In the first stage, the teams are working simultaneously on all phases of the problem. The analysis team is generating requirements. The design team takes these requirements and feeds back complexity issues to the requirement team as well as feeding critical implementation tasks to the implementation team. The testing team prepares and develops the testing environment.
The implementation team has to be focused on the critical tasks. This is usually the hardest task. This contrasts the common practice of doing the simple things first and waiting until late in the product implementation to tackle the harder tasks. Most products that follow this practice end up failing. Once the critical task components have been implemented, the system is ready to transition to the prototype stage.
One of the goals of this stage is for the teams to convince themselves that a solution can be accomplished.