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TrInc: Small Trusted Hardware for Large Distributed Systems
"... A simple yet remarkably powerful tool of selfish and malicious participants in a distributed system is “equivocation”: making conflicting statements to others. We present TrInc, a small, trusted component that combats equivocation in large, distributed systems. Consisting fundamentally of only a non ..."
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Cited by 58 (9 self)
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A simple yet remarkably powerful tool of selfish and malicious participants in a distributed system is “equivocation”: making conflicting statements to others. We present TrInc, a small, trusted component that combats equivocation in large, distributed systems. Consisting fundamentally of only a non-decreasing counter and a key, TrInc provides a new primitive: unique, once-in-alifetime attestations. We show that TrInc is practical, versatile, and easily applicable to a wide range of distributed systems. Its deployment is viable because it is simple and because its fundamental components—a trusted counter and a key—are already deployed in many new personal computers today. We demonstrate TrInc’s versatility with three detailed case studies: attested append-only memory (A2M), PeerReview, and BitTorrent. We have implemented TrInc and our three case studies using real, currently available trusted hardware. Our evaluation shows that TrInc eliminates most of the trusted storage needed to implement A2M, significantly reduces communication overhead in PeerReview, and solves an open incentives issue in BitTorrent. Microbenchmarks of our TrInc implementation indicate directions for the design of future trusted hardware. 1
Antfarm: Efficient Content Distribution with Managed Swarms
"... This paper describes Antfarm, a content distribution system based on managed swarms. A managed swarm couples peer-to-peer data exchange with a coordinator that directs bandwidth allocation at each peer. Antfarm achieves high throughput by viewing content distribution as a global optimization problem ..."
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Cited by 55 (1 self)
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This paper describes Antfarm, a content distribution system based on managed swarms. A managed swarm couples peer-to-peer data exchange with a coordinator that directs bandwidth allocation at each peer. Antfarm achieves high throughput by viewing content distribution as a global optimization problem, where the goal is to minimize download latencies for participants subject to bandwidth constraints and swarm dynamics. The system is based on a wire protocol that enables the Antfarm coordinator to gather information on swarm dynamics, detect misbehaving hosts, and direct the peers ’ allotment of upload bandwidth among multiple swarms. Antfarm’s coordinator grants autonomy and local optimization opportunities to participating nodes while guiding the swarms toward an efficient allocation of resources. Extensive simulations and a PlanetLab deployment show that the system can significantly outperform centralized distribution services as well as swarming systems such as BitTorrent. 1
Incentive-Aware Routing in DTNs
"... Abstract—Disruption tolerant networks (DTNs) are a class of networks in which no contemporaneous path may exist between the source and destination at a given time. In such a network, routing takes place with the help of relay nodes and in a storeand-forward fashion. If the nodes in a DTN are control ..."
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Cited by 31 (0 self)
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Abstract—Disruption tolerant networks (DTNs) are a class of networks in which no contemporaneous path may exist between the source and destination at a given time. In such a network, routing takes place with the help of relay nodes and in a storeand-forward fashion. If the nodes in a DTN are controlled by rational entities, such as people or organizations, the nodes can be expected to behave selfishly and attempt to maximize their utilities and conserve their resources. Since routing is an inherently cooperative activity, system operation will be critically impaired unless cooperation is somehow incentivized. The lack of end-to-end paths, high variation in network conditions, and long feedback delay in DTNs imply that existing solutions for mobile ad-hoc networks do not apply to DTNs. In this paper, we propose the use of pair-wise tit-for-tat (TFT) as a simple, robust and practical incentive mechanism for DTNs. Existing TFT mechanisms often face bootstrapping problems or suffer from exploitation. We propose a TFT mechanism that incorporates generosity and contrition to address these issues. We then develop an incentive-aware routing protocol that allows selfish nodes to maximize their own performance while conforming to TFT constraints. For comparison, we also develop techniques to optimize the system-wide performance when all nodes are cooperative. Using both synthetic and real DTN traces, we show that without an incentive mechanism, the delivery ratio among selfish nodes can be as low as 20 % as what is achieved under full cooperation; in contrast, with TFT as a basis of cooperation among selfish nodes, the delivery ratio increases to 60 % or higher as under full cooperation. We also address the practical challenges involved in implementing the TFT mechanism. To our knowledge, this is the first practical incentive-aware routing scheme for DTNs. I.
Public and private bittorrent communities: A measurement study
- In IPTPS
, 2010
"... Abstract—BitTorrent communities, both public and private, are immensely popular in the Internet, with tens of millions of users simultaneously active at any given moment. Public and private BitTorrent communities are managed in different ways – for instance, some private communities enforce sharing ..."
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Cited by 20 (8 self)
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Abstract—BitTorrent communities, both public and private, are immensely popular in the Internet, with tens of millions of users simultaneously active at any given moment. Public and private BitTorrent communities are managed in different ways – for instance, some private communities enforce sharing ratios, have strict rules for content management, have a certain level of community oversight, and maintain a strong sense of exclusiveness. In this paper, we present the results of extensive measurements of more than half a million peers in five communities, ranging from highly popular and well-known public communities to elite private communities that can only be joined by invitation. We observe that the performance experienced by downloaders in the private communities is by far superior to the performance in the public communities, and we observe significant differences in connectability, seeder/leecher ratio, and seeding duration. Based on our results, we conjecture that when effective ratio enforcement mechanisms are in place, BitTorrent’s tit-for-tat mechanism is hardly influential anymore. Our multi-community, multi-swarm measurements are significantly broader and more extensive than any earlier measurement study on BitTorrent. I.
The Role of Game Theory in Human Computation Systems
, 2009
"... The paradigm of “human computation” seeks to harness human abilities to solve computational problems or otherwise perform distributed work that is beyond the scope of current AI technologies. One aspect of human computation has become known as “games with a purpose ” and seeks to elicit useful compu ..."
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Cited by 14 (1 self)
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The paradigm of “human computation” seeks to harness human abilities to solve computational problems or otherwise perform distributed work that is beyond the scope of current AI technologies. One aspect of human computation has become known as “games with a purpose ” and seeks to elicit useful computational work in fun (typically) multi-player games. Human computation also encompasses distributed work (or “peer production”) systems such as Wikipedia and Question and Answer forums. In this short paper, we survey existing game-theoretic models for various human computation designs, and outline research challenges in advancing a theory that can enable better design.
FairTorrent: Bringing Fairness to Peer-to-Peer Systems
"... Peer-to-Peer file-sharing applications suffer from a fundamental problem of unfairness. Free-riders cause slower download times for others by contributing little or no upload bandwidth while consuming much download bandwidth. Previous attempts to address this fair bandwidth allocation problem suffer ..."
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Cited by 13 (1 self)
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Peer-to-Peer file-sharing applications suffer from a fundamental problem of unfairness. Free-riders cause slower download times for others by contributing little or no upload bandwidth while consuming much download bandwidth. Previous attempts to address this fair bandwidth allocation problem suffer from slow peer discovery, inaccurate predictions of neighboring peers ’ bandwidth allocations, underutilization of bandwidth, and complex parameter tuning. We present FairTorrent, a new deficit-based distributed algorithm that accurately rewards peers in accordance with their contribution. A FairTorrent peer simply uploads the next data block to a peer to whom it owes the most data as measured by a deficit counter. FairTorrent is resilient to exploitation by free-riders and strategic peers, is simple to implement, requires no bandwidth over-allocation, no prediction of peers ’ rates, no centralized control, and no parameter tuning. We implemented FairTorrent in a BitTorrent client without modifications to the BitTorrent protocol, and evaluated its performance against other widely-used BitTorrent clients. Our results show that FairTorrent provides up to two orders of magnitude better fairness, up to five times better download times for contributing peers, and 60 % to 100% better performance on average in live BitTorrent swarms.
Contracts: Practical Contribution Incentives for P2P Live Streaming
"... PPLive is a popular P2P video system used daily by millions of people worldwide. Achieving this level of scalability depends on users making contributions to the system, but currently, these contributions are neither verified nor rewarded. In this paper, we describe the design and implementation of ..."
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Cited by 13 (1 self)
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PPLive is a popular P2P video system used daily by millions of people worldwide. Achieving this level of scalability depends on users making contributions to the system, but currently, these contributions are neither verified nor rewarded. In this paper, we describe the design and implementation of Contracts, a new, practical approach to providing contribution incentives in P2P live streaming systems. Using measurements of tens of thousands of PPLive users, we show that widely-used bilateral incentive strategies cannot be effectively applied to the live streaming environment. Contracts adopts a different approach: rewarding globally effective contribution with improved robustness. Using a modified PPLive client, we show that Contracts both improves performance and strengthens contribution incentives. For example, in our experiments, the fraction of PPLive clients using Contracts experiencing loss-free playback is more than 4 times that of native PPLive. 1
No more crash or crunch: sustainable credit dynamics in a P2P community
"... Abstract—Many peer-to-peer file sharing communities implement credit policies to incentivise users to contribute upload resources. Such policies implicitly assume a user model- how the user controlling each peer behaves. We show using an agent-based model that credit policies, based on bandwidth con ..."
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Cited by 11 (4 self)
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Abstract—Many peer-to-peer file sharing communities implement credit policies to incentivise users to contribute upload resources. Such policies implicitly assume a user model- how the user controlling each peer behaves. We show using an agent-based model that credit policies, based on bandwidth contribution, and a selfish user model, can lead to both “crunches ” and “crashes” where the system seizes completely due to too little credit or too much credit. We explore the conditions that lead to these system pathologies and present a theoretical analysis that allows us to determine if a community is sustainable or will eventually crunch or crash. Finally we apply the analysis to produce a novel adaptive credit system that automatically adjusts credit policies to maintain sustainability. Keywords—P2P, economics, agent-based simulation, credits, incentives. I.
Improving efficiency and fairness in p2p systems with effort-based incentives
- In Proceedings of ICC
, 2010
"... Abstract — 1 Most P2P systems that have any kind of incentive mechanism reward peers ’ contribution in terms of uploaded volume. Due to the disparity in bandwidth capacity between P2P users on the Internet, the common effect of such mechanisms is that the fastest peers reap the highest benefits. We ..."
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Cited by 8 (3 self)
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Abstract — 1 Most P2P systems that have any kind of incentive mechanism reward peers ’ contribution in terms of uploaded volume. Due to the disparity in bandwidth capacity between P2P users on the Internet, the common effect of such mechanisms is that the fastest peers reap the highest benefits. We take a different approach and study how to incentivize cooperation in P2P systems based on peers ’ effort, i.e., contribution relative to capacity. We make the following contributions: 1) we propose that volume-based incentive schemes in P2P systems unnecessarily punish slow peers and decrease overall system performance; 2) we advocate that principles from an alternate economic vision, Participatory Economics (Parecon), can inspire systems which are fair and ensure maximization of the social welfare, while being efficient at the same time and 3) we present simulation results of applied principles from Parecon to two popular real life systems: a) the popular file sharing BitTorrent protocol, b) a generic credit based sharing ratio enforcement scheme. Our approach yields higher system performance and fairness for both, and offers interesting new insights into P2P incentive design. I.
Distributed algorithms via gradient descent for fisher markets.
- In Proc. 12th ACM Conference on Electronic Commerce,
, 2011
"... ABSTRACT Designing distributed algorithms that converge quickly to an equilibrium is one of the foremost research goals in algorithmic game theory, and convex programs have played a crucial role in the design of algorithms for Fisher markets. In this paper we shed new light on both aspects for Fish ..."
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Cited by 7 (2 self)
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ABSTRACT Designing distributed algorithms that converge quickly to an equilibrium is one of the foremost research goals in algorithmic game theory, and convex programs have played a crucial role in the design of algorithms for Fisher markets. In this paper we shed new light on both aspects for Fisher markets with linear and spending constraint utilities. We show fast convergence of the Proportional Response dynamics recently introduced by Wu and Zhang [WZ07]. The convergence is obtained from a new perspective: we show that the Proportional Response dynamics is equivalent to a gradient descent algorithm (with respect to a Bregman divergence instead of euclidean distance) on a convex program that captures the equilibria for linear utilities. We further show that the convex program program easily extends to the case of spending constraint utilities, thus resolving an open question raised by
