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Past Projects

DNS Performance

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 Impact of misconfigurations

DNS hierarchy

During the past twenty years the Domain Name System (DNS) has sustained phenomenal growth while maintaining satisfactory performance. However, the original design focused mainly on system robustness against physical failures, and neglected the impact of operational errors such as misconfigurations. Our recent measurement effort revealed three specific types of misconfigurations in DNS today: lame delegation, diminished server redundancy, and cyclic zone dependency. Zones with configuration errors suffer from reduced availability and increased query delays up to an order of magnitude. Furthermore, while the original DNS design assumed that redundant DNS servers fail independently, our measurements show that operational choices made at individual zones can severely affect the availability of other zones. We found that, left unchecked, DNS configuration errors are widespread, with lame delegation affecting 15% of the DNS zones, diminished server redundancy being even more prevalent, and cyclic dependency appearing in 2% of the zones. We also noted that the degrees of misconfiguration vary from zone to zone, with most popular zones having the lowest percentage of errors. Our results indicate that DNS, as well as any other truly robust large-scale system, must include systematic checking mechanisms to cope with operational errors.

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Using overlay networks to improve VoIP performance

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VoIP is widely used today, given its lower cost to service providers and end users. However, because VoIP calls use UDP, they are affected by packet loss due to congestion and routing protocol reconfigurations. These losses result in lower user-perceived call quality. Even relatively small packet loss (i.e. ~1-2%) can degrade the quality of VoIP calls below what is called PTSN level quality. Moreover, these packet losses can not be repaired by end-to-end retransmissions because interactive VoIP calls have very tight delay budgets (e.g. 100-150 msec one-way delay, a large portion of which is consumed by packetization and compression).

To address the problem of congestive packet loss, we propose an approach that routes VoIP calls through a network of application-level routers. These routers form an overlay network used to forward the callers' traffic. The virtual links between overlay routers implement a limited form of reliability, whereby the receiving router uses NACKs to indicate packet loss, while the application router on the other side of the virtual link retransmits lost packets as long as they do not exhaust their delay budget. We have shown that this limited hop-by-hop retransmission scheme is able to provide PSTN-level quality even under packet loss conditions worse than those reported on the Internet today.

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Landslide Detection

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A landslide occurs when the balance between a hill’s weight and the countering resistance forces is tipped in favor of gravity. While the physics governing the interplay between these competing forces is fairly well understood, prediction of landslides has been hindered thus far by the lack of field measurements over large temporal and spatial scales necessary to capture the inherent heterogeneity in a landslide.

We propose a network of sensor columns deployed at hills with landslide potential with the purpose if detecting the early signals preceding a catastrophic event. Detection is performed through a three-state algorithm: First, sensors collectively detect small movements consistent with the formation of a slip surface separating the sliding part of hill from the static one. Once the sensors agree on the presence of such a surface, they conduct a distributed voting algorithm to separate the subset of sensors that moved from the static ones. In the second phase, moved sensors self-localize through a trilateration mechanism and their displacements are calculated. Finally, the direction of the displacements as well as the locations of the moved nodes are used to estimate the position of the slip surface. This information along with collected soil measurements (e.g. soil pore pressure) are subsequently passed to a Finite Element Model that predicts whether and when a landslide will occur.

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Botnet Tracking

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Botnets are one of the major threats to the Internet today. This project aims to shed light on this phenomenon. Towards this goal, we established a scalable distributed data collection infrastructure to capture and track large collections of Botnets. Currently, our system is tailored to capture Botnets that use IRC to disseminate the Botmaster commands to his Bot armies. Our infrastructure collects Malware using a distributed Honeynet. The collected Malware is then analyzed to discover new IRC Botnets and extract their features to enable infiltration and longitudinal lightweight tracking. For more information, please visit the project's web page (no longer updated).

 

Multimodal Sensor Networks

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Outline

We investigate the benefits that multiple modalities bring to the problems of target and self localization in sensor networks. Specifically,our work focuses on coupling motes equipped with magnetometers with cameras.

We first looked at how feedback from cameras can be used to calibrate the magnetometers. In our model the magnetic field signal strength follows a power law with unknown exponent beta. The goal of the calibration process is to estimate the value of beta. The process works as follows: Motes use trilateration to estimate the position of the target. This information is then passed to the cameras which locate the actual position of the target. We then solve a non-linear optimization problem to minimize the distance between the target's actual location and the location estimated using the magnetometer measurements. Our simulation results show that the estimation process converges in a small number of iterations.

 

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