PHP でリモートサーバーポートに ping を実行するにはどうすればよいですか?

<code class="php"><?php

function ping($host, $port, $timeout) 
{ 
  $tB = microtime(true); 
  $fP = fsockopen($host, $port, $errno, $errstr, $timeout); 
  if (!$fP) { return "down"; } 
  $tA = microtime(true); 
  return round((($tA - $tB) * 1000), 0)." ms"; 
}

// Usage example: ping a server at IP address 127.0.0.1, port 80
echo ping("127.0.0.1", 80, 10);

?></code>

<code class="php"><?php

function pingDomain($domain){
    $starttime = microtime(true);
    $file      = fsockopen ($domain, 80, $errno, $errstr, 10);
    $stoptime  = microtime(true);
    $status    = 0;

    if (!$file) $status = -1;  // Site is down
    else {
        fclose($file);
        $status = ($stoptime - $starttime) * 1000;
        $status = floor($status);
    }
    return $status;
}

// Usage example: ping a server at domain name example.com
echo pingDomain("example.com");

?></code>