共查询到19条相似文献,搜索用时 359 毫秒
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由于IP组播存在可扩展性差、难以管理等方面的缺陷,研究人员提出了应用层组播。实时传输是应用层组播技术的一个主要应用领域,对网络延迟有严格的限制。文中着重研究构建最小延迟应用层组播树的算法,提出一种基于策略函数构造应用层最小直径组播树的启发式算法BCT-H。该算法采用策略函数迭代的选择使生成树直径最短的路径,从而有效地减少了网络中的转发时延和同一条链路的重复分组数量。模拟实验表明该算法能够有效地降低链路强度,减少组播树的时延。 相似文献
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一种基于策略函数的应用层组播路由算法 总被引:1,自引:1,他引:0
由于IP组播存在可扩展性差、难以管理等方面的缺陷,研究人员提出了应用层组播.实时传输是应用层组播技术的一个主要应用领域,对网络延迟有严格的限制.文中着重研究构建最小延迟应用层组播树的算法,提出一种基于策略函数构造应用层最小直径组播树的启发式算法BCT-H.该算法采用策略函数迭代的选择使生成树直径最短的路径,从而有效地减少了网络中的转发时延和同一条链路的重复分组数量.模拟实验表明该算法能够有效地降低链路强度,减少组播树的时延. 相似文献
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为了改善网状优先的应用层组播协议可扩展性差等缺点,提出一种新的应用组播协议,协议采用特殊的二维层次结构。在低层,将距离近的结点划分为同一个域,域内成员组织成车轮状,域成员只和邻居结点交换信息,减少了维护通信量。在高层,将距离较远的域首组织成网状结构,上下层通过不同的路由算法并行地传输数据,使得数据可以尽快到达远处的结点,提高了传输效率。仿真结果表明,该组播协议具有较小的控制开销、链路压力和端到端延迟。 相似文献
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针对异构网络环境中由于节点转发能力异构而引起的应用层组播稳定性不足的问题,对异构overlay拓扑建模进行了研究,分析出组播稳定所需满足的约束条件,提出了一种基于gossip协作机制的应用层组播方案。在所提机制能够均衡节点间负载,缓解能力弱的节点负载过重的问题;如果组播过程中有成员节点动态离开或转发能力不足,其他节点相互协作共同分担其负载以维持组播的稳定性。随后的链路强度分析表明,与传统的应用层组播方案相比,本方案能够大幅降低拓扑的平均链路强度,提高组播系统的稳定性。最后通过OMNeT 仿真平台对本方案进行仿真验证,实验证明在动态的异构overlay拓扑下,本方案能够显著提高数据分发成功率,保证组播的连续性和稳定性。 相似文献
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为了扩大导航差分信息的应用领域,并且在城市或室内可以接收修正信息,针对导航增强信息需在具有实时性、可扩展性和异构性的网络上播发的特点,结合应用层组播和i3组播,采用IP路由信息表构建了基于节点异构性的分层混合组播系统.分析了网络模型和通信协议,并基于OPNET进行了性能仿真.仿真结果表明,HMMA实时性好、可扩展性强,可以满足应用的需求. 相似文献
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IP multicast is one of the best techniques for video streaming on the Internet. It faces issues with respect to address allocation, routing, authorization, group management, security, and scalability. By default, local Internet Service Providers did not enable IP multicast services, because of the cost incurred in using multicast-enabled routers. To solve these issues some of the IP layer functionalities have been shifted to the Application Layer, thus leading to Application Layer Multicast (ALM) protocols. However, ALM protocols face issues related to synchronous data delivery, scalability, link stress, link stretch and node failures. Some of the existing protocols are CoolStreaming, and mTreebone. A novel ALM protocol based Push/Pull Smooth video Streaming Multicast (PPSSM) protocol is proposed in this paper, to increase the throughput and reduce the packet loss rate. The PPSSM protocol involves three stages, such as tree-mesh construction, dynamic buffer management and network coding techniques. In the tree-mesh construction, a tree consists of stable nodes and a mesh consists of unstable nodes. The proposed PPSSM optimizes the stable nodes in the tree, which minimizes or eliminates the pull operations from the unstable mesh overlay nodes, by exploring the potential of the stable nodes. Dynamic buffer management is achieved by setting the optimal buffer threshold value, using the optimization of the sensitivity parameters, such as packet loss and packet workload/delay by the Infinitesimal Perturbation Analysis and Stochastic Approximation algorithms. In addition to the tree-mesh construction and buffer management, the introduction of the network coding technique will enhance the throughput and minimize the packet loss and delay. Finally, the performance of the proposed PPSSM protocol is compared with those of CoolStreaming, and mTreebone, and it shows improvement in respect of throughput, packet loss, and average decoding time. 相似文献
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Kazushi Ikeda Thilmee M. Baduge Takaaki Umedu Hirozumi Yamaguchi Teruo Higashino 《Computer Communications》2011,34(14):1673-1684
This paper presents a new middleware called ALMware for supporting development and performance evaluation of ALM (application layer multicast) protocols on real environments. To facilitate the development of ALM protocols, ALMware provides APIs which allow protocol developers to re-use typical operations used in existing ALM algorithms. Some additional APIs for transmitting video and audio between peers also mitigate the cost of writing application codes. Performance evaluation on real environments is also supported by ALMware. To prove the usefulness of ALMware, we have implemented well-known but different types of ALM protocols, ALMI, NARADA, NICE and OMNI, and conducted various kinds of performance evaluation experiments on PlanetLab, which clearly demonstrate the usability of ALMware. We believe that this is the first effort made to develop this kind of ALM supporting middleware. 相似文献
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该文针对舰艇模拟训练系统的需要,提出一种可扩展的可靠应用层组播模型,它采用心跳机制与序列号相结合的方法进行差错检测和基于NAK否定信息的ARQ机制进行数据差错恢复,同时设计了相应的机制来保障组播数据的可靠传输。该模型弥补了普通应用层组播协议在可靠性传输上的不足,使通信网络具有良好的可扩缩性、可选择和可靠性功能。实验证明:基于心跳机制的差错控制模型可以很好克服传统方法可靠组播通信的"反馈风暴"和NAK算法中的缓冲区无法控制的问题,与基于TCP的单播可靠方式相比,该模型不需要中心节点服务器,节省了网络资源,网络带宽占有率相比也减少约两倍。 相似文献
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《Computer Networks》2007,51(1):31-42
Recently a number of application-layer multicast (ALM) protocols have been proposed as a promising alternative to deploying multicast services in the unicast-only Internet. Current ALM protocols work very well for low data-rate applications but can suffer from link-level load imbalance, and consequently link congestions, when applied to high data-rate applications. This work addresses this problem by extending the well-known NICE protocol to use multiple parallel overlays in the same ALM session to spread the data traffic across more available network links, and thus leading to significantly improved performance. Extensive simulation results show that the proposed protocol can support three times the data-rate compared to NICE and yet can reduce the end-to-end data delivery delay by more than 50%. 相似文献
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In recent years, there has been an increasing interest in peer-to-peer (P2P) multimedia streaming. In this paper, we consider constructing a high-bandwidth overlay tree for streaming services. We observe that underlay information such as link connectivity and link bandwidth is important in tree construction, because two seemingly disjoint overlay paths may share common links on the underlay. We hence study how to construct a high-bandwidth overlay tree given the underlay topology. We formulate the problem as building a Maximum Bandwidth Multicast Tree (MBMT) or a Minimum Stress Multicast Tree (MSMT), depending on whether link bandwidth is available or not. We prove that both problems are NP-hard and are not ap-proximable within a factor of (2/3 + epsiv), for any epsiv > 0, unless P = NP. We then present approximation algorithms to address them and analyze the algorithm performance. Furthermore, we discuss some practical issues (e.g., group dynamics, resilience and scalability) in system implementation. We evaluate our algorithms on Internet-like topologies. The results show that our algorithms can achieve high tree bandwidth and low link stress with low penalty in end-to-end delay. Measurement study based on Plan-etLab further confirms this. Our study shows that the knowledge of underlay is important for constructing efficient overlay trees. 相似文献
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应用层组播研究进展 总被引:7,自引:0,他引:7
组播技术是一种针对多点传输和多方协作应用的组通信模型,有高效的数据传输效率,是下一代Internet应用的重要支撑技术。早期的组播技术研究试图在IP层提供组播通信功能,但IP组播的实施涉及到对现有网络基础设施的调整,因此,大规模应用受到限制。近两年来,随着Peer-to-Peer(P2P)研究的兴起,基于应用层的组播技术也逐渐受到广泛关注。应用层组播协议将组成员节点自组织成覆盖网络,在主机节点实现组播功能,为数据多点并发传输提供服务。将组播功能从路由器迁移到主机上能有效解决许多与IP组播有关的问题,但同时也带来了一些新的挑战。本文分析了目前应用层组播研究的主要内容及技术特点,描述了协议设计所涉及的关键技术及面临的主要挑战,总结了现有工作及相关进展。 相似文献