Connect to Cellular Network.... Help Me

Hi.
I posted a question through a translator, so please understand what was translated incorrectly…

My development environment is as follows:
-mbed-os-6.4.0
-STM32L152RE board
-EC21 LTE module

I have a question about connecting to a network using cellular.

I am trying to use cellular to get network allocation on EC21 with PPP protocol.
So, I have a question about using cellular to connect to the network.

           https://github.com/ARMmbed/mbed-os-example-cellular

It is under development by referring to the address above.

The content of mbed_app.json I wrote is as follows:

{
“config”: {
“sock-type”: “TCP”,
“echo-server-hostname”: {
“help”: “Echo server host name.”,
“value”: ““echo.mbedcloudtesting.com””
},
“echo-server-port”: {
“help”: “Echo server port number.”,
“value”: 7
},
“trace-level”: {
“help”: “Options are TRACE_LEVEL_ERROR,TRACE_LEVEL_WARN,TRACE_LEVEL_INFO,TRACE_LEVEL_DEBUG”,
“macro_name”: “MBED_TRACE_MAX_LEVEL”,
“value”: “TRACE_LEVEL_INFO”
}
},
“target_overrides”: {
“*”: {
“target.network-default-interface-type”: “CELLULAR”,
“mbed-trace.enable”: true,
“lwip.ipv4-enabled”: true,
“lwip.ipv6-enabled”: false,
“lwip.ethernet-enabled”: false,
“lwip.ppp-enabled”: true,
“lwip.tcp-enabled”: true,
“platform.stdio-convert-newlines”: true,
“platform.stdio-baud-rate”: 115200,
“platform.default-serial-baud-rate”: 115200,
“platform.stdio-buffered-serial”: true,
“cellular.debug-at”: true,
“nsapi.default-cellular-plmn”: 0,
“nsapi.default-cellular-sim-pin”: "“1234"”,
“nsapi.default-cellular-apn”: ““lte-internet.sktelecom.com””,
“nsapi.default-cellular-username”: 0,
“nsapi.default-cellular-password”: 0,
“QUECTEL_EC2X.provide-default”: true,
“QUECTEL_EC2X.tx”: “PA_9”,
“QUECTEL_EC2X.rx”: “PA_10”
}
}
}

The result log according to the above json file and URL example is as follows.

[MAIN], plmn: NULL
Establishing connection
[00000004ms][INFO][CELL]: New CellularContext (0x20006b08)
[00000005ms][INFO][CELL]: CellularContext plmn NULL
[00000007ms][INFO][CELL]: CellularContext connect
[00000010ms][INFO][CELL]: AT TX ( 6): AT+CSQ
[00000012ms][INFO][CELL]: AT TX ( 1):
[00000016ms][INFO][CELL]: AT RX (16): AT+CSQ+CSQ: 3
[00000024ms][INFO][CELL]: AT RX (12): 1,99OK
[00000031ms][INFO][CELL]: RSSI -51 dBm
[00000035ms][INFO][CELL]: Start connecting (timeout 5000 ms)
[00000042ms][INFO][CELL]: AT TX ( 2): AT
[00000047ms][INFO][CELL]: AT TX ( 1):
[00000052ms][INFO][CELL]: AT RX ( 9): ATOK
[00000059ms][INFO][CELL]: AT TX ( 2): AT
[00000063ms][INFO][CELL]: AT TX ( 1):
[00000068ms][INFO][CELL]: AT RX ( 9): ATOK
[00000076ms][INFO][CELL]: AT TX ( 6): AT+CSQ
[00000080ms][INFO][CELL]: AT TX ( 1):
[00000085ms][INFO][CELL]: AT RX (16): AT+CSQ+CSQ: 3
[00000093ms][INFO][CELL]: AT RX (12): 1,99OK
[00000100ms][INFO][CELL]: RSSI -51 dBm
[00000104ms][INFO][CELL]: AT TX ( 4): ATE0
[00000109ms][INFO][CELL]: AT TX ( 1):
[00000114ms][INFO][CELL]: AT RX (11): ATE0OK
[00000122ms][INFO][CELL]: AT TX ( 9): AT+CMEE=1
[00000127ms][INFO][CELL]: AT TX ( 1):
[00000132ms][INFO][CELL]: AT RX ( 6): OK
[00000138ms][INFO][CELL]: AT TX ( 9): AT+CFUN=1
[00000144ms][INFO][CELL]: AT TX ( 1):
[00000149ms][INFO][CELL]: AT RX ( 6): OK
[00000155ms][INFO][CELL]: Modem ready
[00000160ms][INFO][CELL]: AT TX ( 6): AT+CSQ
[00000165ms][INFO][CELL]: AT TX ( 1):
[00000170ms][INFO][CELL]: AT RX (16): +CSQ: 31,99
[00000177ms][INFO][CELL]: AT RX ( 5): OK
[00000183ms][INFO][CELL]: RSSI -51 dBm
[00000188ms][INFO][CELL]: Setup SIM (timeout 5000 ms)
[00000194ms][INFO][CELL]: AT TX ( 8): AT+CPIN?
[00000199ms][INFO][CELL]: AT TX ( 1):
[00000205ms][INFO][CELL]: AT RX (16): +CPIN: READY
[00000211ms][INFO][CELL]: AT RX ( 6): OK
[00000218ms][INFO][CELL]: SIM is ready
[00000222ms][INFO][CELL]: AT TX ( 8): AT+COPS?
[00000228ms][INFO][CELL]: AT TX ( 1):
[00000233ms][INFO][CELL]: AT RX (16): +COPS: 0,0,“SK
[00000240ms][INFO][CELL]: AT RX (16): Telecom”,7OK
[00000246ms][INFO][CELL]: AT RX ( 2):
[00000252ms][INFO][CELL]: AT TX ( 8): AT+CEREG
[00000257ms][INFO][CELL]: AT TX ( 1): =
[00000262ms][INFO][CELL]: AT TX ( 1): 2
[00000267ms][INFO][CELL]: AT TX ( 1):
[00000272ms][INFO][CELL]: AT RX ( 6): OK
[00000278ms][INFO][CELL]: AT TX ( 8): AT+CGREG
[00000283ms][INFO][CELL]: AT TX ( 1): =
[00000288ms][INFO][CELL]: AT TX ( 1): 2
[00000293ms][INFO][CELL]: AT TX ( 1):
[00000298ms][INFO][CELL]: AT RX ( 6): OK
[00000304ms][INFO][CELL]: AT TX ( 7): AT+CREG
[00000310ms][INFO][CELL]: AT TX ( 1): =
[00000314ms][INFO][CELL]: AT TX ( 1): 2
[00000319ms][INFO][CELL]: AT TX ( 1):
[00000324ms][INFO][CELL]: AT RX ( 6): OK
[00000331ms][INFO][CELL]: AT TX ( 9): AT+CGACT?
[00000336ms][INFO][CELL]: AT TX ( 1):
[00000342ms][INFO][CELL]: AT RX (16): +CGACT: 1,1+
[00000348ms][INFO][CELL]: AT RX (15): CGACT: 16,0+C
[00000355ms][INFO][CELL]: AT RX (14): GACT: 17,0+C
[00000361ms][INFO][CELL]: AT RX (14): GACT: 2,1+CG
[00000367ms][INFO][CELL]: AT RX (13): ACT: 3,0+CG
[00000374ms][INFO][CELL]: AT RX (13): ACT: 4,0O
[00000381ms][INFO][CELL]: AT RX ( 3): K
[00000386ms][INFO][CELL]: AT TX ( 9): AT+CGATT?
[00000392ms][INFO][CELL]: AT TX ( 1):
[00000397ms][INFO][CELL]: AT RX (16): +CGATT: 1O
[00000404ms][INFO][CELL]: AT RX ( 3): K
[00000410ms][INFO][CELL]: AT TX (10): AT+CGEREP=
[00000415ms][INFO][CELL]: AT TX ( 1): 1
[00000420ms][INFO][CELL]: AT TX ( 1):
[00000425ms][INFO][CELL]: AT RX ( 6): OK
[00000432ms][INFO][CELL]: AT TX ( 6): AT+CSQ
[00000437ms][INFO][CELL]: AT TX ( 1):
[00000442ms][INFO][CELL]: AT RX (16): +CSQ: 31,99
[00000449ms][INFO][CELL]: AT RX ( 5): OK
[00000456ms][INFO][CELL]: AT TX ( 6): AT+CSQ
[00000460ms][INFO][CELL]: AT TX ( 1):
[00000465ms][INFO][CELL]: AT RX (16): +CSQ: 31,99
[00000472ms][INFO][CELL]: AT RX ( 5): OK
[00000478ms][INFO][CELL]: RSSI -51 dBm
[00000483ms][INFO][CELL]: AT TX ( 8): AT+CEREG
[00000488ms][INFO][CELL]: AT TX ( 1): ?
[00000493ms][INFO][CELL]: AT TX ( 1):
[00000498ms][INFO][CELL]: AT RX (16): +CEREG: 2,1,“3
[00000505ms][INFO][CELL]: AT RX (16): 705”,“21EA31F”,7
[00000511ms][INFO][CELL]: AT RX ( 8): OK
[00000518ms][INFO][CELL]: Registering network => Attaching network
[00000526ms][INFO][CELL]: AT TX ( 6): AT+CSQ
[00000530ms][INFO][CELL]: AT TX ( 1):
[00000535ms][INFO][CELL]: AT RX (16): +CSQ: 31,99
[00000543ms][INFO][CELL]: AT RX ( 5): OK
[00000549ms][INFO][CELL]: RSSI -51 dBm
[00000553ms][INFO][CELL]: Attaching network (timeout 5000 ms)
[00000560ms][INFO][CELL]: AT TX ( 9): AT+CGATT?
[00000565ms][INFO][CELL]: AT TX ( 1):
[00000571ms][INFO][CELL]: AT RX (16): +CGATT: 1O
[00000578ms][INFO][CELL]: AT RX ( 3): K
[00000585ms][INFO][CELL]: AT TX (11): AT+CGDCONT?
[00000589ms][INFO][CELL]: AT TX ( 1):
[00000595ms][INFO][CELL]: AT RX (16): +CGDCONT: 1,“I
[00000602ms][INFO][CELL]: AT RX (16): PV4V6”,“lte-inte
[00000608ms][INFO][CELL]: AT RX (16): rnet.sktelecom.c
[00000614ms][INFO][CELL]: AT RX (16): om”,“0.0.0.0.0.0
[00000620ms][INFO][CELL]: AT RX (16): .0.0.0.0.0.0.0.0
[00000626ms][INFO][CELL]: AT RX (16): .0.0”,0,0,0,0+
[00000632ms][INFO][CELL]: AT RX (15): CGDCONT: 16,“IP
[00000638ms][INFO][CELL]: AT RX (16): V4V6”,“lte-inter
[00000644ms][INFO][CELL]: AT RX (16): net.sktelecom.co
[00000650ms][INFO][CELL]: AT RX (16): m”,“0.0.0.0.0.0.
[00000656ms][INFO][CELL]: AT RX (16): 0.0.0.0.0.0.0.0.
[00000662ms][INFO][CELL]: AT RX (16): 0.0”,0,0,0,0+C
[00000669ms][INFO][CELL]: AT RX (14): GDCONT: 17,“IP
[00000675ms][INFO][CELL]: AT RX (16): “,“internet”,“0.
[00000681ms][INFO][CELL]: AT RX (16): 0.0.0”,0,0,0,0
[00000687ms][INFO][CELL]: AT RX (16): +CGDCONT: 2,“IPV
[00000693ms][INFO][CELL]: AT RX (16): 4V6”,“IMS”,“0.0.
[00000699ms][INFO][CELL]: AT RX (16): 0.0.0.0.0.0.0.0.
[00000706ms][INFO][CELL]: AT RX (16): 0.0.0.0.0.0”,0,0
[00000712ms][INFO][CELL]: AT RX (16): ,0,0+CGDCONT:
[00000718ms][INFO][CELL]: AT RX (16): 3,“IPV4V6”,””,"0
[00000724ms][INFO][CELL]: AT RX (16): .0.CGDCONT: 4,"I
[00000730ms][INFO][CELL]: AT RX ( 3): PV4
[00005585ms][WARN][CELL]: AT timeout
[00005586ms][INFO][CELL]: Found PDP context 16
[00005587ms][INFO][CELL]: CellularContext PPP connect
[00005589ms][INFO][CELL]: AT TX ( 9): ATD99**
[00005591ms][INFO][CELL]: AT TX ( 2): 16
[00005593ms][INFO][CELL]: AT TX ( 1): #
[00005595ms][INFO][CELL]: AT TX ( 1):
[00005613ms][INFO][CELL]: AT RX (11): CONNECT 3

++ MbedOS Error Info ++
Error Status: 0x80020125 Code: 293 Module: 2
Error Message: CMSIS-RTOS error: Stack overflow
Location: 0x80199F5
Error Value: 0x1
Current Thread: lwip_tcpip Id: 0x200014A0 Entry: 0x800B765 StackSize: 0x4B0 StackMem: 0x200076B8 SP: 0x20013F24
For more info, visit: https://mbed.com/s/error?error=0x80020125&tgt=NUCLEO_L152RE
– MbedOS Error Info –

Looking at someone else’s log results, I used AT + CGDATA = “PPP” instead of ATD * 99 ***. Is there a problem?

And I’m curious about why it doesn’t work because of a stackoverflow and an Mbed OS error.

I’ve been struggling with this for a month.
Help.