TcpListener server = null;

        // Buffer for reading data
        Byte[] bytes = new Byte[256];
        String data = null;

        private void buttonStart_Click(object sender, EventArgs e)
        {
            try
            {
                Int32 port = Int32.Parse(textBoxPort);
                IPAddress localAddr = IPAddress.Parse(textBoxIpAdr.Text);

                server = new TcpListener(localAddr, port);
                server.Start();

            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

STATUS TCP_ClientConnect (char *serverName, int *soc_desc) 
{ 
    struct sockaddr_in  serverAddr;    /* server's socket address */ 
    int                 sockAddrSize;  /* size of socket address structure */ 
    int                 sFd;           /* socket file descriptor */ 
    int optval;
    socklen_t optlen;
    
    int status =0 ;
    int dontblock =1;
    /* create client's socket */ 
    if ((sFd = socket (AF_INET, SOCK_STREAM, 0)) == ERROR) 
    { 
        //perror ("socket"); 
        printf ("SOCKET ERROR\n");
        return (ERROR); 
    } 
    else
    	 printf ("SOCKET DESC = %d\n", sFd);
 
    /* bind not required - port number is dynamic */ 
    /* build server socket address */ 
    sockAddrSize = sizeof (struct sockaddr_in); 
    bzero ((char *) &serverAddr, sockAddrSize); 
    serverAddr.sin_family = AF_INET; 
    serverAddr.sin_len = (u_char) sockAddrSize; 
    serverAddr.sin_port = htons (SERVER_PORT_NUM); 
 
    
    if (((int)(serverAddr.sin_addr.s_addr = inet_addr (serverName)) == ERROR) && 
        ((int)(serverAddr.sin_addr.s_addr = hostGetByName (serverName)) == ERROR)) 
    { 
        //perror ("unknown server name");
        printf ("UNKNOWN SERVER NAME\n");
        close (sFd); 
        return (ERROR); 
    } 
    else
    {
    	printf ("ADDR = %d\n", serverAddr.sin_addr.s_addr);
    	printf ("PORT = %d\n", serverAddr.sin_port);
    	
    }
    
    #if KEEPALIVE_ON
    /* Set the option active */
    optval = 1;
    optlen = sizeof(optval);
    if(setsockopt(sFd, SOL_SOCKET, SO_KEEPALIVE, &optval, optlen) < 0)
    {
        close(sFd);
        return (ERROR); 
    }
    printf("SO_KEEPALIVE set on socket\n");
    
    /* Interval (in seconds) between keepalives */
    optval = 1; //every one sec
    setsockopt(sFd, IPPROTO_TCP, TCP_KEEPINTVL, &optval, optlen);
    /* Maximum number of keepalives before dropping the connection */
    optval = 10;
    setsockopt(sFd, IPPROTO_TCP, TCP_KEEPCNT, &optval, optlen);
    /* Send first keepalive probe when the connections been idle this time (in seconds) */
    optval = 5;
    setsockopt(sFd, IPPROTO_TCP, TCP_KEEPIDLE, &optval, optlen);
    #endif
    /* bind a port number to the socket 
    if (bind(sFd, (struct sockaddr *) &serverAddr, sizeof(serverAddr)) == ERROR)
    {
    	printf("BIND ERROR\n");
    	return (ERROR); 
    }
*/
       
    /* connect to server */ 
    optval = 1;
    setsockopt(sFd, IPPROTO_TCP, TCP_NODELAY, &optval, sizeof(int));

    if (connect (sFd, (struct sockaddr *) &serverAddr, sockAddrSize) != OK) 
    { 
        //perror ("connect");
    	printf ("CONNECTION ERROR\n");
        close (sFd); 
        return (ERROR); 
    } 
     
	printf ("CONNECTION GOOD\n");

	
    *soc_desc = sFd;
    
    
	dontblock = 1;
	status = ioctl(sFd, FIONBIO, (char*) dontblock);
	if (status == ERROR)
	{
		printf("messages IOCTL ERROR ");
		printf("messages IOCTL errno = %d\n", errnoGet());
	}
	
    
    return (OK); 
}

int TCP_ClientRead(char *read_buff, int soc_desc)
{
	int mlen;  /* length of message */ 
	int sock_len;
	
	//mlen = read (soc_desc, read_buff, sizeof(read_buff));
	mlen = recv (soc_desc, read_buff, sizeof(read_buff) , 0);

	if (mlen < 0) 
	{  
	    //close (soc_desc); 
	    return (ERROR); 
	}
	
	return (mlen); 
}


STATUS TCP_ClientWrite(int soc_desc , char *write_buff , int size)
{
	if (send (soc_desc, write_buff, size , 0) == ERROR) 
	{ 
	    //printf("Error %x", errno);
	    close (soc_desc); 
	    return (ERROR); 
	} 
	
	return (OK); 
}