The problem of upload competition in peer‐to‐peer systems with incentive mechanisms

As peer‐to‐peer (P2P) file‐sharing systems revolve around cooperation, the design of upload incentives has been one of the most important topics in P2P research for more than a decade. Several deployed systems, such as private BitTorrent communities, successfully manage to foster cooperation by banning peers when their sharing ratio becomes too low. Interestingly, recent measurements have shown that such systems tend to have an oversupply instead of an undersupply of bandwidth designers that have been obsessed with since the dawn of P2P. In such systems, the ‘selfish peer’ problem is finally solved, but a new problem has arisen: because peers have to keep up their sharing ratios, they now have to compete to upload. In this paper, we explore this new problem and show how even highly cooperative peers might in the end not survive the upload competition. On the basis of recent measurements of over half a million peers in private P2P communities, we propose and analyze several algorithms for uploader selection under oversupply. Our algorithms enable sustained sharing ratio enforcement and are easy to implement in both existing and new systems. Overall, we offer an important design consideration for the new generation of P2P systems in which selfishness is no longer an issue. Copyright © 2012 John Wiley & Sons, Ltd.     

Securing BitTorrent using a new reputation-based trust management system

Nowadays, BitTorrent as a means of sharing files has become highly popular among internet users. However, due to the open nature of BitTorrent protocol and lack of any security mechanism, number of attacks against BitTorrent has significantly increased. Sybil, Collusion, Lying-Piece, Fake-Block, and Chatty-Peer are attack types which have been considered in this paper to secure BitTorrent against them. These attacks can decrease the download performance of BitTorrent clients considerably. In this paper a new reputation based trust management system to cover aforementioned attack types is presented. The proposed approach calculates a local score at peers and a global score at the tracker for each peer. First, peers are sorted according to their cumulative score at the tracker and then top 10 % of these peers are used to determine other peers global score. These local and global scores are used to find attackers. In addition, a novel formula has been utilized to calculate peers local score. Using the global score concept makes our mechanism robust and swift to detect collusion attack which has not been considered in most of similar previous works. In order to evaluate the effectiveness of the proposed system, several simulation and real experiments in the Emulab testbed were performed. The outcomes indicate that our method is highly effective in detection of rogue peers and Free-Riders; moreover, performance of honest peers has significantly improved.     

K网络节点标识符重复与别名现象测量

为方便P2P网络的内容投递,Kademlia协议作为一个鲁棒性强的分布式Hash表协议,被BitTorrent和eMule等P2P文件共享应用部署.在此,将这些被部署的基于Kademlia协议的网络称为K网络.K网络中每个节点拥有唯一的IP地址(或ID)是至关重要的,因为K网络中的"节点查询"和"资源搜索"都依赖于此.然而,据分析发现,K网络中相当一部分节点存在IP重复与ID别名.为深入理解IP重复与ID别名的分布特征,提出了几个度量IP重复与ID别名的测度.基于这些测度和Rainbow采集器,对K网络中的IP重复与ID别名进行了测量,发现了许多有助于P2P网络挖掘研究的IP重复与ID别名特征.     

基于BitTorrent网络实现大规模DDos攻击的策略研究

P2P应用已经成为Internet上最流行和成功的应用之一,基于P2P的DDos攻击是国内外研究的重点。本文首先概述了BitTorre nt的协议原理运行过程,并用MTTrace工具采集和分析了Tracker服务器的节点集合的链路特征,发现节点集合的链路的拥塞链路特征,针对此特征本文设计了一种新的DDos攻击策略,并在模拟环境中对其进行了验证,然后我们对其防御手段进行了讨论,最后,我们对所做的工作进行了总结,并对下一步的工作进行了说明。     

特定P2P网络的主动测量研究*

为了实现信息可控的安全网络环境,需要对特定的P2P 应用系统进行测量与分析。测量的出发点在于寻找协议的主导节点或服务节点,在一定意义上是该应用协议可能存在的瓶颈。选取BitTorrent、Skype和Tor分别作为这三类不同的P2P应用系统的代表,分析其协议特性,并对它们的覆盖网络进行主动测量,最终得到互联网上协议主导节点的总量及分布情况,以便于进一步的监管分析。     

Modeling resource constrained BitTorrent proxies for energy efficient mobile content sharing

In this paper we present a solution that makes BitTorrent content transfer for mobile device more energy efficient. The main idea of the research is that instead of downloading the content via BitTorrent directly to the mobile phone, an intermediate proxy is used which sends the data to the phone in high speed bursts. This results in smaller energy footprint compared with regular BitTorrent data transfer. Furthermore, we focus on how the proxy can be hosted on memory limited broadband routers which are available in almost every home. We define an analytical model which can be used to analyze the memory allocation strategies of the proxy peers and predict how proxy peers influence the P2P community performance. We verify our model via simulations. We also present measurement results with real life torrents using our prototype system running on home routers and Symbian based mobile phones.     

Measurement,modeling and enhancement of BitTorrent-based VoD system

BitTorrent is one of the most popular Peer-to-Peer (P2P) applications for file sharing over the Internet. Video files take up a large proportion of space among the BitTorrent shared files. Recently, BitTorrent has attracted researchers’ interests, as an alternative method of providing video on demand (VoD) service. In this paper, we concentrate on enabling BitTorrent to support VoD service in existing swarms while maintaining the download efficiency of file-sharing users. We first examine the content properties of the BitTorrent system to explore the demands and challenges of VoD service in BitTorrent swarms. The efficiency of BitTorrent for various piece selection policies is then compared through measurement on PlanetLab. We also use an optimization mathematical model to analyze the hybrid BitTorrent system in which downloading peers and streaming peers coexist. Both measurement results and model analysis indicate the problem of system efficiency decline in the BitTorrent-based VoD systems, in comparison with the original BitTorrent file-sharing system. Our proposed approach, unlike existing strategies that are limited to changing the piece selection policy to allow BitTorrent to support streaming services, modifies both piece and peer selection policies to provide a “streaming while downloading” service in the BitTorrent system with downloading peers. For the peer selection policy, a CAP (Closest-Ahead Peers) method is applied to make better use of the peers’ upload bandwidths. For the piece selection policy, a sliding window-based hybrid method that combines the rarest-first policy with the sequential policy is proposed. To demonstrate the performance of our proposed approach, an evaluation is made using various metrics on PlanetLab. The results show that our proposed method has higher throughput and better streaming continuity than the sequential policy and BiToS.     

WuKong: a practical video streaming service based on native BitTorrent and scalable video coding

Many researches on peer-to-peer video streaming have focused on dealing with highly dynamic, high-churn P2P environment. Most of P2P streaming protocols were modified from a P2P file sharing protocol. Inspired by the high performance on peer-to-peer file sharing of BitTorrent, we propose an overlaying streaming mechanism on the native BitTorrent protocol and realize a practical P2P video streaming service, called WuKong. WuKong not only takes advantages of BitTorrent but also combines the video scalability of layered video coding. In this paper, we depict an overlaid streaming mechanism in WuKong and an adaptive layer-downloading process to balance between the video quality and bandwidth utilization on heterogeneous peers. WuKong is carried out by using an open-sourced library of the BitTorrent protocol, coding schemes of the Windows Media Video (WMV), and the Scalable Video Coding (SVC). We measured and compared the service quality of end-users served by WuKong on heterogeneous peers. In addition, we evaluated the effectiveness of WuKong with peers that are randomly joining and leaving the P2P network. The results show that WuKong not only provides high quality P2P video streaming services but also supports different scaling abilities over heterogeneous devices.     

BitTorrent协议Choking／Unchoking机制的度量和分析

BitT0rrent是一个用于内容分发的P2P协议,现在已经发展成为互联网的一项重要的应用.本文从性能的角度,度量BitTorrent的行为,解释BitTorrent协议的关键元素,分析BitTorrent是否是高效的.本文有以下贡献:①提出一种有效度量BitTorrent式的内容分发协议的方法.②确认BitTorrent的Choking/Unchoking机制存在缺陷,不是高效的.③设计ShareStorm协议,证明BitTorrent的缺陷可以避免.经初步验证,在下载完成时间这个最主要的性能指标上,ShareStorm比BitTbrrent至少减少50 %.     

BitTorrent网络主动测量技术与特性分析*

对BitTorrent进行了系统的研究,详细阐述了一种用于测量BitTorrent网络拓扑的爬虫设计与实现,并通过主动测量所获取的信息分析研究了BitTorrent的网络节点分布情况、在线节点周期特性、扩散跟踪、做种节点变化趋势,研究结果为BitTorrent网络的监管提供了良好的依据。