InstantLeap: an architecture for fast neighbor discovery in large-scale P2P VoD streaming

In large-scale peer-to-peer (P2P) video-on-demand (VoD) streaming applications, a fundamental challenge is to quickly locate new supplying peers whenever a VCR command is issued, in order to achieve smooth viewing experiences. For many existing commercial systems which use tracker servers for neighbor discovery, the increasing scale of P2P VoD systems has overloaded the dedicated servers to the point where they cannot accurately identify the suppliers with the desired content and bandwidth. To avoid overloading the servers and achieve instant neighbor discovery over the self-organizing P2P overlay, we design a novel method of organizing peers watching a video. The method features a light-weight indexing architecture to support efficient streaming and fast neighbor discovery at the same time. InstantLeap separates the neighbors at each peer into a streaming neighbor list and a shortcut neighbor list, for streaming and neighbor discovery respectively, which are maintained loosely but effectively based on random neighbor list exchanges. Our analysis shows that InstantLeap achieves an O(1) neighbor discovery efficiency upon any playback “leap” across the media stream in streaming overlays of any size, and low messaging costs for overlay maintenance upon peer join, departure, and VCR operations. We also verify our design with large-scale simulation studies of dynamic P2P VoD systems based on real-world settings.     

An experimental analysis of Joost peer-to-peer VoD service

Despite strong interest in peer-to-peer (P2P) Video-on-Demand (VoD) services, existing studies mostly focus on peer-to-peer or overlay protocol design based on simulations under various topological constraints. We believe experimental studies on a real-life P2P VoD system will provide valuable information to ISPs, network administrators, and content owners. In this paper we present a comprehensive analytical and experimental study on Joost, one of the first commercial P2P VoD systems used for distributing various forms of video over the Internet. Our extensive experiments prove that Joost is a server-assisted peer-to-peer VoD system. With several envisioned typical scenarios we have further investigated the peer management in terms of time pattern, bandwidth consumption and locality considerations. Our major findings include: (1) the current Joost system is capable of providing high-quality VoD service through the use of an overlay network deployed with a set of centralized content servers; (2) inter-continental links are often used regardless of the number of local users, which may pose a high burden on the network providers; (3) easily reachable, high-capacity nodes are selected as main relaying nodes, similar to super nodes in Skype, to facilitate the traversal of symmetric NATs and firewalls. We also provide insights on the potential ways to construct more efficient P2P VoD systems (e.g. considering topological locality-awareness, using adaptive/layered video).     

Measurement study on P2P streaming systems

Originally used as the default infrastructure for efficient file sharing, peer-to-peer (P2P) architecture achieved great successes. Now, the P2P model has been adopted for many other distributed applications, such as instant message and phone services, Internet gaming, and large-scale scientific computing. In recent years, P2P streaming systems experienced tremendous growth and became one of the largest bandwidth consumers on the Internet. Compared to standard file sharing systems, the streaming services show unique characteristics with more stringent time constraints and require much higher network bandwidth. It is extremely important to evaluate and analyze existing applications, and investigate the merits and weaknesses in these systems for future development. In this paper, we conduct a comprehensive measurement study on two of the most popular P2P streaming systems, namely, PPLive and PPStream. They are very popular P2P streaming applications, and serving millions of registered users with hundreds of live TV channels and millions of other video clips. In our measurement, we deploy our collectors in China, and both live TV and video-on-demand (VoD) channels are evaluated. We record run-time network traffic on the client side, compare and analyze the characteristics of these channels based on their popularity. For both categories, we perceive that, in general, the two measured P2P streaming systems provide satisfactory experience to the audiences for all channels regardless of popularity. However, the most of data are downloaded from the dedicated servers for unpopular channels. We also observe that live TV channels show better peer coordination than VoD channels. Beside the traffic, we have also collected cache replacement information for VoD channels, and these measurement results can help us understand the caching mechanism of P2P streaming systems. With the support of the cache, VoD channels perform better than their counterparts in the live TV category in terms of data transmission, workload distribution, and signal traffic overhead. Overall, our results reveal that although P2P streaming systems can usually provide excellent viewing experience for popular channels, there are still challenges to fully support unpopular channels. New designs and algorithms are in urgent need, especially for unpopular live TV channels.     

Distributed Throughput Maximization in P2P VoD Applications

In peer-to-peer (P2P) video-on-demand (VoD) systems, a scalable source coding is a promising solution to provide heterogeneous peers with different video quality. In this paper, we present a systematic study on the throughput maximization problem in P2P VoD applications. We apply network coding to scalable P2P systems to eliminate the delivery redundancy. Since each peer receives distinct packets, a peer with a higher throughput can reconstruct the video at a higher quality. We maximize the throughput in the existing buffer-forwarding P2P VoD systems using a fully distributed algorithm. We demonstrate in the simulations that the proposed distributed algorithm achieves a higher throughput compared to the proportional allocation scheme or the equal allocation scheme. The existing buffer-forwarding architecture has a limitation in total upload capacity. Therefore we propose a hybrid-forwarding P2P VoD architecture to improve the throughput by combining the buffer-forwarding approach with the storage-forwarding approach. The throughput maximization problem in the hybrid-forwarding architecture is also solved using a fully distributed algorithm. We demonstrate that the proposed hybrid-forwarding architecture greatly improves the throughput compared to the existing buffer-forwarding architecture. In addition, by adjusting the priority weight at each peer, we can implement the differentiated throughput among different users within a video session in the buffer-forwarding architecture, and the differentiated throughput among different video sessions in the hybrid-forwarding architecture.      

P2P网络下一种基于DHT的视频点播方案

在基于P2P的视频点播系统中,节点邻居选择策略对服务质量有很大的影响。提出一种基于DHT（Distributed Hash Table）的P2P覆盖网络下视频点播（Video-on—demand）的解决方案。通过网络坐标系统的拓扑发现能力,充分结合DHT网络高速搜索和VoD视频点播的特性、构造一种具有高效邻居选择能力、高用户自由度、高可靠性、扩展性的体系架构。针对架构设计中资源发布份发、资源的搜索、视频点播的实现等关键问题提出了解决方案,分析了系统的特性。     

P2P异步传输点播系统设计与仿真

互联网上大规模Peer-to-Peer(P2P)点播服务存在高效资源调度和不可预知用户行为等挑战.借鉴BitTor-rent(BT)算法原理,提出基于异步传输的P2P点播系统.该系统采用集中式节点定位以及非结构化拓扑,通过异步传榆机制提升文件资源共享度和利用率,并引入视频数据块的优先级和稀有程度改进系统播放连续度.数据包及仿真实验表明本系统在播放连续度、启动时延以及服务器压力等性能指标上的良好性能,充分验证了点播系统中异步传榆机制的可行性.     

Evaluation of a comprehensive P2P video-on-demand streaming system

Video-on-demand (VoD) streaming has recently become a popular service on the Internet, with several companies offering videos to a global audience. However, traditional client/server based VoD streaming systems can be very bandwidth intensive and expensive to maintain, especially for high quality video content. To improve the scalability these systems, the use of peer-to-peer (P2P) networking has been proposed, but despite the efficiency of applications such as BitTorrent for downloading of large files, it is not simple to use P2P techniques for streaming. Problems such as firewalls and freeloaders reduce the efficiency of both types of P2P systems, but for real-time services such as streaming, the result can be reduced playback quality. Other issues include the traffic load imposed on ISPs by P2P networks, which can motivate ISPs to interfere with the P2P traffic. Finally, protecting against malicious modification of content can increase overhead, response times, and startup delays.We consider these issues to be fundamental to the problem of P2P based VoD, but despite the large amount of research that has been done in this field, these issues have largely been ignored. To address this, we present an evaluation of the Streaming P2P Protocol (SPP) architecture. By studying the problem as a whole we have found a simple and comprehensive solution that addresses all the four issues listed above. To show that the system is not only scalable, but also that it can be implemented efficiently, we have used both simulations and experiments on PlanetLab for evaluation. The results show that the combination of cache nodes and use of end-user resources found in the SPP architecture can give a low load on servers and ISPs, even when firewalls are taken into consideration. Furthermore, we observed low startup delays and few playback errors during the PlanetLab experiments. The scalable and low-cost distribution of content possible with the SPP architecture should be suitable for both large-scale commercial distributors and users of community networks with limited resources.     

Modeling and analysis of multi-channel P2P VoD systems

Peer-to-Peer (P2P) technology has recently become a tremendously attractive solution to offload servers in large-scale Video-on-Demand (VoD) applications by utilizing the upload capability of participating peers. However, the alleviation of server load may not be very effective in the multi-channel P2P VoD systems due to the intra-channel and inter-channel upload bandwidth imbalances. In this paper, we evaluate the impact of these bandwidth imbalances on the system performance through two analytically models: a queuing network model which describes the whole system, and a stage-based model which describes a single channel. Our models capture several aspects of peer behavior, such as participating in the system, sojourning in a channel, downloading and uploading the content, wandering around channels and leaving the system. We apply our models to three potential P2P VoD designs: Naive bandwidth Allocation Design (NAD), Independent-channel Chunk-aware bandwidth Allocation design (ICA) and Cross-channel Chunk-aware bandwidth Allocation design (CCA). By developing an asymptotic theory to provide theoretical results, we analytically show that ICA can perform better than NAD, and CCA can perform best of the three designs in terms of server load. We also present optimization problems and simple heuristic strategies for ICA and CCA. Our analytical results are validated by extensive simulations.     

A Trace-Driven Approach to Evaluate the Scalability of P2P-Based Video-on-Demand Service

Peer-to-Peer (P2P) networks have emerged as one of the most promising approaches to improve the scalability of Video-on-Demand (VoD) service over Internet. However, despite a number of architectures and streaming protocols have been proposed in past years, there is few work to study the practical performance of P2P-based VoD service especially in consideration of real user behavior which actually has significant impact on system scalability. Therefore, in this paper, we first characterize the user behavior by analyzing a large amount of real traces from a popular VoD system supported by the biggest television station in China, cctv.com. Then we ex-amine the practical scalability of P2P-based VoD service through extensive trace-driven simula-tion under a general system framework. The results show that P2P networks scale well in provid-ing VoD service under real user behavior by obtaining a considerable good cache hit ratio. Moreover, it is observed that adopting hard cache at client side help achieves better system scal-ability than that with soft cache. We also identify the impact of various aspects of user behavior upon system scalability through detailed simulation. We believe that our study will shine insight-ful light on the understanding of practical scalability of P2P-based VoD service and be helpful to future system design and optimization.     

Measurement-based study on the relation between users’ watching behavior and network sharing in P2P VoD systems

P2P-based Video on Demand (P2P VoD) systems can provide higher quality video services than P2P live systems. However, owing to the unavailability of open source codes, the characteristics of P2P VoD systems have not been fully explored. For this purpose, in this paper, we first implemented reverse engineering to the protocols of two most popular VoD systems used in China. Peers’ watching behavior and network sharing were then studied through the measured buffer messages. Based on our study, we found that uploading-only peers were more than downloading peers, and smooth-watching peers were more than randomly-seeking peers in the current P2P VoD systems. This finding is significantly different from the existing P2P-based file dissemination systems and the results obtained in the previous work on VoD systems. Furthermore, this study revealed the relations between watching behavior and network sharing. It has been observed that randomly-seeking peers will provide more regular as well as rare chunks than smooth-watching peers. A simple mathematical model was established to analytically demonstrate the relation between the watching index (WI) distribution and network-sharing profile, and this relation was also validated by our measured data.     

CircleSearch：流媒体VoD环境下的P2P搜索算法

在基于P2P的流媒体VoD环境下,搜索机制是影响服务质量的关键因素之一。该文提出一种新的基于环状网络的分布式自适应概率搜索算法——CircleSearch。它依据节点本体内容生成结构化的环状拓扑网络,保证算法的可扩展性、健壮性和分布性。自发组织基于本体距离和连接可靠性的small world覆盖网络,减小消息的转发次数,采用自适应搜索算法提高文件定位的准确性。仿真实验表明,CircleSearch以其高成功率、低服务器负载和很小的平均搜索长度实现媒体流传输的即时、稳定、可控和连续,为VoD服务提供QoS保证。     

一个真实VoD/P2P系统Novasky的设计与实现

近年来,基于对等网络的视频点播系统(VoD/P2P)备受人们关注.这类系统的实现还面临诸多挑战,如存储策略、用户激励、媒体版权等.本文提出一种高效率、低成本、易扩展的VoD/P2P系统设计方案Novasky.与已有系统相比,Novasky的最大不同是引入了编码存储策略与虚拟货币机制.经过三年多的开发与完善,Novasky已发展成为一个跨平台的分布式系统.它是少数几个使用人数较多的研究性VoD/P2P系统之一.自2009年9月在清华大学开放使用以来,已接受1100多用户对346个视频的6288次点播,累计点播数据量2.1TB.     

基于P2P的视频点播系统综述

近十年来,基于对等网络(Peer-to-Peer,P2P)的视频点播系统(Video-on-Demand,VoD)受到了越来越多的关注.它吸引人的原因在于,与传统的基于服务器/客户机结构的视频点播系统相比,P2P技术具有成本低、扩展性好的优点.但是,由于对等网络内在的不稳定性、异构性,这类系统在实现上面临着诸多挑战.文中对现有的该类系统的体系结构进行模块划分,并对各模块的实现策略进行讨论;特别是对VoD/P2P实现中的3个主要方面,即数据传输、数据存储、激励机制进行了综述.     

P2P视频点播内容分发策略

视频点播目前已成为对等(peer-to-peer,简称P2P)网络中一项重要的应用,引起了人们的不少研究兴趣.由于P2P网络能够为VoD(video-on-demand)应用的大规模实现提供底层网络的支持,许多正在出现的P2P VoD分发策略都能够提供在P2P网络中最基本的数据传输方式.对以往主要的P2P VoD内容分发策略进行了总结和概括.首先介绍了设计P2P VoD策略的相关重要问题,并把策略根据内容分发方式的不同分成4种类型.最后讨论了它们的应用层性能,并提出未来可以延续的工作.     

P2P VoD系统的关键技术研究进展

结合现有的对等网络视频点播系统,分析了P2P VoD系统的关键技术及其研究进展,主要包括视频点播系统结构的构建、节点失效时的修复策略、数据片断的缓存和调度策略、对VCR操作的支持策略、以及QoS保证机制等等.     

An identity-based approach to secure P2P applications with Likir

Structured overlay networks are highly susceptible to attacks aimed at subverting their structure or functionalities. Although many secure architectural design proposals have been presented in the past, a widely accepted and comprehensive solution is lacking. Likir (Layered Identity-based Kademlia-like Infrastructure) is our solution for implementing a secure Peer-to-Peer network based on a Distributed Hash Table. Our purpose is to focus on three main goals: (1) providing security services and a secure overlay infrastructure against the vast majority of security threats on P2P systems, (2) dynamically creating a bridge between randomly generated peer identifiers and user identities, and (3) supplying the developer with a middleware API that can easily deal with peers’ identities. Placing the emphasis on user identity results in a highly secure distributed framework which is very fitting for privacy-aware and efficient implementation of identity-based applications like social networking applications. Detailed security analysis and performance evaluation are provided. Moreover, an implementation of Likir is introduced and a case study is presented in order to show its practical use in a real-life example.     

一种基于节点可选度的P2P点播流媒体数据调度算法

当前的P2P(Peer-to-Peer)点播流媒体系统中数据调度算法未能充分利用每个用户节点自身的特性.在分析典型数据调度算法基础上提出一种基于节点可选度的数据调度算法(SSP算法).该算法一方面在调度下载数据块时综合考虑了邻居节点带宽能力及其所拥有的数据信息.另一方面对服务节点的请求处理过程进行了优化.SSP算法有利于提高用户节点播放视频的连续性,降低流媒体服务器的负载压力,从而改善P2P点播流媒体系统的整体服务质量.仿真结果和实际应用表明算法性能良好,适用于用户节点能力差异较大的P2P点播流媒体环境.     

非结构化P2P系统Overlay优化技术综述

非结构化P2P Overlay网络的结构松散, 网络中资源的分布没有明确的限制, 这使得非结构化P2P Overlay网络中的资源搜索在很大程度上依赖于通信开销巨大的泛洪法, 因而非结构化P2P系统在伸缩性, 可用性等方面, 存在明显的不足. 非结构化P2POverlay网络的上述特点决定了非结构化P2P Overlay优化技术的重要性. 本文分四大类别, 对非结构化P2P Overlay优化技术进行了介绍, 分析比较了各类方法的优劣以及它们的适用场合, 并在此基础上对未来工作进行了展望.     

基于图状模型的多源P2P点播架构设计和实现

针对互联网视频点播服务(VoD)集中数据源的负载大、扩展性差,成为性能和容量瓶紧等问题[1],通过动态规划节点之间通讯提高系统整体吞吐率、设计支持多数据源调度的Tracker的服务器,以及相关的预处理缓存策略,实现了一个基于分时偏移图状结构的可适应多数据来源的P2P视频点播系统架构.