In a phase of configuration, a state machine is constructed with states and transitions configured according to at least one type of data to be extracted from a data stream travelling around an IP network. The transitions between states are activated by conditions defined as a function of rules of organization of the data of the stream according to an application layer protocol. One or more states are moreover selected for the extraction of data from the stream. Thereafter, in a phase of real-time analysis of the stream, the stream data arising from IP packets travelling successively around the network are observed. When the state machine is in a current state, a search is conducted as to whether a condition of activation of a transition to a target state is realized by the data observed from the stream, and when such an activation condition is realized, the state machine is toggled into the target state. The data from the stream are extracted when the state machine is in a state selected in the configuration phase.