A super-peer is a node in a peer-to-peer network that operates both as a server to a set of clients, and as an equal in a network of super-peers. Super-peer networks strike a balance between the efficiency of centralized search, and the autonomy, load balancing and robustness to attacks provided by distributed search. Furthermore, they take advantage of the heterogeneity of capabilities (e.g., bandwidth, processing power) across peers, which recent studies have shown to be enormous. Hence, new and old P2P systems like KaZaA and Gnutella are adopting super-peers in their design. Despite their growing popularity, the behavior of super-peer networks is not well understood. For example, what are the potential drawbacks of super-peer networks? How can super-peers be made more reliable? How many clients should a super-peer take on to maximize efficiency? we examine super-peer networks in detail, gaming an understanding of their fundamental characteristics and performance tradeoffs. We also present practical guidelines and a general procedure for the design of an efficient super-peer network.

Designing an Super-Peer Network

Test-retest reliabilities of resting-state FMRI measurements in human brain functional connectomics: A systems neuroscience perspective

This paper introduces a lightweight, scalable and accurate framework, called Meridian, for performing node selection based on network location. The framework consists of an overlay network structured around multi-resolution rings, query routing with direct measurements, and gossip protocols for dissemination. We show how this framework can be used to address three commonly encountered problems, namely, closest node discovery, central leader election, and locating nodes that satisfy target latency constraints in large-scale distributed systems without having to compute absolute coordinates. We show analytically that the framework is scalable with logarithmic convergence when Internet latencies are modeled as a growth-constrained metric, a low-dimensional Euclidean metric, or a metric of low doubling dimension. Large scale simulations, based on latency measurements from 6.25 million node-pairs as well as an implementation deployed on PlanetLab show that the framework is accurate and effective.

/pdf/meridian-a-lightweight-network-location-service-without-2ljlk2vtts.pdf

Meridian: a lightweight network location service without virtual coordinates

Nowadays, mobile users with global positioning devices canaccess Location Based Services (LBS) and query about pointsof interest in their proximity. For such applications to succeed,privacy and confidentiality are essential. Encryptionalone is not adequate; although it safeguards the systemagainst eavesdroppers, the queries themselves may disclosethe location and identity of the user. Recently, there havebeen proposed centralized architectures based on K-anonymity,which utilize an intermediate anonymizer between themobile users and the LBS. However, the anonymizer mustbe updated continuously with the current locations of allusers. Moreover, the complete knowledge of the entire systemposes a security threat, if the anonymizer is compromised.In this paper we address two issues: (i) We show thatexisting approaches may fail to provide spatial anonymityfor some distributions of user locations and describe a noveltechnique which solves this problem. (ii) We propose Prive,a decentralized architecture for preserving the anonymityof users issuing spatial queries to LBS. Mobile users self-organizeinto an overlay network with good fault toleranceand load balancing properties. Prive avoids the bottleneckcaused by centralized techniques both in terms of anonymizationand location updates. Moreover, the system state isdistributed in numerous users, rendering Prive resilient toattacks. Extensive experimental studies suggest that Priveis applicable to real-life scenarios with large populations ofmobile users.

/pdf/prive-anonymous-location-based-queries-in-distributed-mobile-3qwz7zs4si.pdf

PRIVE: anonymous location-based queries in distributed mobile systems

We propose a balanced tree structure overlay on a peer-to-peer network capable of supporting both exact queries and range queries efficiently. In spite of the tree structure causing distinctions to be made between nodes at different levels in the tree, we show that the load at each node is approximately equal. In spite of the tree structure providing precisely one path between any pair of nodes, we show that sideways routing tables maintained at each node provide sufficient fault tolerance to permit efficient repair. Specifically, in a network with N nodes, we guarantee that both exact queries and range queries can be answered in O(log N) steps and also that update operations (to both data and network) have an amortized cost of O(log N). An experimental assessment validates the practicality of our proposal.

/pdf/baton-a-balanced-tree-structure-for-peer-to-peer-networks-2qr77ax50c.pdf

BATON: a balanced tree structure for peer-to-peer networks

We propose a new distributed, fault-tolerant peer-to-peer index structure called the P-tree. P-trees efficiently evaluate range queries in addition to equality queries.

/pdf/querying-peer-to-peer-networks-using-p-trees-1kduskei51.pdf

Querying peer-to-peer networks using P-trees

Resource Description Framework (RDF) was designed with the initial goal of developing metadata for the Internet. While the Internet is a conglomeration of many interconnected networks and computers, most of today's best RDF storage solutions are confined to a single node. Working on a single node has significant scalability issues, especially considering the magnitude of modern day data. In this paper we introduce a scalable RDF data management system that uses Accumulo, a Google Bigtable variant. We introduce storage methods, indexing schemes, and query processing techniques that scale to billions of triples across multiple nodes, while providing fast and easy access to the data through conventional query mechanisms such as SPARQL. Our performance evaluation shows that in most cases, our system outperforms existing distributed RDF solutions, even systems much more complex than ours.

https://www.usna.edu/Users/cs/adina/research/Rya_CloudI2012.pdf

Rya: a scalable RDF triple store for the clouds

This article proposes the image intraclass correlation (I2C2) coefficient as a global measure of reliability for imaging studies. The I2C2 generalizes the classic intraclass correlation (ICC) coefficient to the case when the data of interest are images, thereby providing a measure that is both intuitive and convenient. Drawing a connection with classical measurement error models for replication experiments, the I2C2 can be computed quickly, even in high-dimensional imaging studies. A nonparametric bootstrap procedure is introduced to quantify the variability of the I2C2 estimator. Furthermore, a Monte Carlo permutation is utilized to test reproducibility versus a zero I2C2, representing complete lack of reproducibility. Methodologies are applied to three replication studies arising from different brain imaging modalities and settings: regional analysis of volumes in normalized space imaging for characterizing brain morphology, seed-voxel brain activation maps based on resting-state functional magnetic resonance imaging (fMRI), and fractional anisotropy in an area surrounding the corpus callosum via diffusion tensor imaging. Notably, resting-state fMRI brain activation maps are found to have low reliability, ranging from .2 to .4. Software and data are available to provide easy access to the proposed methods.

/pdf/quantifying-the-reliability-of-image-replication-studies-the-4yhrprgy6s.pdf

Quantifying the reliability of image replication studies: The image intraclass correlation coefficient (I2C2)

Peer-to-peer systems have emerged as a robust, scalable and decentralized way to share and publish data In this paper, we propose P-Ring, a new P2P index structure that supports both equality and range queries P-Ring is fault-tolerant, provides logarithmic search performance even for highly skewed data distributions and efficiently supports large sets of data items per peer We experimentally evaluate P-Ring using both simulations and a real distributed deployment on PlanetLab, and we compare its performance with Skip Graphs, Online Balancing and Chord

https://www.cs.cornell.edu/johannes/papers/2007/sigmod2007-pring.pdf

P-ring: an efficient and robust P2P range index structure

We propose a new distributed, fault-tolerant Peer-to-Peer index structure for resource discovery applications called the P-tree. P-trees efficiently support range queries in addition to equality queries.

/pdf/p-tree-a-p2p-index-for-resource-discovery-applications-5csdofxj1b.pdf

Adina Crainiceanu

Papers

Querying peer-to-peer networks using P-trees

Rya: a scalable RDF triple store for the clouds

Quantifying the reliability of image replication studies: The image intraclass correlation coefficient (I2C2)

P-ring: an efficient and robust P2P range index structure

P-tree: a p2p index for resource discovery applications