TrafficView: Towards a Scalable Traffic Monitoring System

Vehicles are part of people's life in modern society, into which more and more high-tech devices are integrated, and a common platform for inter-vehicle communication is necessary to realize an intelligent transportation system supporting safe driving, dynamic route scheduling, emergency message dissemination, and traffic condition monitoring. TrafficView, which is a part of the e-Road project, defines a framework to disseminate and gather information about the vehicles on the road. Using such a system will provide a vehicle driver with road traffic information, which helps driving in situations as foggy weather, or finding an optimal route in a trip several miles long. This paper describes the basic design of TrafficView and different algorithms used in the system. (UMIACS-TR-2003-98

Encryption Servers: A scalable distributed method for Internet security

A model of IP security based on software encryption has been implemented. The implemen-tation was done on Encryption servers, that support encryption and authentication of forwarded IP packets and function as secure gateways to the Internet. A destination based security pol-icy was supported. The feasibility and performance of the implementation on Linux operating system was experimentally validated using a number of system performance measurements. A system call interface was provided for easy access to the encryption facilities and a few popu-lar encryption methods were implemented in software to provide flexible, extensible and cost effective secure communication. Variable key lifetime is used to support a constant level of security and performance for a wide range of network bandwidths. Authentication of keys is done by a voting based protocol that avoids the use of a single trusted third party. The auto-mated propagation of public keys and secure destinations is implemented as an autonomous key exchange protocol. ii Acknowledgements I am thankful and feel a deep sense of gratitude towards my professor, Liviu Iftode, for his con

Improving performance, privacy and relevance of location-based services for mobile users

Location-based services are becoming increasingly popular due to the ubiquity of smartphones and the emergence of vehicular computing applications. Mobile clients have traditionally been consumers of location-based services, but various social applications have recently demonstrated that mobile clients can also be producers of location-based data. Our thesis is that the quality of the location-based services critically depends on the performance of the service, the privacy assurances offered to the clients, and the quality of the data provided by the service. In this dissertation, we propose three contributions addressing key aspects of these challenges: network performance, location privacy for the mobile clients, and relevance of data provided by the service. With respect to the wireless network performance for location-based services, we present Context-Aware Rate Selection (CARS), a rate adaptation algorithm that makes use of knowledge of speed and distance between communicating nodes to choose the optimum transmission rate. Our experimental evaluation in real outdoor vehicular environments shows that CARS adapts to changing link conditions at high vehicular speeds significantly faster than existing rate-adaptation algorithms. With respect to the client location privacy, we present SybilQuery, a fully decentralized and autonomous k-anonymity-based scheme that generates synthetic queries that resemble a real client query. Our experiments on real mobility traces of approximately 500 cabs in the San Francisco Bay area show that SybilQuery can efficiently generate synthetic queries and that these queries are indistinguishable from real queries. Finally, with respect to improving the relevance of location-based data, we present SocialTelescope, a novel location-based service that leverages user interactions in mobile social networks to infer people's preference for places. Our results evaluating the coverage and relevance of our system in comparison to current state-of-the-art approaches show that our approach returns results that are at least as relevant as those returned by current approaches, at a substantially lower cost. The main conclusion of this dissertation is that location-based services can become truly ubiquitous services by providing mobile clients with good network performance, privacy guarantees, as well as relevant results.Ph. D.Includes bibliographical referencesby Pravin Shanka

Improving the Performance of Reliable Transport Protocols in Mobile Computing Environments

We explore the performance of reliable data communication in mobile computing environments. Motion across wireless cell boundaries causes increased delays and packet losses while the network learns how to route data to a host's new location. Reliable transport protocols like TCP interpret these delays and losses as signs of network congestion. They consequently throttle their transmissions, further degrading performance. We quantify this degradation through measurements of protocol behavior in a wireless networking testbed. We show how current TCP implementations introduce unacceptably long pauses in communication during cellular handoffs (800 milliseconds and longer), and propose an end-to-end fast retransmission scheme that can reduce these pauses to levels more suitable for human interaction (200 milliseconds). Our work makes clear the need for reliable transport protocols to differentiate between motion-related and congestion-related packet losses, and suggests how to adapt these p..