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With more than 250 million active users [1], Facebook (FB) is currently one of the most important online social networks. Our goal in this paper is to obtain a representative (unbiased) sample of Facebook users by crawling its social graph. In this quest, we consider and implement several candidate techniques. Two approaches that are found to perform well(More)
Our goal in this paper is to develop a practical framework for obtaining a uniform sample of users in an online social network (OSN) by crawling its social graph. Such a sample allows to estimate any user property and some topological properties as well. To this end, first, we consider and compare several candidate crawling techniques. Two approaches that(More)
Our goal in this paper is to develop a practical framework for obtaining a uniform sample of users in an online social network (OSN) by crawling its social graph. Such a sample allows to estimate any user property and some topological properties as well. To this end, first, we consider and compare several candidate crawling techniques. Two approaches that(More)
A key challenge faced by peer-to-peer (P2P) video-ondemand (VoD) systems is their ability, or lack thereof, to provide DVD-like functionality, such as pause, forward and backward seeking (or jumps). Such operations can significantly degrade the performance of a P2P system as arbitrary video segments may need to be served timely on demand. Currently, little(More)
Our objective is to sample the node set of a large unknown graph via crawling, to accurately estimate a given metric of interest. We design a random walk on an appropriately defined weighted graph that achieves high efficiency by preferentially crawling those nodes and edges that convey greater information regarding the target metric. Our approach begins by(More)
With the increasing demand for low-latency applications in the Internet, the slow convergence of the existing routing protocols is a growing concern. A number of IP fast reroute mechanisms have been developed by the IETF to address the issue. The goal of the IPFRR mechanisms is to activate alternate routing paths which avoid micro loops under node or link(More)
Network tomography infers internal network characteristics by sending and collecting probe packets from the network edge. Traditional tomographic techniques for general topologies typically use a mesh of multicast trees and/or unicast paths to cover the entire graph, which is suboptimal from the point of view of bandwidth efciency and estimation accuracy.(More)
State-of-the-art techniques for probability sampling of users of online social networks (OSNs) are based on random walks on a single social relation (typically friendship). While powerful, these methods rely on the social graph being fully connected. Furthermore, the mixing time of the sampling process strongly depends on the characteristics of this graph.(More)
The goal of this paper is to infer features of urban ecology (i.e., social and economic activities, and social interaction) from spatiotemporal cell phone activity data. We present a novel approach that consists of (i) time series decomposition of the aggregate cell phone activity per unit area using spectral methods, (ii) clustering of areal units with(More)