适用于无线网络流媒体传输的可靠多播协议设计

无线网络具有高误码率和高丢失率的特点,现有的组播协议无法为具有时延敏感特点的流媒体应用提供理想的传输质量.将FEC编码与基于NACK的反馈机制相结合,提出了一种以端到端方式运作的轻量级可靠传输协议.协议应用NACK抑制和NACK积累机制防止NACK风暴;引入了TCP友好的拥塞控制机制,与其他传输协议公平共享带宽;使用反馈轮(feedback round)机制,以"轮"为单位实现NACK控制,将接收端等待修复的时间平均到每一轮中,防止了抖动.实验表明,在最大发送速率为2Mbps的设定下,本协议在无线网络上的吞吐量是同类协议NORM的1.5倍,且消除了抖动,具有低延迟的特点,更适合于流媒体传输应用的需要.     

无线网络可靠多播反馈算法的优化

无线网络具有高误码率和高丢失率的特点。可靠多播协议NORM使用基于时间片的反馈补偿机制,反馈周期长,不能充分利用带宽,尤其不能适用于无线网络上具有时延敏感特点的流媒体应用的要求。应用反馈轮机制优化NORM协议的反馈算法,以“轮”为单位实现NACK（Negative-Acknowledgment）控制,及时响应接收端的修复请求,将接收端等待修复的时间平均到每一轮中,有效降低了时延,且提高了带宽利用率。实验结果表明,在最大发送速率为2 Mb/s的设定下,协议在无线网络上的有效载荷吞吐量提高了0.5倍,且消除了抖动,具有低延迟的特点,更适合于流媒体传输应用的需要。     

基于无线网络编码的速率自适应协作MAC协议

传统无线网络编码协议在单播传输模式中较少考虑速率自适应对网络性能的改善作用,而利用RTS/CTS握手信号进行信道估计的速率自适应机制则存在开销大、网络吞吐性能差等缺陷。为此,提出一种基于网络编码的速率自适应协作介质访问控制协议RACNC。该协议使用网络编码模型和基于ACK帧的速率自适应机制,当源节点传输的原始数据帧未被成功接收时,选取中继节点对原始数据帧进行编码处理,然后转发编码数据帧,在保证数据帧可靠传输的同时减少其在网络上的传输次数。同时利用改进的ACK帧进行速率反馈,避免在估计信道质量时发送多余的RTS/CTS控制帧。仿真结果表明,与基于网络编码的NCAC-WTC协议相比,RACNC协议可有效减小平均端到端时延,提高网络吞吐量。     

移动Ad Hoc网络中基于NACK的可靠多播协议

如何采用有效的机制来保证多播数据的可靠传输是移动Ad Hoc网络中的一个难题.针对IEEE 802.11 MAC层进行改进,提出了一种基于使用NACK消息的可靠多播协议,该协议仅当数据分组传输出错时才发送NACK消息要求重传数据.仿真结果表明使用该协议能提高多播路由传输数据的吞吐量,同时降低了平均时延.     

面向编码机会路由的无线Mesh 网络广播信道接入

编码机会路由是有损无线Mesh网络中提供高吞吐量和高可靠性传输的理想方案.该路由机制建立在无线广播的多用户分集优势和随机网络编码的纠删特性之上,为广播MAC的设计引入了新的机会和挑战.基于最优停止理论,研究面向编码机会路由的机会广播信道接入问题,提出一种在接入延迟和信道交付能力之间加以折衷,以获得最优的平均有效速率的方法,并在IEEE 802.11 DCF协议基础上设计实现面向NCOR的广播MAC协议O-BCast.仿真结果表明,该协议显著提高了编码机会路由的端到端吞吐量,具有网络负载自适应的良好特性.     

基于RTP的h.264无线视频传输和Qos控制

本文在RTP协议原理和H264编码特性的基础上,提出了适用于H264无线视频传输结构.利用RTP/RTCP端到端的反馈机制实现流量控制、拥塞控制以及H264在视频编码层和网络提取层的错误恢复措施.使整个传输过程在提供良好的视觉质量又满足实时播放的前提下,充分利用带宽.     

基于有线电视网络的可靠组播技术研究

可靠组播数据传输协议主要有基于NACK的协议、基于树的ACK协议、异步分层编码协议（ALC）以及路由辅助协议。ALC协议采用发送方分多个组播通道发送数据,通过前向纠错编码来保证数据的可靠性。基于有线电视网的可靠组播传输系统就是以ALC协议作为数据传送的基础,同时以SAP／SDP协议作为会话管理的基础,加上可靠组播传输技术来实现的。实验验证了该系统的合理性及可行性,并应用于远程教育。     

一种基于网络计算机的虚拟设备音频传输模型和实现

网络计算机是新一代的计算模式,该文提出并实现了一种基于共享虚拟设备的网络音频传输模型,为网络计算机提供多媒体扩展。通过RAB协议传输音频流,端到端链路带宽测量、自适应编码和分布式实时传输控制为网络音频流提供QoS支持。     

基于数字喷泉码相关链提取的水声传感器网络HARQ协议

由于水声信道具有高噪声、高误比特率的特点,水声传感器网络链路可靠性非常差,很容易出现信息的丢失情况。为此,文章提出了一种基于喷泉码相关链提取的HARQ协议以解决水下不可靠传输问题的方法。协议通过在接收端提取译码状况的相关链信息并反馈,使得发送端能够根据反馈信息提供更有效的重传编码,从而降低了传输冗余,提高了端到端吞吐量。在此基础上,借助OPNET网络仿真平台对提出的协议进行仿真分析,论证了提出协议同现有的UW-HARQ协议相比,能够实现更好的吞吐量与传输冗余性能。     

基于位图索引的无线传感器网络可靠传输协议

根据无线传感器网络中大量上行数据流实时传输的需求,提出一种基于位图索引的可靠传输协议(BRDT)。该协议使用迭代方式完成一组大量数据的传输。每次迭代的上行数据流采用无重传传输以减少延迟,并采用可靠后项传输传送带有错误标识的位图索引以恢复丢失数据。在已有低功耗无线图像传感器网络Z-EYE系统中实现并进行验证,结果表明,与RMST协议相比,BRDT对下层的服务需求少,在网络质量较差的情况下,BRDT的性能明显优于NACK重传方法,在同等测试条件下,BRDT的传输效率优于PSFQ协议。     

An overlay multicast protocol for live streaming and delay-guaranteed interactive media

In many collaborative multimedia applications, there is often a requirement for simultaneously supporting live streaming and shareable interaction. A major challenge in designing such an application by overlay multicast is how to simultaneously provide scalable live streaming and delay-guaranteed interactive media. Live streaming by overlay multicast incurs additional application-layer latency, which conflicts with the delay-sensitive property of interactive media. To handle this dilemma, in this paper, we propose a layered degree-constrained overlay multicast protocol, which organizes the overlay multicast tree as a layered degree-constrained core tree and an extended tree. The core tree maintains available resources in its top layers for subsequent two-way interaction, whereas the extended tree expands the core tree for one-way live streaming. Our simulation and experimental results show that the proposed overlay multicast protocol can simultaneously provide delay-guaranteed interactive media as well as scalable live streaming.     

基于应用层组播的流媒体直播系统

应用层组播技术不需要网络层设备的支持，适合用于流媒体服务。在基于单播的流媒体直播系统基础上，设置应用层组播服务器，赋予客户端转发数据的能力，设计符合流媒体特点的应用层组播协议，形成了基于应用层组播的流媒体直播系统。按照该方案开发的原型系统运行状况表明，该设计方案能够稳定地提供流媒体服务。相比于基于单播的流媒体直播系统，采用应用层组播技术可以明显提高系统的用户数量，并保持较好的服务质量。     

Software-Defined Multicast for Over-the-Top and Overlay-based Live Streaming in ISP Networks

The increasing amount of over-the-top (OTT) live streams and the lack of global network layer multicast support poses challenges for a scalable and efficient streaming over the Internet. Content Delivery Networks (CDNs) help by delivering the streams to the edge of almost every Internet Service Provider (ISP) network of the world but usually also end there. From there on, the streams are to be delivered to the clients using IP unicast, although an IP multicast functionality would be desirable to reduce the load on CDN nodes, transit links, and the ISP infrastructure. IP multicast is usually not available due to missing control and management features of the protocol. Alternatively, Peer-to-Peer (P2P) mechanisms can be applied to extend the overlay multicast functionality of the CDN towards the clients. Unfortunately, P2P only improves the situation for the CDN but makes it more challenging for the ISP as even more unicast flows are generated between clients inside and outside the ISP network. To tackle this problem, a Software-Defined Networking-based cross-layer approach, called Software-Defined Multicast (SDM), is proposed in this paper, enabling ISPs to offer network layer multicast support for OTT and overlay-based live streaming as a service. SDM is specifically tailored towards the needs of P2P-based video stream delivery originating from outside the ISP network and can easily be integrated with existing streaming systems. Prototypical evaluations show significantly improved network layer transmission efficiencies when compared to other overlay streaming mechanisms, down to a level as low as for IP multicast, at linearly bounded costs.     

基于用户行为分析的应用层组播树生成算法

应用层组播采用终端主机转发数据的方式,在一对多的媒体内容分发方面具有广阔的应用前景．与IP组播相比,应用层组播具有灵活和易实施的特点,但是因为终端主机可以自由地退出组播树,应用层组播也存在数据传递易中断的缺点,这对实时性要求严格的视频直播应用的影响尤为严重．通过对超过1000万条实际视频直播系统的真实用户记录进行统计分析,发现用户平均剩余在线时间随着已经在线时间的增大而增大,并据此提出了一种适用于视频直播的应用层组播树生成算法．模拟结果表明,算法对减少视频直播应用下应用层组播树的数据传递中断次数有明显作用．     

面向QoS的域间实时流覆盖组播方法研究

针对跨域远程协作中的实时流通信质量问题,构建了实时流服务网格（LSSG）,这是一个可扩展的且面向用户QoS需求的覆盖组播通信中间件结构,LSSG服务由网络服务提供商策略部署的服务代理（SvB）提供。论文主要采用面向QoS的域间覆盖组播算法（QIOM）来组织SvB建立实时流组播服务树,根据用户服务质量请求提供跨自治系统的实时流组通信服务,将域间资源管理转变为流媒体应用的动态协同服务管理。仿真结果表明QIOM能有效地发现和提供QoS满意的覆盖服务及实现SvB间的覆盖流量负载平衡。     

Dynamic overlay multicast for live multimedia streaming in urban VANETs

Infotainment service has been a foreseeing trend in VANETs (Vehicular Ad Hoc Networks), and multimedia streaming has a high potential in VANET infotainment service. This paper considers the scenario of live multimedia streaming multicast to vehicles of the same group using a dynamic application layer overlay. Due to the willingness for cooperation of non-group nodes, application layer overlay multicast is more feasible than other kinds of multicast such as network-coding-based multicast and network-layer multicast. To adapt to high mobility and full of obstacles in urban VANETs, we propose an effective dynamic overlay multicast scheme for multimedia streaming, called OMV (Overlay Multicast in VANETs). The proposed OMV enhances an overlay’s stability with two strategies: (1) QoS-satisfied dynamic overlay and (2) mesh-structure overlay. The QoS-satisfied strategy to adjust the overlay selects potential new parents based on their streams’ packet loss rates and end-to-end delays. The mesh-structure strategy allows a child to have multiple parents. We evaluate the proposed OMV in urban VANETs with obstacles using two real video clips to demonstrate the feasibility of the OMV for real videos. Evaluation results show that comparing the proposed OMV to Qadri et al.’s work, which is a static mesh overlay and is the best method available in VANETs, the packet loss rate is reduced by 27.1% and the end-to-end delay is decreased by 11.7%, with a small control overhead of 2.1%, on average. Comparing the proposed OMV for tree overlays to ALMA, which is for dynamic tree multicast overlays and is also the best method available in MANETs, the packet loss rate is reduced by 7.1% and the end-to-end delay is decreased by 13.1%. In addition, to address the problem of obstacle-prone urban VANETs, we also derive feasible stream rates and overlay sizes for city maps with different road section sizes. To the best of our knowledge, how to organize and dynamically adjust an application layer multicast overlay for live multimedia streaming have not been studied in existing VANET literatures. In summary, to deal with highly dynamic topologies in urban VANETs, we propose a QoS-satisfied strategy for group nodes to switch to new parents that can offer better QoS. The proposed OMV is feasible for live multimedia streaming applications, such as emergency live video transmission and live video tour guides for passengers in different vehicles that belong to the same multicast group.     

Network Coding in Live Peer-to-Peer Streaming

In recent literature, network coding has emerged as a promising information theoretic approach to improve the performance of both peer-to-peer (P2P) and wireless networks. It has been widely accepted and acknowledged that network coding can theoretically improve network throughput of multicast sessions in directed acyclic graphs, achieving their cut-set capacity bounds. Recent studies have also supported the claim that network coding is beneficial for large-scale P2P content distribution, as it solves the problem of locating the last missing blocks to complete the download. We seek to perform a reality check of using network coding for P2P live multimedia streaming. We start with the following critical question: How helpful is network coding in P2P streaming? To address this question, we first implement the decoding process using Gauss-Jordan elimination, such that it can be performed while coded blocks are progressively received. We then implement a realistic testbed, called Lava, with actual network traffic to meticulously evaluate the benefits and tradeoffs involved in using network coding in P2P streaming. We present the architectural design challenges in implementing network coding for the purpose of streaming, along with a pull-based P2P live streaming protocol in our comparison studies. Our experimental results show that network coding makes it possible to perform streaming with a finer granularity, which reduces the redundancy of bandwidth usage, improves resilience to network dynamics, and is most instrumental when the bandwidth supply barely meets the streaming demand.     

应用层多播协议NICE及其在移动无线网络中的应用

随着Internet的发展,在诸如音频和视频流等多种的应用中多播技术显得日益重要,然而传统的IP多播技术却不能满足ISP的要求.介绍了应用层多播的概念及其特点,讨论并分析了一种应用层多播协议NICE.越来越多的多播应用是面向移动无线网络的,移动无线网络是一种无基础设施的拓扑结构可变的网络,NICE能有效、强健地解决移动无线网络中的多播问题.