Abstract: The present invention relates to a method for checking a data exchange between participants in a call established on a communication medium in compliance with a protocol. In order to identify the various stages in a call process conforming to the protocol and to break said protocol once the checking procedure has started, the invention suggests that the data exchange be captured by-means of a protocol monitor (PM) connected to a communication medium (CM) and based on the finite state automaton principle. The test automaton contains the same states and state variables as the protocol automaton designed to define the communication protocol, apart from the fact that the test automaton is allocated a plurality of values within the same range of corresponding state variable values in the protocol automaton.