Storage and Search in Dynamic Peer-to-Peer Networks

We study robust and efficient distributed algorithms for searching, storing, and maintaining data in dynamic Peer-to-Peer (P2P) networks. P2P networks are highly dynamic networks that experience heavy node churn (i.e., nodes join and leave the network continuously over time). Our goal is to guarantee, despite high node churn rate, that a large number of nodes in the network can store, retrieve, and maintain a large number of data items. Our main contributions are fast randomized distributed algorithms that guarantee the above with high probability (whp) even under high adversarial churn: 1. A randomized distributed search algorithm that (whp) guarantees that searches from as many as $n - o(n)$ nodes ($n$ is the stable network size) succeed in ${O}(\log n)$-rounds despite ${O}(n/\log^{1+\delta} n)$ churn, for any small constant $\delta > 0$, per round. We assume that the churn is controlled by an oblivious adversary (that has complete knowledge and control of what nodes join and leave and at what time, but is oblivious to the random choices made by the algorithm). 2. A storage and maintenance algorithm that guarantees (whp) data items can be efficiently stored (with only $\Theta(\log{n})$ copies of each data item) and maintained in a dynamic P2P network with churn rate up to ${O}(n/\log^{1+\delta} n)$ per round. Our search algorithm together with our storage and maintenance algorithm guarantees that as many as $n - o(n)$ nodes can efficiently store, maintain, and search even under ${O}(n/\log^{1+\delta} n)$ churn per round. Our algorithms require only polylogarithmic in $n$ bits to be processed and sent (per round) by each node. To the best of our knowledge, our algorithms are the first-known, fully-distributed storage and search algorithms that provably work under highly dynamic settings (i.e., high churn rates per step).Comment: to appear at SPAA 201

Evidence Collection for Forensic Investigation in Peer to Peer Systems

Abstract Peer to Peer(P2P) file sharing networks are amongst the best free sources of information on the internet. Voluntary participation and lack of control makes them a very attractive option to share data anonymously. However a small group of people take advantage of the freedom provided by these networks and share content that is prohibited by law. Apart from copyrighted content, there are cases where people share les related to Child Pornography which is a criminal offense. Law enforcement attempts to track down these offenders by obtaining a court order for search and seizure of computers at a suspect location. These seized computers are forensically examined using storage and memory-forensics tools. However before the search warrant is issued strong evidence must be presented to provide a reason for suspiscion. Deficient investigation in the intial stages might lead to mis-identification of the source and steer the investigation in a wrong direction. Initial evidence collection on peer to peer le sharing networks is a challenge due to the lack of a central point of control and highly dynamic nature of the networks. The goal of this work is to create a working prototype of an initial evidence collection tool for forensics in P2P networks. The prototype is based on the idea that P2P networks could be monitored by introducing modified peer nodes onto the network for a certain time period and recording relevant information about nodes that possess criminally offensive content. Logging information sent by a suspicious node along with timestamps and unique identication information would provide a strong, verfiiable initial evidence. This work presents one such working prototype in alignment with the goals stated above

Stochastic Analysis of a Churn-Tolerant Structured Peer-to-Peer Scheme

We present and analyze a simple and general scheme to build a churn (fault)-tolerant structured Peer-to-Peer (P2P) network. Our scheme shows how to "convert" a static network into a dynamic distributed hash table(DHT)-based P2P network such that all the good properties of the static network are guaranteed with high probability (w.h.p). Applying our scheme to a cube-connected cycles network, for example, yields a $O(\log N)$ degree connected network, in which every search succeeds in $O(\log N)$ hops w.h.p., using $O(\log N)$ messages, where $N$ is the expected stable network size. Our scheme has an constant storage overhead (the number of nodes responsible for servicing a data item) and an $O(\log N)$ overhead (messages and time) per insertion and essentially no overhead for deletions. All these bounds are essentially optimal. While DHT schemes with similar guarantees are already known in the literature, this work is new in the following aspects: (1) It presents a rigorous mathematical analysis of the scheme under a general stochastic model of churn and shows the above guarantees; (2) The theoretical analysis is complemented by a simulation-based analysis that validates the asymptotic bounds even in moderately sized networks and also studies performance under changing stable network size; (3) The presented scheme seems especially suitable for maintaining dynamic structures under churn efficiently. In particular, we show that a spanning tree of low diameter can be efficiently maintained in constant time and logarithmic number of messages per insertion or deletion w.h.p. Keywords: P2P Network, DHT Scheme, Churn, Dynamic Spanning Tree, Stochastic Analysis

Caring About the Plumbing: On the Importance of Architectures in Social Studies of (Peer-to-Peer) Technology

International audienceThis article discusses the relevance, for scholars working on social studies of network media, of "caring about the plumbing" (to paraphrase Bricklin, 2001), i.e., addressing elements of application architecture and design as an integral part of their subject of study. In particular, by discussing peer-to-peer (P2P) systems as a technical networking model and a dynamic of social interaction that are inextricably intertwined, the article introduces how the perspective outlined above is particularly useful to adopt when studying a promising area of innovation: that of "alternative" or "legitimate" (Verma, 2004) applications of P2P networks to search engines, social networks, video streaming and other Internet-based services. The article seeks to show how the Internet's current trajectories of innovation increasingly suggest that particular forms of architectural distribution and decentralization (or their lack), impact specific procedures, practices and uses. Architectures should be understood an "alternative way of influencing economic systems" (van Schewick, 2010), indeed, the very fabric of user behavior and interaction. Most notably, the P2P "alternative" to Internet-based services shows how the status of every Internet user as a consumer, a sharer, a producer and possibly a manager of digital content is informed by, and shapes in return, the technical structure and organization of the services (s)he has access to: their mandatory passage points, places of storage and trade, required intersections. In conclusion, this article is a call to study the technical architecture of networking applications as a "relational property" (Star & Ruhleder, 1996), and integral part of human organization. It suggests that such an approach provides an added value to the study of those communities, groups and practices that, by leveraging socio-technical dynamics of distribution, decentralization, collaboration and peer production, are currently questioning more traditional or institutionalized models of content creation, search and sharing

Self-organizing peer-to-peer social networks

This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2008 The Authors.Peer-to-peer (P2P) systems provide a new solution to distributed information and resource sharing because of its outstanding properties in decentralization, dynamics, flexibility, autonomy, and cooperation, summarized as DDFAC in this paper. After a detailed analysis of the current P2P literature, this paper suggests to better exploit peer social relationships and peer autonomy to achieve efficient P2P structure design. Accordingly, this paper proposes Self-organizing peer-to-peer social networks (SoPPSoNs) to self-organize distributed peers in a decentralized way, in which neuron-like agents following extended Hebbian rules found in the brain activity represent peers to discover useful peer connections. The self-organized networks capture social associations of peers in resource sharing, and hence are called P2P social networks. SoPPSoNs have improved search speed and success rate as peer social networks are correctly formed. This has been verified through tests on real data collected from the Gnutella system. Analysis on the Gnutella data has verified that social associations of peers in reality are directed, asymmetric and weighted, validating the design of SoPPSoN. The tests presented in this paper have also evaluated the scalability of SoPPSoN, its performance under varied initial network connectivity and the effects of different learning rules.National Natural Science of Foundation of Chin