code: public int sendRR(MessageOut<? extends IMutation> message,
                        InetAddress to,
                        AbstractWriteResponseHandler handler,
                        boolean allowHints)
      {
          int id = addCallback(handler, message, to, message.getTimeout(), handler.consistencyLevel, allowHints);
          sendOneWay(message, id, to);
          return id;
      }
docs: Send a mutation message to a given endpoint. This method specifies a callback
  which is invoked with the actual response.
  Also holds the message (only mutation messages) to determine if it
  needs to trigger a hint (uses StorageProxy for that).
  
  @param message message to be sent.
  @param to      endpoint to which the message needs to be sent
  @param handler callback interface which is used to pass the responses or
  suggest that a timeout occurred to the invoker of the send().
  @return an reference to message id used to match with the result