UDP server NRF9151 using Hologram

RE: UDP server NRF9151 using Hologram

dejans — Wed, 17 Dec 2025 11:04:23 GMT

Hi,

"PPP can be used in conjunction with CMUX in order to use a single UART for both AT data and PPP. When CMUX is also enabled, PPP is usable only through a CMUX channel."
You can read more in CMUX AT commands, PPP AT commands and configuration options documentation.

Best regards,
Dejan

RE: UDP server NRF9151 using Hologram

Deval — Tue, 16 Dec 2025 17:18:31 GMT

In the Serial Modem are we able to use CMUX and PPP at the same time?

My application requires AT commands at the same time as running a PPP connection.

RE: UDP server NRF9151 using Hologram

dejans — Fri, 12 Dec 2025 10:38:58 GMT

Hi,

I have discussed your problem with our developers. Below you can find some points to consider.
To get both PPP and UDP connection to work, you need to have 2 working PDN connections. If I remember correctly (because I cannot see your previous replies) there was no IP address in your second PDN context. In this case, it seems that either your PDN context does not work or you have not activated it using AT+CGACT=1,1. In addition, two 2 different PDN connections might not be supported by the operator. You could check with your operator if they support 2 different PDN connections.
If #XUDPSRV cannot be bound to a non-primary PDN connection (as it is the case in older SLM versions), it is possible to create a socket, bind it to the port 6002 and poll/recv the data.

You can also consider moving over to Serial Modem. You can read more about it in Serial Modem documentation and application description. This is recommended way going forward for getting better maintained base for your product. UDPSRV has been removed in Serial Modem Add-On in favor of using sockets and binding them.

Best regards,
Dejan

RE: UDP server NRF9151 using Hologram

Deval — Thu, 11 Dec 2025 20:48:14 GMT

I can see all the replies but they are nested within the other replies.

Serial LTE Modem example with NCS version is 3.1.0, with the overlay-ppp-cmux-linux added.

You must use a Hologram SIM and the UDP messaging feature on the specific port -- we are using port 6002.

I have the UDP server and messaging working BUT only when I close the PPP explicitly. I am wondering WHY I need to close PPP in order to use the UDP server?

Is there a way to use the second PDN context for the UDP server?

RE: UDP server NRF9151 using Hologram

dejans — Thu, 11 Dec 2025 19:09:29 GMT

Hi,

I have noticed that all our replies are missing from the conversation. Do you see the same on your end?

Can you please specify all required steps for replicating your issue on the nrf9151-dk?
Please also include information about NCS version and modem firmware version.

Best regards,
Dejan

RE: UDP server NRF9151 using Hologram

Deval — Thu, 11 Dec 2025 01:21:54 GMT

Another idea is can I create two PDN contexts? I want them to both be the same but how would I go about creating two contexts and setting PPP to one of them and the UDP server to the other?

I created two PDN contexts but it didn't do anything...

RE: UDP server NRF9151 using Hologram

Deval — Thu, 11 Dec 2025 01:11:17 GMT

Okay I think I am able to make it work BUT only when I turn the PPP connection off with AT#XPPP=0

Why is this the case?

Is there a patch you can give me that will make it work when the PPP connection is running as well?

My application requires BOTH ppp and the UDP messages

RE: UDP server NRF9151 using Hologram

Deval — Wed, 10 Dec 2025 18:37:30 GMT

I have tried with the SLM sample without PPP and CMUX and still don't see it work.

Can you provide an exact sample project configuration I can follow to get the UDP server working with Hologram messaging working?

RE: UDP server NRF9151 using Hologram

dejans — Wed, 10 Dec 2025 14:35:13 GMT

Hi,

Can you verify that you have built serial LTE modem sample without PPP overlay?

Best regards,
Dejan

RE: UDP server NRF9151 using Hologram

Jimy — Tue, 09 Dec 2025 23:31:25 GMT

Jennifer Gibbs Here is where we are having issues.

RE: UDP server NRF9151 using Hologram

Deval — Tue, 09 Dec 2025 21:54:35 GMT

Turning off the XPPP does not work.

I can add a second PDN context but still don't get the UDP messages. Is there a way to get the PDN context to be set for the UDP server and then other PDN context for the PPP?

AT+CGDCONT?
+CGDCONT: 0,"IP","hologram","10.90.66.67",0,0
+CGDCONT: 1,"IP","hologram","",0,0

I am using the Serial LTE Modem example.

NCS version is 3.1.0

Is there another sample project I could use that would give me better success?

RE: UDP server NRF9151 using Hologram

dejans — Tue, 09 Dec 2025 09:37:25 GMT

Hi,

[quote user="Deval"]I am using CMUX + PPP overlay for the Serial LTE Modem example project. Is the UDPSVR functionality not something that should work with this configuration?[/quote]

Are you using Serial LTE modem sample or Serial Modem Add-on? Which NCS version do you use?

[quote user="Deval"]So if I am understanding this right -- you are saying I cannot have a PPP connection and receive UDP messages if I have one PDP context?[/quote]

PPP connection is in essence a raw socket. One PDN context can have only a single raw socket and nothing else. If other sockets are created into the PDN, raw socket continues to work but other sockets do not work. This happens due to routing of all packets to the raw socket.

[quote user="Deval"]If I close the XPPP connection I should get the UDP messages?[/quote]

You can try this and let me know the result.

Best regards,
Dejan

RE: UDP server NRF9151 using Hologram

Deval — Mon, 08 Dec 2025 21:09:44 GMT

I am using CMUX + PPP overlay for the Serial LTE Modem example project. Is the UDPSVR functionality not something that should work with this configuration?

So if I am understanding this right -- you are saying I cannot have a PPP connection and receive UDP messages if I have one PDP context?

If I close the XPPP connection I should get the UDP messages?

RE: UDP server NRF9151 using Hologram

dejans — Mon, 08 Dec 2025 14:00:17 GMT

Hi,

The issue might be related to the use of cellular network that your device connects to. Using NAT might only be possible for several minutes. It is problematic to wait for connection on cellular device. It is recommended that (if you need to use UDP) you use device in such a way that it regularly checks for messages.

We have removed support for #UDPSVR functionality in Serial Modem Add-On. It is still possible to use UDP server with socket interface but it is not recommended.
Another issue is that since PPP in Serial Modem uses RAW socket and receiving UDP data for the same PDN context is not possible. You need to choose another PDN context if you want to use PPP and receive anything on UDP socket.

Best regards,
Dejan

RE: UDP server NRF9151 using Hologram

dejans — Mon, 08 Dec 2025 13:09:50 GMT

Hi,

Which application has been flashed to nrf9151-dk?

Best regards,
Dejan

RE: UDP server NRF9151 using Hologram

Jimy — Fri, 05 Dec 2025 17:53:49 GMT

dejans we don't have IPv6 so your recommendation is not possible. Can we escalate this issue to someone who is an expert in UDP messaging?

RE: UDP server NRF9151 using Hologram

dejans — Tue, 11 Nov 2025 13:07:19 GMT

Hi,

[quote user="dejans"]Is UDP server functionality working locally on your private network?[/quote]

For testing, you could try to run python client script on your local private network.

Which network does your device connect to?

Looking at AT+CGDCONT, your device has IPv4 address from private addressing range. Documentation suggests that in this case you should use IPv6 address instead. Please have a look at udp server.

To act as a UDP server, the nRF91 Series DK must have a public IP address and the radio network must be configured to route incoming IP packets to the nRF91 Series DK. These depend on the network and SIM card used.

Best regards,
Dejan

RE: UDP server NRF9151 using Hologram

Deval — Mon, 10 Nov 2025 23:10:05 GMT

Yes the Nordic modem is a UDP server and the Hologram API allows us to send UDP messages to it.

It uses this service: docs.hologram.io/.../send-messages-to-sims

RE: UDP server NRF9151 using Hologram

dejans — Mon, 10 Nov 2025 13:11:50 GMT

Hi,

Is UDP server functionality working locally on your private network?

[quote user=""]I am using the example on the Nordic DK to get UDP messages from the Hologram API to the Nordic Modem. [/quote]

What is the role of Nordic modem in your setup? Is it intended to be used as UDP server?

Best regards,
Dejan

RE: UDP server NRF9151 using Hologram

Deval — Thu, 06 Nov 2025 21:36:44 GMT

So I don't have a public IP address so I cannot use the python script. But I know the service that Hologram provides will let you send a UDP message to their SIMs since it uses their internal API and I see confirmation that the message was sent.

And I have seen it work with this cell modem with the Hologram SIM it is just very inconsistent.

For example when it worked:

#XUDPDATA: 24,"10.254.0.75",15694
how long does this take?
#XUDPDATA: 9,"10.254.0.75",20100
try again

I can see that I have a private IP

AT+CGDCONT?
+CGDCONT: 0,"IP","hologram","10.90.66.67",0,0

OK

So I know the service does work.

Additionally, I am seeing low (or undefined signal quality), but a successful PPP connection. Is it possible causing the issue? Because I am seeing inconsistent results from SMS as well.

AT+CSQ
+CSQ: 99,99

OK
AT+CESQ
+CESQ: 99,99,255,255,255,255

OK

RE: UDP server NRF9151 using Hologram

dejans — Thu, 06 Nov 2025 15:38:21 GMT

Hi,

Have you tried to test UDP connection using python script as shown in UDP server (points 1 and 2)?

Best regards,
Dejan