Papers by Mario Schlosser

Journal of Web Semantics, Feb 1, 2004
RDF-based P2P networks have a number of advantages compared to simpler P2P networks such as Napst... more RDF-based P2P networks have a number of advantages compared to simpler P2P networks such as Napster, Gnutella or to approaches based on distributed indices on binary keys such as CAN and CHORD. RDF-based P2P networks allow complex and extendable descriptions of resources instead of fixed and limited ones, and they provide complex query facilities against these metadata instead of simple keyword-based searches. In this paper we will discuss RDF-based P2P networks like Edutella as a specific example of a new type of P2P networks -schema-based P2P networks -and describe the use of super-peer based topologies for these networks. Super-peer based networks can provide better scalability than broadcast based networks, and provide support for inhomogeneous schema-based networks, with different metadata schemas and ontologies (crucial for the Semantic Web). Based on (dynamic) metadata routing indices, stated in RDF, the superpeer network supports sophisticated routing and distribution strategies, as well as preparing the ground for advanced mediation and clustering functionalities.
Assessing the performance of peer-to-peer algorithms is impossible without simulations since test... more Assessing the performance of peer-to-peer algorithms is impossible without simulations since testing new algorithms by deploying them in an existing P2P network is prohibitively expensive. However, some P2P algorithms are sensitive to the network and traffic models that are used in the simulations. In order to produce realistic results, we therefore require simulations that resemble real-world P2P networks as closely as possible. We describe the Query-Cycle Simulator, a simulator for file-sharing P2P networks networks. We link the Query-Cycle Simulator to measurements on existing P2P networks and discuss some open issues in simulating these networks.
Sigmod Record, Sep 1, 2003
Availability and locality measurements of peer-to-peer file systems
Availability and locality measurements of peer-to-peer file systems. [Proceedings of SPIE 4868, 3... more Availability and locality measurements of peer-to-peer file systems. [Proceedings of SPIE 4868, 310 (2002)]. Jacky C. Chu, Kevin S. Labonte, Brian N. Levine. Abstract. Although peer-to-peer networking applications continue to ...
Lecture Notes in Computer Science, 2003
We address the freerider problem on P2P networks. We first propose a specific participation metri... more We address the freerider problem on P2P networks. We first propose a specific participation metric, which we call a peer's EigenTrust score. We show that EigenTrust scores accurately capture several different participation criteria. We then propose an incentive scheme that may be used in conjunction with any numerical participation metric. We show that, when these incentives are used in conjunction with EigenTrust scores, they reward participatory peers but don't exclude less active peers.

Peer-to-peer file-sharing networks are currently receiving much attention as a means of sharing a... more Peer-to-peer file-sharing networks are currently receiving much attention as a means of sharing and distributing information. However, as recent experience shows, the anonymous, open nature of these networks offers an almost ideal environment for the spread of self-replicating inauthentic files. We describe an algorithm to decrease the number of downloads of inauthentic files in a peer-to-peer file-sharing network that assigns each peer a unique global trust value, based on the peer's history of uploads. We present a distributed and secure method to compute global trust values, based on Power iteration. By having peers use these global trust values to choose the peers from whom they download, the network effectively identifies malicious peers and isolates them from the network. In simulations, this reputation system, called EigenTrust, has been shown to significantly decrease the number of inauthentic files on the network, even under a variety of conditions where malicious peers cooperate in an attempt to deliberately subvert the system.

Ontology-Based Search and Broadcast in HyperCuP
ABSTRACT Introduction Peer-to-peer networks are envisioned to be deployed in a wide range of appl... more ABSTRACT Introduction Peer-to-peer networks are envisioned to be deployed in a wide range of applications, including the Semantic Web [2]. However, unorganized P2P networks exhibit characteristics that severely hamper their scalability to a large number of nodes, among them long search times, network traffic overload and traffic hotspots. In [1], we present HyperCuP, a topology for P2P networks which allows for very efficient search and broadcast, as well as a distributed construction and maintenance algorithm which organizes peers in a P2P network automatically into the desired topology. On this poster, we present a concept extending this scheme with ontology-based routing which can be exploited for directed search and broadcast on HyperCuP-based P2P networks. 2 HyperCuP: Shaping Up P2P Networks A P2P network based on HyperCuP organizes its peers into a deterministic graph topology which features symmetry (i.e. every node can equally originate searches and broadcasts), low network diameter,

Peer-to-peer file-sharing networks are currently receiving much attention as a means of sharing a... more Peer-to-peer file-sharing networks are currently receiving much attention as a means of sharing and distributing information. However, as recent experience with P2P networks such as Gnutella shows, the anonymous, open nature of these networks offers an almost ideal environment for the spread of self-replicating inauthentic files. We describe an algorithm to decrease the number of downloads of inauthentic files in a peer-to-peer file-sharing network that assigns each peer a unique global reputation value, based on the peer's history of uploads. We present a distributed and secure method to compute global reputation values, based on Power iteration. By having peers use these global reputation values to choose the peers from whom they download, the network effectively identifies malicious peers and isolates them from the network. In simulations, this reputation system has been shown to significantly decrease the number of inauthentic files on the network, even under a variety of conditions where malicious peers cooperate in an attempt to deliberately subvert the system.
P2P networks have become increasingly popular in the recent years. However, their open, distribut... more P2P networks have become increasingly popular in the recent years. However, their open, distributed and anonymous nature makes them very vulnerable against malicious users who provide bad responses to requests from other peers. Motivated by this observation, various solutions for distributed reputation systems have been presented recently. In this paper, we describe the first reputation system which incorporates both user-individual personalization and global experiences of peers in the network, for the distributed computation of reputation values. We also present a secure method to compute global trust values, thus assuring identification and isolation of malicious peers. Finally, our simulations show that our system is robust even against attacks from groups of malicious peers deliberately cooperating to subvert it.
Circuits and Systems
Atrial fibrillation following routine cardiac surgery is a major cause of post-operative patient ... more Atrial fibrillation following routine cardiac surgery is a major cause of post-operative patient morbidity. Reliable prediction of the imminent onset of atrial fibrillation can be achieved by monitoring and analyzing electrical signals from the patient’s heart, thus allowing prophylactic treatment of those patients at risk. However, predicting atrial fibrillation manually remains a complicated and daunting task. We have therefore developed a chip which is capable of predicting the onset of atrial fibrillation automatically, based on the monitoring of the monophasic action potential recorded from the patient’s heart. Our system operates fully autonomously and it is stable, resource-conserving and extensible.

Proceedings of the twelfth international conference on World Wide Web - WWW '03, 2003
RDF-based P2P networks have a number of advantages compared with simpler P2P networks such as Nap... more RDF-based P2P networks have a number of advantages compared with simpler P2P networks such as Napster, Gnutella or with approaches based on distributed indices such as CAN and CHORD. RDF-based P2P networks allow complex and extendable descriptions of resources instead of fixed and limited ones, and they provide complex query facilities against these metadata instead of simple keyword-based searches. In previous papers, we have described the Edutella infrastructure and different kinds of Edutella peers implementing such an RDFbased P2P network. In this paper we will discuss these RDF-based P2P networks as a specific example of a new type of P2P networks, schema-based P2P networks, and describe the use of super-peer based topologies for these networks. Super-peer based networks can provide better scalability than broadcast based networks, and do provide perfect support for inhomogeneous schema-based networks, which support different metadata schemas and ontologies (crucial for the Semantic Web). Furthermore, as we will show in this paper, they are able to support sophisticated routing and clustering strategies based on the metadata schemas, attributes and ontologies used. Especially helpful in this context is the RDF functionality to uniquely identify schemas, attributes and ontologies. The resulting routing indices can be built using dynamic frequency counting algorithms and support local mediation and transformation rules, and we will sketch some first ideas for implementing these advanced functionalities as well.

HyperCuP/O – Shaping up peer-to-peer networks
Abstract. Peer-to-peer networks are envisioned to be deployed for a wide range of applications. H... more Abstract. Peer-to-peer networks are envisioned to be deployed for a wide range of applications. However, P2P networks evolving in an unorganized manner suffer from serious scalability problems, limiting the number of nodes in the network, creating network overload and pushing search times to unacceptable limits. We address these problems by imposing a deterministic shape on P2P networks: We propose a graph topology which allows for very efficient broadcast and search, and we describe a broadcast algorithm that exploits the topology to reach all nodes in the network with the minimum amount of messages possible. We provide an efficient topology construction and maintenance algorithm which, crucial to symmetric peer-to-peer networks, does not require any central server nor super nodes in the network. Nodes can join and leave the self-organizing network at any time, and the network is resilient against failure. 1
3.2 A Web Services Protocol Stack........................... 10
Assessing the performance of peer-to-peer algorithms such as topology construction protocols, dis... more Assessing the performance of peer-to-peer algorithms such as topology construction protocols, distributed trust or search algorithms is impossible without simulations since testing new algorithms by deploying them in an existing P2P network is prohibitively expensive. However, some P2P algorithms are sensitive to the network and traffic models that are used in the simulations. In order to produce realistic results, we therefore require models that resemble real-world P2P networks as closely as possible. In this paper, we describe a model for P2P file-sharing networks, link it to measurements on existing P2P networks and discuss open issues in modeling these networks.

Peer-to-peer networks are envisioned to be deployed for a wide range of applications. However, P2... more Peer-to-peer networks are envisioned to be deployed for a wide range of applications. However, P2P networks evolving in an unorganized manner suffer from serious scalability problems, limiting the number of nodes in the network, creating network overload and pushing search times to unacceptable limits. We address these problems by imposing a deterministic shape on P2P networks: We propose a graph topology which allows for very efficient broadcast and search, and we describe a broadcast algorithm that exploits the topology to reach all nodes in the network with the minimum number of messages possible. We provide an efficient topology construction and maintenance algorithm which, crucial to symmetric peer-to-peer networks, does neither require a central server nor super nodes in the network. Nodes can join and leave the self-organizing network at any time, and the network is resilient against failure. Moreover, we show how our scheme can be made even more efficient by using a global ontology to determine the organization of peers in the graph topology, allowing for efficient concept-based search.

Peer-to-peer file-sharing networks are currently receiving much attention as a means of sharing a... more Peer-to-peer file-sharing networks are currently receiving much attention as a means of sharing and distributing information. However, as recent experience shows, the anonymous, open nature of these networks offers an almost ideal environment for the spread of self-replicating inauthentic files. We describe an algorithm to decrease the number of downloads of inauthentic files in a peer-to-peer file-sharing network that assigns each peer a unique global trust value, based on the peer's history of uploads. We present a distributed and secure method to compute global trust values, based on Power iteration. By having peers use these global trust values to choose the peers from whom they download, the network effectively identifies malicious peers and isolates them from the network. In simulations, this reputation system, called EigenTrust, has been shown to significantly decrease the number of inauthentic files on the network, even under a variety of conditions where malicious peers cooperate in an attempt to deliberately subvert the system.

Www, 2003
Peer-to-peer file-sharing networks are currently receiving much attention as a means of sharing a... more Peer-to-peer file-sharing networks are currently receiving much attention as a means of sharing and distributing information. However, as recent experience with P2P networks such as Gnutella shows, the anonymous, open nature of these networks offers an almost ideal environment for the spread of self-replicating inauthentic files. We describe an algorithm to decrease the number of downloads of inauthentic files in a peer-to-peer file-sharing network that assigns each peer a unique global reputation value, based on the peer's history of uploads. We present a distributed and secure method to compute global reputation values, based on Power iteration. By having peers use these global reputation values to choose the peers from whom they download, the network effectively identifies malicious peers and isolates them from the network. In simulations, this reputation system has been shown to significantly decrease the number of inauthentic files on the network, even under a variety of conditions where malicious peers cooperate in an attempt to deliberately subvert the system.
Assessing the performance of peer-to-peer algorithms is impossible without simulations since test... more Assessing the performance of peer-to-peer algorithms is impossible without simulations since testing new algorithms by deploying them in an existing P2P network is prohibitively expensive. However, some P2P algorithms are sensitive to the network and traffic models that are used in the simulations. In order to produce realistic results, we therefore require simulations that resemble real-world P2P networks as closely as possible. We describe the Query-Cycle Simulator, a simulator for file-sharing P2P networks networks. We link the Query-Cycle Simulator to measurements on existing P2P networks and discuss some open issues in simulating these networks.
Acm Sigmod Record, Sep 1, 2003
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Papers by Mario Schlosser