tcp_sent problem

Hi everyone.

I've questino to ask you guys.

I've written my own tcp functions. They work fine but my send function.

It work in Im_TCPVeriGonder(this echos the received ethernet packets).

But it does not work alone.

Here is my codework:

// close connection

static void Im_TCPBaglantiKapa(struct tcp_pcb *pcb)
{
       tcp_arg(pcb, NULL);
       tcp_sent(pcb, NULL);
      tcp_recv(pcb, NULL);
      tcp_close(pcb);
}

// sent data

void Im_TCPVeriGonder(struct tcp_pcb *pcb,unsigned char * uc_gonderilecek_veri,unsigned int ui_veri_uzunlugu)
{
      tcp_write(pcb, uc_gonderilecek_veri, ui_veri_uzunlugu, 0); /* Tampona atılan veri gönderiliyor.*/
      tcp_sent(pcb, NULL); /* Paket sonunda boş karakter yollanıyor. */

     pbuf_free(paket1);
}

// get received data
static err_t Im_TCPVeriAl(void *arg,struct tcp_pcb *pcb,struct pbuf *paket,err_t err)
{
    if (err == ERR_OK && paket1 != NULL)
    {
         tcp_recved(pcb, paket1->tot_len);

         g_p_uc_gelen_paket = (unsigned char *)paket1->payload;

         g_ui_paket_uzunlugu = paket1->tot_len;

         for(g_ui_index = 0; g_ui_index < g_ui_paket_uzunlugu; g_ui_index++)
         {
              g_uc_yigin_veri[g_ui_index] = g_p_uc_gelen_paket[g_ui_index];
         }

         // sent data

         Im_TCPVeriGonder(pcb, "aliveli", 7);
    }
    else
       {
        pbuf_free(paket1); /* Paket tamponunu serbest bırakır. */
       }

       if (err == ERR_OK && paket1 == NULL)
        {
             Im_TCPBaglantiKapa(pcb);
        }

return ERR_OK;
}

// Get the received data
static err_t Im_TCPTransferKontrol(void *arg, struct tcp_pcb *pcb, err_t err )
{
     LWIP_UNUSED_ARG(arg);
     LWIP_UNUSED_ARG(err);

     tcp_setprio(pcb, TCP_PRIO_MIN);

     tcp_recv(pcb, Im_TCPVeriAl);
      tcp_err(pcb, NULL);
     tcp_poll(pcb, NULL, 4);

      return ERR_OK;
}

// Listening
void Im_BaglantiDinle()
{
    if(baglanti_durumu == ERR_OK)
    {
         pcb = tcp_listen(pcb);

         tcp_accept(pcb, Im_TCPTransferKontrol);
     }
}

// Connect
void Im_BaglantiAc(void)
{
      pcb = tcp_new();

      baglanti_durumu = tcp_bind(pcb, IP_ADDR_ANY, PORT_NUMARASI);

}

My sent function works in Im_TCPVeriAl function(it gets the data sent from ethernet and echos it back) but can't work alone

Why can't I use my sent function?

Please give me suggestions.

My best regards...