sockets dont ever send data

Plz take a look at the code in my main function:

        init_parameters(&parameters);
        parse_config(&parameters);
        send_diff(&parameters,qdisc_stats);
        reset_server((void *)NULL);
        configure((void *)NULL,"add"); /*Configure initially the diffserv */
//      configure((void *)NULL,"change"); /*Configure initially the diffserv */


        sleep(3);
        if (pthread_create(&thread_id[0],NULL,init_diffserv,NULL)>0)
                printf("Error creating thread \n");
        if (pthread_create(&thread_id[1],NULL,reconfigure,NULL)>0)
                printf("Error creating thread \n");


        if (pthread_join(thread_id[0],(void **) p_status) >0)
               perror("Error joining diffserv thread");
        if (pthread_join(thread_id[1],(void **) p_status) >0)
               perror("Error joining reconfigure thread");

        printf("Lalalala");
        return 0;
}

The function send_diff(&parameters,qdisc_stats)is implemented like that

    void send_diff(struct configuration *diff,union qdisc *qdisc){

        int                     sock,n;
        socklen_t               server_len;
        struct sockaddr_in      server,client;
        struct hostent          *host;

        if (!(host=gethostbyname(DIFFSERV))){ //?? Huge problem how to read value from file
                perror("Client gethostname");
        }
        memset(&server,0,sizeof(server));
        server.sin_family= AF_INET;
        memcpy(&server.sin_addr,host->h_addr,host->h_length);
        server.sin_port=htons((9997));
        if ((sock=socket(PF_INET, SOCK_DGRAM, 0)) < 0){
                perror("Client socket ");
        }
        memset(&client,0,sizeof(client));
        client.sin_family       = AF_INET;
        client.sin_addr.s_addr  = htonl(INADDR_ANY);
        client.sin_port         = htons(9997);

        if ( bind(sock, (struct sockaddr *) &client, sizeof(client)) <0){
                perror("Client bind ");
        }
        server_len=sizeof(server);
        printf("To i exei timi %d \n",i);
        if (sendto( sock, diff , sizeof(struct configuration), 0,(struct sockaddr *) &server, server_len) <0){
                perror("Client send to");
                close(sock);
        }



        if (sendto( sock, qdisc, sizeof(qdisc_stats[10]), 0, (struct sockaddr *) &server, server_len) <0){
                perror("Client send to");
                close(sock);
        }
        printf("Finished sending structs \n");
        close(sock);
}

As u can easily see use two times the sendto system call. Using tcpdump -i eth0 -vvv -n port 9997 (filter for the specific post)
I have noticed that my programme NOT always send packets to the network.. The packets are not created... Firewall is shut down... Sometimes the packets are created and some others not...
What should i do?

How often is "NOT always?" A few packets out of every 100? Every 1000? Every other packet? The UDP protocol isn't guaranteed to deliver packets, and it's not guaranteed to deliver them in order. In my experience, packet loss isn't usually too great on a local network, but it can still occur. If what you are seeing is typical packet loss, and you absolutely cannot lose those packets, you may have to implement some sort of reliability into it by using acks, etc. Or, switch to TCP sockets.