【作者】 赵鑫；

【导师】 叶德信；

【作者基本信息】 北京邮电大学 ， 通信与信息系统， 2010， 博士

【摘要】 Internet的高速发展和宽带网络的迅速普及使得流媒体应用速发展成为当今主流的网络应用。相比传统的C/S网络应用模式,P2P技术为部署成本合理、可扩展性高、良好服务质量和用户体验的大规模流媒体内容分发服务提供了更为有效的手段,研究P2P流媒体内容分发的关键技术也因此具有重要的现实意义。然而,P2P网络自身的自由、开放和无中心特性以及流媒体服务所具有的带宽资源消耗大、传输实时性要求高和传输持续时间长等特点,使得提供可靠、可管、可控的P2P流媒体内容分发服务极具挑战性。P2P流媒体内容分发所涉及的关键技术主要包括覆盖网络构建和节点组织、“内容”和“带宽”管理、编码技术、安全和管理机制等几个方面；本文对这些关键技术进行了研究,并重点研究了再编码无比率编码方式下数据存储和传输的相关问题,主要工作和研究成果概括如下(1)利用C/S模式或者其演进模式(内容分发网络)部署大规模流媒体服务,不仅系统的可扩展性、并发处理能力存在不足,而且部署成本高昂；在充分发挥P2P技术优势的基础上,提出一种采用编码技术且具有良好可管理性的P2P流媒体内容分发模式：借鉴网络编码的思想引入可有效提高数据存储和传输性能的再编码无比率编码方式,在服务器端及各个节点对多媒体数据进行编码处理,并以“边缘化”索引维护为目的构建基于中心域和分治域服务器的“多域分治”体系结构,同时给出完整的层次化功能模块划分。(2)P2P视频点播系统的高动态性和交互性特点使得其设计和实现较P2P文件共享系统和直播系统更加复杂；具有良好服务质量和用户体验的视频点播服务主要依赖于系统的节点组织、数据存储和数据传输三个核心方面；采用混合式方式进行节点组织、基于再编码无比率编码方式综合考虑数据存储和传输、并引入多源(视频文件)共享交叉存储方式设计了一个具有高可扩展性、高可靠性、额外开销小的P2P视频点播系统——xVoD;利用与用户播放记录相关的“动态起始点”进行邻居节点选择,使得系统能够很好地支持用户的VCR操作；利用多源共享交叉存储方式可充分发挥用户节点的上载能力、提高资源利用率；按照“稀缺优先”原则使用启发式算法分配各数据块存储空间能够增加各数据块分布的“均匀”程度,以提高数据块在用户节点存储空间的命中率；利用基于无比率编码请求驱动的调度方式大大简化数据块调度的同步问题和数据提供者的选择问题；按照紧急度、稀缺度相关的数据块请求优先级响应请求,并采用贪心算法分配带宽,以尽力服务请求优先级高的节点从而保证用户播放质量；实验仿真结果显示,xVoD在源服务器负载、启动时延、VCR时延和数据路由开销等方面都表现出良好的性能,且系统性能随着所分配存储空间大小的增加呈上升趋势。(3)P2P流媒体系统中“内容”分布状态随着一些系统参数以及用户节点的在线状况和观看行为不断变化,并对用户的播放质量和服务器负载产生一定影响；结合流媒体系统的特性,从节点间资源共享的角度出发,提出P2P流媒体系统“数据可得率”的定义并给出概率形式描述；然后基于给定的采用无比率编码技术的视频点播系统模型和相关假设进行数据块可得率的分析和计算；利用离散马尔可夫链模型对用户的观看行为进行建模分析,得出数据块访问率和拥有率的计算方法；并借助实验仿真,探讨和总结数据可得率与文件分块数、数据块编码分片数、邻居节点数量等系统参数以及用户节点的在线规律和行为之间的关系,初步给出一些指导系统设计和优化的参数选择策略。(4)高可运营性的P2P流媒体内容分发系统需要合理、高效的安全机制给予保障,既能抵御“外部”入侵——确保只有合法用户才可以得到服务且保证他们之间数据传输的机密性、完整性和可鉴别性又能防范“内部”污染——快速鉴别不良行为用户制造的不可用污染数据、减少污染数据的传播；通过引入基于椭圆曲线自认证公钥系统构建系统安全体系,并设计一套高效的认证和密钥建立机制以提供给合法用户节点之间安全的通信环境；利用同态哈希函数对编码数据的有效性进行鉴别以防范数据污染,并辅以一定的管理机制有力保障系统健康、高效运转。更多还原

【Abstract】 The streaming media application has become more and more popular with the rapid development of Internet and broadband networks. Compared with traditional framework of client/server (C/S), peer-to-peer (P2P) technologies provide effective means of deploying large-scale streaming media distribution with low cost, high scalability as well as good quality of service and experience. Driven by application requirements, the key technologies of P2P streaming media distribution draw more and more attentions from both industry and academia. However, there are still full of challenges for providing reliable and manageable P2P streaming service, for the nature of P2P networks (free, open and centreless) and streaming service (large bandwidth consumption, real-time requirement and long transmission duration). The key technologies for P2P streaming media distribution includes overlay networks construction coupled with peer organization, management of "content" and "bandwidth" resources, coding technologies, together with mechanisms of security and management etc.. In this paper, these issues are studied, with a special focus on data storage and transmission using recoded rateless coding.Firstly, using either C/S framework or its evolution form CDN to deploy large-scale streaming media service not only leads to the system’s lack of scalability and concurrent processing capacity, but also brings high cost. Taking advantage of P2P, a novel manageable P2P streaming media distribution framework using coding technology is proposed. Learning from the idea of network coding, the recorded rateless coding is processed at both the server and peer to improve the performance of data storage and transmission. At the same time, in order to maintain the index with edge servers, a "multi-domain divide and conquer" architecture is designed, attached by the entire layered function module partition.Secondly, the high dynamics and interactivity of P2P video-on-demand (VoD) system make it more complex to design and implement than P2P file sharing and live systems. Building P2P VoD system with high quality of service and experience depends on three core aspects:peer organization, data storage and data transmission. Hybrid peer organization mechanism, recoded rateless coding for data storage and transmission, as well as cross-sharing multi-channel architecture are adopted for designing a novel VoD system, namely xVoD, which has high resilience and scalability, low communication overhead etc.. In xVoD, "dynamic starting point" is introduced for neighbor nodes selection, which supports VCR operations well; cross-sharing multi-channel architecture aims to make full use of the peer’s uploading and storage capacities; following "rare first" strategy, a heuristic storage allocation algorithm is used to make the distribution of each data block more uniform, which can improve the probability of getting blocks from neighbors (not server); rateless coding-based request-driven scheduling not only eliminates the need for reconciling packets inside each block, but also simplifies the retrieval of different providers; according to the request priority relying on urgency and rarity, block request is responded and bandwidth is allocated using greedy algorithm by the provider. The experiment results show that xVoD substantially reduces server stress, and also has significantly good performance in terms of startup latency, VCR latency and block seeking overhead. Meanwhile the performance improves with more storage of each peer.Thirdly, the distribution state of "content" changes constantly, according to some system parameters, the user’s online status and viewing behavior, which has some influence upon playback quality and server stress. Considering the nature of streaming media application, from the perspective of resource sharing among peers, data-get-rate of P2P streaming system is defined, and the probability description is also presented. Then for the given model under some assumptions of a rateless coding-based P2P VoD system, the data-get-rate is analyzed and calculated. In addition, the modeling analysis of user behavior is given using discrete Markov chain model. By means of experiments, the relationship between data-get-rate and system parameters (including number of file blocks, number of coded pieces, number of neighbor nodes) as well as the law of user behavior is studied. Furthermore, some preliminary guidelines for VoD system design and optimization are given.Fourthly, reasonable and efficient security mechanism is needed for the operation of P2P streaming systems. It requires not only protecting against attacks from the outside to guarantee that only registered user can access services with data confidentiality, integrity and authenticity, but also detecting the data pollution from the inside to reduce the propagation of bad encoded packets. ECC-based self-certified public key cryptosystems (ECCSCPKC) is introduced to construct the system security infrastructure; and its related security schemes, with a few modifications, are used for designing an efficient authentication and key agreement (AKA) protocol. Meanwhile, homomorphic hash function is used for checking the validity of an encoded packet without decoding; in addition, some strategies are established to support effective management of the system.更多还原