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Cellular API

CellularInterface class hierarchy

The CellularInterface class provides a C++ API for connecting to the internet over a Cellular device.

Getting started

  1. Choose an Mbed board that supports cellular, such as the UBLOX-C027 or MTS-DRAGONFLY.

  2. Clone mbed-os-example-cellular. Follow the instructions in the repository.

    1. Compile the code.
    2. Flash the board.

    You see output similar to the excerpt below:

Establishing connection ......

Connection Established.
TCP: connected with echo.mbedcloudtesting.com server
TCP: Sent 4 Bytes to echo.mbedcloudtesting.com
Received from echo server 4 Bytes

Success. Exiting

Basic working principles

You can use and extend a cellular interface in various different ways. For example,

  • Using AT commands to control sockets in an existing IP stack built into the cellular modem.

  • Using a PPP (Point-to-Point Protocol) pipe to pass IP packets between an Mbed OS supported IP stack and cellular modem device.

mbed-os-example-cellular uses PPP or AT mode depending on the modem. We can summarize this particular design as follows:

  • It uses an external IP stack, such as LWIP, or on-chip network stacks such as when the modem does not support PPP.
  • The easy cellular connection uses standard 3GPP AT 27.007 AT commands to set up the cellular modem and to register to the network.
  • After registration, the driver opens a PPP pipe using LWIP with the cellular modem and connects to the internet. If AT only mode is in use, then modem-specific AT commands are used for socket data control.

CellularInterface class reference

Public Types
typedef mbed::Callback< void(nsapi_error_t result, SocketAddress *address)> hostbyname_cb_t
 Hostname translation callback (for use with gethostbyname_async()). More...
Public Member Functions
virtual void set_credentials (const char *apn, const char *uname=0, const char *pwd=0)=0
 Set the cellular network credentials. More...
virtual void set_plmn (const char *plmn)=0
 Set the plmn. More...
virtual void set_sim_pin (const char *sim_pin)=0
 Set the PIN code for SIM card. More...
virtual nsapi_error_t connect (const char *sim_pin, const char *apn=0, const char *uname=0, const char *pwd=0)=0
 Attempt to connect to a cellular network with a PIN and credentials. More...
virtual nsapi_error_t connect ()=0
 Attempt to connect to a cellular network. More...
virtual nsapi_error_t disconnect ()=0
 Stop the interface. More...
virtual bool is_connected ()=0
 Check if the connection is currently established. More...
virtual const char * get_ip_address ()=0
 Get the local IP address. More...
virtual const char * get_netmask ()=0
 Get the local network mask. More...
virtual const char * get_gateway ()=0
 Get the local gateways. More...
virtual CellularInterfacecellularBase ()
 Return pointer to a CellularInterface. More...
virtual CellularInterfacecellularInterface ()
 Return pointer to a CellularInterface. More...
virtual void set_default_parameters ()
 defined(DOXYGEN_ONLY) More...
virtual void set_as_default ()
 Set network interface as default one. More...
virtual const char * get_mac_address ()
 Get the local MAC address. More...
virtual char * get_interface_name (char *interface_name)
 Get the network interface name. More...
virtual nsapi_error_t set_network (const char *ip_address, const char *netmask, const char *gateway)
 Configure this network interface to use a static IP address. More...
virtual nsapi_error_t set_dhcp (bool dhcp)
 Enable or disable DHCP on connecting the network. More...
virtual nsapi_error_t gethostbyname (const char *host, SocketAddress *address, nsapi_version_t version=NSAPI_UNSPEC, const char *interface_name=NULL)
 Translate a hostname to an IP address with specific version using network interface name. More...
virtual nsapi_value_or_error_t gethostbyname_async (const char *host, hostbyname_cb_t callback, nsapi_version_t version=NSAPI_UNSPEC, const char *interface_name=NULL)
 Translate a hostname to an IP address (asynchronous) using network interface name. More...
virtual nsapi_error_t gethostbyname_async_cancel (int id)
 Cancel asynchronous hostname translation. More...
virtual nsapi_error_t add_dns_server (const SocketAddress &address, const char *interface_name)
 Add a domain name server to list of servers to query. More...
virtual void attach (mbed::Callback< void(nsapi_event_t, intptr_t)> status_cb)
 Register callback for status reporting. More...
void add_event_listener (mbed::Callback< void(nsapi_event_t, intptr_t)> status_cb)
 Add event listener for interface. More...
void remove_event_listener (mbed::Callback< void(nsapi_event_t, intptr_t)> status_cb)
 Remove event listener from interface. More...
virtual nsapi_connection_status_t get_connection_status () const
 Get the connection status. More...
virtual nsapi_error_t set_blocking (bool blocking)
 Set asynchronous operation of connect() and disconnect() calls. More...
virtual EthInterfaceethInterface ()
 Return pointer to an EthInterface. More...
virtual WiFiInterfacewifiInterface ()
 Return pointer to a WiFiInterface. More...
virtual MeshInterfacemeshInterface ()
 Return pointer to a MeshInterface. More...
virtual EMACInterfaceemacInterface ()
 Return pointer to an EMACInterface. More...
Static Public Member Functions
static CellularInterfaceget_default_instance ()
 Get the default cellular interface. More...


To bring up the network interface:

  1. Instantiate an implementation of the CellularInterface class.
  2. Call the connect(pincode, apn) function with a PIN code for your SIM card and an APN for your network.
  3. Once connected, you can use Mbed OS network sockets as usual.

Cellular example: connection establishment

This example establishes connection with the cellular network using Mbed OS CellularInterface.

 * Copyright (c) 2017 ARM Limited. All rights reserved.
 * SPDX-License-Identifier: Apache-2.0
 * Licensed under the Apache License, Version 2.0 (the License); you may
 * not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an AS IS BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.

#include "mbed.h"
#include "common_functions.h"
#include "UDPSocket.h"
#include "CellularLog.h"

#define UDP 0
#define TCP 1

// Number of retries /
#define RETRY_COUNT 3

NetworkInterface *iface;

// Echo server hostname
const char *host_name = MBED_CONF_APP_ECHO_SERVER_HOSTNAME;

// Echo server port (same for TCP and UDP)

static rtos::Mutex trace_mutex;

static void trace_wait()

static void trace_release()

static char time_st[50];

static char* trace_time(size_t ss)
    snprintf(time_st, 49, "[%08llums]", Kernel::get_ms_count());
    return time_st;

static void trace_open()
    mbed_trace_prefix_function_set( &trace_time );



static void trace_close()


Thread dot_thread(osPriorityNormal, 512);

void print_function(const char *format, ...)
    va_list arglist;
    va_start( arglist, format );
    vprintf(format, arglist);
    va_end( arglist );

void dot_event()
    while (true) {
        if (iface && iface->get_connection_status() == NSAPI_STATUS_GLOBAL_UP) {
        } else {

 * Connects to the Cellular Network
nsapi_error_t do_connect()
    nsapi_error_t retcode = NSAPI_ERROR_OK;
    uint8_t retry_counter = 0;

    while (iface->get_connection_status() != NSAPI_STATUS_GLOBAL_UP) {
        retcode = iface->connect();
        if (retcode == NSAPI_ERROR_AUTH_FAILURE) {
            print_function("\n\nAuthentication Failure. Exiting application\n");
        } else if (retcode == NSAPI_ERROR_OK) {
            print_function("\n\nConnection Established.\n");
        } else if (retry_counter > RETRY_COUNT) {
            print_function("\n\nFatal connection failure: %d\n", retcode);
        } else {
            print_function("\n\nCouldn't connect: %d, will retry\n", retcode);
    return retcode;

 * Opens a UDP or a TCP socket with the given echo server and performs an echo
 * transaction retrieving current.
nsapi_error_t test_send_recv()
    nsapi_size_or_error_t retcode;
    TCPSocket sock;
    UDPSocket sock;

    retcode = sock.open(iface);
    if (retcode != NSAPI_ERROR_OK) {
        print_function("TCPSocket.open() fails, code: %d\n", retcode);
        print_function("UDPSocket.open() fails, code: %d\n", retcode);
        return -1;

    SocketAddress sock_addr;
    retcode = iface->gethostbyname(host_name, &sock_addr);
    if (retcode != NSAPI_ERROR_OK) {
        print_function("Couldn't resolve remote host: %s, code: %d\n", host_name, retcode);
        return -1;


    int n = 0;
    const char *echo_string = "TEST";
    char recv_buf[4];
    retcode = sock.connect(sock_addr);
    if (retcode < 0) {
        print_function("TCPSocket.connect() fails, code: %d\n", retcode);
        return -1;
    } else {
        print_function("TCP: connected with %s server\n", host_name);
    retcode = sock.send((void*) echo_string, sizeof(echo_string));
    if (retcode < 0) {
        print_function("TCPSocket.send() fails, code: %d\n", retcode);
        return -1;
    } else {
        print_function("TCP: Sent %d Bytes to %s\n", retcode, host_name);

    n = sock.recv((void*) recv_buf, sizeof(recv_buf));

    retcode = sock.sendto(sock_addr, (void*) echo_string, sizeof(echo_string));
    if (retcode < 0) {
        print_function("UDPSocket.sendto() fails, code: %d\n", retcode);
        return -1;
    } else {
        print_function("UDP: Sent %d Bytes to %s\n", retcode, host_name);

    n = sock.recvfrom(&sock_addr, (void*) recv_buf, sizeof(recv_buf));


    if (n > 0) {
        print_function("Received from echo server %d Bytes\n", n);
        return 0;

    return -1;

int main()
    print_function("\n\nBuilt: %s, %s\n", __DATE__, __TIME__);

    print_function("Establishing connection\n");

    // sim pin, apn, credentials and possible plmn are taken atuomtically from json when using get_default_instance()
    iface = NetworkInterface::get_default_instance();

    nsapi_error_t retcode = NSAPI_ERROR_NO_CONNECTION;

    /* Attempt to connect to a cellular network */
    if (do_connect() == NSAPI_ERROR_OK) {
        retcode = test_send_recv();

    if (iface->disconnect() != NSAPI_ERROR_OK) {
        print_function("\n\n disconnect failed.\n\n");

    if (retcode == NSAPI_ERROR_OK) {
        print_function("\n\nSuccess. Exiting \n\n");
    } else {
        print_function("\n\nFailure. Exiting \n\n");


    return 0;
// EOF

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