code: public void send(CEMI frame, BlockingMode mode) throws KNXTimeoutException,
  		KNXConnectionClosedException
  	{
  		if (layer == BUSMONITOR_LAYER)
  			throw new KNXIllegalStateException("send not permitted in busmonitor mode");
  		if (!(frame instanceof CEMILData))
  			throw new KNXIllegalArgumentException("unsupported cEMI type");
  		super.send(frame, mode);
  	}
docs: Sends a cEMI frame to the remote server communicating with this endpoint.
  <p>
  Sending in busmonitor mode is not permitted.<br>
  
  @param frame cEMI message to send, the expected cEMI type is according to the used
  tunneling layer