Having worked on a quick version of XMPPong in Chapter 8, Building a Basic XMPP-Based Pong Game, as we plan to engage in some more intense engineering of our solution in this chapter, let's take a moment to think about how we would like XMPPong to work.

First, we are going to create a server component that knows how to manage an XMPPong game. We will expect two players to be connected to the component through their own clients. We expect messages to be sent between the component and the clients. Naturally, the component will handle all of the game logic (or business logic if we weren't building a game!), and clients will handle the graphical output and report on input from the players.

In preparation for all of this, let's talk about the messages we expect to be sent between the controller and the clients.