基于BitTorrent的P2P-VoD系统设计与实现

针对在互联网上提供大规模VoD服务的困难,提出一种采用P2P技术的VoD系统VoDBB,该系统能以较小的服务器代价实现大规模的VoD应用.VoDBB通过修改BitTorrent的片段选择算法改进系统播放连续度,加入后备流媒体服务器和相应的下载源选择算法保障服务质量(QoS),并通过磁盘管理模块和锚点机制支持用户交互操作.仿真实验结果表明,该系统能提供良好的用户观看体验,降低流媒体服务器负载,并具有很强的扩展能力.     

基于多任务下载的P2P-VoD系统的测量与分析

近些年,P2P点播系统(P2P-Vo D)受到广泛关注,其大多研究工作基于理论性的传统假设,这些假设在真实的系统中是如何表现的不得而知。因此,在真实P2P-Vo D系统中对传统假设进行全面的测量和验证就显得十分迫切。对实际运行的P2P-Vo D系统Cool Fish进行了大量的测量与分析,发现了一些不同于以往假设的结果:节点加入不是简单地服从泊松分布;观看时间和影片流行度不呈严格的正相关性;跳转频率和影片流行度不呈负相关。最后对这些结果进行了深入的分析和讨论。     

Hierarchically Clustered P2P Video Streaming: Design,implementation, and evaluation

P2P based live streaming has been gaining popularity. The new generation P2P live streaming systems not only attract a large number of viewers, but also support better video quality by streaming the content at higher bit-rate. In this paper, we propose a novel P2P streaming framework, called Hierarchically Clustered P2P Video Streaming, or HCPS, that can support the streaming rate approaching the optimal upper bound while accommodating large viewer population. The scalability comes with the hierarchical overlay architecture by grouping peers into clusters and forming a hierarchy among them. Peers are assigned to appropriate cluster so as to balance the bandwidth resources across clusters and maximize the supportable streaming rate. Furthermore, individual peers perform distributed queue-based scheduling algorithms to determine how to retrieve data chunks from source and neighboring peers, and how to utilize its uplink bandwidth to serve data chunks to other peers. We show that queue-based scheduling algorithms allow to fully utilize peers’ uplink bandwidths, and HCPS supports the streaming rate close to the optimum in practical network environment. The prototype of HCPS is implemented and various design issues/tradeoffs are investigated. Experiments over the PlanetLab further demonstrate the effectiveness of HCPS design.     

P2P组播网络容量分析

最近几年来,P2P技术在研究领域受到广泛关注,很多系统开始采用P2P架构进行组网,向用户提供各种服务,如下载服务和组播服务.人们普遍认为P2P系统中节点越多,P2P对等技术的优势也越明显,系统的容量几乎没有限制.但对P2P组播网络,这一结论必须满足一定条件才能成立,本文从基本的流量关系出发,推出P2P组播网络理论上能够容纳的最大节点数量和节点流复制能力的关系,并以构造方式证明了对任何数量的节点,只要总的复制能力超过节点数量,理论上存在一种组播组织方式,实现稳定组播,为P2P组播网络的优化提供了理论指导.     

基于无比率编码的P2P-VoD中数据调度策略

在P2P多媒体系统中,由于节点能力的限制和多媒体应用的高带宽要求,高性能的数据调度策略成为提高媒体服务质量的关键。该文提出一个基于无比率编码的P2P视频点播系统,并以最小延迟为目标对系统的数据调度策略进行分析,得到一个线性最优化模型,对系统的节点动态性进行讨论,并说明下一步的研究工作。     

一种无线mesh网络下P2P-VoD系统的资源查询算法

针对mesh网络下基于Gossip协议的资源查找算法带来的资源查找效率低、消息负载高的问题,本文设计一个mesh网络下P2P-VoD(Peer-to-Peer Video-on-Demand)系统的资源查找算法。将P2P-VoD系统划分为两层结构:利用Chord算法将mesh路由器进行组织作为顶层逻辑结构,负责资源的分配与索引;移动设备为底层结构。根据本文提出的资源查询算法,P2P-VoD系统能够为移动节点快速定位最优服务资源。实验结果表明,该算法能够有效地提高资源查找效率以及降低数据传输时延。     

Flat and hierarchical epidemics in P2P systems: Energy cost models and analysis

In large scale distributed systems, epidemic or gossip-based communication mechanisms are preferred for their ease of deployment, simplicity, robustness against failures, load-balancing and limited resource usage. Although they have extensive applicability, there is no prior work on developing energy cost models for epidemic distributed mechanisms. In this study, we address power awareness features of two main groups of epidemics, namely flat and hierarchical. We propose a dominating-set based and power-aware hierarchical epidemic approach that eliminates a significant number of peers from gossiping. To the best of our knowledge, using a dominating set to build a hierarchy for epidemic communication and provide energy efficiency in P2P systems is a novel approach. We develop energy cost model formulations for flat and hierarchical epidemics. In contrast to the prior works, our study is the first one that proposes energy cost models for generic peers using epidemic communication, and examines the effect of protocol parameters to characterize energy consumption. As a case study protocol, we use our epidemic protocol ProFID for frequent items discovery in P2P systems. By means of extensive large scale simulations on PeerSim, we analyze the effect of protocol parameters on energy consumption, compare flat and hierarchical epidemic approaches for efficiency, scalability, and applicability as well as investigate their resilience under realistic churn.     

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.     

Anonymity analysis of P2P anonymous communication systems

Compared with traditional static Client/Server architecture, the P2P architecture is more suitable for anonymous communication systems because it is more flexible and can keep load balance better. However, in order to make the system usable and reliable, some system designs make tradeoffs between anonymity and performance such as reliability, latency and throughput. Tradeoffs are sometimes unavoidable in system design, but which tradeoffs are acceptable and which are not is very important for developers. This paper models the P2P anonymous communications and takes quantitative analysis of anonymity by information theory with entropy. Based on this analysis, it studies the effect of key system design strategies on anonymity in network architecture, routing and message relay, and measures which strategies should be used in anonymous communications and which are unreasonable. Some analysis results are contrary to our intuition. For example, it quantitatively concludes that in some cases the anonymity is not enhanced when the system scale increases, and too long an anonymous tunnel may not provide higher anonymity but lowers performance. These analysis results are valuable for developers of P2P anonymous communication systems. Besides, this paper also discusses some possible strategies such as trust and reputation to enhance the P2P anonymous communications.     

An efficient server bandwidth costs decreased mechanism towards mobile devices in cloud-assisted P2P-VoD system

Recently, more and more devices with small buffer size such as PDAs or mobile phones are joining in the VoD system, which leads to two major challenges: how to efficiently distribute their bandwidth resources with small buffer size, and how to provide assistant mechanism to make them playback smoothness. In face of this situation and for the purpose of decreasing the server bandwidth costs, we propose a peers’ downloading mechanism called NCDLT to solve above challenges. It contains two algorithms. The first is neighbors and chunks downloading selection (NCS) algorithm and it ensures peers to find neighbors who can provide video data with lower refusal rate. The second is distributed linear taxation algorithm (DLT) and it makes peers with lower capability acquire enough download rate to reduce the request to servers. The simulation results demonstrate that our algorithms can offload the server bandwidth costs and improve the download rate of peers with small buffer size.     

P2P存储系统中基于用户体验的可用性模型与应用

保证数据的可用性是Peer-to-Peer(P2P)存储系统最重要的属性之一.可用性分析模型和数据的放置是P2P存储系统设计的两个关键问题.由于用户在P2P存储系统中同时作为服务节点和访问节点,决定了可用性分析必须以用户为中心,从而提高服务质量,并降低系统开销.目前广泛使用的可用性分析模型以及随机放置方法存在以下缺点:1.忽视了节点在线时间的模式,会在不同时间段高估或低估节点的可用性;2.忽视了节点对数据的访问规律,不能准确评估用户体验到的可用性;3.忽视了节点可用性差异,缺乏激励机制.本文提出了一个新的基于用户体验的可用性模型,它能够从用户体验的角度,评价P2P存储系统的可用性,同时它也可以兼容传统的可用性分析模型.在新模型的基础上,本文针对两种典型的P2P存储应用:数据共享和个人备份,提出了相应的分布式数据分发算法.通过真实日志驱动实验证明,新的算法在数据共享应用中能大大降低可用性方差,减少低可用性数据;同时,在个人备份应用中能针对不同用户的贡献提供不同层次的服务,起到有效的激励作用.     

User-experience-based availability analysis model and its application in P2P storage systems

Data availability is one of the most important properties of peer-to-peer (P2P) storage systems.Availability analysis model and data placement are two key design choices.Users in P2P storage system are both providers and customers.This characteristic determines that the availability analysis must be user-centric,and thereby enhance the quality of service and decrease the system cost.The popular approach in recent studies is simple random placement with steady-state model,which has the following drawbacks:1)...     

An analysis of peer similarity for recommendations in P2P systems

In this paper, we propose a novel recommender framework for partially decentralized file sharing Peer-to-Peer systems. The proposed recommender system is based on user-based collaborative filtering. We take advantage from the partial search process used in partially decentralized systems to explore the relationships between peers. The proposed recommender system does not require any additional effort from the users since implicit rating is used. The recommender system also does not suffer from the problems that traditional collaborative filtering schemes suffer from like the Cold start and the Data sparseness. To measure the similarity between peers, we propose Files?? Popularity Based Recommendation (FP) and Asymmetric Peers?? Similarity Based Recommendation with File Popularity (ASFP). We also investigate similarity metrics that were proposed in other fields and adapt them to file sharing P2P systems. We analyze the impact of each similarity metric on the accuracy of the recommendations. Both weighted and non weighted approaches were studied.     

Design and evaluation of P2P overlays for energy negotiation in smart micro-grid

The increasing availability of distributed renewable energy sources such as photo-voltaic (PV) panels has introduced new requirements for innovative power grid infrastructures. Information technologies provide new opportunities for developing techniques to optimize the energy usage by a new generation of smart-grids. Here we investigate an original solution that aims at maximizing the self-consumption within a neighborhood based on a collaborative approach. Distributed software agents plan and enforce the optimal schedule of consuming appliances according to the prediction of energy production by PV panels, the estimated energy profile of consuming devices and the user's preferences and constraints. Finally we focus on the performance evaluation of a negotiation protocol that allows agents to find a sub-optimal solution for the global schedule, comparing results obtained by a prototype implementation and experimenting different technologies.     

Cooperative Caching in Wireless P2P Networks: Design, Implementation, and Evaluation

Some recent studies have shown that cooperative cache can improve the system performance in wireless P2P networks such as ad hoc networks and mesh networks. However, all these studies are at a very high level, leaving many design and implementation issues unanswered. In this paper, we present our design and implementation of cooperative cache in wireless P2P networks, and propose solutions to find the best place to cache the data. We propose a novel asymmetric cooperative cache approach, where the data requests are transmitted to the cache layer on every node, but the data replies are only transmitted to the cache layer at the intermediate nodes that need to cache the data. This solution not only reduces the overhead of copying data between the user space and the kernel space, it also allows data pipelines to reduce the end-to-end delay. We also study the effects of different MAC layers, such as 802.11-based ad hoc networks and multi-interface-multichannel-based mesh networks, on the performance of cooperative cache. Our results show that the asymmetric approach outperforms the symmetric approach in traditional 802.11-based ad hoc networks by removing most of the processing overhead. In mesh networks, the asymmetric approach can significantly reduce the data access delay compared to the symmetric approach due to data pipelines.     

基于BitTorrent的P2P安全模型的设计

本文以基于BitTorrent的P2P安全模型设计为研究对象,从基于BitTorrent的P2P安全模型设计原则、设计结构框架这两个方面入手,对其做出了详细说明,在此基础之上侧重从基础安全服务层以及综合安全服务层这两点针对基于BitTorrent系统安全模型的设计作业进行了分析与研究,据此论证了BitTorrent在P2P网络安全建设与安全管理中深远的应用意义与价值。     

Security and privacy issues in P2P streaming systems: A survey

Streaming applications over Peer-To-Peer (P2P) systems have gained an enormous popularity. Success always implies increased concerns about security, protection, privacy and all the other ‘side’ properties that transform an experimental application into a service. Research on security for P2P streaming started to flourish, but no comprehensive security analysis over the current P2P solutions has yet been attempted. There are no best practices in system design, no (widely) accepted attack models, no measurement-based studies on security threats to P2P streaming, nor even general surveys investigating specific security aspects for these systems. This paper addresses this last aspect. Starting from existing analyses and security models in the related literature, we give an overview on security and privacy considerations for P2P streaming systems. Our analysis emphasizes two major facts: (i) the Byzantine–Altruistic–Rational (BAR) model offers stronger security guarantees compared to other approaches, at the cost of higher complexity and overhead; and (ii) the general perception (not necessarily the truth, but a commonplace belief) that it is necessary to sacrifice accuracy or performance in order to tolerate faults or misbehaviors, is not always true.     

On the feasibility of exploiting P2P systems to launch DDoS attacks

We show that malicious nodes in a peer-to-peer (P2P) system may impact the external Internet environment, by causing large-scale distributed denial of service (DDoS) attacks on nodes not even part of the overlay system. This is in contrast to attacks that disrupt the normal functioning, and performance of the overlay system itself. We demonstrate the significance of the attacks in the context of mature and extensively deployed P2P systems with representative and contrasting membership management algorithms—Kad, a DHT-based file-sharing system, and ESM, a gossip-based video broadcasting system. We then present an evaluation study of three possible mitigation schemes and discuss their strength and weakness. These schemes include (i) preferring pull-based membership propagation over push-based; (ii) corroborating membership information through multiple sources; and (iii) bounding multiple references to the same network entity. We evaluate the schemes through both experiments on PlanetLab with real and synthetic traces, and measurement of the real deployments. Our results show the potential of the schemes in enhancing the DDoS resilience of P2P systems, and also reveal the weakness in the schemes and regimes where they may not be sufficient.     

P2P文件共享系统中的复制策略

复制技术可以提高P2P文件共享系统的可靠性,改善查询性能和负载均衡。对文献中出现的各种复制策略进行总结综述,列出了各种复制策略背后的思想和拟解决的问题。在详细分析这些复制策略的特点基础上,对复制策略进一步的工作进行了展望并提出了建议。对进一步的研究复制策略有一定的参考价值。