code: private long guessIndex(int seqNo) {
  		if (this.seqNum < 32768) {
  			if (seqNo - this.seqNum > 32768) {
  				guessedROC = roc - 1;
  			} else {
  				guessedROC = roc;
  			}
  		} else {
  			if (seqNum - 32768 > seqNo) {
  				guessedROC = roc + 1;
  			} else {
  				guessedROC = roc;
  			}
  		}
  
  		return ((long) guessedROC) << 16 | seqNo;
  	}
docs: Compute (guess) the new SRTP index based on the sequence number of a
  received RTP packet.
  
  @param seqNo
  sequence number of the received RTP packet
  @return the new SRTP packet index