Enhancing tit-for-tat for incentive in BitTorrent networks

BitTorrent achives great success in its high performance for file distribution. It is commonly believed that this owes to Tit-for-Tat strategy adopted in choking algorithm for incentive in BitTorrent protocol. But there are still many issues in incentive mechanism in BitTorrent. In this paper, we study Tit-for-Tat strategy by constructing a game model in P2P environments and deducing the constraint under which the strict Tit-for-Tat is an equilibrium strategy. We then enhance and adapt the Tit-for-Tat strategy to the dynamic property in P2P networks, and deduce the constraint under which it is still an equilibrium strategy. We also study through simulations the performance improvement of the enhanced Tit-for-Tat, and give suggestion on how to choose proper system parameters under different network conditions. Finally, based on the enhanced Tit-for-Tat strategy, we propose a method to improve incentive in BitTorrent networks to cope with free-riding and fairness issues.     

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.     

跨越NAT的P2P应用UDP通讯

随着基于Internet的P2P网络技术的广泛应用，更多的内网主机需要参与到P2P中来。NAT之后的主机IP地址在Internet上是不可见的．Internet上的主机不能主动访问这些NAT之后的主机，但P2P网络要求任何主机之间都能够直接对等交换信息，这就使得P2P网络应用必须解决穿越NAT实现双向对等通讯的问题。本文在介绍了NAT基本原理和NAT对P2P应用的影响基础上，分析了客户端位于同一个NAT的后面、客户端位于不同的NAT的后面和客户瑞位于多级NAT的后面这三种情况下．P2P软件跨越NAT的UDP通讯问题。     

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。     

ModelNet-TE: An emulation tool for the study of P2P and traffic engineering interaction dynamics

In the Internet, user-level performance of P2P applications may be determined by the interaction of two independent dynamics: on the one hand, by the end-to-end control policies applied at the P2P application layer (L7); on the other hand, by Traffic Engineering (TE) decisions taken at the network level (L3). Currently available tools do not allow to study L7/L3 interactions in realistic settings due to a number of limitations. Building over ModelNet, we develop a framework for the real-time emulation of TE capabilities, named ModelNet-TE, that we make available to the scientific community as open source software. ModelNet-TE allows (i) to deploy real unmodified Internet P2P applications, and to test their interaction with (ii) many TE algorithms, as its design allows to easily integrate other TE algorithms than those we already provide, (iii) in a furthermore controlled network environment. Due to these features, ModelNet-TE is a complementary tool with respect to hybrid simulation/protoyping toolkits (that constrain application development to a specific language and framework, and cannot be used with existing or proprietary applications) and to other open testbeds such as PlanetLab or Grid5000 (lacking of control or TE-capabilities respectively). ModelNet-TE can thus be useful to L7-researchers, as it allows to seamlessly and transparently test any existing P2P application without requiring any software modification. At the same time, ModelNet-TE can be useful to L3-researchers as well, since they can test their TE algorithms on the traffic generated by real applications. As a use case, in this work we carry on an experimental campaign of L7/L3 routing layers interaction through ModelNet-TE. As TE we consider the classic minimum congestion load-balancing, that we compare against standard IP routing. As example P2P applications, we take BitTorrent, one among the most popular file-sharing applications nowadays, and WineStreamer, an open source live-streaming application. We emulate BitTorrent and WineStreamer swarms over both realistic topologies (e.g., Abilene) and simplistic topologies that are commonly in use today (e.g., where the bottleneck is located at the network edge) under a variety of scenarios. Results of our experimental campaign show that user-level performance may be significantly affected by both the TE mechanism in use at L3 (e.g., due to interactions with TCP congestion control or P2P chunk trading logic), as well as scenario parameters that are difficult to control in the wild Internet, which thus testifies the interest for tools such as ModelNet-TE.     

Locality-Awareness in BitTorrent-Like P2P Applications

This paper presents the measurement study of locality-aware P2P solutions over real-world Internet autonomous systems (AS) topology. By using the accesses of nodes of PlanetLab testbed, we create a detailed AS-level map including the end-to-end path of all nodes, as well as the relationship of all involved ASes. Based on this map, we evaluate the performance of a set of locality-aware P2P solutions, including an optimal solution guaranteeing the minimum AS hop count, as well as modified BitTorrent system with locality-awareness built into its neighbor selection, peer choking/unchoking, and piece selection processes. Our findings suggest that locality-awareness can help existing P2P solution to significantly decrease load on Internet, and achieve shorter downloading time. By comparing the performance of different kinds of locality-aware and traditional BitTorrent systems, we also point out the necessity to tradeoff between the goals of optimizing AS-related performance and achieving fairness among peers such as intra-AS traffic and peer burden fairness.      

Downloading trace study for BitTorrent P2P performance measurement and analysis

With the increasing client population and the explosive volume of Internet media content, the peer-to-peer networking technologies and systems provide a rapid and scalable content distribution mechanism in the global networks. The BitTorrent protocol and its derivatives are among the most popular peer-to-peer file sharing applications, which contribute a dominant fraction of today??s Internet traffic. In this paper, we conduct the performance measurement and analysis of BitTorrent systems with an extensive volume of real trace logs. We use several downloading-side metrics, including overall downloading time, maximum of downloading bandwidth, average bandwidth utilization, maximum of downloading connections, and average number of active connections, to derive various interesting results from the downloading-side aspect of network resource usage. Performance examination learns many new observations and characteristics into the virtue of BitTorrent protocols and systems, thereby providing beneficial information for bandwidth allocation and connection control in BitTorrent client applications. Therefore, this study is complementary to many previous research works that mainly focused on system-oriented and uploading-side performance measurements.     

Optimal scheduling of peer-to-peer file dissemination

Peer-to-peer (P2P) overlay networks such as BitTorrent and Avalanche are increasingly used for disseminating potentially large files from a server to many end users via the Internet. The key idea is to divide the file into many equally-sized parts and then let users download each part (or, for network coding based systems such as Avalanche, linear combinations of the parts) either from the server or from another user who has already downloaded it. However, their performance evaluation has typically been limited to comparing one system relative to another and has typically been realized by means of simulation and measurements. By contrast, we provide an analytic performance analysis that is based on a new uplink-sharing version of the well-known broadcasting problem. Assuming equal upload capacities, we show that the minimal time to disseminate the file is the same as for the simultaneous send/receive version of the broadcasting problem. For general upload capacities, we provide a mixed integer linear program (MILP) solution and a complementary fluid limit solution. We thus provide a lower bound which can be used as a performance benchmark for any P2P file dissemination system. We also investigate the performance of a decentralized strategy, providing evidence that the performance of necessarily decentralized P2P file dissemination systems should be close to this bound and, therefore, that it is useful in practice. Research of G. Weiss is supported in part by Israel Science Foundation Grants 249/02 and 454/05. Collaboration of the authors was supported in part by European Network of Excellence Euro-NGI.     

基于蜂拥的P2P流媒体系统可扩展性分析

P2P流媒体直播系统在互联网上显示出了巨大的潜在吸引力,但此类系统的大规模部署严重依赖于它们处 理高动态变化的效率,特别是在蜂拥时期。其主要原因是P2P流媒体直播系统的扩展在很大程度上取决于流媒体应 用的时间需求。在分析和实验的基础上,提出了系统规模与时间约束的内在联系及其制约因素,构建了一个通用的 P2P流媒体系统模型,来集中分析节点在蜂拥时期加入系统的过程。首先说明了简单使用“需求供给”概念模型来描 述系统的规模是不够的,然后利用类似Gossip协议的随机伙伴选择机制,推出系统规模随时间变化的上限,在Matlab R2010a平台上比较分析了一些关键性因素的变化对系统扩展的影响。     

On the collaboration of different peer-to-peer traffic management schemas

The fast-growing traffic of peer-to-peer (P2P) applications, most notably BitTorrent, is putting unprecedented pressure to Internet Service Providers (ISPs). To address this challenge, a number of P2P traffic management schemes have been proposed in recent years, among which caching and redirection are two representatives. Both of them have shown their success in theory and in practice. Yet, their implementations are largely independent, making the overall effectiveness sub-optimal. In this paper, we for the first time examine the joint implementation of these two promising solutions under a coherent framework, Tod-Cache (Traffic Orientated Distributed Caching). We show that the combination of caching and redirection can dramatically reduce the P2P traffic traversing across ISPs. Under this framework, we formulate the optimal caching and redirection problem, and show its complexity. We then present a highly adaptive and scalable heuristic algorithm which achieves close-to-optimal performance with much lower computational complexity. We extensively evaluate our framework under diverse network and end-system configurations. Our simulation results show that, under the same configuration, it can achieve at least 85 % of performance of the traditional cache with at most 1/10 of the device number.     

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.     

一种基于Netfilter的BitTorrent流量测量方法

BitTorrent是目前互联网上广泛使用的一种基于P2P的文件共享协议。它使用了动态端口，这给BitTorrent流量的准确测量带来了很大的困难。本文在分析BitTorrent协议基础上，给出了一种基于应用层特征匹配的BitTorrent流量测量方法。首先提取出BitTorrent流的应用层特征，利用Linux Netfilter／Iptables扩展架构实现数据包的应用层特征匹配。将TCP流分成了BitTorrent流和非BitTorrent流，对BitTorrent流进行统计。实验表明，该方法能实时准确地测量BitTorrent流量。     

基于BitTorrent的激励机制的研究与改进

BitTorrent系统面临着严重的搭便车问题。研究BitTorrent系统的搭便车问题及其激励机制,对P2P文件共享系统有重要意义。介绍当前BitTorrent系统激励机制的研究现状,分析BitTorrent文件共享系统的搭便车现象及其激励机制,提出了一个种子带宽分配策略。通过模拟实验实现了该策略,并分析了模拟实验的结果。     

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 %.     

一种基于BitTorrent的节点选择改进算法

当前P2P业务占据了大量的互联网流量,在一定程度上对其他网络业务造成了巨大的冲击,该文主要以P2P典型软件Bit-Torrent下载为例设计一个改进的节点选择算法,有效降低节点对出口下载带宽占用率。     

基于S-RTT策略的BitTorrent文件共享模型

分析了BitTorrent文件共享系统的工作流程,指出了在种子节点选取和连接方式上的缺点。介绍了网络定位技术GNP,详细分析了GNP的工作流程,说明了它在网络中定位主机的优越性能。提出了一种S-RTT策略,进行种子节点选取和连接。将此策略引入BitTorrent文件共享系统中,使得BitTorrent系统能够灵活选择优质的种子节点、控制信息流量,有效改善了BitTorrent网络性能。     

Secure seamless peer-to-peer (P2P) UDP communication using IPv4 LSRR option and IPv4+4 addresses

The current structure of the Internet, with hosts behind network address translation (NAT) boxes, causes well-known problems for P2P applications. There are several proposals, e.g., STUN, UPnP, MIDCOM, TURN among others, to enable P2P UDP communication for nodes behind NAT boxes, but each technique offers a partial solution that works in special limited cases and fails in others. In this paper, we present a framework based on the use of IPv4+4 addresses and the standard IPv4 Loose Source Record Route (LSRR) option that offers a complete solution to the secure seamless P2P UDP communication problem. Our proposal requires no changes whatsoever to end-host protocol stacks and Internet routers. The only requirement is a simple upgrade of border routers with a new LSRR-based packet forwarding algorithm for the P2P UDP traffic. We detail our implementation of a Linux-based border router that runs the proposed forwarding algorithm, and describe how applications requiring P2P UDP communication such as Voice over IP (VoIP) using SIP can benefit from our framework.     

使用UDP穿越P2P网络中NAT的方法

介绍了基于Internet的P2P技术和NAT的基本原理，分析了NAT对P2P的影响。讨论了在现有通信协议上实现点对点应用传输所必须解决的，端到端定位，局域网IP地址解析等技术。最后给出了一个利用UDP Sockets技术实现P2P网络应用的实例。     

IP组播在BitTorrent中的应用研究

针对BitTorrent(BT)应用会占用大量网络带宽的问题,通过改进BT协议,提出一种应用IP层组播技术优化传输的MBitTorrent(MBT)协议。该协议引入基于区域和优先级的Peer阻塞策略,适用于组播域分离的网络环境。仿真结果表明,与BT协议相比,MBT显著降低了网络流量,提升了整体下载性能。     

Towards efficient data distribution on computational desktop grids with BitTorrent

Datacentric applications are still a challenging issue for large-scale distributed computing systems. The emergence of new protocols and software for collaborative content distribution over the Internet offers a new opportunity for efficient and fast delivery of a high volume of data. This paper presents an evaluation of the BitTorrent protocol for computational desktop grids. We first present a prototype of a generic subsystem dedicated to data management and designed to serve as a building block for any desktop grid system. Based on this prototype we conduct experiments to evaluate the potential of BitTorrent compared to a classical approach based on FTP data server. The preliminary results obtained with a 65-node cluster measure the basic characteristics of BitTorrent in terms of latency and bandwidth and evaluate the scalability of BitTorrent for the delivery of large input files. Moreover, we show that BitTorrent has a considerable latency overhead compared to FTP but clearly outperforms FTP when distributing large files or files to a high number of nodes. Tests on a synthetic application show that BitTorrent significantly increases the communication/computation ratio of the applications eligible to run on a desktop grid system.