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ItemWhat Where Wi: an Analysis of Millions of Wi-Fi Access Points(Georgia Institute of Technology, 2006) Jones, R. Kipp ; Liu, LingWith the growing demand for wireless Internet access and increasing maturity of IEEE 802.11 technologies, wireless networks have sprung up by the millions throughout the world as a popular means for Internet access at homes, in offices and in public areas, such as airports, cafés and coffee shops. An increasingly popular use of IEEE 802.11 networking equipment is to provide wireless "hotspots" as the wireless access points to the Internet. These wireless access points, commonly referred to as WAPs or simply APs, are installed and managed by individuals and businesses in an unregulated manner ^Ö allowing anyone to install and operate one of these radio devices using unlicensed radio spectrum. This has allowed literally millions of these APs to become available and ^Ñvisible^Ò to any interested party who happens to be within range of the radio waves emitted from the device. As the density of these APs increases, these ^Ñbeacons^Ò can be put into multiple uses. From home networking to wireless positioning to mesh networks, there are more alternative ways for connecting wirelessly as newer, longer-range technologies come to market. This paper reports an initial study that examines a database of over 5 million wireless access points collected through wardriving by Skyhook Wireless. By performing the analytical study of this data and the information revealed by this data, including the default naming behavior, movement of access points over time, and density of access points, we found that the AP data, coupled with location information, can provide a fertile ground for understanding the "What, Where and Why" of Wi-Fi access points. More importantly, the analysis and mining of this vast and growing collection of AP data can yield important technological, social and economical results
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ItemLIRA: Lightweight, Region-aware Load Shedding in Mobile CQ Systems(Georgia Institute of Technology, 2006) Gedik, Bugra ; Liu, Ling ; Wu, Kun-Lung ; Yu, Philip S.Position updates and query re-evaluations are two predominant, costly components of processing location-based, continual queries (CQs) in mobile systems. To obtain high-quality query results, the query processor usually demands receiving frequent position updates from the mobile nodes. However, processing frequent updates oftentimes causes the query processor to become overloaded, under which updates must be dropped randomly, bringing down the quality of query results, negating the benefits of frequent position updates. In this paper, we develop LIRA − a lightweight, region-aware load-shedding technique for preventively reducing the position-update load of a query processor, while maintaining high-quality query results. Instead of having to receive too many updates and then randomly drop some of them, LIRA uses a region-aware partitioning mechanism to identify the most beneficial shedding regions to cut down the position updates sent by the mobile nodes within those regions. Based on the number of mobile nodes and queries in a region, LIRA judiciously applies different amounts of update reduction for different regions, maintaining better overall accuracy of query results. Experimental results show that LIRA is vastly superior to random update dropping and clearly outperforms other alternatives that do not possess full-scale, region-aware load-shedding capabilities. Moreover, due to its lightweight nature, LIRA introduces very little overhead.
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ItemProcess Mining, Discovery, and Integration Using Distance Measures(Georgia Institute of Technology, 2006) Bae, Joonsoo ; Caverlee, James ; Liu, Ling ; Rouse, William B.Business processes continue to play an important role in today's service-oriented enterprise computing systems. Mining, discovering, and integrating process-oriented services has attracted growing attention in the recent year. In this paper we present a quantitative approach to modeling and capturing the similarity and dissimilarity between different workflow designs. Concretely, we introduce a graph-based distance measure and a framework for utilizing this distance measure to mine the process repository and discover workflow designs that are similar to a given design pattern or to produce one integrated workflow design by merging two or more business workflows of similar designs. We derive the similarity measures by analyzing the workflow dependency graphs of the participating workflow processes. Such an analysis is conducted in two phases. We first convert each workflow dependency graph into a normalized process network matrix. Then we calculate the metric space distance between the normalized matrices. This distance measure can be used as a quantitative and qualitative tool in process mining, process merging, and process clustering, and ultimately it can reduce or minimize the costs involved in design, analysis, and evolution of workflow systems.
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ItemScalable Access Control in Content-Based Publish-Subscribe Systems(Georgia Institute of Technology, 2006) Srivatsa, Mudhakar ; Liu, LingContent-based publish-subscribe (pub-sub) systems are an emerging paradigm for building a large number of distributed systems. Access control in a pub-sub system refers to secure distribution of events to clients subscribing to those events without revealing its secret attributes to the unauthorized subscribers. To provide confidentiality guarantees the secret attributes in an event is encrypted so that only authorized subscribers can read them. However, in a content-based pub-sub system, every event can potentially have a different set of authorized subscribers. In the worst case, for NS subscribers, there are 2^NS subgroups, and each event can potentially go to a different subgroup. Hence, efficient key management is a big challenge for implementing access control in pub-sub systems. In this paper, we describe efficient and scalable key management algorithms for securely implementing access control rules in pub-sub systems. We ensure that the key management cost is linear in the number of subscriptions and completely independent of the number of subscribers NS. We present a concrete implementation of our proposal on an operational pub-sub system. An experimental evaluation of our prototype shows that our proposal meets the security requirements while maintaining the scalability and performance of the pub-sub system.