In IP world, interoperability testing is heavily used to check the correctness of different implementations. Internet protocols have growing importance in communicating systems. In our paper we show an automatic interoperability test approach and also present its application on an IP-based protocol, ROHC. The primary goal of our work was to define an interoperability testing framework in TTCN-3 that can be used in general. After giving an overview on the ROHC protocol, we also describe the way we have conformance tested it. Then we present MAIT (Model for Automated Interoperability Test) and give detailed explanation on its components and their roles. At the end, we compare the advantages and disadvantages of conventional conformance testing and our interoperability testing model.