Due to the current limited IPv4 address space, the cellular industry has decided tostart using the IPv6 for mobile users in the 3G network. However, there is a potentialthreat to the success of a 3G network deployment, as the success will depend on thedata services offered to the end users. These services all reside in the computernetwork using the current IPv4 address space, which makes them inaccessible tousers in the IPv6 address space. Previous studies on network address translation haveshown that the REBEKAH-IP with Port Extension RPX is promising in that it providesexcellent scalability and also supports all types of services without limitation for themobile users in a cellular network. In this paper, we propose a method to evaluate theperformance of the RPX scheme in terms of the scalability and the extent of publicIPv4 address utilization. We provide a mathematical model as a guideline to determinethe range of public IPv4 addresses allocated to an RPX gateway. These addresses areused to translate the IPv6 address space for service to the mobile terminals in a 3Gnetwork. In addition, we present all results on the practical scalability of RPX throughmathematical analysis and simulations.