Abstract-The rapid advancement and ubiquity of social virtual environments is bringing geographically distant users to interact as if they are in the same physical location, leading to the emergence of new application areas that adopt virtual environment technologies. In this article, we present our experiences of enhancing The 3rd International Workshop on Massively Multiuser Virtual Environments (MMVE 2010) by virtual environment technology to allow participants to attend remotely. Based on a survey conducted with both the virtual and physical participant, we find that virtual participation is a valuable addition for conference hosting, but informal social interactions may still be missing and require further support.

Although Multi-Avatar Distributed Virtual Environments (MAVEs) such as Real-Time Strategy (RTS) games entertain daily hundreds of millions of online players, their current designs do not scale. For example, even popular RTS games such as the StarCraft series support in a single game instance only up to 16 players and only a few hundreds of avatars loosely controlled by these players, which is a consequence of the Event-Based Lockstep Simulation (EBLS) scalability mechanism they employ. Through empirical analysis, we show that a single Area of Interest (AoI), which is a scalability mechanism that is sufficient for single-avatar virtual environments (such as Role-Playing Games), also cannot meet the scalability demands of MAVEs. To enable scalable MAVEs, in this work we propose Area of Simulation (AoS), a new scalability mechanism, which combines and extends the mechanisms of AoI and EBLS. Unlike traditional AoI approaches, which employ only update-based operational models, our AoS mechanism uses both event-based and updatebased operational models to manage not single, but multiple areas of interest. Unlike EBLS, which is traditionally used to synchronize the entire virtual world, our AoS mechanism synchronizes only selected areas of the virtual world. We further design an AoS-based architecture, which is able to use both our AoS and traditional AoI mechanisms simultaneously, dynamically trading-off consistency guarantees for scalability. We implement and deploy this architecture and we demonstrate that it can operate with an order of magnitude more avatars and a larger virtual world without exceeding the resource capacity of players' computers.

Existing architectures designed to host large-scale virtual environments (VEs) use a variety of approaches, but they often limit the interaction range with other users or with the VE. How densely users can populate a given region is also limited by the hosting machine's CPU or bandwidth resources. We are motivated to remove such restrictions and present SPEX, an infrastructure that supports scalable spatial publish/subscribe for VE applications. SPEX is scalable and fault-tolerant, with adaptive load balancing and low latency as its key features. It is designed for the state and overlay management in VEs with many concurrent users. We evaluate a practical SPEX implementation within Amazon's EC2 Cloud and present a feasible approach to supporting 750 users across a continent with low latency, opening the possibility for hosting fast-paced games (e.g., first-person shooters) or applications on a large-scale.

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