| Abstract:
The access link quality experienced by the end users depends on the amount of traffic and on the presence of network anomalies. Different techniques exist to detect anomalies, but little attention has been devoted to quantify the access link quality and to which extent network anomalies affect the end user's access link experience. We refer to this aspect as the impact factor of the anomaly, that we define as the percentage of affected destinations. In the ideal case, a node should continuously monitor all possible routes to detect any degradation in performance, but this is not practical in reality. In this paper we show how a node can estimate the quality of Internet access through a limited set of measurements. We initially study the user's access network to understand the typical features of its connectivity tree. Then, we define an unbiased estimator for the quality of access and we compute the minimum number of paths to monitor, so that the estimator achieves a desirable accuracy without knowing the underlying topology. We use real data to construct a network graph and we validate our solution by causing a large number of anomalies and by comparing the real and the estimated quality of access for all available end hosts. Our results show that the impact factor is a meaningful metric to evaluate the quality of Internet access. |
| Abstract:
The easy deployment of P2P self-organized systems has contributed to their wide diffusion and to the definition of a new communication paradigm. Mobile communities can now spontaneously emerge to enable users to become both consumer and service providers. However, the presence of selfish and malicious nodes can thwart the sustainability of these systems as nodes try to exploit services without contributing resources. In these P2P systems reputation management schemes can promote collaboration, but they are mostly ineffective in communities that last for short time. In this paper we propose a token based mechanism that extends existing reputation management schemes to support mobility. It reduces the problem of bootstrapping the reputation values and provides incentives for nodes to properly behave. Simulation results show that the token based extension enables the correlation of transactions in different contexts efficiently. |
| Abstract:
Content distribution systems benefit from network coding in terms of error/loss protection and faster dissemination at the cost of exposing the data to intermediate nodes that are not the intended recipients. In these systems data secrecy is at risk and it can be guaranteed by using encryption as a straightforward method. However, this inevitably increases the communication costs and decreases the willingness to cooperate of intermediate nodes, which have no expectation of recovering the file. In this paper we propose an incentive secrecy preserving scheme based on obfuscation for time-sensitive data. The source intentionally obscures the original file and informs only the intended recipients which file blocks are corrupted. This scheme, combined with network coding, preserves the data secrecy and, in the meantime, fosters the cooperation of intermediate nodes. The evaluation of our solution shows that the proposed scheme is more efficient than encryption based secrecy preserving methods. In particular, the distribution of content in term of downloading speed is greatly enhanced. |
| Abstract:
Vehicular networks create a new communication paradigm that enables to exploit the movement of cars to disseminate content. If network coding is used, vehicles have much more flexibility in content sharing and the system stability and scalability are promoted also in presence of mobility. Along this line, we propose an efficient mechanism to provide secrecy of the information. Traditional approaches based on encryption decrease the cooperation willingness of intermediate nodes, which have no expectation of recovering the file. Our scheme is based on obfuscation by processing and polluting the original file so that only the intended recipients, informed of corrupted blocks, can recover the information timely. We present several alternatives to efficiently provide weak secrecy and to foster cooperation. We simulate the file distribution in a vehicular network and show that the proposed scheme enhances content distribution in term of downloading speed and it is much more efficient than the ones that use encryption. |
| Abstract:
The specific objective of a reputation management system is to facilitate nodes to decide whom to trust for providing the correct quality of services or resources. The enforcement of reputation-based mechanisms in self-organized systems has a cost in terms of messages required to disseminate feedbacks and to synchronize reputation values. In this paper we discuss the implementation of a reputation management system and consider two approaches to collect and disseminate data: proactive and reactive schemes. We analyze the impact of these approaches in terms of extra-signalling and evaluate the performance of reputation management systems. This enables the quantification of the costs and benefits of the use of reputation management systems. |
| Abstract:
Peer-to-peer networks need to have self-organization properties because of the lack of a centralized authority. This implies that nodes should self-manage and cooperate to sustain the availability of the resources in the system. In this context reputation management schemes have been proven in the past to be a useful tool to foster cooperation. In this paper we discuss the importance for a node to build and use its reputation value. We propose a game-theoretical framework, based on the generalized form of the Iterated Prisoner's Dilemma, to model the interactions of rational and selfish nodes in distributed systems. We study how a node takes into account the change of its reputation when deciding its behaviour in a transaction and discuss the Nash Equilibrium in the system. Then, we also simulate nodes' interactions under different strategies to analyze how cooperation and reputation evolve in the system. |
| Abstract:
Reputation management systems have been proven in the past to be a valuable tool to foster cooperation in distributed systems, as they rely on the nodes' active participation to sustain the availability of the resources and scalability. In this paper, we exploit ideas from Game Theory to propose a game theoretical framework to model the interactions of rational and selfish nodes in distributed systems. Our approach differs from previous works in the field as we introduce reputation in the definition of the utility function along with a punishment factor for nodes cooperating with untrustworthy entities. |
| Abstract:
Leveraging social networks in computer systems can be effective in dealing with a number of trust and security issues. Spam is one such issue where the "wisdom of crowds" can be harnessed by mining the collective knowledge of ordinary individuals. In this paper, we present a mechanism through which members of a virtual community can exchange information to combat spam. Previous attempts at collaborative spam filtering have concentrated on digest-based indexing techniques to share digests or fingerprints of emails that are known to be spam. We take a different approach and allow users to share their spam filters instead, thus dramatically reducing the amount of traffic generated in the network. The resultant diversity in the filters and cooperation in a community allows it to respond to spam in an autonomic fashion. As a test case for exchanging filters we use the popular SpamAssassin spam filtering software and show that exchanging spam filters provides an alternative method to improve spam filtering performance. |
| Abstract:
In order for autonomic systems to function, the individual components must cooperate and not indulge in malicious behavior. However, it is almost certain that autonomous systems in Next Generation Networks will inadvertently include less than trustworthy components. Identifying such entities is critical to the smooth and effective functioning. We present new experiments conducted with the ROCQ scheme, a reputation-based trust management system that computes the trustworthiness of peers on the basis of transaction-based feedback. The ROCQ model combines four parameters: Reputation (R) or a peer's global trust rating, Opinion (O) formed by a peer's first-hand interactions, Credibility (C) of a reporting peer and Quality (Q) or the confidence a reporting peer puts on the feedback it provides. In this paper, we demonstrate that ROCQ is robust against churn and also examine the effect of credibility and quality on the performance of the scheme. |
| Abstract:
We propose a reputation-based trust management system, ROCQ, to reduce inauthentic and corrupted file transfers in end-user collaborative content-distribution systems. Such systems are characterized by the splitting of large files into (optionally encoded) blocks and the simultaneous downloading of several blocks from different nodes to speed up content distribution. All nodes must cooperate and provide correct content for such systems to function smoothly. If malicious nodes are present, they can quickly bring the system to a halt by introducing fake blocks in the network making it impossible to reconstruct the original file. ROCQ (Reputation, Opinion, Credibility and Quality), uses feedback from past interactions between nodes to create node reputations. This allows detection of malicious nodes in a transaction-based network. In this paper, we study the performance of ROCQ as used in a content distribution network. We find that ROCQ decreases the likelihood of a user receiving fake blocks by upto 16% and hence significantly reduces bandwidth waste. |
| Abstract:
Peer-to-peer (P2P) networks are being actively used to facilitate the collaborative distribution of content by avoiding the bottlenecks due to a single server. P2P content distribution systems are characterized by the splitting of large files into (optionally encoded) blocks and the simultaneous downloading of several blocks from different nodes to speed up content distribution. However, the success of these systems depends heavily on the users' behavior: they can cooperate and distribute the content, they can act selfishly (free-riders) or, even worse, they can insert tampered content into the network. All nodes must cooperate and provide correct content for such systems to function smoothly. If malicious nodes are present, they can quickly bring the system to a halt by introducing fake blocks in the network making it impossible to reconstruct the original file. In the absence of any common goals shared by the nodes of a peerto- peer network, external motivation to cooperate and be trustworthy is crucial. Digital Reputations can be used to inject trust among the nodes of a network. In this thesis, we propose to investigate the issues concerning the development of a digital reputation-based trust management system in order to propose a viable solution to reduce inauthentic and corrupted file transfers in end-user collaborative content-distribution systems. |
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