Multicast: how make it work?

Hi everyone,

I want to send downlink messages from TTS to STM32WL end-nodes (class C enabled) by using multicast. However, I am not sure I have understood all the multicast process, especially on the server side (I work with TTS).

If I have already created an end-node device on my application and it already joined (with the OTAA) and sent uplink to my application, is it possible to add my end-node to a multicast group? If so, I am wondering about the device address. Indeed, when you want to create a multicast group with TTS, it works like an ABP profile. Device address, AppSKey and NwkSKey are asked. But which address and keys should I choose here?

Eager to learn, I am a beginner with multicast protocol! So, any advice is welcome!

Really appreciate your attention, thank you!

1 Like

Hi again,
I forgot to mention that my gateway does not support GPS synchronisation. Is it a prerequisite to multicast?

Hi everyone,

I have managed a successful Multicast session.
My team has worked on this feature and we’ve documented it. But not just that. We also worked on Clock Synchronization, Data Fragmentation and FUOTA.

If anyone wants to learn more about these features, feel free to check:

For all intents and purposes, I am posting the link of our website where you’ll find more information about LoRaWAN: [Home - LoRaWAN]

Hope this will help,


Hello @ogui

I have seen your videos on Youtube - they are great!
Also trying to build Multicast environment with TTN.
But have some strange issue: multicast packet are queued but never rich a gateway interface.
Looks like they silently dropped by Network server.
Can you help me or show a right way?

Thanks a lot!
Kind regards

Hello @olegt,

Thanks for the videos! Really appreciated!

In that situation, I assume the NS doesn’t know the path to use (it doesn’t know the gateway that must emit the downlink frame).
A solution is to specify that path with a JSON payload sent through a MQTT server or a HTTP webhook. The TTN documentation gives that JSON object (see Multicast | The Things Stack for LoRaWAN). However, I faced issues while using that JSON example (wrong place of comma, etc.). I recommend using that JSON example, adapting it to your application and checking the JSON syntax with a JSON tester (a dozen of them are online for free, e.g.:

After that, there is another point to be aware of: the radio settings (frequency and data rate). They must be the same, both in the end-device and on the server for your multicast session.

Hope this will help!


Hi @olegt. I’m happy that you were able to config the downlink path. Before your message, I was skeptical that it was possible. Could you share your JSON config, please? Even though I managed to send the downlink path JSON (with corrections) through curl as the documentation suggests, I keep receiving the “no downlink path available” error. Did you use the MQTT/Webhook or the console (web) to send the JSON? Any detailed info regarding the procedure will be highly appreciated. Best regards!