mdot mqtt message format

[Dave]

I’ve written code to connect to the Conduit’s MQTT server and subscribed to “lora/+/+”. I have an MDOT (MTDOT-915) sending messages to the MQTT server, which I can collect but I need some help sorting out the data values.

The topic name that I’m receiving is

lora/00-80-00-00-00-00-b3-fd/packet_recv

Can I assume that the portion of the topic name between the two slashes (00-80-00-00-00-00-b3-fd) is the unique ID of the MDOT device? If not, how do I identify the device.

Looking at the payload, I get a nice JSON string:

{
	"chan":	7,
	"codr":	"4/5",
	"data":	"QAIAAAYACAABKK25/65Ao9VDgrEdSGrDhyH6",
	"datr":	"SF7BW125",
	"freq":	903.700000,
	"lsnr":	10.200000,
	"modu":	"LORA",
	"rfch":	1,
	"rssi":	-55,
	"size":	27,
	"stat":	1,
	"time":	"2016-05-25T21:38:19.699738Z",
	"tmst":	736539996
}

What are all these fields? I assume ‘data’ is the data sent from the mdot and when I decoded it (I’m assuming is base64) and get an array of bytes:

40 02 00 00 06 00 08 00 01 28 ad b9 ff ae 40 a3 d5 43 82 b1 1d 48 6a c3 87 21 fa

But how to I decode this? I was expecting something like that data packet formats on
Data Packet Format
but this doesn’t look like anything from that page.

Is there some place that describes the fields in the JSON string and format the ‘data’ bytes?

thanks,
Dave.

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