PHP Cookieがオフの場合の対処方法

<?php
session_cache_expire(60); // 30 is 30min
session_start();
$a = isset($_GET[‘a’]) && strlen($_GET[‘a’]) > 0 ? $_GET[‘a’] : ”;
$welcome_page_session = isset($_SESSION[‘welcome_page_session’]) && $_SESSION[‘welcome_page_session’] == ‘true’ ? ‘true’ : ‘false’;
//$welcome_page_session = isset($_SESSION[‘2’]) && $_SESSION[‘w’] == ‘true’ ? ‘true’ : ‘false’;
if($a == ‘welcome’):
$_SESSION[‘welcome_page_session’] = ‘true’;
header(“Location:/test.php?a=w”);
exit();
endif;
if($a == ‘w’ && $welcome_page_session == ‘true’):
echo ‘available session’;
else:
//echo $_SESSION[‘t’];
echo ‘not available session’;
endif;
?>
<div><a href=”/test.php?a=welcome”>welcome</a></div>