6 research outputs found
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Stable and Accurate Network Coordinates
Synthetic coordinate systems that mirror latencies between physical hosts have become a part of the toolbox networking researchers would like to use in real deployments. However, the most promising algorithm for building these coordinate systems, Vivaldi, breaks down when run under real world conditions. Previous work on network coordinates has examined their performance in simulation through the use of a latency matrix, which summarizes each link with a single latency. In a deployment, instead of perceiving a single latency for each link, nodes see a stream of distinct observations that may vary by as much as three orders-of-magnitude. With no means to discern an appropriate latency for each link, coordinate systems are prone to high error and instability in live deployments. Two simple enhancements improved Vivaldi’s accuracy by 54% and coordinate stability by 96% when run on a real large-scale network. First, we use a non-linear low pass filter to ascertain a clear underlying signal from each link. These filters primarily improve accuracy. Second, we introduce a distinction between system- and application-level coordinates. We evaluate a set of change-detection heuristics that allow coordinates to evolves at the system-level and only initiate an application-level update after a coordinate has undergone a significant change. These application-level coordinates retain the filter’s high accuracy and dramatically increase coordinate stability.Engineering and Applied Science
Optimization Algorithms for Information Retrieval and Transmission in Distributed Ad Hoc Networks
An ad hoc network is formed by a group of self-configuring nodes, typically
deployed in two or three dimensional spaces, and communicating with each other
through wireless or some other media. The distinct characteristics of ad hoc networks include the lack of pre-designed infrastructure, the natural correlation between
the network topology and geometry, and limited communication and computation
resources. These characteristics introduce new challenges and opportunities for de-
signing ad hoc network applications. This dissertation studies various optimization
problems in ad hoc network information retrieval and transmission.
Information stored in ad hoc networks is naturally associated with its location.
To effectively retrieve such information, we study two fundamental problems, range
search and object locating, from a distance sensitive point of view, where the retrieval
cost depends on the distance between the user and the target information. We develop
a general framework that is applicable to both problems for optimizing the storage
overhead while maintaining the distance sensitive retrieval requirement. In addition,
we derive a lowerbound result for the object locating problem which shows that
logarithmic storage overhead is asymptotically optimal to achieve linear retrieval cost
for growth bounded networks.
Bandwidth is a scarce resource for wireless ad hoc networks, and its proper utilization is crucial to effective information transmission. To avoid conflict of wireless transmissions, links need to be carefully scheduled to satisfy various constraints. In
this part of the study, we first consider an optimization problem of end-to-end on-
demand bandwidth allocation with the single transceiver constraint. We study its
complexity and present a 2-approximation algorithm. We then discuss how to estimate the end-to-end throughput under a widely adopted model for radio signal
interference. A method based on identifying certain clique patterns is proposed and
shown to have good practical performance
Compact Routing on Euclidian Metrics
We consider the problem of designing a compact communication network that supports e#cient routing in an Euclidean plane. Our network design and routing scheme achieves 1+# stretch, logarithmic diameter, and constant out degree. This improves upon the best known result so far that requires a logarithmic out-degree. Furthermore, our scheme is asymptotically optimal in Euclidean metrics whose diameter is polynomial