private function getTimestamp()
    {
        $zone = date('Z');
        $sign = ($zone < 0) ? '-' : '+';
        $zone = abs($zone);
        $zone = (int)($zone / 3600) * 100 + ($zone % 3600) / 60;
        return sprintf("%s %s%04d", date('D, j M Y H:i:s'), $sign, $zone);
    }