The Dynamics of Vehicular Networks in Urban Environments

Vehicular Ad hoc NETworks (VANETs) have emerged as a platform to support intelligent inter-vehicle communication and improve traffic safety and performance. The road-constrained, high mobility of vehicles, their unbounded power source, and the emergence of roadside wireless infrastructures make VANETs a challenging research topic. A key to the development of protocols for inter-vehicle communication and services lies in the knowledge of the topological characteristics of the VANET communication graph. This paper explores the dynamics of VANETs in urban environments and investigates the impact of these findings in the design of VANET routing protocols. Using both real and realistic mobility traces, we study the networking shape of VANETs under different transmission and market penetration ranges. Given that a number of RSUs have to be deployed for disseminating information to vehicles in an urban area, we also study their impact on vehicular connectivity. Through extensive simulations we investigate the performance of VANET routing protocols by exploiting the knowledge of VANET graphs analysis.Comment: Revised our testbed with even more realistic mobility traces. Used the location of real Wi-Fi hotspots to simulate RSUs in our study. Used a larger, real mobility trace set, from taxis in Shanghai. Examine the implications of our findings in the design of VANET routing protocols by implementing in ns-3 two routing protocols (GPCR & VADD). Updated the bibliography section with new research work

Self-optimizing block transfer in web service grids

Nowadays, Web Services (WSs) play an increasingly impor-tant role in Web data management solutions, since they offer a practical solution for accessing and manipulating data sources spanning administrative domains. Neverthe-less, they are notoriously slow and transferring large data volumes across WSs becomes the main bottleneck in such WS-based applications. This paper deals with the problem of minimizing at runtime, in a self-managing way, the data transfer cost of a WS encapsulating a data source. To reduce the transfer cost, the data volume is typically divided into blocks. In this case, response time exhibits a quadratic-like, non-linear behavior with regards to the block size; as such, minimizing the transfer cost entails finding the optimum block size. This situation is encountered in several systems

A Grid-Enabled Digital Library System for Natural Disaster Metadata

Abstract. The need to organize and publish metadata about European research results in the field of natural disasters has been met with the help of two innovative technologies: the Open Grid Service Architecture (OGSA) and the Resource Description Framework (RDF). OGSA provides a common platform for sharing distributed metadata securely. RDF facilitates the creation and exchange of metadata. In this paper, we present the design and implementation of a Grid-based digital library for natural-disaster research metadata. We describe the EU-MEDIN RDF schema that we propose to standardize the description of natural-disaster resources, and the gDisDL Grid service-based architecture for storing and querying of RDF metadata in a secure and distributed manner. Finally, we describe a prototype implementation of gDisDL using the Jena RDF Library by HP and the Globus 3 toolkit

Intermediary infrastructures for the World

Intermediaries are software entities, deployed on hosts of the wireline and wireless network, that mediate the interaction between clients and servers of the World Wide Web. In this paper we present a survey of intermediaries, focusing on systems beyond simple caching proxies. We classify different intermediary systems into three categories, based on their functionality and focus: First, we investigate notification intermediaries, which are driven by end-user profiles and operate even in the absence of end-user connection. Then, we study intermediaries developed to support wireless connectivity, mobility, and ubiquity. Finally, we examine intermediary infrastructures designed to extend the support of the core network for the development and deployment of new services. Based on this survey, we propose a detailed taxonomy of intermediaries and identify key features of emerging intermediary infrastructures. Taking into account recent advances and trends in wireless and pervasive Internet technologies, we present a number of research challenges, which need to be addressed in order to integrate intermediary systems in next-generation Internet infrastructures. Ó 2004 Elsevier B.V. All rights reserved

Comparison of tree and straight-line clocking for long systolic arrays

Abstract. A critical problem in building long systolic arrays lies in efficient and reliable synchronization. We address this problem in the context of synchronous systems by introducing probabilistic models for two alternative clock distribution schemes: tree and straight-line clocking. We present analytic bounds for the Probability of Failure and the Mean Time to Failure, and examine the trade-offs between reliability and throughput in both schemes. Our basic conclusion is that as the one-dimensional systolic array gets very long, tree clocking becomes more reliable than straight-line clocking. 1