Distributed Interactive Simulation (DIS) is an emerging simulation system requiring state-of-the art communication services and protocols. The communication services identified by the DIS Communication Architecture and Security Subgroup (CASS) fall into two classes, interim and long-term. DIS has two choices for Commercial-Off-The-Shelf communication protocols, Internet or Open System Interconnection (OSI) standards. Both protocol suites meet interim requirements; however, neither protocol suite can meet the full range of multicast requirements. Work has begun in national standards organizations to develop these protocols, and this work is based on the OSI/GOSIP architecture. The DIS interim architecture will be based on Internet standards but, if DIS is to comply with the GOSIP mandate, a strategy for the transition to OSI must be devised. This paper develops a transition plan which addresses GOSIP compliance and a strategy for meeting long-range multicast requirements.