Fehler gegen sendto() zu andere server, den mit UDP socket verbindet ist

//Main SERVER

#include <sys/types.h>

#include <sys/socket.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#include <stdio.h>

#include <unistd.h>

#include <errno.h>

#include <string.h>

#include <stdlib.h>

#include <sys/select.h>//use select() for multiplexing

#include <sys/fcntl.h> // for non-blocking

#define MAX_LENGTH 100000

#define PORT 1901

/* Select() params

 * int select(int n, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);

 * FD_SET(int fd, fd_set *set);

 * FD_CLR(int fd, fd_set *set);

 * FD_ISSET(int fd, fd_set *set);

 * FD_ZERO(fd_set *set);

*/

void error(char *message)

{

    perror(message);

    exit(1);

}

int main()

{

  // select parameters declared

  fd_set original_socket;

  fd_set original_stdin;

  fd_set readfds;

  fd_set writefds;

  struct timeval tv;

  int numfd, numfd2;

  // socket parameters declared

  int socket_fd_ob, socket_fd_hm;

  int bytes_read, bytes_sent;

  char address_length, address_length2;

  char recieve_data[MAX_LENGTH];

  char send_data[MAX_LENGTH];

  struct sockaddr_in server_address_ob, server_address_hm, client_address;

  int z = 0;

  //Socket creation done separately for both OB and HM communications

  if ((socket_fd_ob = socket(AF_INET, SOCK_DGRAM, 0)) == -1) 

  {

      error("socket()");

  }

  if ((socket_fd_hm = socket(AF_INET, SOCK_DGRAM, 0)) == -1) 

  {

      error("socket()");

  }

  fcntl(socket_fd_ob, F_SETFL, O_NONBLOCK); //set socket to non-blocking

  fcntl(socket_fd_hm, F_SETFL, O_NONBLOCK); //set socket to non-blocking

  // clear the set ahead of time

  FD_ZERO(&original_socket);

  FD_ZERO(&original_stdin);

  FD_ZERO(&readfds);

  FD_ZERO(&writefds);

  // add our descriptors to the set (0 - stands for STDIN)

  FD_SET(socket_fd_ob, &original_socket);//instead of 0 put socket_fd_ob

  FD_SET(socket_fd_ob, &readfds);

  FD_SET(0,&original_stdin);

  FD_SET(0, &writefds);

  // since we got s2 second, it's the "greater", so we use that for

  // the n param in select()

  numfd  = socket_fd_ob + 1;

  numfd2 = socket_fd_hm + 1;

  // wait until either socket has data ready to be recv()d (timeout 10.5 secs)

  tv.tv_sec = 1;

  tv.tv_usec = 500000;

  server_address_ob.sin_family = AF_INET;

  server_address_ob.sin_port = htons(1901);

  server_address_ob.sin_addr.s_addr = inet_addr("127.0.0.3");

  bzero(&(server_address_ob.sin_zero),sizeof(server_address_ob));

  server_address_hm.sin_family = AF_INET;

  server_address_hm.sin_port = htons(1901);

  server_address_hm.sin_addr.s_addr = inet_addr("127.0.0.1");

  bzero(&(server_address_ob.sin_zero),sizeof(server_address_hm));

  // Bind socket to the particular addresses

  if (bind(socket_fd_ob,(struct sockaddr *)&server_address_ob, sizeof(struct sockaddr)) == -1)

  {

      error("bind()");

  }

  if (bind(socket_fd_hm,(struct sockaddr *)&server_address_hm, sizeof(struct sockaddr)) == -1)

  {

      error("bind()");

  }

  address_length  = sizeof(struct sockaddr);

  address_length2 = sizeof(struct sockaddr);

  printf("\nMain server waiting for client to respond...\n");

  fflush(stdout);

  while (1)

  {

    readfds = original_socket;

    writefds = original_stdin;//problem

    int recieve = select(numfd, &readfds, &writefds,/*NULL,*/ NULL, &tv);

    int sent    = select(numfd2, &readfds, &writefds,/*NULL,*/ NULL, &tv);

    if (recieve == -1 || sent == -1) 

    {

      perror("select"); // error occurred in select()

    } 

    else if (recieve == 0 || sent == 0) 

    {

      printf("Timeout occurred!  No data after 1.5 seconds.\n");

    } 

    else 

    {

        // one or both of the descriptors have data

        if (FD_ISSET(socket_fd_ob, &readfds)) //if set to read

        { 

          FD_CLR(socket_fd_ob, &readfds);

          bytes_read = recvfrom(socket_fd_ob,recieve_data,MAX_LENGTH,0,(struct sockaddr *)&server_address_hm, &address_length); 

   for (z = 0; z < bytes_read; ++z) {

   FD_ISSET(socket_fd_hm, &writefds);

          FD_CLR(socket_fd_hm, &writefds);

          //recvfrom speech recognition client and decide what to send to HM accordingly..

          send_data[bytes_read] = recieve_data[bytes_read];

          //block call, will wait till client enters something, before proceeding

          //send the corresponding to HM

          bytes_sent = sendto(socket_fd_hm,send_data,strlen(send_data)+1,0,(struct sockaddr *)&server_address_hm, &address_length2); 

          fflush(stdout);

      }                  

          recieve_data[bytes_read] = '\0'; //add null to the end of the buffer

          send_data[bytes_read] = '\0'; //add null to the end of the buffer

          printf("\n(%s , %d) rcvd: %02x\n",inet_ntoa(server_address_hm.sin_addr),ntohs(server_address_hm.sin_port),recieve_data);

          printf("\n(%s , %d) sent: %02x\n",inet_ntoa(server_address_hm.sin_addr),ntohs(server_address_hm.sin_port),send_data);

        }

    } //end else

  }//end while

  close (socket_fd_ob);

  return 0;

}