This is an example based on mbed-os cellular APIs that demonstrates a TCP or UDP echo transaction with a public echo server. Included TPB23 NB-IoT module which is can use LGU+ in Korea.


This guide is how to use NB-IOT(SECOM TPB23 module) of LGU+ network in Korea. The NB-IOT module seller provided a document on how to start based on Mbed OS 5.11 created by CodeZoo. This guide has been updated to Mbed OS 5.12.


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Tested with

1. Import the application into your desktop

mbed import

cd mbed-os-example-cellular-TPB23

2. Compile and program

mbed compile -t <toolchain> -m <TARGET_BOARD>

(supported toolchains : GCC_ARM / ARM / IAR)

3. Download binary to a target board

4. Result


Built: Aug  7 2019, 06:10:47

[MAIN], plmn: NULL
Establishing connection
[00000001ms][INFO][CELL]: New CellularContext  (20000a08)
[00000002ms][INFO][CELL]: CellularContext plmn NULL
[00000003ms][INFO][CELL]: CellularContext connect
[00000036ms][INFO][CELL]: RSSI -69 dBm
[00000036ms][INFO][CELL]: Start connecting (timeout 1 s)
[00000087ms][INFO][CELL]: RSSI -69 dBm
[00000116ms][INFO][CELL]: Modem ready
[00000146ms][INFO][CELL]: RSSI -69 dBm
[00000146ms][INFO][CELL]: Setup SIM (timeout 1 s)
[00001233ms][INFO][CELL]: Looked up APN internet
[00001362ms][ERR ][CELL]: AT error code 50
[00001362ms][WARN][CELL]: Packet domain event reporting set failed!
[00001393ms][INFO][CELL]: RSSI -65 dBm
[00001393ms][INFO][CELL]: Network registration (timeout 180 s)
[00001443ms][INFO][CELL]: Registering network => Attaching network
[00001473ms][INFO][CELL]: RSSI -65 dBm
[00001473ms][INFO][CELL]: Attaching network (timeout 60 s)
[00001601ms][INFO][CELL]: Found PDP context 1
[00001649ms][INFO][CELL]: Activate PDP context 1

Connection Established.
[00001671ms][INFO][CELL]: Socket 0 open
[00001707ms][INFO][CELL]: Socket 1 open
[00001748ms][INFO][CELL]: Socket create id: 1
[00001883ms][INFO][CELL]: Socket 1 sent 43 bytes to port 53
[00004311ms][INFO][CELL]: Socket 1 recv 59 bytes from port 53
[00004331ms][INFO][CELL]: Close socket: 1 error: 0
[00004331ms][INFO][CELL]: Socket 1 closed
[00004373ms][INFO][CELL]: Socket create id: 1
TCP: connected with server
[00004448ms][INFO][CELL]: Socket 0 sent 4 bytes to port 7
TCP: Sent 4 Bytes to
[00007560ms][INFO][CELL]: Socket 0 recv 4 bytes
[00007580ms][INFO][CELL]: Close socket: 1 error: 0
[00007580ms][INFO][CELL]: Socket 0 closed
Received from echo server 4 Bytes
[00007581ms][INFO][CELL]: CellularContext disconnect()
[00007630ms][INFO][CELL]: cb: CellularContext disconnected

Success. Exiting

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