code: public void setTransactionID(byte[] tranID) throws StunException {
  		if (tranID == null || (tranID.length != TRANSACTION_ID_LENGTH && tranID.length != RFC3489_TRANSACTION_ID_LENGTH))
  			throw new StunException(StunException.ILLEGAL_ARGUMENT, "Invalid transaction id length");
  
  		int tranIDLength = tranID.length;
  		this.transactionID = new byte[tranIDLength];
  		System.arraycopy(tranID, 0, this.transactionID, 0, tranIDLength);
  	}
docs: Copies the specified tranID and sets it as this message's transactionID.
  
  @param tranID
  the transaction id to set in this message.
  
  @throws StunException
  ILLEGAL_ARGUMENT if the transaction id is not valid.