Massively Multiuser Online Games (MMOG), now supporting millions of simultaneous participants on a regular basis, have become a significant contributor in human-tohuman communications. While originally designed for games, they have now moved into serious realms of socialization, business, commerce, scientific experimentation, and others. As more and more people participate in these massive environments, the underlying infrastructure is starting to exhibit shortcomings that limit the progress,

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... acticality, and applicability of MMOGs. This thesis explores various architectural challenges inherent in MMOGs and offers effective solutions in the context of a hybrid model. The key objective of this hybrid model, named Massively Multiuser VIrtual Simulation Architecture (MM-VISA), is to form a stable and scalable collaboration platform that economically combines the resources of both servers and player peers, incorporating the advantages of a centralized architecture and a scalable Peer-to-Peer distributed system, which in turn leads to improved support for the participating masses. Synchronous communication among massive number of users in an MMOG is a prime concern, and difficult and/or expensive to support. This massiveness causes challenges that cannot be solved with conventional techniques used in traditional collaborative environments. Massive number of players' frequent and random movements in the virtual environment and zone-switching can easily break synchronous communication and cause substantial strain on the underlying system, networking, and server ii iii infrastructure. To alleviate such problems, this thesis proposes a model consisting of interest-driven zone crossing, dynamic shared regions, clustering of players based on their attributes, multilevel multiphase load-balancing with several plug-able solutions, hybrid routing based on a combination of centralized and Peer-to-Peer (P2P) networking, and interest-management techniques considering dynamics of the area of interest and graphical computing. It is then revealed that the model significantly improves overall system performance and enhances infrastructure stability in terms of load, network overlay, and other performance characteristics.