set up session lifetime

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title></title>
<script type="text/javascript">
var xmlHttp = false;
function createXMLHttpRequest()
{
    var http;
    if(window.ActiveXObject)
    {
        http = new ActiveXObject('Microsoft.XMLHTTP');
    }
    else if(window.XMLHttpRequest)
    {
        http = new XMLHttpRequest();
    }
    return http;
}
function setSessionLifetime(checked) {
    xmlHttp = createXMLHttpRequest();
    var url = 'session_setup.php';
    if (checked == true) {
        url += '?set=1';
    } else {
        url += '?set=0';
    }
    xmlHttp.open("GET", url, true);
    xmlHttp.onreadystatechange = function() {
        if(xmlHttp.readyState==4 && xmlHttp.status==200)
        {
            window.location.href='session_printlifetime.php';
        }
    }
    xmlHttp.send(null);
}
</script>
</head>

<body>
<?php ?>
<input type="checkbox" name="setlifetime" id="setlifetime" value="1" onclick="setSessionLifetime(this.checked)" />set one life's session lifetime
</body>
</html>