nRF9151 Configuration and UDP Data Transmission over NTN Issue

RE: nRF9151 Configuration and UDP Data Transmission over NTN Issue

JonesGW — Fri, 27 Feb 2026 07:57:47 GMT

That's good to know, thanks Achim.

RE: nRF9151 Configuration and UDP Data Transmission over NTN Issue

JonesGW — Thu, 26 Feb 2026 20:04:34 GMT

Thanks Amanda.

RE: nRF9151 Configuration and UDP Data Transmission over NTN Issue

Amanda Hsieh — Thu, 26 Feb 2026 20:02:31 GMT

Hi Gareth,

Happy to hear it works. I have forwarded the request to the team. Hope it will get updated soon.

Regards,
Amanda H.

RE: nRF9151 Configuration and UDP Data Transmission over NTN Issue

Achim Kraus — Thu, 26 Feb 2026 18:33:43 GMT

You're welcome.

(I was luckily able to test the nRF9151 NTN stuff since Sept. 2025 and in my experience it works pretty well.)

RE: nRF9151 Configuration and UDP Data Transmission over NTN Issue

JonesGW — Thu, 26 Feb 2026 18:31:18 GMT

Thank you for the clarification Achim.

I have tried again, not using AT#XCONNECT, but instead

> AT#XSENDTO=0,0,0,"192.168.217.100",4781,"26022026_6"

#XSENDTO: 0,0,10

%MDMEV: PRACH CE-LEVEL 0

+CSCON: 1,7,4

#XAPOLL: 0,1
> AT#XRECV=0,0,0,10

#XRECV: 0,0,3
ACK
OK

So with the new serial modem application firmware I am able to send a UDP packet and get an ACK back with the original UDP server configuration, i.e. the 'ACK' comes back from port 4782.

Thank you for explaining what I was doing wrong. This is the first time I've tested a Nordic model in detail, so these sort of things aren't obvious to me, I'm afraid.

RE: nRF9151 Configuration and UDP Data Transmission over NTN Issue

JonesGW — Thu, 26 Feb 2026 18:26:01 GMT

Hi Amanda,

Thank your for sharing the GitHub URL for the correct serial modem application firmware. I have installed it and can now execute the socket AT commands with the same syntax as specified in 'NTN operation AT examples v1.3.pdf'.

Could I please suggest that page https://www.nordicsemi.com/Products/Development-hardware/nRF9151-SMA-DK/Evaluate-NTN?lang=en#infotabs be updated to refer to the correct version of the firmware as it currently refers to:

Serial Modem v0.3.0 application firmware: serial_modem_v0.3.0_nrf9151dk_ppp_cmux.hex

Thanks.

RE: nRF9151 Configuration and UDP Data Transmission over NTN Issue

Achim Kraus — Thu, 26 Feb 2026 08:42:51 GMT

> (and has worked for testing other manufacturers' modules).

as long as you "connect" the UDP socket to port 4781, it will filter a message from 4782. But the modem in general received the message (see modem trace).

> reluctant to change the behaviour of the UDP server as it's used for other things (and has worked for testing other manufacturers' modules).

As I wrote, if that works, then not with "connect". With "connect" other modems will fail as well.

It's pretty simply: even if I don't prefer to use "connect" for UDP, it's pretty common practice.I guess, therefore Nordic uses it. And so your server fails with a common practice used by Nordic's setup.

Anyway, your server, your clients, your experience.

RE: nRF9151 Configuration and UDP Data Transmission over NTN Issue

Amanda Hsieh — Wed, 25 Feb 2026 18:07:29 GMT

Hi Gareth,

Could you use the latest Serial Modem add-on from here? https://github.com/nrfconnect/ncs-serial-modem/releases/download/v1.0.0/serial_modem_v1.0.0_nrf9151…

While testing, it would be recommended to use the image that has modem tracing enabled serial_modem_v1.0.0_nrf9151dk_normal_mtrace.hex

Regards,
Amanda H.

RE: nRF9151 Configuration and UDP Data Transmission over NTN Issue

JonesGW — Wed, 25 Feb 2026 08:39:52 GMT

Thanks for the suggestion Achim, but I'm reluctant to change the behaviour of the UDP server as it's used for other things (and has worked for testing other manufacturers' modules).

I will wait for an official response from Nordic.

Thank you.

RE: nRF9151 Configuration and UDP Data Transmission over NTN Issue

Achim Kraus — Wed, 25 Feb 2026 08:34:46 GMT

Maybe you try to send your ACK from the socket/port you received the message?

(I'm an other user, maybe Nordic can help you more.)

RE: nRF9151 Configuration and UDP Data Transmission over NTN Issue

JonesGW — Wed, 25 Feb 2026 08:30:14 GMT

Hi Achim,

Thank you for your response.

I use 'AT#XCONNECT' because that's what the Nordic documentation 'NTN operation AT examples v1.3.pdf' states I should use, i.e.:

; Or alternatively UDP over the IPv4 type PDN Connection. At the
; same time set the destination IP address and the port number.
; Syntax: #XCONNECT=<handle>,<url>,<port>
AT#XCONNECT=0,"FQDN-or-IP-address-dotted-format-for-your-server",port-address-as-integer
AT#XSEND=0,0,0,"Your Hello World(tm) payload"

Other manufacturer modules have their own proprietary AT commands. I'm just following the manufacturers' instructions because that's what our customers will do.

If there's another set of commands that I should use to send UDP packets to a UDP server, and get an ACK back, then I would be happy to use those.

Thank you.

RE: nRF9151 Configuration and UDP Data Transmission over NTN Issue

Achim Kraus — Wed, 25 Feb 2026 07:20:36 GMT

> 1)

What I see in the modem trace is, that you use different UDP service ports:

6 18.973786 192.168.217.141 192.168.217.100 UDP 50 61987 → 4781 Len=10
18 28.905335 192.168.217.100 192.168.217.141 UDP 43 4782 → 61987 Len=3

I don't know, why you use "connect" for UDP, but that enables mainly a packet filter for the destination address.

So, I guess with the other modem you don't use connect?

Would it be possible to send the message to the same UDP port back?
If not, try to not use "connect". Beside AS-RAI I don't see, that this is required.