Multicast Downlink to XDOT devices

ChirpStack Application Server
1

Hi,

Thank you for this great work. I would like to send a multicast downlink message to multiple XDots through a single Multitech gateway. From your previous post, I understand that I should setup a multicast node using LoRa AppServer (using ABP and Class C) and configure all of my nodes with this multicast configuration (DevAddr, NwkSKey, AppSKey, etc…) to send a multicast downlink. However, XDots have factory defined DeviceEUI (which cannot be changed). So, how can I setup multiple XDOTs to have the same DevAddr or send a multicast message to multiple XDots with different DeviceEUI ?

Thanks a lot

2

I think what you could do is generate a random one which is known to LoRa App Server and your application, but unknown to the xDot. During the multicast transmissions, the DevEUI is not used for addressing (only the DevAddr), so this should not cause any issues.

1 Like
3

Thanks a lot. That seems to have worked. Now I can successfully receive downlink multicast messages at all XDots. However, now, when one of these XDOTs sends an uplink message, I see that the message is registered under a different device in the app-server device frame logs, since all devices share the same DevAddr (which is the network address in this case). What can be a solution around it? Thanks again…

4

Brocaar, thanks a lot for your support.Your suggestion helped me. Now I can successfully receive downlink multicast messages at all XDots.
However, now, when one of these XDOTs sends an uplink message, I see that the message is registered under a different device in the app-server device frame logs, since all devices share the same DevAddr (which is the network address in this case). Also, when i send a downlink unicast message, to a particular XDot, the packet is received at the wrong XDOT, as they share same DevAddr.

How to fix this? What can be a solution around it? Thanks again…

Should I open up a new question thread or just ask this question here in this thread as it is related to my previous problem. Thanks

5

A multicast device stores two device addresses. One is used for multicast downlink, the other is for individual communication. Depending multicast or unicast, it will use one or the other DevAddr (and currently LoRa App Server will then use one or the other associated DevEUI).

6

Thanks for your reply. Yes, a multicast device should essentially have two device address, however, I can currently notice only one device address. For all uplink and downlink unicast messages, only the multicast address is always used currently, which leads to packet reception at a different device than the one intended. How do you advise me to assign two device addresses to a single device, and to enable both multicast and unicast communication simultaneously? Thanks a lot

7

I don’t know. That depends on your device firmware. Each vendor implements this in a different way.

8

No, I mean at the LORA App Server side, how do i configure one device to have two different device addresses? Currently, when I create a device using the UI, it lets me specify only 1 device address for a specific Device EUI. There doesn’t seem a way to define two different device addresses for a particular device in the UI. By the way, I am using multitech xDots as end-devices. What do you suggest? I really appreciate your help. Thanks

9

That is currently not possible (yet).