Interoperability testing aims at verifying the possibility for two or more components to communicate correctly while providing the foreseen services. In this paper, we describe a new method for generating interoperability test cases. This method is equivalent to classical methods in terms of non-interoperability detection. Contrary to classical approaches, this method avoids the well-known state-space explosion problem. It has been implemented in the CADP Toolbox and applied to a simplified version of the ISDN connection protocol. The obtained results confirm the real contribution of this method: test cases has been derived while classical approaches face the state-space explosion problem.