code: private byte[] getExtraDataBytes()
  	{
  		byte[] buf = new byte[MAX_EXTRA_DATA];
  		byte[] ret;
  		int bytesCopied = 0;
  
  		if (grouped)
  		{
  			buf[bytesCopied] = group;
  			bytesCopied++;
  		}
  		if (encrypted)
  		{
  			buf[bytesCopied] = encrType;
  			bytesCopied++;
  		}
  		if (lengthIndicator)
  		{
  			System.arraycopy(Helpers.convertIntToDWord(dataLength), 0, buf, bytesCopied, 4);
  			bytesCopied += 4;
  		}
  
  		ret = new byte[bytesCopied];
  		System.arraycopy(buf, 0, ret, 0, bytesCopied);
  
  		return ret;
  	}
docs: A helper function for the getFrameBytes function that returns an array
  of all the data contained in any extra fields that may be present in
  this frame.  This includes the group, the encryption type, and the
  length indicator.  The length of the array returned is variable length.
  
  @return an array of bytes containing the extra data fields in the frame