Analysis of a Reputation System for Mobile Ad-Hoc Networks with Liars

The application of decentralized reputation systems is a promising approach to ensure cooperation and fairness, as well as to address random failures and malicious attacks in Mobile Ad-Hoc Networks. However, they are potentially vulnerable to liars. With our work, we provide a first step to analyzing robustness of a reputation system based on a deviation test. Using a mean-field approach to our stochastic process model, we show that liars have no impact unless their number exceeds a certain threshold (phase transition). We give precise formulae for the critical values and thus provide guidelines for an optimal choice of parameters.Comment: 17 pages, 6 figure

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 alower 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 practic

Analysis of peer-to-peer file dissemination

In recent years, overlay networks have proven a popular way of disseminating potentially large files from a single server S to a potentially large group of N end users via the Internet. A number of algorithms and protocols have been suggested, implemented and studied. In particular, much attention has been given to peer-to-peer (P2P) systems such as BitTorrent, Slurpie, SplitStream, Bullet and Avalanche. The key idea is that the file is divided into M parts of equal size and that a given user may download any one of these -- or, for Avalanche, linear combinations of these -- either from the server or from a peer who has previously downloaded it. However, performance analysis of P2P systems for file dissemination has typically been limited to comparing one system relative to another and typically been realized by means of simulations and measurements. We give the minimal time to fully disseminate the file of M parts from a server to N end users in a centralized scenario. In the scheduling literature this completion time is referred to as makespan. We thereby provide a lower bound which can be used as a performance benchmark for any P2P file dissemination system. We also investigate the part of the loss in efficiency that is due to the lack of centralized control in practice. Using simulation as well as direct computation, we show that even a simple and natural randomized strategy disseminates the file in an expected time that grows with N in a similar manner to the minimal time achieved with a centralized controller. This suggests that the performance of necessarily decentralized P2P file dissemination systems should still be close to our performance bound

Reputation Systems for Self-Organized Networks

Self-organized networks such as mobile ad-hoc, Internet-based peer-to-peer, wireless mesh and Fourth Generation (4G) Wireless networks depend on cooperation of nodes. Reputation systems help nodes decide with whom to cooperate and which nodes to avoid. They have been studied and applied almost separately in diverse disciplines such as economics, computer science and social science, resulting in effort duplication and inconsistent terminology. In this paper, we aim at bringing together these efforts by outlining features and fundamental questions common to reputation systems in general. We derive methodologies to address these questions and lessons for both reputation system design and research from our own experiences and evaluations by simulation and analytical modelling. We argue for using deviation tests, discounting, only passing on of first-hand information, secondary response, and stressing the importance of identity

Introduction to Library Trends 29 (1) 1980: Current library use instruction

published or submitted for publicatio

The impact of liars on reputation in social networks

In this paper we consider a closed social network with a certain proportion of liars who are trying to influence their peers ’ reputation about some subject. Each person’s reputation about this subject is based on both own direct experience and second hand information from their peers which cannot be verified. Given certain assumptions on when people believe or do not believe second hand information, we investigate the liars ’ impact on their peers ’ reputation about the subject. We present a mathematical model for this situation and show that there is a threshold proportion of liars below which they have no impact. Above it, liars do have an impact. We quantify this impact and give the threshold proportions. We compare our results in two fundamentally different scenarios: In the first one, reputation is passed on as second hand information. In the second one, direct experience only is passed on as second hand information. We find that in the latter scenario liars have less impact