def send_message(self, msg, seq):
        """
        Convenience routine for services to send a message across a
        particular connection. NOTE: write_data is much more efficient
        if same message is being sent to multiple connections. Not
        threadsafe.
        @param msg: message to send
        @type  msg: Msg
        @param seq: sequence number for message
        @type  seq: int
        @raise TransportException: if error occurred sending message
        """
        # this will call write_data(), so no need to keep track of stats
        serialize_message(self.write_buff, seq, msg)
        self.write_data(self.write_buff.getvalue())
        self.write_buff.truncate(0)