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。     

分布式地学虚拟环境研究

讨论了分布式地学虚拟环境的概念,特征以及与GIS的相互关系,从系统结构,数据模型,交互界面和开发工具方面,对分布式地学虚拟环境的系统框架进行了研讨。最后,从理论,技术和应用层面介绍了关于分布式地学虚拟环境的研究热点和难点,并讨论了进一步的研究方向。     

发布/订阅系统及其在分布虚拟环境中的应用

文章首先通过讨论发布/订阅系统和分布式虚拟环境各自的特点,提出在开发分布式虚拟环境时引入发布/订阅系统。结合分布式虚拟环境的要求设计了一个发布/订阅系统。详细描述了系统的原理和基本结构,及主要实现机制。实现了一个基于双层服务器结构的分布式虚拟开发环境。简单介绍了各层服务器的功能。通过引入共享组使各节点属性可以清晰地结构存储在服务器上。并论述了将订阅/发布系统应用在分布式虚拟开发环境NSVRT中的具体方案。结果表明该系统在NSVRT的应用,简化了开发分布式虚拟环境的工作,同时满足了分布式虚拟环境开发的实时性要求,最后提出今后的工作重点。     

分布式虚拟环境的远程教育系统浅议

本文简要介绍了分布式虚拟环境，探讨了如何在分布式虚拟环境中设计与实现远程教育的思想和方法，并给出一个Client-Sever型分布式虚拟环境远程教育学习系统和在线个性化电子教材生成系统。     

在分布式虚拟现实的环境中数据传输的研究

分布式虚拟现实技术可以在分布式环境下满足多人实时参与虚拟环境的要求．较好地实现了信息的交互、文中从分布式虚拟现实的特征、网络模型以及数据的传输进行了分析和讨论，减少网络通讯负载一直是分布式虚拟现实致力解决的问题，本文基于分布式虚拟环境介绍了兴趣管理技术，并提出了多阈值DR技术的思想。多阈值DR技术为解决大规模分布式虚拟环境的通讯负载提供了新的思路。     

分布式虚拟环境的网络通信机制研究与应用

分布式虚拟环境(Distributed Virtual Environments,简称DVEs),其网络通信模块的开发,技术复杂,工作量大.而WTK支持分布式虚拟环境,可实现高效系统开发.介绍了WTK的网络体系结构,重点分析了分布式虚拟环境的网络结构、通信模型,深入研究了状态更新消息传递机制.在此基础上,给出了一个基于WTK实现分布式虚拟环境的设计方案,并介绍了应用程序仿真循环.实验结果表明:基于该设计方案的DVEs应用可较好满足交互的动态性和一致性要求,具有可行性.     

分布式虚拟环境中的聊天机器人的研究

该文探索了通过自然语言界面从基于Web的应用中获取知识的一种方法。介绍了一些著名聊天机器人程序着重给出了基于AIML的聊天机器人A.L.I.C.E的运行机制,并分析了其适合于分布式应用的特点。通过对其进行改进将其结合进分布式虚拟环境中,构造了一个基于Web的分布式虚拟环境中的聊天机器人。     

面向电子商务的分布式协同虚拟环境的研究

首先介绍了分布式虚拟现实、协同虚拟环境的基本概念、特征和技术需求，然后阐述了分布式协同虚拟环境的需求特性，最后分析并给出了一个面向电子商务的分布式协作虚拟环境的实现技术和系统应用框架。     

分布式虚拟环境综述

在分布式虚拟环境中,位于不同物理位置的多个用户或多个虚拟环境通过网络相互联结,进行信息共享和交互.该文结合作者的研究工作,从分布式虚拟环境的产生、需求和特征、模型和结构以及系统关键技术这几个方面对分布式虚拟环境的研究情况进行综述,讨论了存在的问题和进一步的发展方向.     

一种基于VRML—Java的分布式虚拟环境模型及其实现

以分布式虚拟环境下的协同工作为根本目的,分析了采用VRML—Java作为开发平台的可行性,并在此基础上提出了基于VRML—Java的分布式虚拟环境的一种模型,对其实现作了简要介绍。     

An efficient partitioning algorithm for distributed virtualenvironment systems

Distributed virtual environment (DVE) systems model and simulate the activities of thousands of entities interacting in a virtual world over a wide area network. Possible applications for DVE systems are multiplayer video games, military and industrial trainings, and collaborative engineering. In general, a DVE system is composed of many servers and each server is responsible to manage multiple clients who want to participate in the virtual world. Each server receives updates from different clients (such as the current position and orientation of each client) and then delivers this information to other clients in the virtual world. The server also needs to perform other tasks, such as object collision detection and synchronization control. A large scale DVE system needs to support many clients and this imposes a heavy requirement on networking resources and computational resources. Therefore, how to meet the growing requirement of bandwidth and computational resources is one of the major challenges in designing a scalable and cost-effective DVE system. In this paper, we propose an efficient partitioning algorithm that addresses the scalability issue of designing a large scale DVE system. The main idea is to dynamically divide the virtual world into different partitions and then efficiently assign these partitions to different servers. This way, each server will process approximately the same amount of workload. Another objective of the partitioning algorithm is to reduce the server-to-server communication overhead. The theoretical foundation of our dynamic partitioning algorithm is based on the linear optimization principle. We also illustrate how one can parallelize the proposed partitioning algorithm so that it can efficiently partition a very large scale DVE system. Lastly, experiments are carried out to illustrate the effectiveness of the proposed partitioning algorithm under various settings of the virtual world     

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.     

Constructing communication subgraphs and deriving an optimalsynchronization interval for distributed virtual environmentsystems

The author considers problems of constructing a communication subgraph and deriving an optimal synchronization interval for a distributed virtual environment system (DVE). In general, a DVE system is a distributed system which allows many clients who are located in different parts of the network to concurrently explore and interact with each other under a high resolution, 3D, graphical virtual environment. Each client in a DVE system is represented by an avatar in the virtual environment, and each avatar can move and interact freely in the virtual environment. There are many challenging issues in designing a cost-effective DVE system. The article addresses two important design issues, namely: 1) how to construct a communication subgraph which can efficiently carry traffic generated by all clients in a DVE system, and 2) how to guarantee that each participating client has the same consistent view of the virtual world. In other words, if there is an action taken by an avatar or if there is any change in the state of an object in the virtual world, every participating client will be able to view the change. To provide this consistent view, a DVE system needs to perform synchronization actions periodically, We present several algorithms for constructing a communication subgraph. In the subgraph construction, we try to reduce the consumption of network bandwidth resources or reduce the maximum delay between any two clients in a DVE system. Based on a given communication subgraph, we then derive the optimal synchronization interval so as to guarantee the view consistency among all participating clients. The derivation of the optimal synchronization interval is based on the theory of Markov chains and the fundamental matrix     

异步DVE系统中生命周期约束下的因果一致性控制方法研究

分布式虚拟环境是模拟现实世界的虚拟空间,对因果一致性控制具有实时性要求,必须在事件生命周期结束前得到维护.然而,在大规模网络条件下,网络传输高延迟和动态性会导致部分事件不能及时到达,使已传到事件间因果关系无法在生命周期限制内有效传递.在现有方法中,部分方法基于所有事件一定能及时传到的假设,没有考虑生命周期对因果关系的制约;而另一部分方法虽然考虑了生命周期的约束,但其因果关系传递要求仿真时钟精确同步,且因果控制效率随系统规模的扩大而快速降低,限制了虚拟环境的普适性和实时性.提出了生命周期约束下的因果一致性控制方法LCO,突破了异步时钟间的时间值比较、多路径因果控制信息选择的终止条件、网络状况敏感的因果控制信息动态调节等关键技术,能够在事件无法及时传到时,仍可以根据已传到的事件计算出因果传递关系.实验证明,LCO既能维护生命周期内的因果一致性,又使因果控制信息量与系统规模无关,降低网络传输和计算开销.     

An architecture to support scalable distributed virtual environment systems on grid

A Distributed Virtual Environment (DVE) system offers a computer-generated virtual world in which individuals located at different places in the physical world can interact with one another. In order to achieve real-time response for a large user base, DVE systems need to have a scalable architecture. In this paper, we present the design of a grid-enabled service oriented framework for facilitating the construction of scalable DVE systems on computing grids. A service component called “gamelet” is proposed, whose distinctive mark is its high mobility for supporting dynamic load sharing. We propose a gamelet migration protocol which can ensure the transparency and efficiency of gamelet migration, and an adaptive gamelet load-balancing (AGLB) algorithm for making gamelet redistribution decisions at runtime. The algorithm considers both the synchronization costs of the DVE system and network latencies inherent in the grid nodes. The activities of the users and the heterogeneity of grid resources are also considered in order to carry out load sharing more effectively. We evaluate the performance of the proposed mechanisms through a multiplayer online game prototype implemented using the Globus toolkit. The results show that our approach can achieve faster response times and higher throughputs than some existing approaches. This research is supported in part by the China National Grid project (863 program) and the HKU Foundation Seed Grant 28506002.     

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。     

DVE-RTI:一个基于组播技术的分布交互仿真运行基础机构

分布交互仿真运行基础机构(run—time infrastructure，RTI)的研究与实现是当前HLA研究的一个难题和热点．介绍了研究实现的一个基于组播技术的RTI，即DVE_RTI．重点给出了DVE_RTI的设计方法，包括分布式交互体系设计、松耦合模块化结构设计、基于组播的逻辑数据通道过滤技术和RTI_RTI交互协议等内容．DVE_RTI具有规模扩展性好、系统可维护性强、网络资源利用率高等优点．为了实现DVL_RTI之间的数据通信而设计的RTI_RTI交互协议可以解决不同种类RTI之间的互联问题．     

分布式虚拟环境的可扩充性研究

讨论了与分布式虚拟环境系统扩充性相关的两类技术，一类是通过简单的硬件并行来实现系统扩容,典型的例子是多服务器并行分区技术。这类技术能够支持大规模的分布式虚拟环境(DVE)系统，缺点是费用太高;另一类技术试图通过减少服务器通信负载来实现系统容量的增加，主要包括感兴趣区域（AOI）技术，DR算法和组播技术。此外，还讨论了一些复合方法：如基于AOI的组播技术等。网络负载的减少意味着相同的硬件条件可以支持更大规模的客户,从而有助于解决大规模DVE系统的扩充性问题。