How to send a UDP packet to a GPRS module

Question

I use a GSM/GPRS module called SIM340DZ, and use AT commands to be able manage the module.

I am able to send a UDP packet to a remote computer at a specific port from the GPRS module. Now, I would like to transfer a UDP packet from computer to the GPRS unit. But, the GPRS unit has a private IP address (e.g. 10.46.123.25), and the access point name (APN) is internet.tele2.se

Could anyone please explain how I can send a UDP data from a (linux) computer to the GPRS unit? What information do I need to know and how can I find it out?

Additionally, if you have experience in AT commands, I would also appreciate if you could explain me what command sequence do I need to use to configure the module on UDP listening mode?

Answer 1

For the ones who needs to deal with similar system, I am posting the code that you can send UDP packets to a destinated port and IPaddress through the serial port by using AT commands. Explanations are included as comment on the code:

int Serial_Close(int *fd);
int Serial_Send(int *fd, char *string);
int Serial_Open(int* fd, char *serial_Name, speed_t baudrate);



int main(int argc, char** argv)
{
    int fd;

    Serial_Open(&fd, "/dev/ttyAPP0", B115200); //open the UART interface with 115200 boundrate, 8 1 N
    if(tcflush(fd, TCIOFLUSH) != 0)
    {
        exit(1);   //error
        fprintf(stderr, "tcflush error\n");
    }

    Serial_Send(&fd, "ATE0\r\n");   //ATE0 = echo mode(ATE) is off (0)
    sleep(1);
    Serial_Send(&fd, "AT+CGATT=1\r\n");
    sleep(1);
    Serial_Send(&fd, "AT+AT+CSTT=\"internet.tele2.se\"\r\n");  //here you define the name the APN
    sleep(1);
    Serial_Send(&fd, "AT+CIICR\r\n");
    sleep(1);
    Serial_Send(&fd, "AT+cipstart=\"UDP\",\"85.1.2.3\",\"20000\"\r\n"); //85.1.2.3 is the destination IP address, 20000 is the destination Port number
    sleep(1);
    Serial_Send(&fd, "AT+CIPSEND=5\r\n");
    sleep(1);
    Serial_Send(&fd, "12345\r\n"); //12345 is the message
    sleep(1);
    Serial_Send(&fd, "AT+CIPSHUT\r\n");
    sleep(1);
    Serial_Close(&fd);

    return 0;
}


int Serial_Open(int* fd, char *serial_Name, speed_t baudrate)
{

    struct termios serCfg;
    memset(&serCfg, 0, sizeof(serCfg));
    if((*fd = open(serial_Name, O_RDWR)) < 0)
        return -1;
    else
        if(tcgetattr(*fd, &serCfg) != 0)
            return -1;

    cfsetispeed(&serCfg, baudrate);
    cfsetospeed(&serCfg, baudrate);
    cfmakeraw(&serCfg);

    if(tcsetattr(*fd, TCSANOW, &serCfg) != 0)
        return -1;
    return 0;
}


int Serial_Send(int *fd, char *string)
{
    int len;
    char *buffer;
    int bytes_sent;


    len = strlen(string);
    if(len > 255)
        return -1;
    buffer = (char*)malloc((len+1)*sizeof(char));
    if(buffer == NULL)
        return -1;
    strcpy(buffer, string);
    buffer[len] = 0;

    bytes_sent = write(*fd, buffer, strlen(buffer));
    if(bytes_sent < 0)
    {
        close (*fd);
        return -1;
    }
    else
    {
        free(buffer);
        return 0;
    }
}



int Serial_Close(int *fd)
{
        if(close (*fd) < 0)
            return -1;
        else
            return 0;
}

I hope it helps to someone.