def __handle_low_seq_resend(self, msg, req):
        """special error case - low sequence number (update sequence number & resend if applicable). Returns True if
           a resend was scheduled, False otherwise. MUST be called within self.__requests lock."""
        if msg[M_TYPE] == E_FAILED and msg[M_PAYLOAD][P_CODE] == E_FAILED_CODE_LOWSEQNUM:
            with self.__seqnum_lock:
                self.__seqnum = int(msg[M_PAYLOAD][P_MESSAGE])
            # return value indicating shutdown not useful here since this is run in receiver thread
            self.__retry_enqueue(PreparedMessage(req._inner_msg_out, req.id_))
            return True
        return False