Pedro Morillo

Improving the performance of distributed virtual environment systems

The 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 nonlinear 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 percent 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.

A Latency-Aware Partitioning Method for Distributed Virtual Environment Systems

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.

On the Characterization of Peer-To-Peer Distributed Virtual Environments

Large scale distributed virtual environments (DVEs) have become a major trend in distributed applications, mainly due to the enormous popularity of multi-player online games in the entertainment industry. Since architectures based on networked servers seem to be not scalable enough to support massively multi-player applications, peer-to-peer (P2P) architectures have been proposed as an efficient and truly scalable solution for this kind of systems. However, in order to design efficient DVEs based on peer-to-peer architectures these systems must be characterized, measuring the impact of different client behaviors on system performance. This paper presents the experimental characterization of peer-to-peer distributed virtual environments in regard to well-known performance metrics in distributed systems. Characterization results show that system saturation is inherently avoided due to the peer-to-peer scheme, as it could be expected. Also, these results show that the saturation of a given client exclusively has an effect on the surrounding clients in the virtual world, having no noticeable effect at all on the rest of avatars. Finally, the characterization results show that the response time offered to client computers greatly depends on the number of new connections that these clients have to make when new neighbors appear in the virtual world. These results can be used as the basis for an efficient design of peer-to-peer DVE systems.

A new AR authoring tool using depth maps for industrial procedures

Several augmented reality systems have been proposed for different target fields such as medical, cultural heritage and military. However, most of the current AR authoring tools are actually programming interfaces that are exclusively suitable for programmers. In this paper, we propose an AR authoring tool which provides advanced visual effect, such as occlusion or media contents. This tool allows non-programming users to develop low-cost AR applications, specially oriented to on-site assembly and maintenance/repair tasks. A new 3D edition interface is proposed, using photos and Kinect depth information to improve 3D scenes composition. In order to validate our AR authoring tool, two evaluations have been performed, to test the authoring process and the task execution using AR. The evaluation results show that overlaying 3D instructions on the actual work pieces reduces the error rate for an assembly task by more than a 75%, particularly diminishing cumulative errors common in sequential procedures. Also, the results show how the new edition interface proposed, improves the 3D authoring process making possible create more accurate AR scenarios and 70% faster.

A new system architecture for crowd simulation

Crowd simulation requires both rendering visually plausible images and managing the behavior of autonomous agents. Therefore, these applications need an efficient design that allows them to simultaneously handle 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 distributed virtual environments. Also, we propose a distributed computer architecture which is 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.

Implementing immersive clustering with VR juggler

Continuous, rapid improvements in commodity hardware have allowed users of immersive visualization to employ high-quality graphics hardware, high-speed processors, and significant amounts of memory for much lower costs than would be possible with high-end, shared memory computers traditionally used for such purposes. Mimicking the features of a single shared memory computer requires that the commodity computers act in concert—namely, as a tightly synchronized cluster. In this paper, we describe the clustering infrastructure of VR Juggler that enables the use of distributed and clustered computers for the display of immersive virtual environments. We discuss each of the potential ways to synchronize a cluster for immersive visualization in use today. Then, we describe the VR Juggler cluster infrastructure in detail, and we show how it allows virtual reality application developers to combine various existing clustering techniques to meet the needs of their specific applications.

On the characterization of avatars in Distributed Virtual Worlds

Abstract In a Distributed Virtual Environment system several users connected from different computers can share the same virtual world. Current DVE systems run simulations based on a server-network architecture, where the population of avatars should be properly assigned to the servers in the DVE. This goal, called partitioning problem, is a hot research problem in the field of networked 3D real time graphics. Some approaches have been proposed for resolving this problem, all of them based on a very basic model which describes the behaviour of an avatar in a virtual world. This model estimates the workload gener-ated by an avatar to the server where is allocated as an independent and static value. In order to design scalable and accurate partitioning schemes we propose a new characterization of the workload generated by the avatars in the system. In our model this behaviour has been successfully correlated with the move-ment rate of the avatars and a new parameter proposed, called factor of presence, which measures the density of avatar in a virtual scene.

Ensuring the performance and scalability of peer-to-peer distributed virtual environments

Large scale distributed virtual environments (DVEs) have become a major trend in distributed applications. Peer-to-peer (P2P) architectures have been proposed as an efficient and truly scalable solution for these kinds of systems. However, in order to design efficient P2P DVEs these systems must be characterized, measuring the impact of different client behavior on system performance. This paper presents the experimental characterization of P2P DVEs. The results show that the saturation of a given client has an exclusive effect on the surrounding clients in the virtual world, having no noticeable effect at all on the rest of clients. Nevertheless, the interactions among clients that can take place in this types of systems can lead to the temporal saturation of an unbounded number of clients, thus limiting the performance of P2P DVEs. In this paper, we also discuss and propose a technique for avoiding the saturation of the client computers in P2P DVEs. The evaluation results show that the performance and the scalability of P2P DVEs are significantly improved. These results can be used as the basis for an efficient design of P2P DVEs.

An ACS-based partitioning method for distributed virtual environment systems

Fast Internet connections and the widespread use of high performance graphic cards are making distributed virtual environment 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 DVE system. One of these key issues is the partitioning problem. This problem consists of efficiently assigning clients (3D avatars) to the servers in the system. This paper proposes a new implementation of the ant colony system (ACS) search method for solving the partitioning problem in DVE systems. The ACS method is an heuristic search method based on evolutionary computation. Performance evaluation results show that, due to its ability for both finding good search paths and escaping from local minima, the proposed method can provide better solutions with shorter execution times than the methods proposed in the literature, particularly for large DVE systems. Therefore, the proposed implementation of the ACS search method improves the scalability and efficiency of DVE systems.

A comparison study of evolutive algorithms for solving the partitioning problem in distributed virtual environment systems

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 (3D 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 ad hoc 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.