Send multicast message by using MQTT

Hi friends, just a quick question. I am planning to use MQTT to send multicast message to the devices created in Chirpstack platform. However, I am unable to find out topic template for setting multicast message. The guide found from website is about using MQTT multicast function in REST API.

Appreciate very much if someone can share relevant resource or information.


This is (currently) not possible.

Many thanks. Finally I managed to send multicast msg via API. However a new question raised…

After initializing, I am unable to send any multicast msg until at least one of devices (contained in multicast group) actively sends a message to app server. In my case, I need all devices keep silent after successfully joining network, which means no one will actively sends a message to application server until I ask them to do so. But I still need to send multicast msg during silent period.
Is there any way to force multicast sending even no device has sent a message to application server?

Hi All, another question I would like to ask. In my application, I tried to send multicast message with DR=0, however stack responds that “exceeds maximum frame payload size. Max frame payload size =0”. If I change DR to 1, 2,3,4, the message can be sent without problem.

I am using frequency band “CN470”. Previously, I can manage to send multicast with DR=0 (Chirpstack version = 2.6 or 2.8).

Is there any changes or new regulation applied to multicast message?

Have you consulted the Regional Parameter spec version which is implemented by your device. It contains the tables with the max. payload sizes per data-rate.

Hello, is it now possible to send a multicast message via basic MQTT interface?
If yes, how does the downlinkpath look like?

Best regards Corsin Obrist

Hi @chirpstack_obrist

Not possible to send multicast messages via a basic MQTT interface.

Use REST API to send multicast messages.

@sagarpatel @brocaar Thanks for the answer.

Do you have a example for the python API?
I have seen this one: Python examples - ChirpStack open-source LoRaWAN<sup>®</sup> Network Server
and this also works nice for normal downlinks but I cant find a example for setup a multicast group and add devices to it and then send messages via the multicast group.

I also found the locahlhost http://localhost:8080/api but I don’t get how to implement these functions in python?

best regards