【作者】 陈继明；

【导师】 孙家广； 鞠时光；

【作者基本信息】 江苏大学 ， 计算机应用技术， 2008， 博士

【摘要】 分布式虚拟环境将虚拟现实与网络通讯相结合,提供一个共享虚拟空间以支持对象的仿真以及多个分布用户的交互和通讯。尽管近年来网络速度和主机处理能力在不断提高,但当虚拟环境中存在大量的用户和对象时,即使每个用户只需要少量带宽,成千上万的用户通讯需求累加起来也必定超过网络所能承受的限度;同时随着用户交互需求的不断提高,用户对虚拟环境中通讯服务质量提出了更高的要求,且在异构的广域网中各个用户的接入速度和主机处理能力均有差异,速度慢的主机必然影响其他主机的响应速度乃至降低整个环境的响应性能。因此,随着网络通讯技术的发展,目前分布式虚拟环境研究主要面临着两个方面的问题:一是系统的可扩展性问题,即如何建立一个用于兴趣管理的易扩展的通讯结构,满足分布式虚拟环境中大量对象之间多对多的动态通讯要求;二是网络服务质量问题,即如何提高系统的网络服务性能和服务质量,从而为用户提供满足于他们协作要求的数据传输链路服务。在对分布式虚拟环境和兴趣管理技术等相关工作进行总结的基础上,本文着重对上述两方面的问题进行了详细的分析和研究。首先,借鉴主动路由技术和发布一订购模式的研究成果,设计一种适合兴趣管理的具有较强可扩展性的分布式虚拟环境网络模型(Scalable Distribute Virtual Environment Network model,SDVENM);然后,在SDVENM模型的基础上,进一步引入了QoS技术来提高系统的网络服务质量,满足对系统有较高服务要求的协作应用的需求;最后,采用SDVENM作为系统的网络通讯结构,设计并实现一种基于XML的可扩展分布式虚拟环境系统。具体研究内容如下:(1)借鉴了基于内容的发布-订购系统的研究成果,把组播路由算法和主动路由技术结合起来,提出了一种适合分布式虚拟环境的具有较强可扩展性的网络通讯模型SDVENM。首先,我们通过比较SBT与CBT结构在可扩展性方面的优缺点,选择基于CBT结构的双向—共享组播树作为系统设计的通讯拓扑结构;然后,提出一种新型的基于内容的双向共享组播路由协议CBSMRP,该协议在CBT组播树中,能根据数据包的内容实现主动路由和双向过滤,不仅解决了组播地址的维护和分配等问题,而且能有效地减轻系统的网络负载;最后通过仿真实验和分析进一步验证了SDVENM网络模型具有良好的可扩展性。(2)从三个方面对QoS技术在SDVENM的通讯模型中的实现进行了研究:①采用了一种基于时延的对象接入控制技术,将QoS的时延参数作为对象接入控制的依据,即根据当前的网络链路状况来控制对象的接入,有效地减少无效信息在系统中传播,从而达到缓解系统负载的目的;②提出了一种QoS主动路由技术,将QoS属性作为对象发布和订购信息的一个重要参数,主动路由器则将QoS属性和与兴趣区域同时作为信息过滤的衡量标准,能够尽早判定和过滤无法满足其QoS要求的数据包,提高网络利用率;③借鉴了TCP协议中拥塞控制的经验,提出了一种可行的拥塞控制方法,该方法从通讯底层保证了分布式虚拟环境的通讯量不超过给定阈值,在很大程度上提高了系统网络传输性能的稳定性。最后通过实验及结果分析进一步验证了上述三种方法在SDVENM的通讯模型中的可行性和有效性。(3)针对分布式虚拟环境中,协作对象对数据报文的传送有着不同服务要求,提出了一种层次式动态带宽分配方法。该方法通过带宽预留的方式,根据协作服务等级和网络链路状况对带宽进行动态调整,为协作用户提供了高质量的带宽传输保证;同时设计了一种动态带宽分配协议,并给出了相应的协议消息类型及其实现。仿真结果及其分析表明,该方法可有效解决SDVENM的模型中结构的层次数对网络时延的影响,同时在系统网络负载的变化时,能保证紧耦合式协作用户间的数据信息传输质量。(4)针对传统的分布式虚拟环境在实现时存在的对象兴趣表达能力差、依赖于特定应用以及不具有通用性等问题,将XML技术引入到兴趣管理技术的实现中,采用XPath查询表达式和XML文件的形式分别来描述用户的订购信息和发布的内容,在XML路由网络上构造并实现了基于兴趣管理的分布式虚拟环境系统。首先,探讨了系统的通讯结构、协议结构及其配置;然后根据分布式虚拟环境的特点,提出了一种基于SPA谓词匹配法的XML路由算法,并给出了XML路由器的体系结构;最后详细介绍了原型系统的实现过程,并通过实际应用验证了该原型系统的可行性和实用性。本文的创新之处体现在以下五个方面:(1)提出一种适合兴趣管理的具有较强可扩展性的网络模型SDVENM,该模型结合运用了基于内容的发布-订购模式和主动路由思想,在基于CBT结构的双向共享组播树中,采用CBSMRP协议根据数据包的内容实现主动路由和双向过滤,不仅解决了组播地址的维护和分配等问题,而且能减轻系统的网络负载,有效地提高了系统的可扩展性。(2)在SDVENM模型的基础上,提出了一种基于时延的接入控制方法,根据当前的网络链路状况来控制对象加入或者挂起,从而达到稳定网络流量,提高系统网络服务质量,减少系统负载的目的。(3)借鉴了TCP协议中拥塞控制的经验,提出了一种适合发布-订购通讯模式的拥塞控制方法,利用发布和订购区域作为一种窗口进行流量控制,从通讯底层保证了分布式虚拟环境的通讯量不超过给定阈值,有效地提高了系统网络传输的稳定性。(4)针对分布式虚拟环境中不同层次的协作应用,提出了一种层次式动态带宽分配机制,根据链路状况和服务等级的改变,动态地调整链路上的资源预留值,为协作用户提供高质量的带宽传输保证。(5)针对传统的分布式虚拟环境在实现时存在的对象兴趣表达能力差、依赖于特定应用以及不具有通用性等问题,将XML技术引入到系统实现中,在XML路由网络上构造基于兴趣管理的分布式虚拟环境系统,提高兴趣管理技术的实用性和系统的可扩展性。更多还原

【Abstract】 Distributed Virtual Environment(DVE),which combines virtual reality with network communication,offers a shared virtual space to support the interaction among multiple distributed users.Although network bandwidth and computer capability are increasing rapidly during recent years,the cumulative network consumption can still possibly exceed the limit if there are a huge number of users and objects existing in the same virtual environment simultaneously.Meanwhile,with their increasingly interaction request,users also demand the improvement of network service quality in virtual environment.Moreover,due to the differences of admission speeds and processing capabilities among different users in heteromerous Wide Area Network(WAN),the slower user can decrease the response speed and performance of other users and even the entire environment.Therefore,there are two problems which need to be carefully addressed.One is system’s scalability,i.e.,how to build a scalable interest management system to satisfy the dynamic communication requirements among lots of objects in DVE;the other is quality of service(QoS),i.e., how to improve the performance and quality of network services so as to provide the data link that meets users’ cooperation requirements.Based on the review of related work in DVE and interest management,this dissertation analyzes and researches the above two problems in detail.First,a Scalable DVE Network Model(SDVENM) is presented for interest management by utilizing the techniques of active routing and content-based publish-subscribe pattern. Second,QoS techniques are applied to SDVENM to improve network service quality to meet user cooperation requirements.Finally,a XML-based scalable DVE system is designed based on SDVENM.The main contents of this dissertation are as follows.(1) A SDVENM is proposed by combining active routing techniques with publish-subscribe patterns.First,a CBT-based bi-directional shared multicast tree is selected as the system’s topology accounting for the advantages and disadvantages of CBT and SBT on their scalability.Second,a new content-based bi-directional shared multicast routing protocol(CBSMRP),which can support active routing and bi-directional filtering according to package contents in a bi-directional shared multicast tree,is presented to not only solve the problems in allocation and maintenance of multicast addresses but also efficiently reduce the network load. Finally,the scalability of SDVENM is proved by experimental results. (2) This dissertation researches the application of QoS techniques to SDVENM from three different aspects.First,a QoS-based dynamic admission control method is proposed to control user access based on the current network link state-by considering the delay parameter in QoS-to efficiently reduce redundant message transmission and entire network load.Second,by considering QoS attributes as important parameters of publishing and subscribing areas,a QoS-based active routing approach is proposed to filter the datagram with invalid QoS parameters as early as possible so as to improve network utilization ratio.Third,a new congestion control method is presented by borrowing the ideas form traditional TCP congestion control to restrict the traffic volume at the kernel of communication protocols and greatly improve system’s stability.Finally,the efficiency and effectivity of the above three methods are verified by experiment results.(3) Addressing the different collaborative service requirements of data transmission in distributed virtual environment,a hierarchical and dynamic bandwidth allocation method is presented.This method can dynamically adjust bandwidth allocation based on service level by using a bandwidth resource reservation method, so as to provide high-quality data transmission for collaborative users.This dissertation also designs a dynamic bandwidth allocation protocol and introduces its corresponding protocol message types.The simulation results and analysis show that this method can effectively solve the impact of network latency in SDVENM and guarantee data transmission quality among close collaborative users with the change of network workload.(4) Aiming at the poor capacity in expressing interest management and high dependence on specific applications in the implementation of traditional DVE systems, a new scalable active interest management method,which applies XML to active interest management,is presented.This new approach uses XPath query and XML document to describe participant’s subscription and publication,respectively,and implements an active interest management-based DVE system on XML routing networks.After introducing the communication structure,protocols and configuration of the new system,an XML routing algorithm,which uses SPA predicate matching method,is presented for DVE systems.The implementation of its prototype system is introduced,and its practicality and efficiency are verified by some practical applications. The main contributions of this dissertation are summarized as follows.(1) A SDVENM,which combines active routing methods with content-based publish/subscribe patterns,is presented for interest management.This model uses CBSMRP to active route and bi-directional filtering packages according to their contents in a CBT-based bi-directional shared multicast tree.The new approach not only solves the problems in the allocation and maintenance of multicast addresses,but also efficiently reduces the network volume and improves system’s scalability.(2) A delay-based admission control method is proposed on SDVENM to stabilize network traffic and improve network service quality by controlling user access due to current network link state.(3) A new publish/subscribe pattern-based congestion control method is presented by borrowing the ideas form traditional TCP congestion control.This new approach uses publishing and subscribing areas as "windows" to implement flow control,so as to reduce traffic volume at the kernel of communication protocols and greatly improve system’s stability.(4) Addressing the different collaborative applications in DVE systems,a hierarchical and dynamic bandwidth allocation method is presented to adjust bandwidth resource reservation dynamically according to the change of service levels. This new method can provide better services of data transmission for close collaborative users.(5) Aiming at the poor capacity in expressing interest management and high dependence on specific applications in the implementation of traditional DVE systems, a new scalable active interest management method,which applies XML to interest management,is presented.This new approach implements an active interest management-based DVE system on XML routing networks to improve the practicality of active interest management and scalability of DVE systems.更多还原