Abstract — Over the Internet today, computing and communications environments are significantly more complex and chaotic than classical distributed systems, lacking any centralized organization or hierarchical control. There has been much interest in emerging Peer-to-Peer (P2P) network overlays because they provide a good substrate for creating large-scale data sharing, content distribution and application-level multicast applications. These P2P networks try to provide a long list of features such as: selection of nearby peers, redundant storage, efficient search/location of data items, data permanence or guarantees, hierarchical naming, trust and authentication, and, anonymity. P2P networks potentially offer an efficient routing architecture that is self-organizing, massively scalable, and robust in the wide-area, combining fault tolerance, load balancing and explicit notion of locality. In this paper, we present a survey and comparison of various Structured and Unstructured P2P networks. We categorize the various schemes into these two groups in the design spectrum and discuss the application-level network performance of each group.

Abstract — In recent years, BitTorrent has emerged as a very scalable peer-to-peer file distribution mechanism. While early measurement and analytical studies have verified BitTorrent’s performance, they have also raised questions about various metrics (upload utilization, fairness, etc.), particularly in settings other than those measured. In this paper, we present a simulationbased study of BitTorrent. Our goal is to deconstruct the system and evaluate the impact of its core mechanisms, both individually and in combination, on overall system performance under a variety of workloads. Our evaluation focuses on several important metrics, including peer link utilization, file download time, and fairness amongst peers in terms of volume of content served. Our results confirm that BitTorrent performs near-optimally in terms of uplink bandwidth utilization, and download time except under certain extreme conditions. We also show that low bandwidth peers can download more than they upload to the network when high bandwidth peers are present. We find that the rate-based tit-for-tat policy is not effective in preventing unfairness. We show how simple changes to the tracker and a stricter, block-based tit-for-tat policy, greatly improves fairness. I.

Abstract—Motivated by the study of peer-to-peer file swarming systems à la BitTorrent, we introduce a probabilistic model of coupon replication systems. These systems consist of users, aiming to complete a collection of distinct coupons. Users are characterised by their current collection of coupons, and leave the system once they complete their coupon collection. The system evolution is then specified by describing how users of distinct types meet, and which coupons get replicated upon such encounters. For open systems, with exogenous user arrivals, we derive necessary and sufficient stability conditions in a layered scenario, where encounters are between users holding the same number of coupons. We also consider a system where encounters are between users chosen uniformly at random from the whole population. We show that performance, captured by sojourn time, is asymptotically optimal in both systems as the number of coupon types becomes large. We also consider closed systems with no exogenous user arrivals. In a special scenario where users have only one missing coupon, we evaluate the size of the population ultimately remaining in the system, as the initial number of users, N, goes to infinity. We show that this decreases geometrically with the number of coupons, K. In particular, when the ratio K / log(N) is above a critical threshold, we prove that this number of left-overs is of order log(log(N)). These results suggest that performance of file swarming systems does not depend critically on either altruistic user behavior, or on load balancing strategies such as rarest first. 1.

1 Introduction Establishing trust is a fundamental problem in distributedsystems. Peer-to-peer systems, in which service functionality is distributed across clients, eliminate the cen-tralized components that have traditionally functioned as de facto trust brokers, and consequently exacerbate trust-related problems. When peers lack meaningful measures on which to base trust decisions, they end up receivingservices from untrustworthy peers, with e ffects that canrange from wasted resources on mislabeled content to

This paper assesses BitTorrent's robustness against selfish peers, who try to download more than their fair share by abusing existing protocol mechanisms. We design and implement three selfish-peer exploits and evaluate their effectiveness on public and private torrents. In practice, BitTorrent appears quite robust against this kind of exploit: selfish peers can sometimes obtain more bandwidth, and honest peers' download rates suffer slightly in consequence, but we observe no considerable degradation of the system's quality of service. We identify private-torrent scenarios in which a selfish peer could benefit more significantly at the expense of honest peers, and discuss the BitTorrent protocol mechanisms that lead to robustness by rendering these scenarios infeasible.

Abstract. A user who wants to use a service forbidden by their site’s usage policy can masquerade their packets in order to evade detection. One masquerade technique sends prohibited traffic on TCP ports commonly used by permitted services, such as port 80. Users who hide their traffic in this way pose a special challenge, since filtering by port number risks interfering with legitimate services using the same port. We propose a set of tests for identifying masqueraded peer-to-peer file-sharing based on traffic summaries (flows). Our approach is based on the hypothesis that these applications have observable behavior that can be differentiated without relying on deep packet examination. We develop tests for these behaviors that, when combined, provide an accurate method for identifying these masqueraded services without relying on payload or port number. We test this approach by demonstrating that our integrated detection mechanism can identify BitTorrent with a 72 % true positive rate and virtually no observed false positives in control services (FTP-Data, HTTP, SMTP). 1

Broadband Internet access using ADSL or cable modems provides sufficient bandwidth for real-time video streaming. If television channels could be distributed on the Internet, each channel would get a world wide audience. However, television distribution from a single server does not scale and IP-level multicasting is complex and costly. We propose a solution based on application-level multicasting using a P2P network, called P2P-TV. Each peer receives a video stream and must also forward this stream to others. This paper presents an architecture for streaming video. Our P2P-TV proposal aims to solve three problems that are currently not addressed in other P2P streaming proposals, namely 1) maximizing the usage of all available peer bandwidth, 2) taking current network conditions into account (network awareness), and 3) the Freeriding problem. Multiple Description Coding is an integral part of our solution. By splitting the video stream into smaller streams we can utilize all the bandwidth of a peer. Multiple streams allow more efficient adaptation of the multicast tree to current network conditions. Bittorrent-like bartering of content is also enabled by using multiple streams.

Abstract. We present a novel method for detecting hit-list worms using protocol graphs. In a protocol graph, a vertex represents a single IP address, and an edge represents communications between those addresses using a specific protocol (e.g., HTTP). We show that the protocol graphs of four diverse and representative protocols (HTTP, FTP, SMTP, and Oracle), as constructed from monitoring for fixed durations on a large intercontinental network, exhibit stable graph sizes and largest connected component sizes. Moreover, we demonstrate that worm propagations, even of a sophisticated hit-list variety in which the attacker has advance knowledge of his targets and always connects successfully, perturb these properties. We demonstrate that these properties can be monitored very efficiently even in very large networks, giving rise to a viable and novel approach for worm detection. We also demonstrate extensions by which the attacking hosts (bots) can be identified with high accuracy.

Abstract — Data-centric applications are still a challenging issue for large scale distributed computing systems. The emergence of new protocols and software for collaborative content distribution over Internet offers a new opportunity for efficient and fast delivery of high volume of data. In a previous paper, we have investigated BitTorrent as a protocol for data diffusion in the context of Computational Desktop Grid. We showed that BitTorrent is efficient for large file transfers, scalable when the number of nodes increases but suffers from a high overhead when transmitting small files. This paper investigates two approach to overcome these limitations. First, we propose a performance model to select the best of FTP and BitTorrent protocols according to the size of the file to distribute and the number of receiver nodes. Next we propose enhancement of the BitTorrent protocol which provides more predictable communication patterns. We design a model for communication performance and evaluate BitTorrent-aware versions BT-MinMin, BT-MaxMin and BT-Sufferage scheduling heuristics against a synthetic parametersweep application. I.

P2P systems that rely on the voluntary contribution of bandwidth by the individual peers may suffer from freeriding. To address this problem, mechanisms enforcing fairness in bandwidth sharing have been designed, usually by limiting the download bandwidth to the available upload bandwidth. As in real environments the latter is much smaller than the former, these mechanisms severely affect the download performance of most peers. In this paper we propose a system called 2Fast, which solves this problem while preserving the fairness of bandwidth sharing. In 2Fast, we form groups of peers that collaborate in downloading a file on behalf of a single group member, which can thus use its full download bandwidth. A peer in our system can use its currently idle bandwidth to help other peers in their ongoing downloads, and get in return help during its own downloads. We assess the performance of 2Fast analytically and experimentally, the latter in both real and simulated environments. We find that in realistic bandwidth limit settings, 2Fast improves the download speed by up to a factor of 3.5 in comparison to state-of-the-art P2P download protocols. 1.