分布式虚拟环境

分布式虚拟环境就是大规模的、网络化的、基于计算机的虚拟世界,在虚拟世界里,许多人和计算机控制的实体能够进行交互作用。该文对分布式虚拟环境技术研究背景及其发展情况进行了介绍,并分析了国外发展趋势及国内状况。最后提出在我国发展分布式虚拟环境所应优先考虑的几点建议。     

A simulation modelling tool for Distributed Virtual Environments

Distributed Virtual Environments simulate the behaviour and activities of a great number of users interacting in a virtual world over a wide area network. The size of the virtual worlds and the tremendous number of users that these environments are called to support require additional bandwidth and computational resources. For supporting large-scale Distributed Virtual Environments, extended infrastructure is needed in terms of both hardware and software. However, both researchers and application designers do not always have access to such an extended infrastructure and the assessment and evaluation of developed performance improvement techniques becomes extremely difficult. To address this issue, this paper presents a simulation modelling tool, called STEADiVE for networked servers Distributed Virtual Environments that could be used by designers for evaluating the performance of their approaches under different scenarios and system settings. The validation of the simulation modelling tool has showed that it achieves high accuracy in representing a real DVE system. STEADiVE comes to fill in the gap in the area of simulation tools for these systems.     

支持协作的分布式虚拟环境

文章首先介绍了支持协作的分布式虚拟环境系统结构,并讨论了模型数据库及通讯的异构性问题。结合作者实现的应用系统,介绍了协作式分布虚拟环境系统所采用的关键技术,包括同步交互、对象分布等。     

Demand-Driven Geometry Transmission for Distributed Virtual Environments

We present a strategy for rendering in distributed virtual environments. A geometry database is maintained by a server, while users invoke individual clients to interact with the environment. Instead of downloading a complete copy of the geometry data, the data is distributed on demand, thus gaining signifcant savings in network bandwidth. Our strategy combines several techniques, including levels of detail, progressive refinement and graceful degradation to deliver the data “just in time” over the network to the rendering process. The method allows operate on a tight resource budget, which important if attempting to use low cost systems for virtual reality applications.     

基于角色的分布式协同虚拟环境建模

目前多数分布式协同虚拟环境建模,主要是解决异构性、可扩充性和行为真实感方面的问题,忽视了系统的安全性问题.而在实际的应用中,不同的用户具有不同的职责和权限.如果不进行安全方面的考虑,就会出现越权操作或非法访问的问题.本文针对分布式协同虚拟环境中用户访问权限的不同,提出了基于角色的分布式协同虚拟环境系统模型,给出了该模型的一种实现,并在应用系统中进行了实例验证.     

Provide Virtual Distributed Environments for Grid computing on demand

Grid users always expect to meet some challenges to employ Grid resources, such as customized computing environment and QoS support. In this paper, we propose a new methodology for Grid computing – to use virtual machines as computing resources and provide Virtual Distributed Environments (VDE) for Grid users. It is declared that employing virtual environment for Grid computing can bring various advantages, for instance, computing environment customization, QoS guarantee and easy management. A light weight Grid middleware, Grid Virtualization Engine, is developed accordingly to provide functions of building virtual environment for Grids. We also present a typical use case, on-demand build a virtual e-Science infrastructure to justify the methodology.     

大规模分布式虚拟环境中的同步问题

从大规模分布式虚拟环境的功能需求着手进行分析,指出了分布式虚拟环境中涉及的同步问题,包括三维对象行为的同步描述问题、保持数据一致性的并发控制问题,以及媒体传输过程中的同步问题,并希望能引出高效的解决方案。     

分布式虚拟环境中的实体划分技术的研究

构建大型的分布式虚拟环境时,系统内各实体的初始物理配置问题对系统性能的影响十分显著。论文首先分析了过去对该问题研究的不足,提出了一种综合性的系统代价度量标准和系统性能改善原则,并在此之上提出了一种初始实体划分算法。     

Scalability Analysis of the Hierarchical Architecture for Distributed Virtual Environments

A distributed virtual environment (DVE) is a shared virtual environment where multiple users at their workstations interact with each other over a network. Some of these systems may support a large number of users, for example, multiplayer online games. An important issue is how well the system scales as the number of users increases. In terms of scalability, a promising system architecture is a two-level hierarchical architecture. At the lower level, multiple servers are deployed; each server interacts with its assigned users. At the higher level, the servers ensure that their copies of the virtual environment are as consistent as possible. Although the two-level architecture is believed to have good properties with respect to scalability, not much is known about its performance characteristics. In this paper, we develop a performance model for the two-level architecture and obtain analytic results on the workload experienced by each server. Our results provide valuable insights into the scalability of the architecture. We also investigate the issue of consistency and develop a novel technique to achieve weak consistency among copies of the virtual environment at the various servers. Simulation results on the consistency/scalability trade-off are presented.     

虚拟人行为控制技术在分布式虚拟环境中的实现

在分布式虚拟环境中加入虚拟人的运动时,一方面要考虑行为建模与姿势控制技术的实现,以生成理想的行为动画,另一方面关节,体模型的复杂性导致运动参数在网络上传输的负载增大。如果采用不同层次的参数来描述虚拟人姿势,则可以实现一些高层的行为控制方式,并将参数关键帧技术和逆向运动学技术等各种动画技术有机结合,同时给网络传输参数的选择提供不同的解决方案,文章对采用不同方案带来的网络负载和计算负载进行了定性比较和分析。     

XML路由技术在分布式虚拟环境中的应用

在对XML路由技术进行研究和分析的基础上,提出一种基于XML路由的分布式虚拟环境系统构建方法.该方法将XML路由技术与主动兴趣管理相结合,采用双向共享组播树作为通信拓扑结构,根据发布-订购模式实现了数据包的主动过滤和转发.不仅减少系统的网络通信量,而且可以快速、动态地改变通信关系,有效地提高了分布式虚拟环境的可扩展性.最后通过原型系统的实现验证了该方法的可行性和有效性.     

A decision-making model for knowledge collaboration and reuse through scientific workflow

Past, present and future, to realize the aim of product CTQS (i.e., lower cost, faster time to market, higher quality and better service) with manufacturing intelligence, few manufacturers have no longer engaged in product related production decision support problem (P-DSP). However, P-DSP solving (P-DSPS) is a multi-criteria decision-making problem, which is context sensitive in solution objects-attributes and chaos in the decision process of manufacturing knowledge collaboration and reuse. To alleviate these limitations, this paper presents a novel triple deep workflow model for P-DSPS. Driven by a wicked task query, the proposed workflow of P-DSPS (WP-DSPS) has the function to retrieve similarity-based alternatives from domain knowledge driven solution flow (KSF) and to evaluate with expert knowledge collaboration from knowledge driven decision flow (KDF) based on utility theory under the task event driven control flow (ECF) strategy and operation logic. In the view of alternative adaption, a domain knowledge ontology-based degree of similarity (DoS) determines the P-DSPS alternatives width, a utility function-based degree of decision (DoD) determines alternatives quality, and a belief-based knowledge fusion technique is used to synthesize decision conflicts with a consensus degree (CD). To support the proposed models, a workflow-based system prototype is proposed and validated in two case studies.     

基于CORBA的分布式多媒体服务的QoS模型

对于分布式多媒体来说,必须保证包括端系统、通讯系统以及网络在内的整个系统的服务质量（QoS）。CORBA提供了一个开放式的分布式对象计算环境,它能使许多普通的网络程序设计自动化,并允许应用在异构环境下无缝链接。文章根据分布式多媒体通讯系统中的层次结构模型（QOS－A）,提出了一种基于CORBA的分布式多媒体模型。     

Evaluating the Impact of the Communication System on Distributed Virtual Environments

This paper analyzes the impact of the communication system on distributed virtual environments. We present a platform model that express the communication requirements of this kind of applications and evaluate it via simulation. Performance measurements varied the number of participants, the partition of the virtual environment, a participant's speed, and the size of the virtual world. Results show that the division of the environment improves the delay both to enter and to exchange groups, and reduces the number of messages exchanged. This partition allows both a participant's speed and the number of participants to increase, thereby ensuring a good interactivity.     

分布式虚拟环境中基于扫描体的碰撞检测研究

在分布式虚拟环境(DVE)中,由于网络传输的不确定性,物体的状态信息无法准确及时地传输到其他节点上,从而使得DVE中传统的基于状态序列的碰撞检测算法存在漏检和错检现象。在分析传统方法不足的基础上,提出了DVE中基于扫描体的碰撞检测算法,并给出了算法步骤,通过试验证明了该方法能够有效地避免网络传输所带来的不确定性,同时能为DVE提供具有较高精度的检测结果。     

A Flexible Architecture for Virtual Humans in Networked Collaborative Virtual Environments

Complex virtual human representation provides more natural interaction and communication among participants in networked virtual environments, hence it is expected to increase the sense of being together within the same virtual world. We present a flexible framework for the integration of virtual humans in networked collaborative virtual environments. A modular architecture allows flexible representation and control of the virtual humans, whether they are controlled by a physical user using all sorts of tracking and other devices, or by an intelligent control program turning them into autonomous actors. The modularity of the system allows for fairly easy extensions and integration with new techniques making it interesting also as a testbed for various domains from “classic” VR to psychological experiments. We present results in terms of functionalities, example applications and measurements of performance and network traffic with an increasing number of participants in the simulation.     

Distributed algorithms for QoS load balancing

We consider a dynamic load balancing scenario in which users allocate resources in a non-cooperative and selfish fashion. The perceived performance of a resource for a user decreases with the number of users that allocate the resource. In our dynamic, concurrent model, users may reallocate resources in a round-based fashion. As opposed to various settings analyzed in the literature, we assume that users have quality of service demands. A user has zero utility when falling short of a certain minimum performance threshold and having positive utility otherwise. Whereas various load-balancing protocols have been proposed for the setting without quality of service requirements, we consider protocols that satisfy an additional locality constraint: The behavior of a user depends merely on the state of the resource it currently allocates. This property is particularly useful in scenarios where the state of other resources is not readily accessible. For instance, if resources represent channels in a mobile network, then accessing channel information may require time-intensive measurements. We consider several variants of the model, where the quality of service demands may depend on the user, the resource, or both. For all cases we present protocols for which the dynamics converge to a state in which all users are satisfied. More importantly, the time to reach such a state scales nicely. It is only logarithmic in the number of users, which makes our protocols applicable in large-scale systems.     

一种用于动态环境的虚拟人行走规划方法

本文提出了一种基于Petn网的虚拟人行走规划方法,主要用于环境中存在静止和运动障碍物的复杂情况。我们实现的系统整体上以Petn网构建,由全局路径规划和局部路径规划两部分组成,Petn网负责两者之间的协调。仿真和试验结果表明,本文提出的方法简便易行。     

A Self Distributing Virtual Machine for Adaptive Multicore Environments

The use of parallel systems is no longer limited to dedicated clusters as multicore chips are more and more appearing in embedded applications. To meet power, performance and cost targets these systems need to be adaptive. The reconfiguration features of recent FPGAs make new approaches for this type of parallel computing possible: Dynamic reconfiguration at runtime offers an important step to adaptive behavior of systems-on-chip (SoCs). This article analyzes the challenges of such an adaptive SoC. It is shown that many of the requirements for an adaptive FPGA-realization are met by the SDVM, the scalable dataflow-driven virtual machine which has been successfully implemented and tested on a cluster of workstations. The SDVM has evolved to a virtualization layer for multicore-FPGAs, now called SDVM ^R . This virtualization layer allows a transparent runtime-reconfiguration of the underlying hardware to adapt to the changing system environment. Results for a basic application for both systems are presented.     

JAPE: A Prototyping System for Collaborative Virtual Environments

We present JAPE, a flexible prototyping system to support the design of a new advanced collaborative virtual environment. We describe the utilization of different hard- and software components to quickly build a flexible, yet powerful test bed for application and algorithm development. These components include a 3-D rendering toolkit, live video acquisition, speech transmission, and the control of tracking and interaction devices. To facilitate the simultaneous design of applications and algorithms that take advantage of unique features of new collaborative virtual environments, we provide the developer with a flexible prototyping toolkit which emulates the functionality of the final system. The applicability of JAPE is demonstrated with several prototype applications and algorithms.