Silvia Rueda

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 Saturation Avoidance Technique for Peer-to-Peer Distributed Virtual Environments

The current expansion of multi-player online games has promoted the growth of large scale distributed virtual environments (DVEs). In these systems, peer-to-peer architectures have been proved as the most scalable scheme for supporting massively multi-player applications. Nevertheless, the interactions among clients that can take place in this type of systems can lead to the temporal saturation of some of the clients. Since a client saturation has an effect on other clients, these situations limit the performance of peer-topeer DVEs. In this paper, we propose an adaptive technique for avoiding the saturation of the client computers in DVE systems based on peer-to-peer architectures. This technique is based on monitoring the client state and discarding some of the messages received from other clients when the client is close to saturation. The evaluation results show that the proposed method improves the system performance without having an effect on the awareness rate, regardless of the movement pattern that avatars can follow. As a result, both the performance and the scalability of peer-to-peer DVEs are significantly improved.

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.

Terrain data compression using wavelet-tiled pyramids for online 3D terrain visualization

Last years have witnessed the widespread use of online terrain visualization applications. However, the significant improvements achieved in sensing technologies have allowed an increasing size of the terrain databases. These increasing sizes represent a serious drawback when terrain data must be transmitted and rendered at interactive rates. In this paper, we propose a novel wavelet-tiled pyramid for compressing terrain data that replaces the traditional multiresolution pyramid usually used in wavelet compression schemes. The new wavelet-tiled pyramid modifies the wavelet analysis and synthesis processes, allowing an efficient transmission and reconstruction of terrain data in those applications based on multiresolution tiled pyramids. A comparative performance evaluation with the currently existing techniques shows that the proposed scheme obtains a better compression ratio of the terrain data, reducing the storage space and transmission bandwidth required, and achieving a better visual quality of the virtual terrain reconstructed after data decompression.

A Peer-To-Peer platform for simulating distributed virtual environments

The current expansion of multi-player online games has promoted the growth of large scale distributed virtual environments (DVEs). In these systems, peer-to-peer architectures have been proved as an efficient scheme for supporting massively multi-player applications. In order to research on this type of architecture, stand-alone simulators do not take into account inconsistencies due to network latency, and it is necessary to develop a distributed tool that allows to simulate large-scale DVEs in an efficient way. In this paper, we propose a distributed platform for simulating the behavior of peer-to-peer DVEs. This simulator is implemented following a modular architecture. It is capable of providing the main performance metrics in distributed systems, and it contains all the elements involved in real DVE simulations like the awareness method and the graphic interface. As a result, this tool can be used in real simulations of peer-to-peer DVEs, becoming an invaluable tool for capturing the behavior of this kind of systems.

A sexual elitist genetic algorithm for providing QoS in distributed virtual environment systems

Architectures based on networked servers have become a de-facto standard for distributed virtual environment (DVE) systems. These systems allow a large number of remote users to share a single 3D virtual scene. In order to provide quality of service in a DVE system, clients should be assigned to servers taking into account system throughput and system latency. This highly complex problem is known as the quality of service (QoS) problem. This paper proposes an elitist sexual genetic algorithm for solving the QoS problem in distributed virtual environment systems. Performance evaluation results show that, due to its ability of both finding good search paths and keeping diversity escaping from local minima, this nature inspired technique can provide significantly better solutions than other heuristic methods with shorter execution times. Therefore, the proposed implementation of GA search method can improve the QoS offered by DVE systems.

A genetic approach for adding QoS to distributed virtual environments

Distributed virtual environment (DVE) systems have been designed last years as a set of distributed servers. These systems allow a large number of remote users to share a single 3D virtual scene. In order to provide quality of service in a DVE system, clients should be properly assigned to servers taking into account system throughput and system latency. The latter one is composed of both network and computational delays. This highly complex problem is known as the quality of service (QoS) problem. In this paper, we study the implementation of a genetic algorithm (GA) for solving the QoS problem in DVE systems. Performance evaluation results show that, due to its ability of both finding good search paths and keeping diversity, this nature inspired technique can provide significantly better solutions than other heuristic methods while requiring shorter execution times. Therefore, the proposed implementation of GA search method can actually improve the QoS offered by DVE systems.

A neural network approach for real-time collision detection

The objective of the present work has been to develop a collision detection algorithm suitable for real-time applications. It is applicable to box-shaped objects and it is based on the relation between the colliding object positions and the impact point. The most known neural network (multilayer perceptron) trained with the familiar backpropagation learning algorithm has been used for this problem; such algorithm models the collision, then decides the impact point and the direction of the forces. The algorithm results are very good for the case of box-shaped objects. Furthermore, the computational cost is independent from the object positions and the way the surfaces are modeled, so it is also suitable for real-time applications. The model is being used and validated in a real harbor crane simulator developed by the Robotics Institute for Valencia Harbor in Spain.

Improving hybrid distributed architectures for interactive terrain visualization

Interactive 3D terrain visualization plays an important role in multiple networked applications like virtual worlds visualization, multiplayer games or distributed simulators. Since the client/server architecture has obvious scalability limitations, different peer-to-peer schemes have been proposed as trade-off solutions that yield good robustness, availability and scalability for this kind of systems. In this paper, we propose a new hybrid distributed architecture that significantly improves the scalability and performance of the existing proposals. The proposed scheme redesigns the relationships between the different elements of a hybrid architecture, modifies the information shared by each client with its neighboring peers and varies the messages exchanged among them, providing a larger number of users with a fluid navigation experience over a large virtual terrain.