A concurrency control mechanism for a networked virtual environment is a key element in many collaborative computer-aided design applications. However, conventional object-based locking mechanisms restrict the behaviors of nonowners, and an attribute-based locking mechanism may produce another problem called task-surprise, which disturbs users' collaboration. In this paper, we propose a hybrid concurrency control mechanism that reduces restrictions of nonowners' behaviors and task-surprises in a networked virtual environment. The proposed method consists of two concurrency control approaches: task-based concurrency control and personal workspaces. The task-based concurrency control approach allows nonowners to do some tasks if they do not conflict with the tasks of the owner of the shared object. The personal workspaces approach provides an independent workspace where a user can manipulate copies of the shared objects. The proposed method was applied to a collaborative level design for a large-scale online game as a case study. We evaluated its performance by experiments and user studies to check acceptance and usability of the proposed method.

Multi-server-based distributed virtual environment (MSDVE) systems have become prevalent, supporting a large number of internet users. In MSDVEs, the load balancing among servers is an important issue to achieve system scalability. However, existing approaches must pay high migration overhead for the state transition of users or regions, thus the excessive holding time during load distribution makes it difficult for the system to keep the interactive performance acceptable. This paper aims to provide an efficient load distribution mechanism in which a group of servers takes charge of regions and shares region information among servers. The proposed mechanism dynamically classifies task types based on features of requested messages, and distributes each task fairly to neighboring servers. We have implemented the proposed mechanism extending our network framework for DVE, ATLAS, and our experiments show that the task distribution reduces both communication and processing overhead during load distribution without significant classification overhead.

A distributed virtual environment (DVE) is a software system that allows users in a network to interact with each other by sharing a common view of their states. As users are geographically distributed over large networks like the internet and the number of users increases, scalability is a key aspect to consider for real-time interaction. Various solutions have been proposed to improve the scalability in DVE systems but they are either focused on only specific aspects or customized to a target application. In this paper, we classify the approaches for improving scalability of DVE into five categories: communication architecture, interest management, concurrency control, data replication, and load distribution. We then propose a scalable network framework for DVEs, ATLAS. Incorporated with our various scalable schemes, ATLAS meets the scalability of a system as a whole. The integration experiences of ATLAS with several virtual reality systems ensure the versatility of the proposed solution.