Does the nRF9160-DK support the MO PS SMS-over-CP/IMS in the NB-IoT system mode?

[avchizhov.de]

Greetings, my name is Toni.

We are trying sending the MO PS SMS-over-CP/NAS or IMS from the nRF9160-DK:
- Hw rev2,
- mfw v1.3.7,
- NCS prebuilt apps from the v2.3.0 and v3.0.0 bundles are tried.

The tested networks were:
- the Deutsche Telecom,
- R&S CMW500 00101 test network,

The modem successfully attaches to the network, like:
AT+CEREG?
> +CEREG: 0,1,"5225","02A29F00",7

AT+CGATT?
> +CGATT: 1

However, the SMS related AT commands fail:
AT+CSMS?
> ERROR

AT+CMGF=1
> +CMS ERROR: 302

AT+CPMS?
> "MT",0,0,...

AT+CNMI?
> returns default config

Also:
AT+CMEE=2
> ERROR (cannot enable verbose errors)
So, there is no indication is of the SMS capability via the AT interface.

This log is from the serial_lte_modem.hex is used.
The almost the same log is when the modem_shell.hex is used.
The same behaviour for the AT%XSYSTEMMODE=1,0,0,0 and for the 0,1,0,0 as well.
The same behaviour is for the CMW500 test network.
From the NB-IoT Signaling log we see, that the modem is RRC = Registered, and EPC = Attached, the default bearer is established, but there is no any registration on the DAU (Data Application Unit) IMS.

There is a couple of questions is:
1. Does the nRF9160-DK generally support the MO PS SMS-over-CP/IMS in the NB-IoT system mode?
2. What is needed for this: which modem version or application version?
3. Is any specific aditional configuration needed for operating the SMS AT commands (Kconfig options, modem library, IMS enablement)?
4. Could you provide a minimal working configuration (SLM or sample) where the AT+CMGF / SMS works on a NB-IoT network?

Additionally, could you clarify:
5. Is SMS over NAS (Control Plane) supported on nRF9160 independently of IMS registration?
6. Under which conditions should AT+CSMS be available on the modem interface (e.g., after attach, after specific network capability negotiation, or only when IMS is active)?
7. Is it expected that AT+CSMS returns ERROR when the network does not advertise SMS capability, or does it indicate that the SMS subsystem is not enabled in the modem firmware?

 ---
ANTON CHIZHOV
Support- und Applikationsingenieur
1SLS3 Technical Sales Support -- Level 2

[Simon D-M]

Hi,

The AT commands that returned errors are wrong:

AT+CSMS?
> ERROR

The actual command is "AT+CGSMS" (link).

AT+CMGF=1
> +CMS ERROR: 302

"1" is not a valid <mode> for "AT+CMGF" (link).

AT+CMEE=2
> ERROR (cannot enable verbose errors)

"2" is not a valid parameter for "AT+CMEE" (link).

Now for your questions:

1. Does the nRF9160-DK generally support the MO PS SMS-over-CP/IMS in the NB-IoT system mode?

Yes, it does support SMS. Here is the SMS Library.

2. What is needed for this: which modem version or application version?

I always recommend going with the latest modem firmware version (currently v1.3.7). I don't remember in which modem firmware version it has been introduced, but it has been here for a long time now.

For the application, if I understood correctly, you want to use the nRF9160 as a "modem-only" solution. Then, I would recommend going to more recent NCS version for both the host and the SLM, and also try to use the same NCS version for both of them.

Actually, the best option would be to use the Serial Modem add-on instead of the SLM as the SLM is already in the process of being deprecated. However, the Serial Modem add-on still doesn't have native support for the nRF9160. But, If you want you are welcome to try making overlay files. I don't see any reason why it shouldn't work on the nRF9160.

3. Is any specific aditional configuration needed for operating the SMS AT commands (Kconfig options, modem library, IMS enablement)?

Yes, please check the SMS library to get more information on that.

4. Could you provide a minimal working configuration (SLM or sample) where the AT+CMGF / SMS works on a NB-IoT network?

We have a sample that is showing the SMS capabilities (link).

5. Is SMS over NAS (Control Plane) supported on nRF9160 independently of IMS registration?

Yes, SMS over NAS (Control Plane) is supported on the nRF9160. It operates independently of IMS. The nRF9160 uses SMS PDU Mode over the cellular control plane, not IMS/VoLTE.

Specifically, when operating in NB-IoT, the nRF9160 exclusively uses Control Plane CIoT EPS optimization for all data transfer (including SMS), as User Plane (S1-U) data transfer is not supported in NB-IoT mode. When operating in LTE-M (eMTC), the modem uses User Plane for data, but SMS is still handled via NAS (over the control plane signaling path), not IMS

This has been documented on this other Ticket : 346989

6. Under which conditions should AT+CSMS be available on the modem interface (e.g., after attach, after specific network capability negotiation, or only when IMS is active)?
7. Is it expected that AT+CSMS returns ERROR when the network does not advertise SMS capability, or does it indicate that the SMS subsystem is not enabled in the modem firmware?

Please try with the correct command (AT+CGSMS).

Best regards,

Simon D-M