==" which is zero coding in base 64.
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Once we send this, the LED will turn off.
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Great.
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So, now we can try to do the same demonstration with MQTT Explorer.
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Now that we know the broker address and the payload to send, it would be quicker. On MQTT Explorer,
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I create a new connection.
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I call it chirpstack.
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And I enter the broker address, again with no credential. For the topic,
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I leave it like this because if you remember, the default topic is #.
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So, that means that if I don't change this configuration, I will receive all messages from all topics.
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I connect my client to the broker and I can send an uplink message from my end-device.
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For that, I just need to press the push button.
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There we go.
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The content is here.
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And I can see the frame payload in base 64.
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That was the uplink traffic.
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So now, how do we send a downlink message?
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We go on the Publisher part.
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We assign the right topic, which is this one, and I enter the JSON object message with the right devEUI,
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the right port and the payload.
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As soon as I publish it, a new message is received from the broker telling us that the message is queued.
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And when I press the push button, I receive two messages one telling me that a new uplink has been
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received and another message telling me that my downlink message has been transmitted.
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And obviously, on the device I've received the command and the LED is now on.
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Great.
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The integration with ChirpStack is now over as we've covered both HTTP and MQTT.
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Please tell us if you've managed to do it on your own server.