This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
In Ivan's notes, p.403, session title "Design an asynchronous document style web service", there is a flow chart diagram showing that the processing layer delegates the interaction layer, which determines if a client call back or polling is necessary. So, from this diagram, the interaction layer does the client callback or polling.
But on p.404, Ivan's notes says "Another way of showing the same thing...." (a sequential diagram), the diagram shows that the client polls response from the interaction layer. Or, the processing layer callback the client.