How to send a UDP packet to a GPRS module - c

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.