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I'm trying to send UDP packets over the t-mobile NB-IoT network using AT-commands on a SIM7020E chip. I used the product wiki as reference. The starter version of the sim card I have doesn't support TCP, but I'm planning on using that later if I can succesfully communicate using UDP.

I created a UDP-socket on a Raspberry Pi using "nc -u -l 9999". I set an A-record on my hosting provider to refer dev.mydomain.com to the IP address of the Raspberry Pi. I verified the portforward and A-record settings by sending UDP packets from my laptop on another network using "nc -u dev.mydomain.com 9999" and typing some teststrings, so this all works.

On the 4G chip I use the following AT-commands:

// Check network
AT+CSQ
+CSQ: 21,0

AT+CGREG?
+CGREG: 0,5

AT+COPS?
+COPS: 0,2,"20416",9

AT+CGCONTRDP
+CGCONTRDP: 1,5,"iot.t-mobile.nl","x.x.x.x.255.255.255.0" <-- crossed out my ip

// Create UDP socket
AT+CSOC=1,2,1
+CSOC: 0

// Connect socket 0 to the listening port on the Raspberry Pi
AT+CSOCON=0,9999,"dev.mydomain.com"
OK

// Send "test"
AT+CSOSEND=0,0,"test"

At this point I expect to see "test" appear in the command line on the Raspberry Pi, but nothing happens. In the T-mobile portal it shows a PDP-context is successfully activated. Also, setting the APN manually with AT*MCGDEFCONT="IP","iot.t-mobile.nl","username","password" doesn't work.

Hans Koene
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1 Answers1

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Did you work this out Hans? I was plodding along with a SIM7020E following https://www.waveshare.com/wiki/Pico-SIM7020E-NB-IoT code examples. Was successfully sending HTTP GETS to a server (without having to use micropython's wretched urequests lib) via the CHTTPCREATE/CHTTPCON/CHTTPSEND AT cmds, that seem to be be able to send packets over LTE to a server without specifying TCP/UDP etc or using a socket. Maybe give it a try?

Sadly I got the bright idea of trying an 'AT+POWD=1' cmd over the uart (was supposed to power the 7020E down) & now the module now does nothing but echo AT cmds (still auto connects to the LTE network & slow flashes the network led, just won't do anything else.) Real shame, nice little module otherwise.

Kris Mclean
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  • I was able to send MQTT packages using the built in AT commands, which is weird because the sim card I used was listed as not supporting TCP. Also the connection appeared to be very unstable, with the module constantly disconnecting from the broker. As I'm using Mbed OS I will try to use a module with a Quectel BG96 because it's already supported and should have better documentation. I'm sorry for your loss :( – Hans Koene May 11 '21 at 10:15