code: @VisibleForTesting
  	static Integer getReceivedStations(AisExtractor extractor, int slotTimeout,
  			int startIndex) {
  		if (slotTimeout == 3 || slotTimeout == 5 || slotTimeout == 7)
  			return extractor.getValue(startIndex + 5, startIndex + 19);
  		else
  			return null;
  	}
docs: Returns received stations as per 1371-4.pdf.
  
  @param extractor
  @param slotTimeout
  @param startIndex
  @return