View source for TTN V3 integrated into MQTT server

=Introduction=
The Application Server exposes an MQTT server to work with streaming events. In order to use the MQTT server you need to create a new API key, which will function as connection password. You can also use an existing API key, as long as it has the necessary rights granted.

=Create device steps at MQTT=
The user creates a new API KEY after creating a device on TTN V3.

Then copy the password and open MQTT.fx.

Fill in Broker Address and Broker port.
[[File:V3 MQTT1 .png|600px|none|thumb|]]

Fill in the username and password into MQTT.
[[File:V3 MQTT2.png|600px|none|thumb|]]

The Application Server publishes uplink traffic on the following topics:

    v3/{application id}@{tenant id}/devices/{device id}/join
    v3/{application id}@{tenant id}/devices/{device id}/up
    v3/{application id}@{tenant id}/devices/{device id}/down/queued
    v3/{application id}@{tenant id}/devices/{device id}/down/sent
    v3/{application id}@{tenant id}/devices/{device id}/down/ack
    v3/{application id}@{tenant id}/devices/{device id}/down/nack
    v3/{application id}@{tenant id}/devices/{device id}/down/failed
    v3/{application id}@{tenant id}/devices/{device id}/service/data
    v3/{application id}@{tenant id}/devices/{device id}/location/solved

Note:
Remember that the format of these topics for The Things Stack Open Source would contain {application id} instead of {application id}@{tenant id}. 

[[File:V3 MQTT3.png|600px|none|thumb|]]

While you could subscribe to all of these topics separately, for the simplicity of this tutorial we use # to subscribe to all topics, i.e. to receive all uplink traffic.
[[File:V3 MQTT4.jpg|600px|none|thumb|]]

Downlinks can be scheduled by publishing the message to the topic v3/{application id}@{tenant id}/devices/{device id}/down/push.

Note:
Remember that the format of this topic for The Things Stack Open Source deployment would be v3/{application id}/devices/{device id}/down/push. 

Instead of /push, you can also use /replace to replace the downlink queue. Replacing with an empty array clears the downlink queue.
Example:
[[File:V3 MQTT5.png|600px|none|thumb|]]

To send an unconfirmed downlink message to the device dev1 in application app1 in tenant tenant1 with the hexadecimal payload BE EF on FPort 15 with normal priority, use the topic v3/app1@tenant1/devices/dev1/down/push with the following contents:

Note:
Use this handy tool to convert hexadecimal to base64. 
[[File:V3 MQTT6.png|600px|none|thumb|]]