13 research outputs found
Dynamic Monopolies in Colored Tori
The {\em information diffusion} has been modeled as the spread of an
information within a group through a process of social influence, where the
diffusion is driven by the so called {\em influential network}. Such a process,
which has been intensively studied under the name of {\em viral marketing}, has
the goal to select an initial good set of individuals that will promote a new
idea (or message) by spreading the "rumor" within the entire social network
through the word-of-mouth. Several studies used the {\em linear threshold
model} where the group is represented by a graph, nodes have two possible
states (active, non-active), and the threshold triggering the adoption
(activation) of a new idea to a node is given by the number of the active
neighbors.
The problem of detecting in a graph the presence of the minimal number of
nodes that will be able to activate the entire network is called {\em target
set selection} (TSS). In this paper we extend TSS by allowing nodes to have
more than two colors. The multicolored version of the TSS can be described as
follows: let be a torus where every node is assigned a color from a finite
set of colors. At each local time step, each node can recolor itself, depending
on the local configurations, with the color held by the majority of its
neighbors. We study the initial distributions of colors leading the system to a
monochromatic configuration of color , focusing on the minimum number of
initial -colored nodes. We conclude the paper by providing the time
complexity to achieve the monochromatic configuration
Multicolored Dynamos on Toroidal Meshes
Detecting on a graph the presence of the minimum number of nodes (target set)
that will be able to "activate" a prescribed number of vertices in the graph is
called the target set selection problem (TSS) proposed by Kempe, Kleinberg, and
Tardos. In TSS's settings, nodes have two possible states (active or
non-active) and the threshold triggering the activation of a node is given by
the number of its active neighbors. Dealing with fault tolerance in a majority
based system the two possible states are used to denote faulty or non-faulty
nodes, and the threshold is given by the state of the majority of neighbors.
Here, the major effort was in determining the distribution of initial faults
leading the entire system to a faulty behavior. Such an activation pattern,
also known as dynamic monopoly (or shortly dynamo), was introduced by Peleg in
1996. In this paper we extend the TSS problem's settings by representing nodes'
states with a "multicolored" set. The extended version of the problem can be
described as follows: let G be a simple connected graph where every node is
assigned a color from a finite ordered set C = {1, . . ., k} of colors. At each
local time step, each node can recolor itself, depending on the local
configurations, with the color held by the majority of its neighbors. Given G,
we study the initial distributions of colors leading the system to a k
monochromatic configuration in toroidal meshes, focusing on the minimum number
of initial k-colored nodes. We find upper and lower bounds to the size of a
dynamo, and then special classes of dynamos, outlined by means of a new
approach based on recoloring patterns, are characterized
Advanced Transport Protocols for Wireless and Mobile Ad Hoc Networks
This thesis comprises transport protocols in the following different areas of research: Fast Handover allows mobile IP end-devices to roam between wireless access routers without interruptions while communicating to devices in an infrastructure (e.g., in the Internet). This work optimizes the Fast Handover algorithm and evaluates the performance of the transport protocols UDP and TCP during fast handovers via measurements. The following part of the thesis focuses on vehicular ad hoc networks. The thesis designs and evaluates through simulations a point-to-point transport protocol for vehicular ad hoc networks and an algorithm to facilitate the reliable and efficient distribution of information in a geographically scoped target area. Finally, the thesis evaluates the impact of wireless radio fluctuations on the performance of an Ad Hoc Network. Measurements quantify the wireless radio fluctuations. Based on these results, the thesis develops a simple but realistic radio model that evaluates by means of simulations the impact on the performance of an ad hoc network. As a result, the work provides guidelines for future ad hoc protocol design
Mobile Ad-Hoc Networks
Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of-the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: quality-of-service and video communication, routing protocol and cross-layer design. A few interesting problems about security and delay-tolerant networks are also discussed. This book is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks
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A new approach to detecting failures in distributed systems
textFault-tolerant distributed systems often handle failures in two steps: first, detect the failure and, second, take some recovery action. A common approach to detecting failures is end-to-end timeouts, but using timeouts brings problems. First, timeouts are inaccurate: just because a process is unresponsive does not mean that process has failed. Second, choosing a timeout is hard: short timeouts can exacerbate the problem of inaccuracy, and long timeouts can make the system wait unnecessarily. In fact, a good timeout value—one that balances the choice between accuracy and speed—may not even exist, owing to the variance in a system’s end-to-end delays. ƃis dissertation posits a new approach to detecting failures in distributed systems: use information about failures that is local to each component, e.g., the contents of an OS’s process table. We call such information inside information, and use it as the basis in the design and implementation of three failure reporting services for data center applications, which we call Falcon, Albatross, and Pigeon. Falcon deploys a network of software modules to gather inside information in the system, and it guarantees that it never reports a working process as crashed by sometimes terminating unresponsive components. ƃis choice helps applications by making reports of failure reliable, meaning that applications can treat them as ground truth. Unfortunately, Falcon cannot handle network failures because guaranteeing that a process has crashed requires network communication; we address this problem in Albatross and Pigeon. Instead of killing, Albatross blocks suspected processes from using the network, allowing applications to make progress during network partitions. Pigeon renounces interference altogether, and reports inside information to applications directly and with more detail to help applications make better recovery decisions. By using these services, applications can improve their recovery from failures both quantitatively and qualitatively. Quantitatively, these services reduce detection time by one to two orders of magnitude over the end-to-end timeouts commonly used by data center applications, thereby reducing the unavailability caused by failures. Qualitatively, these services provide more specific information about failures, which can reduce the logic required for recovery and can help applications better decide when recovery is not necessary.Computer Science
Detection and Evaluation of Clusters within Sequential Data
Motivated by theoretical advancements in dimensionality reduction techniques
we use a recent model, called Block Markov Chains, to conduct a practical study
of clustering in real-world sequential data. Clustering algorithms for Block
Markov Chains possess theoretical optimality guarantees and can be deployed in
sparse data regimes. Despite these favorable theoretical properties, a thorough
evaluation of these algorithms in realistic settings has been lacking.
We address this issue and investigate the suitability of these clustering
algorithms in exploratory data analysis of real-world sequential data. In
particular, our sequential data is derived from human DNA, written text, animal
movement data and financial markets. In order to evaluate the determined
clusters, and the associated Block Markov Chain model, we further develop a set
of evaluation tools. These tools include benchmarking, spectral noise analysis
and statistical model selection tools. An efficient implementation of the
clustering algorithm and the new evaluation tools is made available together
with this paper.
Practical challenges associated to real-world data are encountered and
discussed. It is ultimately found that the Block Markov Chain model assumption,
together with the tools developed here, can indeed produce meaningful insights
in exploratory data analyses despite the complexity and sparsity of real-world
data.Comment: 37 pages, 12 figure
Code: Version 2.0
Discusses the regulation of cyberspace via code, as well as possible trends to expect in this regulation. Additional topics discussed in this context include intellectual property, privacy, and free speech
Of Cigarettes, High Heels, and Other Interesting Things 3/E
Among species, human beings seem to be a peculiar lot. Why is it, for example, that certain members of the species routinely put their survival at risk by
puffing on a small stick of nicotine? Why is it that some females of the species
make locomotion difficult for themselves by donning high-heel footwear? Are
there hidden or unconscious reasons behind such strange behaviors that seem
to be so utterly counter-instinctual, so to speak?
For no manifest biological reason, humanity has always searched, and continues to search, for a purpose to its life. Is it this search that has led it to engage in such bizarre behaviors as smoking and wearing high heels? And is it
the reason behind humanity’s invention of myths, art, rituals, languages,
mathematics, science, and all the other truly remarkable things that set it
apart from all other species? Clearly, Homo sapiens appears to be unique in the
fact that many of its behaviors are shaped by forces other than the instincts.
The discipline that endeavors to understand these forces is known as semiotics.
Relatively unknown in comparison to, say, philosophy or psychology, semiotics probes the human condition in its own peculiar way, by unraveling the meanings of the signs that undergird not only the wearing of high-heel shoes,
but also the construction of words, paintings, sculptures, and the like