rvice may have been performed, but 
      it may have taken more time than expected or
      it may have been performed, 
      but the reply message has failed to arrive.
      If the service is <em>idempotent</em> -
      <em>i.e.</em> calling the service twice has 
      the same effect as calling it once -
      the client, when the timeout has expired,
      can just send the request once again;
      otherwise, it has to use other means to recover 
      from this situation.
</li><li> A pusher will ne