Rak 7258 - Down link data encoding Question

LPWAN Developer Gateways / Concentrators
#1

Hi All,
I have a Rak 7258 and I am using the on-board Lora-Server.
I am sending downlink messages to the server by MQTT to the downlink topic.

I have set my application server to encode/decode as HEX string.

The downlink message I want to send to the node is needs to be finally this ascii string at the node application:

GPIO,2,1

I see that I cannot sent that to the Rak lora Server in this format as it will not send a down link, so I convert it to HEX bytes:

47 50 49 4f 2c 32 2c 31

Now the Rak sends a downlink, great, however when I look at the payload that was sent I see this:

“FRMPayload”: "01 EA 0A F5 82 D3 A7 BC

The Rak config manual - RAKLoRaWANIndustrialGatewayWisDeviceSeriesRAK7249/58Version1.7|October,2019

says (on page 37)

plaintext,willbeencryptedbyLoRaServer

Can anyone help me understand this? do I need a special decoder on my node? how can I just send plain HEX bytes in the downlink?

Cheers
P

#2

First you really shouldn’t send printable strings, but more efficiently encoded messages. In addition to the payload body itself, you also have most of the range of the port to work with, excluding reserved values of 0 and above some number in the 200’s.

“FRMPayload”: "01 EA 0A F5 82 D3 A7 BC

LoRaWan AES encrypts data when it is transmitted. The FRMPayload is a still-encrypted portion of the packet containing your application payload, but it is not yet your application payload. It will only become your application payload again after decryption by the LoRaWan stack on your node.

Ultimately your question comes down to understanding how the LoRaWan stack of your node handles downlinks and presents them to the application part of your node - this is really a question about your node.

#3

Thanks Chris.
I see now, I found out that the node I was working on does not support downlink so I guess I will go back to trying something else.
So far the RaK gateway has been very reliable, Im going to try some work with the Wisblock nodes next,
Cheers
P

#4

FYI if you want to easily simulate a downlink you can do it via the Built-in Application server.

#5

Hi @Chirpper I’m trying to send a downlink to my device, but I’m not abble to do this. Could you help me saying or showing how you configured you RAK 7258?

#6

Hi, Are you using the built-in loraserver ? or TTN, chirpstack etc?
P