Massively multiplayer online games (MMOGs) have become highly popular in the last decade and now attract millions of users from all over the world to play in an evolving virtual world concurrently over the Internet. The high popularity of MMOGs created a rapidly growing market and this highly dynamic market has forced game developers to step up competitively. However, MMOG development is a challenging and expensive process. In this study, we present a high-level network simulation environment, which can be used to model and simulate typical MMOGs that have client-server architectures. The main objective is to provide a simulation environment to MMOG developers that can be used to test, analyze and verify various aspects of the MMOG network architecture. We have also implemented a graphical user interface that allows one to construct the simulation model visually. We have demonstrated the use of the simulation environment by experimental simulations.