LTE-M works but NB-IOT can not be registered

[Artnia]

Hey guys,

I am working with

• nrf9160-dk
• at_client
• Modem Firmware version 1.3.5

and use the iBasis SIM that was delivered with it and also have a new 1nce SIM card. I am located in Germany.

When working with LTE-M everything works as expected. Now I want to switch to NB-IOT and can not make it work.

According to iBasis it has no coverage with NB-IOT but only with LTE-M:
https://ibasis.com/solutions/iot-connectivity/network-coverage/
When scanning with iBasis I can see Telekom, Vodafone and O2. But can only register into Telekom and O2 LTE-M. That is ok for me.

According to 1nce it should have coverage:
www.1nce.com/.../our-coverage
When scanning with 1nce I can see Telekom, Vodafone and O2 LTE-M and can register into all 3 of them.

Now I use the 1nce SIM for NB-IOT.

In Germany these operators are available:
https://www.gsma.com/solutions-and-impact/technologies/internet-of-things/deployment-map/#DE

I tried many different configs to register with 1nce into NB-IOT but always failed.

My approach is using a python script that controls the at_client. The relevant excerpt is here. As you can see I tried many different combinations.

def get_init_commands(mode=None):
    """Get initialization commands based on network mode"""
    base_commands = [
        #("AT+CFUN=1", "Set full functionality mode"),
    ]
    
    # Only add system mode command if mode is specified
    mode_commands = []
    if mode:
        if mode.lower() == "nbiot":
            mode_commands = [
                ("AT+CFUN=0", "Disable radio functionality"),
                ("AT%XSYSTEMMODE=0,1,0,2", "Set NB-IoT mode"),
                ("AT%XSYSTEMMODE?", "Query current system mode"),
                ("AT+CFUN=1", "Re-enable full functionality mode after setting NB-IoT"),
                #("AT+CGDCONT=1,\"IP\",\"internet.telekom\"", "Set APN for Telekom"),
                #("AT+COPS=1,2,\"26201\"", "Manual selection of Telekom network"),
                #("AT+COPS=1,2,\"26202\"", "Manual selection of Vodafone network"),
                ("AT+CPSMS=0", "Disable Power Saving Mode (PSM)"),
                ("AT+CEDRXS=0", "Disable extended DRX (eDRX)"),
                ("AT+CGDCONT=1,\"IP\",\"iot.1nce.net\"", "Set APN for 1NCE"),
                # ("AT+COPS=1,2,\"26201\"", "Manual selection of Telekom network"),
                # ("AT+CGDCONT=1,\"IP\",\"internet.o2.de\"", "Set APN for O2"),
                #("AT+COPS=1,2,\"26203\"", "Manual selection of O2 network"),
                ("AT+COPS=0", "Automatic operator selection (let modem pick any available NB-IoT network)"),
            ]
        elif mode.lower() == "ltem":
            mode_commands = [
                ("AT+CFUN=0", "Disable radio functionality"),
                ("AT%XSYSTEMMODE=1,0,0,0", "Set LTE-M mode"),
                ("AT%XSYSTEMMODE?", "Query current system mode"),
                ("AT+CFUN=1", "Re-enable full functionality mode after setting LTE-M"),
            ]
    
    common_commands = [
        ("AT+CPSMS=0", "Disable Power Saving Mode (PSM)"),
        ("AT+CEDRXS=0", "Disable extended DRX (eDRX)"),
    ]
    
    return base_commands + mode_commands + common_commands

My first question is: What is the correct command sequence?
My second question is: Is it possible that the command sequence is ok, but the signal quality in my exact place is so bad that the network it not available?

Here is a full log of the script and at_client trace. I added some additional info that is logged which is not from the modem:

Fullscreen network_comparison_20250726_165819.log Download

2025-07-26 16:58:19 INFO: Connected to /dev/ttyACM0 at 115200 baud
2025-07-26 16:58:19 INFO: 
Started: 2025-07-26 16:58:19
2025-07-26 16:58:19 INFO: Log file: network_comparison_20250726_165819.log
2025-07-26 16:58:19 INFO: Test duration per network: 3 minutes
2025-07-26 16:58:19 INFO: ============================================================
2025-07-26 16:58:19 INFO: Testing basic connectivity...
2025-07-26 16:58:20 INFO: AT command response: 'OK'
2025-07-26 16:58:20 INFO: Basic AT test successful
2025-07-26 16:58:20 INFO: ============================================================
2025-07-26 16:58:20 INFO: INITIALIZING MODEM (NB-IoT MODE)
2025-07-26 16:58:20 INFO: ============================================================
2025-07-26 16:58:20 INFO: Disable radio functionality
2025-07-26 16:58:20 INFO: Command: AT+CFUN=0
2025-07-26 16:58:20 INFO: ----------------------------------------
2025-07-26 16:58:20 INFO: +CEREG: 0
OK
2025-07-26 16:58:21 INFO: Set NB-IoT mode
2025-07-26 16:58:21 INFO: Command: AT%XSYSTEMMODE=0,1,0,0
2025-07-26 16:58:21 INFO: ----------------------------------------
2025-07-26 16:58:21 INFO: OK
2025-07-26 16:58:22 INFO: Query current system mode
2025-07-26 16:58:22 INFO: Command: AT%XSYSTEMMODE?
2025-07-26 16:58:22 INFO: ----------------------------------------
2025-07-26 16:58:22 INFO: %XSYSTEMMODE: 0,1,0,0
OK
2025-07-26 16:58:23 INFO: Re-enable full functionality mode after setting NB-IoT
2025-07-26 16:58:23 INFO: Command: AT+CFUN=1
2025-07-26 16:58:23 INFO: ----------------------------------------
2025-07-26 16:58:23 INFO: OK
2025-07-26 16:58:24 INFO: Disable Power Saving Mode (PSM)
2025-07-26 16:58:24 INFO: Command: AT+CPSMS=0
2025-07-26 16:58:24 INFO: ----------------------------------------
2025-07-26 16:58:25 INFO: OK
2025-07-26 16:58:26 INFO: Disable extended DRX (eDRX)
2025-07-26 16:58:26 INFO: Command: AT+CEDRXS=0
2025-07-26 16:58:26 INFO: ----------------------------------------
2025-07-26 16:58:26 INFO: OK
2025-07-26 16:58:27 INFO: Set APN for 1NCE
2025-07-26 16:58:27 INFO: Command: AT+CGDCONT=1,"IP","iot.1nce.net"
2025-07-26 16:58:27 INFO: ----------------------------------------
2025-07-26 16:58:27 INFO: OK
2025-07-26 16:58:28 INFO: Automatic operator selection (let modem pick any available NB-IoT network)
2025-07-26 16:58:28 INFO: Command: AT+COPS=0
2025-07-26 16:58:28 INFO: ----------------------------------------
2025-07-26 16:58:28 INFO: OK
2025-07-26 16:58:29 INFO: Disable Power Saving Mode (PSM)
2025-07-26 16:58:29 INFO: Command: AT+CPSMS=0
2025-07-26 16:58:29 INFO: ----------------------------------------
2025-07-26 16:58:29 INFO: OK
2025-07-26 16:58:30 INFO: Disable extended DRX (eDRX)
2025-07-26 16:58:30 INFO: Command: AT+CEDRXS=0
2025-07-26 16:58:30 INFO: ----------------------------------------
2025-07-26 16:58:30 INFO: OK
2025-07-26 16:58:31 INFO: Modem NB-IoT initialization completed!
2025-07-26 16:58:31 INFO: Checking SIM card status...
2025-07-26 16:58:31 INFO: PIN status response: +CPIN: READY
OK
2025-07-26 16:58:31 INFO: ✓ SIM PIN status: Ready (no PIN required)
2025-07-26 16:58:31 INFO: Verifying SIM card with IMSI read...
2025-07-26 16:58:31 INFO: Nordic SIM status: ERROR
2025-07-26 16:58:31 INFO: ℹ️  Nordic SIM command not supported (this is normal for some modems)
2025-07-26 16:58:31 INFO: ✓ SIM card check passed - SIM is present and ready
2025-07-26 16:58:31 INFO: Verifying NB-IoT mode was set correctly...
2025-07-26 16:58:31 INFO: Setting CEREG to report detailed network information with cause codes...
2025-07-26 16:58:33 INFO: Reading network registration status...
2025-07-26 16:58:34 INFO: CEREG response: +CEREG: 5,4
2025-07-26 16:58:34 INFO: Registration status: 4
2025-07-26 16:58:34 INFO: Registration status meaning: Unknown (out of coverage)
2025-07-26 16:58:34 WARNING: Warning: Device not registered to network yet
2025-07-26 16:58:34 INFO: Waiting for network registration (max 120s)...
2025-07-26 16:58:34 INFO: Registration status: 4
OK
2025-07-26 16:58:39 INFO: Registration status: 4
OK
2025-07-26 16:58:44 INFO: Registration status: 4
OK
2025-07-26 16:58:49 INFO: Registration status: 4
OK
2025-07-26 16:58:54 INFO: Registration status: 4
OK
2025-07-26 16:58:59 INFO: Registration status: 4
OK
2025-07-26 16:59:04 INFO: Registration status: 4
OK
2025-07-26 16:59:09 INFO: Registration status: 4
OK
2025-07-26 16:59:14 INFO: Registration status: 4
OK
2025-07-26 16:59:20 INFO: Registration status: 4
OK
2025-07-26 16:59:25 INFO: Registration status: 4
OK
2025-07-26 16:59:30 INFO: Registration status: 4
OK
2025-07-26 16:59:35 INFO: Registration status: 4
OK
2025-07-26 16:59:40 INFO: Registration status: 4
OK
2025-07-26 16:59:45 INFO: Registration status: 4
OK
2025-07-26 16:59:50 INFO: Registration status: 4
OK
2025-07-26 16:59:55 INFO: Registration status: 4
OK
2025-07-26 17:00:00 INFO: Registration status: 4
OK
2025-07-26 17:00:05 INFO: Registration status: 4
OK
2025-07-26 17:00:11 INFO: Registration status: 4
OK
2025-07-26 17:00:16 INFO: Registration status: 4
OK
2025-07-26 17:00:21 INFO: Registration status: 4
OK
2025-07-26 17:00:26 INFO: Registration status: 4
OK
2025-07-26 17:00:31 INFO: Still searching for network... (117.4s)
2025-07-26 17:00:36 ERROR: Network registration failed after 120s
2025-07-26 17:00:36 ERROR: ERROR: Device out of network coverage
2025-07-26 17:00:36 ERROR: Try moving to an area with better signal coverage
2025-07-26 17:00:36 ERROR: ERROR: Failed to set NB-IoT mode correctly!
2025-07-26 17:00:36 ERROR: Exiting due to incorrect network mode...
2025-07-26 17:00:36 ERROR: Modem initialization failed!
2025-07-26 17:00:36 INFO: 
Disconnected from /dev/ttyACM0

[Benjamin]

Hi Artina,

Your AT command sequence seems correct at first glance. Please try this simple step-by-step exercice to confirm whether you can establish a connection.

Best regards,

Benjamin

[hanmira]

It might not be a config issue at all. In Germany, NB-IoT support can be very operator- and SIM-dependent even if LTE-M works fine. I’ve seen some IoT SIMs allow NB-IoT only on specific roaming partners or require activation from the provider side. Geometry Dash Lite