【作者】 张春红；

【导师】 程时端；

【作者基本信息】 北京邮电大学 ， 计算机科学与技术， 2013， 博士

【摘要】 IP多媒体通信系统基于互联网实现话音、数据、图片等多媒体信息端到端的实时通信。传统多媒体通信系统架构采用客户端/服务器模式,部署特定的集中式协议服务器处理用户多媒体信令协议并在终端用户之间传输用户媒体数据。随着分布式对等系统P2P(Peer to Peer)技术的发展,IP多媒体通信系统逐渐采纳了多种分布式系统架构,形成基于分布式覆盖网络(Overlay)的P2P多媒体通信系统。IP多媒体通信系统分别在媒体会话控制层、媒体数据承载层和内容语义层引入P2P技术。在媒体会话控制层,对等网络会话初始化协议P2PSIP(Peer-to-Peer Session Initiation Protocol)取代了集中式SIP协议,基于大量普通用户终端节点或可动态部署的服务器节点,提供分布式多媒体会话控制服务。在媒体数据承载层,用户终端利用P2PSIP对等节点构建分布式覆盖网络层的中继路由,形成独立于IP路由的应用层数据传输通道。同时,P2PSIP架构能够存储多媒体通信系统产生的海量数据信息,形成逻辑内容语义网络。本文针对P2PSIP系统中上述三个层次中的关键技术问题开展研究工作。首先,在媒体会话控制层,P2PSIP系统是否能够满足大规模互联网环境下终端用户对信令会话的性能需求,是在实际系统中推广P2PSIP应用必须回答的问题。为了深入理解P2PSIP系统性能特征,本文对P2PSIP终端用户会话建立时延和服务器集群节点信令消息流量特征进行分析与建模,从系统架构设计角度提出性能优化方案,建立系统吞吐量评估模型。其次,在P2PSIP内容语义网络中,传统结构化对等网络采用精确资源标识符映射机制,导致数据内容与数据在分布式系统中的存储位置无关,难以支持语义搜索功能。本文提出资源语义标签映射算法,由语义标签建立数据内容与数据存储位置的关联,并提出基于两种不同DHT(Distributed Hash Table)拓扑的资源搜索算法。最后,在媒体数据承载层,基于P2PSIP节点之间存在的反三角TIV(Triangle Inequality Violation)现象,能够构建传输时延优于默认IP路由的覆盖网络中继路由。而发现覆盖网络中继路由的前提方法之一是通过网络坐标算法预测P2P终端用户节点之间的传输时延。然而传统网络坐标算法将节点嵌入度量空间,从本质上摒除了对时延反三角现象的预测能力。因此本文提出支持时延反三角属性的松弛度量空间网络坐标算法,为建立覆盖网络中继路由提供前提基础。本文的主要研究成果包括：第一：对P2PSIP系统的会话建立时延性能进行建模,并用于分析纯P2PSIP系统架构、服务器集群P2PSIP系统架构和超级节点P2PSIP系统架构中的呼叫建立时延性能,并基于优化分布式系统结构和业务流程的思想,提出层次化异构P2PSIP系统架构。仿真结果表明P2PSIP架构在多数场景下能够满足端到端的会话呼叫建立时延性能需求。研究成果对应论文的第三章。第二：针对P2PSIP服务器集群应用场景,通过分析DHT系统的工作机理,提出了DHT业务流量评估模型,建立P2PSIP服务器节点业务流量模型与用户终端会话服务请求的基本关系。仿真表明P2PSIP业务流量模型能够近似评估实际到达服务器节点的消息流量。研究成果对应论文的第四章。第三：针对DHT系统中的数据资源语义相似性搜索问题,提出半分布式B-PCA和全分布式D-PCA资源语义标签分配算法,将数据资源直接映射到多维欧式CAN拓扑空间,实现分布式资源语义搜索功能。为了扩展算法的适用性,还提出基于位置感知哈希函数簇的S-Chord算法,将多维语义索引标签映射到一维Chord环中,实现了基于多种DHT拓扑的资源语义搜索。研究成果对应论文的第五章。第四：基于分布式网络节点坐标算法Vivaldi,提出了将互联网节点嵌入松弛度量空间的网络坐标算法KL vivaldi,建立支持时延不对称性和反三角性的时延空间模型,预测时延反三角现象,为建立覆盖网络中继路由提供前提基础。研究成果对应论文的第六章。更多还原

【Abstract】 IP multimedia communication system implements real-time multimedia information exchange such as audio, data and image between users. Based on client/server architecture, the protocols of signaling system and data transportation of traditional multimedia communication system are all designed on the assumption of existence of centric servers. With the increasing development of Peer to Peer (P2P) technology over the last decades, IP multimedia communication system also evolves accordingly from centric architecture to distributed architecture. An overlay network of distributed multimedia communication system is therefore constructed.P2P technologies are introduced into IP multimedia communication system on media session control layer, data transportation layer and content semantic layer respectively. First of all, on media session control layer, P2PSIP (Peer-to-Peer Session Initiation Protocol) takes the place of centric SIP to implement distributed session control based on a P2P SIP overlay consisted by all the user terminals or dynamic deployable servers. Second, the overlay also provides the possibility to build application layer data channels relatively independent with IP routings. Finally, the data resources produced by the multimedia communication system, such as user profile, text data and images, are stored on distributed P2PSIP nodes where a logic content semantic layer is therefore formed.The dissertation is principally concentrated on the critical technology issues of the above three layers. First, the performance of P2PSIP is mainly concerned on whether it can meet the requirements of user session control process in large scale network. To achieve deep understanding of P2PSIP performance, the models of call setup delay and traffic characteristic on server nodes of P2PSIP system are proposed. Accordingly, the optimization solution of session setup delay in terms of hierarchical architectures is further discussed, and traffic of session messages is evaluated. Second, because of the explicit search property caused by the consistent hash of traditional Distributed Hash Table (DHT), it is difficult to implement similar search on the content semantic overlay. To fulfill the semantic search requirements in distributed system, the distributed semantic resource index assignment mechanisms are studied, and algorithms of semantic search are proposed in various DHT systems. Furthermore, individual nodes in P2PSIP system could be used to compose overlay relay path shorter than the default IP path according to the phenomenon of Triangle Inequality Violation (TIV) commonly found in Internet. However, most delay prediction algorithms of network coordination adopt metric space which inherently excludes the existence of TIV. To address the issue of TIV prediction, a TIV-friendly network coordination algorithm in relaxed metric space is proposed. The main contributions of the dissertation include the following aspects:First, the evaluation model of call setup delay is proposed and utilized to analyze the latency performance of three P2PSIP architectures including pure P2PSIP, server farm P2PSIP and super-node P2PSIP. The idea of delay optimization from the aspect of architecture and message processes is discussed and a hierarchical heterogeneous P2PSIP architecture is proposed. Simulation suggests that P2PSIP is generally able to satisfy the delay requirements. The contribution is presented in chapter3.Second, a traffic model on server nodes of P2PSIP server farm is proposed through deep analysis of mechanism of DHT (Distributed Hash Table). The basic relation between traffic property of server nodes and session requests from user terminals is also described and qualified. Simulation proved that the traffic model approximately aligns with the real traffic arrived at P2PSIP server nodes. The contribution is illustrated in chapter4.Third, the issue of semantic search for data resources in DHT system is addressed. A semi-distributed and a fully distributed semantic search algorithms named B-PCA and D-PCA are proposed respectively. The algorithms focus on the assignment mechanisms of semantic index by which the data resources are directly mapped into the Euclidean space of CAN topology. Therefore, the resources can be searched according to their semantic index rather than the explicit hash mapping index. To extend the usability of distributed semantic search algorithms, S-Chord algorithm is also proposed based on location sensitive hash function which implements similar search in one dimension Chord ring. The contribution is presented in chapter5.Fourth, a TIV (Triangle Inequality Violation) friendly network coordination algorithm, embedded in relaxed metric space called KL_vivaldi, is proposed. The delay space model created by the algorithm supports the existence of unbalanced delay and TIV phenomena commonly measured in Internet. Therefore, the TIV could be directly and explicitly predicted by network coordination, which facilitates user terminals to create overlay relay paths with more desirable performance than default IP routes. The contribution is described in chapter6.更多还原