The purpose of interoperability testing is to ensure that interconnected protocol implementations communicate correctly while providing the expected services. However, interoperability test generation is known to be complex. On one hand, most current interoperability test cases are still generated in a manual way, which is time-consuming and error-prone. On the other hand, existing automatic test case generation methods often encounter the state explosion problem due to the multi-component nature of interoperability testing. In this report, we propose an approach for automatic interoperability test case generation. This method, based on formal interoperability de nitions, intends to obtain a composite product of the speci cations of each protocol implementation with respect to a preselected property to be veri ed. To relieve the state explosion problem, only the necessary global behavior of speci cations are calculated. The obtained composite product intends to keep only the events relevant to the property to be veri ed. We show that an interoperability test case derived by using this approach is unbiased and nonpermissive.