Last years have witnessed a dramatic growth in the number as well as in the variety of Distributed Virtual Environment systems. These systems allow multiple users, working on different client computers that are interconnected through different networks, to interact in a shared virtual world. One of the key issues in the design of scalable and cost-effective DVE systems is the partitioning problem. This problem consists of efficiently assigning the existing clients to the servers in the system, and some techniques have been already proposed for solving it. This paper experimentally analyzes the correlation of the quality function proposed in the literature for solving the partitioning problem with the performance of DVE systems. Since the results show an absence of correlation, we also propose the experimental characterization of DVE systems. The results show that the reason for that absence of correlation is the non-linear behavior of DVE systems with regard to the number of clients in the system. DVE systems reach saturation when any of the servers reaches 100% of CPU utilization. The system performance greatly decreases if this limit is exceeded in any server. Also, as a direct application of these results we present a partitioning method that is targeted to keep all the servers in the system below a certain threshold value of CPU utilization, regardless of the amount of network traffic. Evaluation results show that the proposed partitioning method can improve DVE system performance, regardless of both the movement pattern of clients and the initial distribution of clients in the virtual world.

Abstract. Distributed Virtual Environment systems have experienced a spectacular growth last years. One of the key issues in the design of scalable and cost-effective DVE systems is the partitioning problem. This problem consists of efficiently assigning clients (3-D avatars) to the servers in the system, and some techniques have been already proposed for solving it. In this paper, we propose the correlation of the quality function proposed in the literature for solving the partitioning problem with the performance of DVE systems. Since the results show an absence of correlation, we also propose the experimental characterization of DVE systems. The results show that the reason for that absence of correlation is the non-linear behavior of DVE systems with the number of avatars in the system. Also, the results show that workload balancing mainly has an effect on system throughput, while minimizing the amount of inter-server messages mainly has an effect on system latency.

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Distributed virtual environment (DVE) systems allow multiple users working on different client computers interconnected through different networks to interact in a shared virtual world. In these systems, latency is crucial for providing an acceptable quality of service (QoS), since it determines how fast client computers are reported about changes in the shared virtual scene produced by other client computers. This paper presents in a unified manner a partitioning approach for providing a latency below a threshold to the maximum number of users as possible in DVE systems. This partitioning approach searches the assignment of avatars, which represents the best trade-off among system latency, system throughput, and partitioning efficiency when solving the partitioning problem. Evaluation results show that the proposed approach not only maximizes system throughput, but also allows the system to satisfy, if possible, any specific latency requirement needed for providing QoS. This improvement is achieved without decreasing either image resolution or quality of animation, and it can be used together with other techniques already proposed. Therefore, it can contribute to provide QoS in DVEs.

Abstract. In recent years, large scale distributed virtual environments (DVEs) have become a major trend in distributed applications, mainly due to the enormous popularity of multiplayer online games in the entertainment industry. Since architectures based on networked servers seems to be not scalable enough to support massively multiplayer applications, peer-to-peer (P2P) architectures have been proposed as an efficient and truly scalable solution for this kind of systems. However, the main challenge of P2P architectures consists of providing each avatar with updated information about which other avatars are its neighbors. We have denoted this problem as the awareness problem. Although some proposals have been made, none of them provide total awareness to avatars under any situation. This paper presents a new awareness method based on unicast communication that is capable of providing awareness to 100% of avatars, regardless of both their location and their movement pattern in the virtual world. Therefore, it allows large scale DVEs based on P2P architectures to properly scale with the number of users while fully providing awareness to all of them.

Fast Internet connections and the widespread use of high performance graphic cards are making Distributed Virtual Environment (DVE) systems very common nowadays. However, there are several key issues in these systems that should still be improved in order to design a scalable and cost-effective system. One of these key issues is the partitioning problem. This problem consists of efficiently assigning clients (3-D avatars) to the servers in the system. In this paper, we present a comparison study of different modern heuristics for solving the partitioning problem in DVE systems, as an alternative to the adhoc heuristic proposed in the literature. Performance evaluation results show that some of the heuristic methods can greatly improve the performance of the partitioning method, particularly for large DVE systems. In this way, efficiency and scalability of DVE systems can be significantly improved.

Abstract. Network-server architecture has become a de-facto standard for Distributed Virtual Environment (DVE) systems. In these systems, a large set of remote users share a 3D virtual scene. In order to design scalable DVE systems, different approaches have been proposed to maintain the DVE system working under its saturation point, maximizing system throughput. Also, in order to provide quality of service to avatars in a DVE systems, avatars should be assigned to servers taking into account, among other factors, system throughput and system latency. This highly complex problem is called quality of service (QoS) problem in DVE systems. This paper proposes two different approaches for solving the QoS problem, based on modern heuristics (simulated annealing and GRASP). Performance evaluation results show that the proposed strategies are able no only to provide quality of service to avatars in a DVE system, but also to keep the system away from the saturation point.

Crowd simulation requires both rendering visually plausible images and managing the behavior of autonomous agents. Therefore, these applications need an efficient design that allow them to simultaneously tackle these two requirements. Although several proposals have focused on the software architectures for these systems, no proposals have focused on the computer systems supporting them.In this paper, we analyze the computer architectures used in the literature to support virtual environments. Also, we propose a distributed computer architecture efficient enough to support simulations of thousand of autonomous agents.This proposal consists of a cluster of interconnected computers in order to improve flexibility and robustness, as well as a hierarchical software architecture that efficiently provides consistency. Performance evaluation results show that the trade-off between flexibility and consistency allows to efficiently manage thousands of autonomous agents. Therefore, this network-based system architecture can provide the required scalability for large-scale crowd simulations.