OSI (Open Systems Interconnections) communication stacks can be used to interconnect heterogeneous DIS machines and eliminate their incompatibilities. However, the interoperability benefit of OSI stacks could be offset by the computational overhead associated with the complex data transformation process of OSI upper layers. It is feared that an OSI implementation utilizing the transformation process would be too slow to meet the real-time requirements of DIS networks. In this paper, we present the results and conclusions of a detailed performance evaluation study which we have recently conducted to measure the overhead of the OSI transformation process, assess its impact on the delay encountered by DIS PDUs, and evaluate the benefits of using lightweight transfer syntax implementations.