<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def request_start(self):
 """ Indicate readiness to receive stream. This is a blocking call. """

        self._queue.put(command_packet(CMD_START_STREAM))
        _LOGGER.info('Requesting stream')
        self._source.run()