ทำไมส่งภาษาไทยไปแล้วเช็คค่าผิดพลาดครับ (domain check)

http://www.example.com/index.php?domain=ก.com

<?php
function checkDomain($domain_check,$server,$findText){
// Open a socket connection to the whois server
$con = fsockopen($server, 43);
if (!$con) return false;

// Send the requested doman name
fputs($con, $domain_check."\r\n");

// Read and store the server response
$response = ' :';
while(!feof($con)) 
{
    $response .= fgets($con,128); 
}

//echo $response;

// Close the connection
fclose($con);

// Check the response stream whether the domain is available
if (strpos($response, $findText))
{
    return true;
}
else 
{
    return false; 
}
}

function showDomainResult($domain_check,$server,$findText)
{
    if (checkDomain($domain_check,$server,$findText))
    {
       class Emp {
           public $domain = "";
           public $availability = "";
       }
       $e = new Emp();
       $e->domain = $domain_check;
       $e->availability = "available";
       echo json_encode($e);
    }
    else
    {
       class Emp {
           public $domain = "";
           public $availability = "";
       }
       $e = new Emp();
       $e->domain = $domain_check;
       $e->availability = "TAKEN";
       echo json_encode($e);
    }
}
?>



<?php 
if ($_GET['domain'] != '')
    {
        list($domain_name, $tld) = explode(".", urldecode($_GET[domain]));
        $tld_all = $tld;
        $tld_main = $tld;
        $server = "whois.verisign-grs.com";
        $response = "No match for";
        showDomainResult($domain_name.".".$tld_all,$server,$response);	
    }
?>