nrf9151 NTN Sockets

[yayalew]

Hi all,

I'm testing Skylo NTN on nRF9151 SMA DK with the latest pre-commercial/alpha NTN modem firmware (downloaded mid-December 2025).

Registration works fine, and uplink NIDD send succeeds (#XSEND with WAITACK, #XSENDNTF confirm).

However, receiving downlink NIDD is impossible:
- #XSOCKET=1,3,0 succeeds (#XSOCKET: <id>,3,0 OK)
- #XSOCKET? confirms socket open
- #XRECV=<any timeout> (even 5s or 300s) immediately returns ERROR

I tried:
- RAI (#XSOCKETOPT=<id>,61,3) — ERROR (not supported?)
- Disabling PSM/eDRX (CPSMS=0, CEDRXS=0)
- Polling #XRECV multiple times quickly
- Events enabled (%MDMEV=2)

Is this expected behavior in the current alpha firmware?

Modem firmware version: 1.0.0-1.alpha nRF91

Using SLM Application ncs-serial-modem 

Thanks for any guidance — excited for NTN but stuck on receive!

Logs: 

> AT+CGMR

mfw_nrf9151-ntn_1.0.0-1.alpha

OK

> AT#XSEND=128,0,8192,"ECHO: Test msg"

#XSEND: 128,1,14

OK

%MDMEV: PRACH CE-LEVEL 0

+CSCON: 1,7,4
> AT#XRECV=5

ERROR
> AT#XRECV=5

ERROR

#XSENDNTF: 128,0,14

+CSCON: 0,7,4
> AT#XSOCKET=1,3,0

ERROR
> AT#XCLOSE=128

#XCLOSE: 128,0

OK
> AT#XSOCKET=1,3,0

#XSOCKET: 128,3,0

OK
> AT#XSEND=128,0,8192,"ECHO: Test msg"

#XSEND: 128,1,0

ERROR
> AT#XSEND=128,0,8192,"ECHO: Test msg"

#XSEND: 128,1,0

ERROR
> AT#XSEND=128,0,8192,"ECHO: Test msg"

#XSEND: 128,1,0

ERROR
> AT#XSEND=130,0,8192,"ECHO: Test msg"

#XSEND: 130,1,0

ERROR
> AT#XCLOSE=128

#XCLOSE: 128,0

OK
> AT#XSOCKET=0

ERROR
> AT#XSOCKET?

#XSOCKET: 129,3,0,3,0

#XSOCKET: 130,3,0,3,0

#XSOCKET: 131,3,0,3,0

OK
> AT#XCLOSE=129

#XCLOSE: 129,0

OK
> AT#XCLOSE=130

#XCLOSE: 130,0

OK
> AT#XCLOSE=131

#XCLOSE: 131,0

OK
> AT#XSOCKET?

OK
> AT#XSOCKET=1,3,0

#XSOCKET: 128,3,0

OK
> AT#XRECV=5

ERROR
> AT%CSCON=3

ERROR
> AT%MDMEV=2

OK
> AT#XSOCKET?

#XSOCKET: 128,3,0,3,0

OK
> AT#XSOCKETOPT=128,61,3

ERROR
> #XSOCKETOPT=128,61,3

ERROR
> AT#XSOCKET?

#XSOCKET: 128,3,0,3,0

OK
> AT#XSOCKET=1,3,0

#XSOCKET: 129,3,0

OK
> #XSOCKETOPT=129,61,3

ERROR
> AT#XRECV=120

ERROR
> AT#XSOCKET=1,3,0

#XSOCKET: 130,3,0

OK
> AT#XRECV=120

ERROR
> AT#XRECV=120

ERROR
> AT#XRECV=120

ERROR
> AT#XRECV=120

ERROR
> AT#XRECV=120

ERROR
> AT#XRECV=120

ERROR
> AT#XRECV=120

ERROR
> AT#XSOCKET=130

ERROR
> AT#XSOCKET=129

ERROR
> AT#XCLOSE=129

#XCLOSE: 129,0

OK
> AT#XCLOSE=130

#XCLOSE: 130,0

OK
> AT#XSOCKET=1,3,0

#XSOCKET: 129,3,0

OK
> AT#XRECV=300

ERROR
> AT#XRECV=800

ERROR
> AT+CPSMS=0

OK
> AT+CEDRXS=0

OK
> AT#XSOCKET=1,3,0

#XSOCKET: 130,3,0

OK
> AT#XRECV=300

ERROR

[Simon D-M]

Hi Yeab,

I'm sorry we don't have a NTN expert on hand right now due to Christmas / New Year holidays. You might have to wait until next week if you want an expert on the subject.

However, I'll still try to help you .

Did you connect your device to a NTN network (i.e. Skylo) before sending the AT-commands you shared ? 

I see that when you are trying to send the reception command, you write : "AT#XRECV=<x>" but if I check the SLM AT-Commands documentation I see that it should be : "AT#XRECV=<handle>,<mode>,<flags>,<timeout>[,<data_len>]". I think you might be missing some parameters.

I saw that there is a branch on the Asset tracker template application repository that supports NTN. Maybe you can try to take a look into it to see in more details how they did it.

I also found a small tutorial from monogoto on how to use NTN with their SIM card. It seems like they are using the latest NTN modem firmware, but not the latest SLM application. Even tho, I think that it can still be helpful to go through it. 

Tell me if any of my suggestions helped !

Best regards,

Simon D-M

[SimonLou]

Hi,

Thanks for the input, I have try those, but I have no luck to make it work, 

1. I did Quick start, somehow it always roll back to 2.0.3 by default.

2. I follow the steps on motogoto, after I "erase and write"  the right part of partition "orange" part disappear, and LED1 on board one goes off, and nothing work, till I do the "quick start" to go back to 2.0.3 so that I can run AT command