LPC1788 - UDP example

Hi all,

i am trying to send and receive UDP packet on my Hardware. I am using LPC1788 with PHY DP83848TSQ. I already test the Hardware with an example code called "easyweb" and it work. And then i try to use the example programm called "UDP Socket" and it doesn't work. I try to get the netStatus from udp_send and any other function. The net_initialize, udp_open, udp_get_socket seems work finely since it show me "Operations Succeeded". The only problem is udp_send since it show me "unspecified error". Have anyone any idea what happened?
Anyway i am using ARM Keil uVision5

this is the code

#include "LPC177x_8x.h"
#include "RTE_Components.h"
#include "system_LPC177x_8x.h"
#include "rl_net.h"
#include "stdlib.h"
#include "stdio.h"
#include "string.h"
#include "cmsis_os.h"


int32_t sock_udp;
osThreadId g_threadIdUDP;

void disconnect_udp (uint8_t sock_udp)
{
        udp_close(sock_udp);
        udp_release_socket(sock_udp);
}

uint32_t callback_udp (int32_t socket, const uint8_t *ip_addr, uint16_t port, const uint8_t *buf, uint32_t len)
{
        return (0);
}

void udp_send_data (void)
{
  int udp_send_status;
  if (sock_udp >= 0)
   {
    uint8_t dest_ip [IP4_ADDR_LEN];
    uint8_t *sendbuf;

    dest_ip[0] = 192;
    dest_ip[1] = 168;
    dest_ip[2] = 50;
    dest_ip[3] = 172;

    sendbuf = udp_get_buf (2);
    sendbuf[0] = 0x01;
    sendbuf[1] = 0xAA;

    udp_send_status = udp_send (sock_udp, dest_ip, 2000, sendbuf, 2);
    printf("udp_send_status %i\n", udp_send_status);    -> it show me 2, it means "unspecified error" 

  }

}

void udp_thread(void const *arg)
{
        int net_initialize_status;
        int udp_open_status;
        int net_main_status;
        //Initialize Network Component, resources and interfaces
        net_initialize_status = net_initialize ();
        printf("net_initialize %i = Operation succeeded\n", net_initialize_status);   ->netStatus over here also Show me 0. It means Operation succeeded 
        osDelay(100);

        //Allocate a free UDP socket, UDP_OPT_SEND_CHECKSUM   = Calculate transmit checksum, UDP_OPT_VERIFY_CHECKSUM = Verify receive checksum

        sock_udp = udp_get_socket(0,UDP_OPT_SEND_CHECKSUM | UDP_OPT_VERIFY_CHECKSUM, callback_udp);


        printf("sock_udp %i socket handle number \n", sock_udp);

        if (sock_udp >= 0)                   // Initialize UDP socket and open port
        {
                //Open UDP socket for communication
                udp_open_status = udp_open (sock_udp, 2000);
                printf("udp_open_status %i = ",udp_open_status);    -> netStatus show me 0, it means Operation succeeded 
                if(udp_open_status ==0)
                {
                        printf("Operation succeeded, open socket succesful netOK \n");
                }
                else
                {
                        printf("ERROR to open socket! \n");
                }
        }
        while(1)
        {
                net_main_status = net_main();           //Run Network Component main function
                printf("net_main_status = %i \n",net_main_status);
                if(net_main_status == 0) printf("System is idle \n");
                else printf("Another call to this function needed \n");
                osDelay(50);
                udp_send_data();        //Send data to a remote node
                osDelay(100);
        }
}


#define UDPTHREAD_STACKSIZE (2048)
osThreadDef (udp_thread, osPriorityNormal , 1, UDPTHREAD_STACKSIZE);

int main()
{
  g_threadIdUDP =       osThreadCreate(osThread(udp_thread), NULL);
        while(1) {
                osThreadYield();
        }
}