public function setReceiveDelay($milliseconds = null)
    {
        if (is_integer($milliseconds)
            && $milliseconds >= self::DEF_RECEIVE_DELAY
        ) {
            $this->_receivedelay = $milliseconds;
        } else {
            $this->_receivedelay = self::DEF_RECEIVE_DELAY;
        }
        return $this->_receivedelay;
    }