Modeling structured peer-to-peer systems

1 Introduction File sharing software napster and gnutella arouse an increa- sing interest in the peer-to-peer(P2P)network where all the nodes have identical capabilities and responsibilities and directly communicate with each other without centralized con…     

Incentives for large peer-to-peer systems

We consider problems of provisioning an excludable public good amongst n potential members of a peer-to-peer system who are able to communicate information about their private preferences for the good. The cost of provisioning the good in quantity Q depends on Q, and may also depend on n, or on the final number of participating peers m. Our aim is to maximize the expected social welfare in a way that is incentive compatible, rational and budget-balanced. Although it is unfortunately almost never possible to calculate or implement a truely optimal mechanism design, we show that as the number of participants becomes large the expected social welfare that can be obtained by the optimal design is at most a factor 1+O(1/n) or 1+O(1//spl radic/n) greater than that which can be obtained with a very simple scheme that requires only payment of a fixed contribution from any agent who joins the system as a participating peer. Our first application is to a model of file sharing, in which the public good is content availability; the second concerns a problem of peering wireless local area networks, in which the public good is the availability of connectivity for roaming peers. In both problems, we can cope with the requirement that the payments be made in kind, rather than in cash.     

Enhancing peer-to-peer systems through redundancy

Peer-to-peer systems can share the computing resources and services by directly communicating within a widely distributed network. It is important that these systems can efficiently locate, in as few hops as possible, the node storing the desired data in a large system. Thus, it is worth consuming some extra storage to obtain better routing performance. In this paper, we propose redundant strategies to improve the routing performance and data availability on Chord and De Bruijn topologies. Hybrid-Chord combines multiple chord rings and successors, and Redundant D2B maintains successors, to improve the routing performance. The proposed systems can reduce the number of lookup hops significantly (by as much as 50%) compared to the original ones, and have better fault tolerance capabilities, with a small storage overhead     

Free-riding and whitewashing in peer-to-peer systems

We devise a model to study the phenomenon of free-riding and free-identities in peer-to-peer systems. At the heart of our model is a user of a certain type, an intrinsic and private parameter that reflects the user's willingness to contribute resources to the system. A user decides whether to contribute or free-ride based on how the current contribution cost in the system compares to her type. We study the impact of mechanisms that exclude low type users or, more realistically, penalize free-riders with degraded service. We also consider dynamic scenarios with arrivals and departures of users, and with whitewashers -users who leave the system and rejoin with new identities to avoid reputational penalties. We find that imposing penalty on all users that join the system is effective under many scenarios. In particular, system performance degrades significantly only when the turnover rate among users is high. Finally, we show that the optimal exclusion or penalty level differs significantly from the level that optimizes the performance of contributors only for a limited range of societal generosity levels.     

Managing distributed objects in peer-to-peer systems

Peer-to-peer systems that dynamically organize, interact and share resources are increasingly being deployed in large-scale environments. The location, intermittent connectivity, and organization of the peers have significant impact on meeting the quality of service requirements of distributed applications. This article presents the design, implementation, and empirical evaluation of a middleware architecture for managing distributed objects in peer-to-peer systems. The architecture consists of a self-organizing infrastructure that uses only local knowledge to dynamically form overlays of multiple peers and respond to changing processing and networking conditions; and a management layer that monitors the behavior of the applications transparently, schedules object invocations over multiple machines, and obtains accurate resource projections. The system works in a two-level feedback loop structure that uses measurements of elapsed time and resource loads to refine the initial estimates and revise the peer connections. Our empirical evaluation shows that the system manipulates the peer connections dynamically in response to changes in resource utilization to meet application end-to-end soft real-time requirements.     

A Bayesian approach for user aware peer-to-peer video streaming systems

Peer-to-Peer (P2P) architectures for live video streaming has attracted a significant attention from both academia and industry. P2P design enables end-hosts to relay streams to each other overcoming the scalability issue of centralized architectures. However, these systems struggle to provide a service of comparable quality to that of traditional television. Since end-hosts are controlled by users, their behavior has a strong impact on the performance of P2P streaming systems, leading to potential service disruption and low streaming quality. Thus, considering the user behavior in these systems could bring significant performance improvements. Toward this end, we propose a Bayesian network that captures all the elements making part of the user behavior or related to it. This network is built from the information found in a cross-analysis of numerous large-scale measurement campaigns, analyzing the user behavior in video streaming systems. We validate our model through intensive simulations showing that our model can learn a user behavior and is able to predict several activities helping thus in optimizing these systems for a better performance. We also propose a method based on traces collection of the same user type that accelerates the learning process of this network. Furthermore, we evaluate the performance of this model through exploring its applications and comparison with non-contextual models.     

Integrating mobile cellular devices into popular peer-to-peer systems

Today, peer-to-peer content-distribution networks are highly popular among users that have stationary computers with high-bandwidth Internet connections. Mobile devices (e.g. cell phones) that are connected to the Internet via cellular-radio networks, however, could not yet be launched into this field to a satisfactory extent. Although most mobile devices have the necessary hardware resources for joining peer-to-peer content-distribution networks, they are often not able to benefit from participation in an energy efficient way, due to limitations caused by mobility. In this work, mobile devices are identified as providers of advanced mobile features and services that are usually not available to computers in stationary networks. These mobile features and services can be exchanged for services in peer-to-peer networks, turning mobile devices into valuable trading partners. Partnership schemes are set up to define the way of a fair cooperation between mobile devices and other peers. A novel peer-to-peer architecture is suggested that applies partnership schemes to a well-established peer-to-peer content-distribution network and facilitates the integration of mobile devices.     

Structured peer-to-peer systems for telecommunications and mobile environments

The peer-to-peer (P2P) paradigm not only allows end users to share own resources, but is also regarded as a new networking paradigm due to its robust, self-organizing character, abandoning infrastructure and relying on end-users equipment. In contrast to common fixed-line Internet file sharing P2P systems, in this paper, we address critical issues regarding scalable personal communications and heterogeneous mobile systems. We discuss challenges and present our solutions based on structured P2P.     

Study of the relationship between peer-to-peer systems and IP multicasting

Peer-to-peer (P2P) systems, which have attracted public attention, involve a number of directly connected "peers" exchanging various types of information among themselves. However, applications based on P2P systems generally generate a lot of traffic and require not only the resources of every peer (e.g., CPU, memory, and bandwidth) but also many network resources. We think the main problems of P2P systems can be solved using IP multicasting, which is becoming popular as an effective way to transfer streaming media over the network and can reduce network traffic and the load on a streaming server. We propose applying IP multicasting to P2P systems. After mentioning that almost every application can be improved by our proposal, we discuss which routing protocol is suitable. Finally, we show that we can get good results even when part of the network does not support IP multicasting.     

Optimal search performance in unstructured peer-to-peer networks with clustered demands

This paper derives the optimal search time and the optimal search cost that can be achieved in unstructured peer-to-peer networks when the demand pattern exhibits clustering (i.e. file popularities vary across the set of nodes in the network). Clustering in file popularity patterns is evident from measurements on deployed peer-to-peer file sharing networks. In this paper, we provide mechanisms for modeling clustering in file popularity distributions and the consequent non-uniform distribution of file replicas. We derive relations that show the effect of the number of replicas of a file on the search time and on the search cost for a search for that file for the clustered demands case in such networks for both random walk and flooding search mechanisms. The derived relations are used to obtain the optimal search performance for the case of flooding search mechanisms. The potential performance benefit that clustering in demand patterns affords is captured by our results. Interestingly, the performance gains are shown to be independent of whether the search network topology reflects the clustering in file popularity (the optimal file replica distribution to obtain these performance gains, however, does depend on the search network topology)     

A federated peer-to-peer network game architecture

A federated peer-to-peer game is one in which many small areas of interest within a game each supported using a peer-to-peer model are "knitted" together to form a game capable of supporting a very large number of players. Our work has involved determining whether such an architecture is a feasible alternative to the more common central server architecture for supporting large multiplayer network games.     

A peer-to-peer architecture for media streaming

Given that the Internet does not widely support Internet protocol multicast while content-distribution-network technologies are costly, the concept of peer-to-peer could be a promising start for enabling large-scale streaming systems. In our so-called Zigzag approach, we propose a method for clustering peers into a hierarchy called the administrative organization for easy management, and a method for building the multicast tree atop this hierarchy for efficient content transmission. In Zigzag, the multicast tree has a height logarithmic with the number of clients, and a node degree bounded by a constant. This helps reduce the number of processing hops on the delivery path to a client while avoiding network bottlenecks. Consequently, the end-to-end delay is kept small. Although one could build a tree satisfying such properties easily, an efficient control protocol between the nodes must be in place to maintain the tree under the effects of network dynamics. Zigzag handles such situations gracefully, requiring a constant amortized worst-case control overhead. Especially, failure recovery is done regionally with impact on, at most, a constant number of existing clients and with mostly no burden on the server.     

Graph-theoretic analysis of structured peer-to-peer systems: routing distances and fault resilience

This paper examines graph-theoretic properties of existing peer-to-peer networks and proposes a new infrastructure based on optimal-diameter de Bruijn graphs. Since generalized de Bruijn graphs exhibit very short average distances and high resilience to node failure, they are well suited for distributed hash tables (DHTs). Using the example of Chord, CAN, and de Bruijn, we study the routing performance, graph expansion, clustering properties, and bisection width of each graph. Having confirmed that de Bruijn graphs offer the best diameter and highest connectivity among the existing peer-to-peer structures, we offer a very simple incremental building process that preserves optimal properties of de Bruijn graphs under uniform user joins/departures. We call the combined peer-to-peer architecture optimal diameter routing infrastructure.     

Analysis of user-driven peer selection in peer-to-peer backup and?storage systems

In this paper we present a model of peer-to-peer backup and storage systems in which users have the ability to selfishly select remote peers they want to exchange data with. In our work, peer characteristics (e.g., on-line availability, dedicated bandwidth) play an important role and are reflected in the model through a single parameter, termed profile. We show that selecting remote peers selfishly, based on their profiles, creates incentives for users to improve their contribution to the system. Our work is based on an extension to well known results in Matching Theory, which allows us to formulate the Stable Exchange Game, in which we shift the algorithmic nature of matching problems to a game theoretic framework. We propose a polynomial-time algorithm to compute welfare-maximizing stable exchanges between peers and show, using an evolutionary game theoretic framework, that even semi-random peer selection strategies, that are easily implementable in practice, can be effective in providing incentives to users in order to improve their profiles.     

A Lottery-based pricing scheme for peer-to-peer networks

Users in Peer-to-Peer (P2P) networks tend to exploit the maximum resources they are able to obtain, offering minimum resources in response. This behavior undermines the goal of P2P systems in spreading files through the network and imposes the concept of free-riding. In this paper we propose a Lottery-based pricing mechanism to enhance the sharing level in P2P networks and help increase the number of objects disseminated. The scheme is an extension of the traditional micropayment mechanism. Our scheme provides higher payoff for peers who contribute to the P2P network and higher cost for peers who act selfishly and choose not to share resources. We present simulation results to demonstrate the performance of the proposed mechanism.     

A performance bound on random-coded MIMO systems

A closed-form upper bound on the average error probability is proposed for random block codes operating in multi-input multi-output (MIMO) systems. The bound exponentially decays to zero with increasing block length, and the obtained error exponent proves consistent with Gallager's random coding exponent and the information-theoretic channel capacity.     

A comparative study on the performance of MIMO MRC systems with and without cochannel interference

This paper presents exact closed-form expressions for the performance of multiple-input/multiple-output systems employing maximal ratio combining in the absence and presence of cochannel interference. The results are applicable to systems operating over Rayleigh fading channels, and in which the minimum number of antenna elements at the transmitter and receiver is two. The mathematical formalism is illustrated by some numerical examples which study the effects of various parameters on the system performance.     

A performance analysis of optical overlapping PPM-CDMAcommunication systems

Direct-detection optical code-division multiple-access (CDMA) systems employing overlapping pulse-position modulation (OPPM) schemes are proposed. Both upper and lower hounds on the bit error rate (BER) are derived taking into account the effect of both multiple-user interference and receiver shot noise. The photodiodes' dark currents are neglected since their effect is minor. The throughput limitation of this system is evaluated as well. Performance characteristics are then compared to optical CDMA systems employing traditional ON-OFF keying (OOK) and pulse-position modulation (PPM) schemes. It is shown that under fixed data rate and chip time, OPPM-CDMA system superperforms both traditional systems. Moreover, it is shown that the throughput limitation of OPPM-CDMA is almost 6.7 times greater than that of OOK-CDMA     

On the fundamental performance limits of peer-to-peer data replication in wireless ad hoc networks

Wireless ad hoc networks are drawing increasing attention from the research community because of their potential applications. However, the fundamental capacity limits of these networks pose various technological challenges to designers of network protocols. In this paper, we attempt to capture the inherent constraints on information dissemination in a mobile wireless environment, with the emphasis on peer-to-peer (P2P) communications. More specifically, we introduce the notion of "replication-induced gain" to quantify the impact of data replication under the paradigm of P2P query-response mechanisms. Our major contribution lies in presenting several preliminary results with respect to the complexities and trade-offs involved in enhancing data availability. To the best of our knowledge, the data replication problems that arise because of scarce system resources in wireless ad hoc networks have not been investigated from this perspective. We believe that our results could provide additional insights and practical implications for P2P system designers