fsockopen无法访问一个主机

I used 'classic' code with fsockopen() to 'ping' necessary hosts. I had no problem with it at all. But I can't reach one host, always receiving error 110 : Connection timed out.

But other instruments, like paping, or http://www.yougetsignal.com/tools/open-ports/ confirm that the host is online.

$domain = 'XXX.XX.XXX.XXX';

$port = '40001';                                                            

$starttime = microtime(true);
$file      = fsockopen($domain, $port, $errno, $errstr, 20);
$stoptime  = microtime(true);

$status    = 0;

if ($file === false) {
    echo $errno." : ".$errstr."</br>";
}

if (!$file) {
    $status = -1;  // Site is down
    echo 'camera ping failed'.'</br>';
}
else {
    fclose($file);
    $status = ($stoptime - $starttime) * 1000;
    $status = floor($status);
}

Thanks for any advice or ideas.