基于分组差错控制的轨道交通ATS信号可靠组播技术研究

为解决轨道交通中ATS信号组播丢包问题,拟定一种基于分组差错控制的可靠组播传输协议。该协议不需要路由器的支持,在每个接收节点都定义一个申请重传权值列表,根据组播丢包情况,动态更新接收节点的权值列表,从而为接收节点选择最佳的重传请求处理节点,以提高数据重传效率。仿真实验表明：在多个分组中,将该文所提出的基于分组差错控制的可靠组播传输协议应用于轨道交通中ATS信号仿真系统中,与传统的可靠组播传输协议相比,能有效减少差错修复时延,并提高系统整体的吞吐率。     

融合区分服务和速率调整的请求调度策略

针对异构用户服务质量(QoS)需求不同及云数据中心能源浪费等问题,提出了一种融合区分服务和速率调整的请求调度策略。该策略将IaaS云数据中心分为提供速率调整机制的快速云和提供差错恢复机制的可靠云,然后研究新型混合云计算模式。构建了混合排队网络系统模型,从延迟敏感请求的平均响应时间、快速云中虚拟机的节能水平及可靠云中虚拟机的利用率等方面评估了请求调度策略的系统性能。进行了系统实验,验证了策略的有效性及模型的合理性。通过构造系统成本函数,改进Jaya智能寻优算法,给出了请求调度策略的优化方案。     

SIGSDP:一种普适环境下服务信息导向的服务发现协议

针对现有服务发现协议存在的问题,提出了一种普适环境下的服务信息导向的服务发现协议--SIGSDP.该协议基于普适环境下的服务发现协议GSD(一种适用于无线自组网的基于群组的服务发现协议)的思想,提出服务请求转发基于服务群组下的服务信息的思想,使得节点转发服务请求时能准确选择转发节点,避免不必要的转发.理论分析和仿真实验证明SIGSDP大大减少了服务请求包数量和服务响应时间,提高了服务发现效率.     

基于IGMP协议的移动安全移动组播访问控制方案

结合现有的不同移动组播访问控制方案的优点，给出了一个基于IGMP协议的移动安全移动组播访问控制方案。该方案由边缘路由器（Edge Router，ER）和移动组播管理中心（Mobile Multieast Manager，MMM）组成。边缘路由器拦截用户申请加入移动组播组的IGMP请求报文，转发给移动组播管理中心；移动组播管理中心根据定义的访问策略处理请求，返回决策信息；边缘路由器根据移动组播管理中心的决策信息处理相应的请求，决定是否允许用户加入移动组播组，从而实现移动组播访问控制机制。     

网络拓扑结构对IP组播效率影响的研究

研究了不同网络拓扑结构对IP组播效率的影响,给出了一种度量组播效率的方法,并进行了分析与仿真.结果表明:在随机选择组播树根节点的情况下,平均节点度越大的网络,组播效率越低;限制组播路由的通过性和适当选择组播根节点的位置能够有效提高组播效率;有源最短路径树在不同网络拓扑下的性能差异较大,并且不是一种能够适合于各种网络结构的高效组播树构建算法.     

频率选择性信道下基于虚拟MIMO-STBC的无线传感器网络中功率分配的研究

结合频域均衡(FDE)研究了在频率选择性衰落信道下基于虚拟 MIMO-STBC 的无线传感器网络的功率分配(PA)方案.利用从目标簇反馈回信源簇的信道状态信息,在协同传输节点总发送功率一定的情况下,通过最大化信宿节点接收到数据的信噪比推导出了一种基于滤波器组频域加权的 PA 方案.仿真结果表明,在系统一定的误码率要求下,采用这种 PA 方案的无线传感器网络所需要的发射功率要少于等 PA 方案所需要的发射功率,从而减少了无线传感器网络的能耗.     

一种多源协作网络中轮询节点选择算法

针对放大转发(AF)的多源多中继两跳协作通信网络模型,提出了一种基于轮询分组调度算法的节点选择与用户调度策略.与之前所提出的中继选择选择算法相比,所提出的中继节点轮询分组调度算法,不需要额外的信令开销,复杂度低,并保证中继间的负载均衡.此外,为保证用户传输的公平性,提出一种结合多用户分集的轮询分组调度算法.最后在已选择的中继节点和所调度的源节点用户中引入分布式空时编码.仿真结果表明,该节点选择和用户调度算法能保证所有节点使用的公平性,并且结合分布式空时编码之后,可以提高频谱利用率,从而提高了系统性能.     

A P2P media streaming system integrated with live and VoD based on QoS-aware

为了提高P2P流媒体系统性能,深入分析了P2P流媒体系统直播和点播业务的异同,提出采用动态时间坐标系(DTCS)构建直播点播融合的流媒体系统,将系统节点的协作特性与观看内容解耦.此外,充分考虑到节点的异构性与不同频道内容的流行度,提出了融合系统的节点协作模型,通过分布式服务质量感知算法(DQAA)来进行优化分析,充分利用P2P流媒体系统中服务能力较强的节点的剩余带宽提高系统性能.从融合系统架构及节点协作策略两个层次描述了直播点播融合的系统特性.实验表明,融合系统能有效提高节点播放质量与系统整体性能.     

基于动态代理选择的移动网络组播

针对移动网络组播面临的接入点间切换造成组播树频繁重构的问题,提出了一种新的移动网络组播方法DMA(Dynamic Multicast Agent)。DMA在远程加入的基础上,使用动态选择组播代理和局部隧道的方法,为移动网络内的节点提供组播服务。分析与仿真结果表明,DMA不但减少了因移动网络附着点改变而造成的组播树重构次数,在一定程度上屏蔽了移动网络的移动性对组播树造成的影响,而且使得组播数据总是能够以“接近最优”的路径进行转发。     

支持服务关联的全局最优服务选择算法

针对面向服务的军事综合电子信息系统候选服务的服务质量往往依赖于其他候选服务的问题,提出了一种支持服务关联的全局最优服务选择方法.该方法将基于QoS的军事信息服务选择问题建模为带QoS约束的多目标组合优化问题,采用基于独立成分分析(ICA)的多目标分布估计算法同时优化多个目标函数,最终产生一组满足约束条件的Pareto最优解服务组合集.对比实验结果表明,基于ICA的多目标分布估计算法通过概率图模型可以描述服务间的相互关系,可以更好地解决存在服务关联的组合服务选择问题,具有良好的有效性和可行性.     

IP组播路由协议的研究与实现

概述了组播路由协议，分析了协议独立的组播路由－稀疏模式（PIM－SM）的缺陷，提出多个会聚点（RPs)的PIM－SM的改进机制，多个RPs机制有效地提高了原有单个RP的PIM－SM协议的健壮性，有利于实现负载均衡、分类业务及提高系统的容错性能，并讨论多个RPs机制的开销问题。分析了PIM－SM实现细节和组播技术的前景。     

Investigation on wavelength multicasting technology based on XPM in a highly nonlinear fiber

All-optical wavelength conversion with multicasting is investigated in this paper, which is based on cross-phase modulation in a highly nonlinear fiber. With a pump-modulated light and only a single continuous-wave probe, wavelength multicasting is realized by appropriately controlling the powers of two beams. Our simulation work reveals that 10 multicast channels can be obtained with their Q factors being larger than six, if both pump and probe powers are properly selected. These wavelength channels of multicasting are positioned around the central wavelength of the probe on the blue-shifted and red-shifted sides. The central wavelength and the channel spacing can be affected by the wavelengths of the probe and the pump. The wavelength multicasting technique studied in this paper is simpler and can offer more multicast channels than that based on four-wave mixing.     

Reliable multicast for the Grid: a case study in experimental computer science

In its simplest form, multicast communication is the process of sending data packets from a source to multiple destinations in the same logical multicast group. IP multicast allows the efficient transport of data through wide-area networks, and its potentially great value for the Grid has been highlighted recently by a number of research groups. In this paper, we focus on the use of IP multicast in Grid applications, which require high-throughput reliable multicast. These include Grid-enabled computational steering and collaborative visualization applications, and wide-area distributed computing. We describe the results of our extensive evaluation studies of state-of-the-art reliable-multicast protocols, which were performed on the UK's high-speed academic networks. Based on these studies, we examine the ability of current reliable multicast technology to meet the Grid's requirements and discuss future directions.     

Cross-layer distributed approach for optimal rate allocation for homogeneous wireless multicast

Multicast-based data communication is an efficient communication scheme especially in multihop ad hoc networks where the MAC layer is based on one-hop broadcast from one source to multiple receivers. The problem of resource allocation for a set of homogeneous multicast sessions over multihop wireless network is addressed. An iterative algorithm is proposed that achieves the optimal rates for a set of multicast sessions such that the aggregate utility for all sessions is maximised. The authors demonstrate analytically and through simulations that the algorithm achieves optimal resource utilisation while guaranteeing fairness among multicast sessions. The algorithm in network environments with asynchronous distributed computations has been further analysed. Two implementations for the algorithm based on different network settings are presented and show that the algorithm not only converges to the optimal rates in all network settings but it also tracks network changing conditions, including mobility and dynamic channel capacity.     

A two-user approximation-based transmit beamforming for physical-layer multicasting in mobile cellular downlink systems

Multicast has been known as an efficient transmission technique for group-oriented applications such as multi-party video conferencing, video streaming for paid users, online gaming, and social networking. In this paper, we investigate physical-layer multicasting in mobile cellular downlink systems, where the antennas at base station are employed to transmit common signals to multiple users simultaneously. A central design problem of downlink physical-layer multicasting is the search for the optimal beamforming vector that maximizes the multicast rate. Traditionally, the problem has been formulated as a quadratically constrained quadratic programming problem and shown to be NP-hard in general. In this paper, starting from examining the Karush–Kuhn–Tucker stationary conditions, a new method based on two-user approximation is proposed for the search for the optimal beamforming vector. The method is able to achieve a much higher multicast rate than the existing methods and provides an attractive trade-off between performance and complexity, especially for the case of using a large number of antennas. Using a large number of antennas at base station, also known as the large-scale multiple-input and multiple-output technique, has been regarded widely as one of the most promising technologies to increase system capacity, coverage, and user throughput for future generations of mobile cellular systems.     

基于状态反馈的网络分布式拥塞管理方案

提出了一种新型的面向区分服务网络的分布式拥塞管理方案。其基本思想是利用拥塞状态反馈信息在边缘节点或主机上实施拥塞管理，该方案主要包括三个组成部分；拥塞状态控制分组，早期拥塞检测和流量控制算法，实验结果表明，与标准的区分服务网络相比，该方案能在TCP和UDP聚集之间公平地分配带宽并能显著地降低分组丢失率。     

Optimal resource allocation for multicast sessions in multi-hop wireless networks

In this paper, we extend recent results on fair and stable resource allocation in wireless networks to include multicast sessions, in particular multi-rate multicast. The solution for multi-rate multicast is based on scheduling virtual (shadow) 'traffic' that 'moves' in reverse direction from destinations to sources. This shadow scheduling algorithm can also be used to control delays in wireless networks.     

Reliable cross-layer multicast with local backtracking for improving transmission control protocol performance in ad hoc networks

The conventional layered protocols in ad hoc networks tend to suffer from the inability to distinguish between losses due to route failures and congestion because of the inflexible structure. Recently, in efforts to overcome the challenges of dynamic environment, there have been increased interests in protocols that rely on interactions between different layers. The authors propose a cross-layer multicasting scheme based on the concept of local backtracking groups and adequate buffer equipped within nodes to avoid undesired retransmission from the source and further to improve the efficiency of source-to-receivers delivery with the aid of buffer. While encountering route failure, a node can quickly restore its routing paths to multicast subscribers by exploiting the precise notification from the MAC layer and the parent group then opportunely provides it with an unacknowledged packets conserved in the buffer. It is obviously benefic that retransmission packets are issued from the parent group rather than from the source. The authors present both analytic models and simulation results that substantiate the efficiency and robust of our approach based on realistic mobility scenarios.     

Ant Colony Optimization for Multi-Objective Multicast Routing

In the distributed networks, many applications send information from a source node to multiple destination nodes. To support these applications requirements, the paper presents a multi-objective algorithm based on ant colonies to construct a multicast tree for data transmission in a computer network. The proposed algorithm simultaneously optimizes total weight (cost, delay and hop) of the multicast tree. Experimental results prove the proposed algorithm outperforms a recently published Multi-objective Multicast Algorithm specially designed for solving the multicast routing problem. Also, it is able to find a better solution with fast convergence speed and high reliability.     

Distributed multicast routing algorithm with dynamic performance in multimedia networks

The delay and delay variation-bounded multicast tree (DVBMT) problem is known to be NP-complete. In this paper, we propose an efficient distributed dynamic multicast routing algorithm to produce routing trees with delay and delay variation constraints. The proposed algorithm is fully distributed, and supports the dynamic reorganizing of the multicast tree in response to changes for the destination. Simulations demonstrate that our algorithm is better in terms of tree delay and routing success ratio as compared with other existing algorithms, and performs excellently in delay variation performance under lower time complexity, which ensures it to support the requirements of real-time multimedia communications more effectively.