public boolean isOpen() {
		if ( STREAM_TYPE_MBUS_SERIAL == streamType || STREAM_TYPE_MBUS_TCP == streamType) {
			if ( null == mbus )
				return false;

			return mbus.isOpen();	
		}
		if ( STREAM_TYPE_SOUNDMETER_CENTER == streamType ) {
			if ( null == sm )
				return false;

			return sm.isOpen();
		}
		if ( STREAM_TYPE_FTULTRASONIC == streamType ) {
			if ( null == ftu )
				return false;

			return ftu.isOpen();
		}		
		if ( STREAM_TYPE_SYSTEM_COMMAND == streamType ) {
			return true;
		}

		return false;
	}