Multi-server Distributed Virtual Environment Research Articles

Consistency-Aware Zone Mapping and Client Assignment in Multi-Server Distributed Virtual Environments

In Distributed Virtual Environments (DVEs), the primary task is to maintain a consistent view of the virtual world among all users. Multi-server architecture has been shown to have good scalability to support a large population of users in DVEs. In the zone-based Multi-server Distributed Virtual Environment (MSDVE), zone mapping and client assignment are two key issues in the design of an efficient and scalable MSDVE. Most of the existing work on the zone mapping and client assignment issues in MSDVE aims to either balance workload among servers, reduce inter-server communication, and/or reduce transmission delay. In this paper, we study the zone mapping and client assignment issues from a new perspective aiming to reduce the inconsistency of a DVE. Using the time-space inconsistency metric, we formally formulate the problem as a mix integer programming problem. The zone mapping and client assignment strategy is proposed which consists of a centralized algorithm for initialization and a distributed adaptive tuning algorithm for running system. Extensive experiments were conducted both by simulation and real system for evaluating the performance of the proposed solutions and results are reported in the paper.

On View Consistency in Multi-Server Distributed Virtual Environments

A distributed virtual environment (DVE) is a shared virtual environment (VE) that allows remote users to interact with each other through networks. DVEs are becoming very popular due to some prominent applications, such as online games and virtual worlds. To support a large number of users, a multi-server DVE architecture may be adopted, with each server managing a subset of users. However, there are two critical problems with this architecture: view inconsistency caused by delays and server overloading caused by uneven distribution of users. While the first problem affects users' perception of the VE and causes user disputes, the second problem affects the system response time. In this paper, we first show that the view inconsistency problem and the load balancing problem are conflicting objectives. We then propose an efficient joint optimization framework to address both problems. Our results show that the proposed method can improve the view inconsistency problem significantly, which is important to the interactivity of DVE applications.

Update schedules for improving consistency in multi-server distributed virtual environments

Distributed Virtual Environments (DVEs) have been widely used in online games, military training and collaborative engineering applications, etc. In DVEs, the primary task is to maintain a consistent view of the virtual world among all users. Multi-server architecture has been shown to have good scalability to support a large population of users in DVEs. However, servers can still get saturated with network bandwidth due to several reasons. In this case, state updates cannot be disseminated timely and the consistency of the virtual world cannot be guaranteed. This paper investigates update schedules to prioritize state updates from a global perspective for improving consistency in multi-server DVEs where each server has a limit on upload bandwidth. Using time–space inconsistency (TSI) metric, we analyze the problem using Lagrange Multipliers for a DVE in an ideal situation with unchanged configurations and the results are then used to develop an updating algorithm in practical systems. Experimental results show that the proposed algorithm significantly improves the consistency compared to other existing update algorithms.

Reducing view inconsistency by predicting avatars' motion in multi-server distributed virtual environments

Multi-server distributed virtual environment (DVE) system contains a set of servers to support a huge number of geographically distributed users. It provides a shared virtual scenario where users represented by avatars participate in and interact with each other through networks. However, there are two technical challenges in designing an efficient DVE system with this architecture: view inconsistency caused by network delays and server overloading caused by uneven distribution of users. While the first problem affects users' perception of the VE and causes user disputes, the second problem affects the system response time. We present a new partitioning framework to simultaneously address the two problems, in which the DVE scenario is divided into a set of disjoint grids called virtual cells. The virtual cells are then indexed by a region quadtree and an algorithm is proposed to search the region quadtree so as to equally partition avatars among servers. By using probabilistic models to predict each avatar's future motion and the virtual region its area of interest (AOI) will cover, a density-based method is proposed to help each server construct avatar clusters from its local avatars in parallel. By estimating the possible distances of avatar's future position to the geometry center of each cluster, an algorithm is proposed to repartition non-assigned avatars among servers so as to reduce view inconsistency and preserve workload balancing among the servers. We conducted comprehensive experiments to evaluate our method by comparing it with other approaches.

A performance study on multi-server DVE systems

The advance in computer graphics and networking technologies leads to the development of distributed virtual environment (DVE), which allow remote users to share information and interact within a common virtual environment via a local area network or through the Internet. A DVE system needs to perform many tasks, such as processing of clients’ requests, synchronization, object transmission and interaction handling. However, the workload induced by these tasks may become significant in a large scale DVE, where there may be a large number of concurrent users. In such situation, a single server based DVE system may not have enough processing power to maintain the system interactivity. To address this problem, a number of multi-server based DVE systems have been developed. In this paper, we explore how existing multi-server based DVE systems manage large scale DVEs and discuss various issues for implementing a multi-server based DVE system. We study the performance of such a system under various conditions via several simulated experiments.