基于分层多播的视频传输拥塞控制算法研究

分层多播以多速率方式解决了多播接收者异构性问题,对于提高网络服务质量具有重要意义。本文分析了分层多播传输特性,通过提取MPEG视频流中的I帧、P帧、B帧组成3个帧流,分别放到分层多播的基层、增强层1和增强层2上传输,并在中间节点采用优先级队列机制,提出了一种面向视频流传输的分层多播拥塞控制(VLMCC)算法。仿真实验表明,本文提出的VLMCC算法能够适应视频多播接收者的异构性,大大提高了视频多播传输质量。     

多速率多播最大吞吐量问题研究

该文研究了利用network coding的多速率多播最大吞吐量问题。与以往研究重点集中在单速率多播中的network coding研究工作不同,该文考虑了链路的异构性问题并采用多速率多播来解决该问题。文中形式化地描述了多速率多播最大可得吞吐量问题,并证明了在分层独立和层速率固定条件下,利用network coding的多速率多播最大吞吐量问题是NP-hard类问题,同时给出了最大吞吐量的上界。该文同时还研究了分层相关和层速率可变情况下的最大吞吐量问题,并提出了一种满足公平性的近似算法。     

一种新的逐跳TCP友好的主动分层多播拥塞控制方案

基于Internet的多媒体多播应用的迅猛发展对多播拥塞控制提出了要求.分层多播是适应网络异构性较有效的方案.针对现有分层多播存在的问题,将主动网技术思想引入到分层多播拥塞控制中,提出了一种逐跳TCP友好的主动分层多播拥塞控制方案(HTLMA),采用主动标记分层、逐跳探测TCP友好可用带宽,以及主动速率控制机制.仿真实验表明,HTLMA方案大大改进了分层多播拥塞控制的性能,具有较快的拥塞响应速度、较好的稳定性和TCP友好特性.     

一种新的多速率多播拥塞控制策略

本文提出了一种新的多速率多播拥塞控制策略,以满足分层多播接收者的可用带宽异构性。这种接收方驱动的拥塞控制策略,能够根据网络情况变化动态地调整分层的数量及层速率,运用最优层速率分配算法来满足接收者的可用带宽异构性,接收者的可用带宽可以用根据TCP友好经验公式计算出。仿真实验表明,该算法在TCP友好性上有良好的性能,同时它可以明显提高系统的吞吐量。     

一种改进的分层多播拥塞控制方案

针对分层多播接收者的可用带宽异构性问题,提出了一种自适应动态分层多播拥塞控制算法(ADLM).ADLM自适应地运用最优层输率分配算法来满足接收者的异构性,ADLM可以根据网络情况变化动态地调整分层的数量以及每一分层的层速率.仿真实验表明,该拥塞控制策略比分层组播控制常用的典型策略(RLC)更有效地利用网络带宽,解决网络带宽的异构性问题,同时ADLM是TCP友好的,较好地改进了分层多播拥塞控制的性能.     

OFDM系统中考虑信源编码特性的多播资源分配方案

针对OFDM系统单播以及传统多播没有充分发挥无线传播开放性优势的问题,提出了多个多播组保证组间比例公平的资源分配方案.该方案由子载波分配算法及功率分配算法构成,前者通过修正存在的单播子载波分配算法得到;后者基于理论推导的非线性方程组,得到了子载波分配给定条件下的最优功率分配.仿真结果显示,所提方案能够确保完美的多播组间公平性,且和速率容量性能明显优于传统多播方式.结合方案的低复杂度特性,它适合在实际无线系统的音/视频多播中进行应用.     

多播OFDM系统中基于调控因子的资源分配

多媒体多播系统中的动态资源分配技术以其有效利用系统资源,及满足具有差异性信道条件的多用户需求而受到业内广泛研究和重视。针对MRA_LCG算法和MRA_GAT算法存在的弊端,提出了MRA_FCF算法,利用灵活可控的速率均衡因子使得高速率多媒体信息向低速率上分流。仿真结果表明,所提MRA_FCF算法获得的吞吐量明显优于MRA_LCG算法的,且同时在保证组内用户公平性方面比MRA_GAT算法具有优势。     

一种新的分层多播拥塞控制协议

提出了一种新的自适应分层多播拥塞控制方案(ALM)。ALM是发送方与接收方共同驱动、由路由器辅助流量控制的拥塞控制方案,通过把发送方的动态分层和接收方的自适应速率调整有机结合,不仅增强了分层多播的适应能力,提高了系统的吞吐量,而且较好地满足了TCP友好性。仿真实验表明,ALM能有效地利用网络带宽,解决网络带宽的异构性问题,并能通过接收端计算TCP友好速率,使接收端达到与TCP流公平竞争网络资源的目的。     

利用network coding的多速率多播最大吞吐量问题研究

本文研究了利用network coding的多速率多播最大吞吐量问题.与以往研究重点集中在单速率多播中的network coding研究工作不同,本文考虑了链路的异构性问题并采用多速率多播来解决该问题.首先文中形式化地描述了多速率多播最大可得吞吐量问题,并证明了在分层独立和层速率固定条件下,利用network coding的多速率多播最大吞吐量问题是NP-hard类问题,同时给出了最大吞吐量的上界.此外本文同时也研究了分层相关和层速率可变情况下的最大吞吐量问题.     

一种兼顾速率公平的多用户子载波功率联合分配算法

随着无线通信技术的迅猛发展,无线资源的需求量越来越大,用户对服务质量的要求也越来越高,因此,未来通信系统需要智能地在用户服务质量(QoS)需求和无线资源限制间进行一个有效的折中。为了提高认知无线网络频谱利用率,在可用子载波、次级用户功率预算及公平性等约束条件下,基于速率自适应(RA)准则,提出了在认知正交频分复用(OFDM)系统中兼顾速率公平的多用户子载波功率联合分配算法。该算法将子载波和功率分配分为两步,在兼顾各次级用户速率公平性的同时,最大化链路容量。仿真结果表明,该联合分配算法在系统吞吐量与次级用户速率公平性之间可以取得有效的折中。     

A scalable low-overhead rate control algorithm for multirate multicast sessions

In multirate multicasting, different users (receivers) within the same multicast group can receive service at different rates, depending on the user requirements and the network congestion level. Compared with unirate multicasting, this provides more flexibility to the user and allows more efficient usage of the network resources. We address the rate control problem for multirate multicast sessions, with the objective of maximizing the total receiver utility. This aggregate utility maximization problem not only takes into account the heterogeneity in user requirements, but also provides a unified framework for diverse fairness objectives. We propose an algorithm for this problem and show, through analysis and simulation, that it converges to the optimal rates. In spite of the nonseparability of the problem, the solution that we develop is completely decentralized, scalable and does not require the network to know the receiver utilities. The algorithm requires very simple computations both for the user and the network, and also has a very low overhead of network congestion feedback.     

Layered media multicast control (LMMC): rate allocation and partitioning

The objective of layering techniques of distributing multimedia traffic over multicast IP networks is to effectively cope with the challenges in continuous media applications. The challenges include heterogeneity, fairness, real-time constraints, and quality of service. We study the problem of rate allocation and receiver partitioning in layered and replicated media systems. We formulate an optimization problem aimed at maximizing a close approximation of the so-called max-min fairness metric subject to loss and bandwidth constraints. Our optimal layered media multicast control (LMMC) solution to the problem analytically determines the layer rates and the corresponding partitioning of the receivers. Our simulation results show the effectiveness of our proposed solution in realistic scenarios.     

Efficient cross-layer protocol for bandwidth-satisfied multicast in multi-rate MANETs

Since the multi-rate enhancements have been implemented in 802.11 wireless networks, QoS-constrained multicast protocols for multimedia communication should be adapted to exploit them fully. This work proposes a multicast protocol for data rate selection and bandwidth-satisfied multicast tree determination with an efficient cross-layer design based on the integration of PHY and MAC layers into the network layer. To use bandwidth efficiently and increase network capacity (which is the number of multicast flows supported by the network), we aim to select the combination of data rates and a multicast tree whose total amount of bandwidth consumption to the network is minimal in order to maximize the network capacity. The performance of the proposed protocol is compared with two existing protocols. Simulation results indicate that the proposed protocol has the ability to admit more multicast flows.     

面向GEO卫星网络的多速率多播拥塞控制机制

针对GEO卫星网络带宽时延积较大、拥塞控制机制不完善的问题,提出了一种面向GEO卫星网络的多速率多播拥塞控制机制MMCCM_GEO.首先,在保证接收端请求速率最大化的前提下,将GEO卫星网络中的多速率多播问题转化为非线性优化问题,并采用改进的模拟退火算法对其求解,得到了最优的接收端请求速率.其次,通过采用代理节点实现反馈信息的汇集与丢失数据的恢复,有效地解决了反馈内暴及数据恢复问题.仿真结果表明,与目前GEO卫星网络中典型的多速率多播拥塞控制机制相比,本文的拥塞控制机制有效地提高了数据吞吐量和带宽利用率,降低了GEO卫星网络中的数据传输时延,同时也具备了更好的可扩展性.     

认知网络中基于网络辅助的速率控制方法

面向多速率业务的认知网络,为了克服其动态性并实现速率控制的自主性,在改进IEEE 1900.4系统架构的基础上提出了速率控制框架。探讨不同层面不同尺度的速率控制方案。重点研究终端侧短期实时速率控制的问题。首先,基于非合作博弈提出分布式自主速率选择方法;进而,基于合作博弈提出基于网络辅助的中心式速率分配方法。仿真结果表明,后者较前者获得近60%的效能和一定的公平性改善,同时也验证了定价函数设计能够有效地改进公平性。     

Multimedia transmission with adaptive QoS based on real‐time protocols

In this paper, we describe a mechanism for adaptive transmission of multimedia data, which is based on real‐time protocols. The proposed mechanism can be used for unicast or multicast transmission of multimedia data over heterogeneous networks, like the Internet, and has the capability to adapt the transmission of the multimedia data to network changes. In addition, the implemented mechanism uses an inter‐receiver fairness function in order to treat the group of clients with fairness during the multicast transmission in a heterogeneous environment. The proposed mechanism uses a ‘friendly’ to the network users congestion control policy to control the transmission of the multimedia data. We implement a prototype application based on the proposed mechanism and we evaluate the proposed mechanism both in unicast and multicast transmission through a number of experiment and a number of simulations in order to examine its fairness to a group of clients and its behaviour against transport protocols (TCP) and UDP data streams. Copyright © 2003 John Wiley & Sons, Ltd.     

Achieving inter-session fairness for layered video multicast

The Internet is increasingly used to deliver multimedia services. Since there are heterogeneous receivers and changing network conditions, it has been proposed to use adaptive rate control techniques such as layered video multicast to adjust the video traffic according to the available Internet resources. A problem of layered video multicast is that it is unable to provide fair bandwidth sharing between competing video sessions. We propose two schemes, layered video multicast with congestion sensitivity and adaptive join-timer (LVMCA) and layered video multicast with priority dropping (LVMPD), to achieve inter-session fairness for layered video multicast. Receiver-driven layered multicast (RLM), layer-based congestion sensitivity, LVMCA, and LVMPD are simulated and compared. Results show both proposed schemes, especially LVMPD, are fairer and have shorter convergence time than the other two schemes.