def qos(self, prefetch_size=0, prefetch_count=0, is_global=False):
        '''
        Set QoS on this channel.
        '''
        args = Writer()
        args.write_long(prefetch_size).\
            write_short(prefetch_count).\
            write_bit(is_global)
        self.send_frame(MethodFrame(self.channel_id, 60, 10, args))

        self.channel.add_synchronous_cb(self._recv_qos_ok)
Set QoS on this channel.