@inproceedings {INPROC-2012-49, author = {Marius Wernke and Frank D{\"u}rr and Kurt Rothermel}, title = {{Efficient Position Sharing for Location Privacy using Binary Space Partitioning}}, booktitle = {Proceedings of the Ninth Annual International Conference on Mobile and Ubiquitous Systems: Computing, Networking and Services (MobiQuitous '12)}, address = {Beijing, People's Republic of China}, publisher = {ICST}, institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany}, pages = {1--12}, type = {Conference Paper}, month = {December}, year = {2012}, keywords = {Position Sharing; Location Privacy; Location Based Applications; Privacy}, language = {English}, cr-category = {C.2.4 Distributed Systems}, ee = {ftp://ftp.informatik.uni-stuttgart.de/pub/library/ncstrl.ustuttgart_fi/INPROC-2012-49/INPROC-2012-49.pdf, http://www.priloc.de}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {Millions of users use location-based applications (LBAs) to share their positions with friends, request information from points of interest finders, or get notifications from event finders, etc. Such LBAs are typically based on location servers (LSs) managing mobile object positions in a scalable fashion. However, storing precise user positions on LSs raises privacy concerns, in particular, if LS providers are non-trusted. To solve this problem, we present PShare-BSP, a novel approach for the secure management of private user positions on non-trusted LSs. PShare-BSP splits up precise user positions into position shares and distributes them to different LSs of different providers. Thus, a compromised provider only reveals user positions with degraded precision. Nevertheless, LBAs can combine several shares from different LSs to increase their precision. PShare-BSP improves on our previous position sharing approaches: It uses a deterministic share generation approach based on binary space partitioning to avoid probabilistic attacks based, for instance, on Monte Carlo simulations. Moreover, it significantly decreases the computational complexity and increases the efficiency by reducing the update costs for succeeding position updates.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2012-49&engl=1} } @inproceedings {INPROC-2012-41, author = {Boris Koldehofe and Frank D{\"u}rr and Muhammad Adnan Tariq and Kurt Rothermel}, title = {{The Power of Software-defined Networking: Line-rate Content-based Routing Using OpenFlow}}, booktitle = {Proceedings of the 7th MW4NG Workshop of the 13th International Middleware Conference}, publisher = {ACM}, institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany}, pages = {1--6}, type = {Workshop Paper}, month = {December}, year = {2012}, doi = {10.1145/2405178.2405181}, keywords = {Content-Based Routing; Publish/Subscribe; Software Defined Networking; SDN; Network Virtualization}, language = {English}, cr-category = {C.2.1 Network Architecture and Design, C.2.4 Distributed Systems, D.2.11 Software Engineering Software Architectures}, ee = {ftp://ftp.informatik.uni-stuttgart.de/pub/library/ncstrl.ustuttgart_fi/INPROC-2012-41/INPROC-2012-41.pdf, http://doi.acm.org/10.1145/2405178.2405181}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {A lot of research effort has been invested to support efficient content-based routing. Nevertheless, practitioners often fall back to far less expressive communication paradigms like multicast groups. The benefits of content-based routing in minimizing bandwidth consumption are often rendered useless by simpler communication paradigms that rely on line-rate processing of data packets at the switches of the network providers. Contrary content-based routing protocols face the inherent overhead in matching the content of events against subscriptions leading to far lower throughput rates and higher end-to-end delays. However, recent trends in networking such as software defined networking in combination with network virtualization have tremendous potential to change the picture. In our opinion this will significantly increase acceptance of sophisticated middleware like content-based routing in the future. To support our claims we outline in this paper a reference architecture that may be used to build middleware for Future Internet applications. Furthermore, we provide a solution for realizing content-based routing at line-rate relying on this reference architecture and illustrate research problems that need to be addressed.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2012-41&engl=1} } @inproceedings {INPROC-2012-40, author = {Stephan Schnitzer and Hugo Miranda and Boris Koldehofe}, title = {{Content Routing Algorithms to Support Publish/Subscribe in Mobile Ad Hoc Networks}}, booktitle = {Proceedings of the 5th IEEE Workshop on Architectures, Services and Applications for the Next Generation Internet}, publisher = {IEEE Computer Society}, institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany}, pages = {1--8}, type = {Workshop Paper}, month = {October}, year = {2012}, keywords = {MANET; TPSR; Ad Hoc; Wireless Routing}, language = {German}, cr-category = {H.3.4 Information Storage and Retrieval Systems and Software, C.2.1 Network Architecture and Design, C.2.2 Network Protocols}, ee = {ftp://ftp.informatik.uni-stuttgart.de/pub/library/ncstrl.ustuttgart_fi/INPROC-2012-40/INPROC-2012-40.pdf}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {Mobile Ad Hoc Networks (MANETs) allow communication between moving nodes without using infrastructure like access points, stationary routers or GPS. This offers new communication opportunities, especially in challenging environments. To communicate in MANETs we often need routing functionality, which usually provides unicast-based best effort packet delivery. Publish/Subscribe (Pub/Sub) is a well known and powerful paradigm that provides higher expressiveness than unicast routing. It decouples senders from receivers and allows information exchange between network nodes that offer certain data (called publishers) and nodes that declare their interest in data of some pattern (called subscribers). Especially in MANET applications, Pub/Sub provides useful functionality to support realistic scenarios and novel applications. This paper proposes a new algorithm called TPSR, tailored to efficiently support Pub/Sub in MANETs. It is based mainly on two principles: i) it uses the dissemination of subscriptions to create source routes; and ii) it uses the signal strength messages are received with, to optimize routes in terms of striking a good balance between long routes and fragile routes. Simulations based on ns-2 demonstrate its performance, in comparison with flooding and unicast-based solutions.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2012-40&engl=1} } @inproceedings {INPROC-2012-34, author = {Klaus Herrmann and Daniel Fischer and Damian Philipp}, title = {{Resource Management for Public Sensing}}, booktitle = {Activity Context Representation: Techniques and Languages}, editor = {Workshop Chair Lokendra Shastri}, address = {Toronto, Canada}, publisher = {Online}, institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany}, pages = {32--39}, type = {Workshop Paper}, month = {July}, year = {2012}, keywords = {Resource Management; Public Sensing; Ad-Hoc Routing}, language = {English}, cr-category = {C.2.4 Distributed Systems}, ee = {ftp://ftp.informatik.uni-stuttgart.de/pub/library/ncstrl.ustuttgart_fi/INPROC-2012-34/INPROC-2012-34.pdf, http://activitycontext.org/wp-content/uploads/2012/07/AAAI12_W12-05_TechnicalReport_ActivityContextRepresentation.pdf}, contact = {klaus.herrmann@ipvs.uni-stuttgart.de}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {Public sensing is a new research area in the fields of wireless sensor networks and mobile computing. It leverages the mobile sensors and system resources readily available in mobile phones to execute sensing tasks. In order to plan, execute and adapt large-scale sensing tasks, applications need to query for the available resources, e.g. the density of certain sensors. We investigate how such information can be provided, and we propose a resource manager for public sensing. Our primary goal is to minimize the energy consumed by the mobile devices to make public sensing feasible without disturbing users. We propose a cluster-based protocol for collecting local views of the resource state using local ad-hoc communication since this is much more energy-efficient than long-range (e.g. cellular) communication. We compare our solution to a standard approach where mobile devices communicate their resource states using the cellular phone network. We show that 65\% of the energy is saved and the communication load on the infrastructure is reduced by 90\% while an average delivery ratio of 93\% is retained.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2012-34&engl=1} } @inproceedings {INPROC-2012-30, author = {Ben W. Carabelli and Andreas Benzing and Georg Seyboth and Rainer Blind and Mathias B{\"u}rger and Frank D{\"u}rr and Boris Koldehofe and Kurt Rothermel and Frank Allg{\"o}wer}, title = {{Exact Convex Formulations of Network-Oriented Optimal Operator Placement}}, booktitle = {Proceedings of the 51st IEEE Conference on Decision and Control (CDC2012)}, publisher = {IEEE}, institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany}, pages = {3777--3782}, type = {Conference Paper}, month = {December}, year = {2012}, doi = {10.1109/CDC.2012.6426790}, keywords = {Optimization; Computer networks; Sensor networks}, language = {English}, cr-category = {G.1.6 Numerical Analysis Optimization}, ee = {ftp://ftp.informatik.uni-stuttgart.de/pub/library/ncstrl.ustuttgart_fi/INPROC-2012-30/INPROC-2012-30.pdf, http://dx.doi.org/10.1109/CDC.2012.6426790}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {Data processing tasks are increasingly spread across the internet to account for the spatially distributed nature of many data sources. In order to use network resources efficiently, subtasks need to be distributed in the network so data can be filtered close to the data sources. Previous approaches to this operator placement problem relied on various heuristics to constrain the complexity of the problem. In this paper, we propose two generic integer constrained problem formulations: a topology aware version which provides a placement including the specific network links as well as an end-to-end delay aware version which relies on the routing capabilities of the network. A linear programming relaxation for both versions is provided which allows exact and efficient solution using common solvers.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2012-30&engl=1} } @inproceedings {INPROC-2012-26, author = {Patrick Baier and Frank D{\"u}rr and Kurt Rothermel}, title = {{TOMP: Opportunistic Traffic Offloading Using Movement Predictions}}, booktitle = {Proceedings of the 37th IEEE Conference on Local Computer Networks (LCN)}, address = {Clearwater}, publisher = {IEEE Computer Society}, institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany}, pages = {1--8}, type = {Conference Paper}, month = {October}, year = {2012}, language = {English}, cr-category = {C.2 Computer-Communication Networks}, ee = {ftp://ftp.informatik.uni-stuttgart.de/pub/library/ncstrl.ustuttgart_fi/INPROC-2012-26/INPROC-2012-26.pdf, http://www.comnsense.de}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {Recent forecasts predict that the amount of cellular data traffic will significantly increase within the next few years. The reason for this trend is on the one hand the high growth rate of mobile Internet users and on the other hand the growing popularity of high bandwidth streaming applications. Given the fact that cellular networks (e.g. UMTS) have only limited capacity, the existing network infrastructure will soon reach its limits. As a result, the concept of traffic offloading attracts more and more attention in research since it aims at the reduction of cellular traffic by shifting it to local-area networks like Wifi. Within the last few years, some first approaches for automatically offloading cellular traffic were proposed. These approaches either assume the wide availability of publicly accessible Wifi networks or knowledge about social relations of mobile users. However, these assumptions are usually not fulfilled. To face this issue, we developed the TOMP system. TOMP implements a system to distribute data from the infrastructure to a set of mobile devices by partly shifting traffic from the cellular network to the level of inter-device communication. In contrast to the prevailing approaches, TOMP does not rely on open Wifi networks and only uses information about the position and speed of mobile device. By using predictions about the future movement of mobile users, TOMP determines devices that are most suitable targets for traffic offloading. In this paper we show by simulation that TOMP can save up to 40\% of cellular messages in comparison to a typical cellular network.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2012-26&engl=1} } @inproceedings {INPROC-2012-20, author = {Boris Koldehofe and Beate Ottenw{\"a}lder and Kurt Rothermel and Umakishore Ramachandran}, title = {{Moving Range Queries in Distributed Complex Event Processing}}, booktitle = {Proceedings of the 6th ACM International Conference on Distributed Event-Based Systems (DEBS).}, address = {Berlin}, publisher = {ACM}, institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany}, pages = {201--212}, type = {Conference Paper}, month = {July}, year = {2012}, doi = {10.1145/2335484.2335507}, keywords = {Complex Event Processing; Event-based systems; Moving range queries}, language = {English}, cr-category = {C.2.4 Distributed Systems}, ee = {ftp://ftp.informatik.uni-stuttgart.de/pub/library/ncstrl.ustuttgart_fi/INPROC-2012-20/INPROC-2012-20.pdf, http://doi.acm.org/10.1145/2335484.2335507}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {Up to now correlations in complex event processing (CEP) systems are detected by a well defined set of operators whose configuration is determined ahead of deployment time. Although CEP operators involve location specific attributes, state of the art systems are heavily constraint in detecting situations where the interest in a situation changes dependent on the consumer's location, e.g., with the movement of mobile devices. This paper adopts the concept of range queries to CEP systems. We propose a mobility-aware event delivery semantic and present a corresponding execution model that accounts for mobility driven selection of primary event streams to the CEP system. By utilizing the properties of this execution model we derive an algorithm that establishes low cost and coordinated reconfiguration of CEP operators in a distributed system. The algorithm minimizes the amount of information that needs to be streamed between operators and avoids additional delays as a result of a reconfiguration of CEP operators. We present an analysis of the algorithm's properties and evaluate the efficiency of the proposed reconfiguration algorithm.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2012-20&engl=1} } @inproceedings {INPROC-2012-17, author = {Muhammad Adnan Tariq and Boris Koldehofe and Gerald. G Koch and Kurt Rothermel}, title = {{Distributed spectral cluster management: A method for building dynamic publish/subscribe systems}}, booktitle = {Proceedings of the 6th ACM International Conference on Distributed Event-Based Systems (DEBS)}, address = {Berlin, Germany}, publisher = {ACM}, institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany}, pages = {213--224}, type = {Conference Paper}, month = {July}, year = {2012}, doi = {10.1145/2335484.2335508}, keywords = {Content-based; Publish/Subscribe; Broker-less; Spectral clustering; P2P; Event-based}, language = {English}, cr-category = {C.2.4 Distributed Systems}, ee = {ftp://ftp.informatik.uni-stuttgart.de/pub/library/ncstrl.ustuttgart_fi/INPROC-2012-17/INPROC-2012-17.pdf, http://doi.acm.org/10.1145/2335484.2335508}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {In recent years peer-to-peer (P2P) networking has gained high popularity for large-scale content distribution. Prominent systems expect a large user base with rather diversified demands. Yet it is highly challenging to achieve scalability without sacrificing the expressiveness of queries in such systems. This paper proposes distributed spectral cluster management, an approach which adapts the techniques from spectral graph theory to work in distributed settings. The proposed approach is applied to content-based publish/subscribe to i) significantly reduce the cost for event dissemination by clustering subscribers exploiting the similarity of events, ii) preserve the expressiveness of the subscription language, and iii) perform robustly in the presence of workload variations. The evaluations analyze the accuracy of the proposed distributed spectral mechanisms and show their effectiveness to significantly reduce the efforts to disseminate events under many practical workloads.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2012-17&engl=1} } @inproceedings {INPROC-2012-13, author = {Stefan F{\"o}ll and Florian Berg and Klaus Herrmann and Kurt Rothermel}, title = {{A Predictive Protocol for Mobile Context Updates with Hard Energy Constraints}}, booktitle = {Proceedings of the 13th International Conference on Mobile Data Management (MDM 2012)}, address = {Bengaluru, India}, publisher = {IEEE Computer Society}, institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany}, pages = {125--130}, type = {Conference Paper}, month = {July}, year = {2012}, doi = {10.1109/MDM.2012.11}, keywords = {mobile users; update protocols; discrete context; energy efficiency; context accuracy; contrained optimization problem, Markov decision process}, language = {English}, cr-category = {C.2.1 Network Architecture and Design, C.2.4 Distributed Systems}, ee = {http://dx.doi.org/10.1109/MDM.2012.11}, contact = {stefan.foell@ipvs.uni-stuttgart.de}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {As mobile devices have become powerful sensor platforms, new applications have emerged which continuously stream mobile user context (location, activities, etc.). However, energy is a limited resource on battery-equipped mobile devices. Especially frequent transmissions of context updates over energy-expensive wireless channels drain the battery of mobile devices in an uncontrolled manner. It is a fundamental algorithmic challenge to design protocols such that users can control the energy consumption on mobile devices while, at the same time, optimizing the quality of mobile applications. To address this trade-off in the area of context update protocols, we propose a novel protocol that maximizes the context accuracy perceived by a remote consumer while guaranteeing that the consumed energy stays under a given limit. Our update protocol exploits predictions about a user's future behaviour to give priority to the most effective context updates. In our evaluation, we apply our predictive update protocol to a real-world trace of user context and show that the context accuracy is significantly increased compared to an update protocol which operates without predictions under the same energy budget.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2012-13&engl=1} } @inproceedings {INPROC-2012-07, author = {Pavel Skvortsov and Frank D{\"u}rr and Kurt Rothermel}, title = {{Map-aware Position Sharing for Location Privacy in Non-trusted Systems}}, booktitle = {Proceedings of the 10th International Conference on Pervasive Computing (Pervasive 2012)}, editor = {Lecture Notes in Computer Science}, address = {Newcastle, UK}, publisher = {Springer-Verlag}, institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany}, pages = {388--405}, type = {Conference Paper}, month = {June}, year = {2012}, keywords = {location-based service; privacy; obfuscation; sharing; map-awareness}, language = {English}, cr-category = {C.2.4 Distributed Systems, H.3.5 Online Information Services}, ee = {ftp://ftp.informatik.uni-stuttgart.de/pub/library/ncstrl.ustuttgart_fi/INPROC-2012-07/INPROC-2012-07.pdf, http://www.springerlink.com/content/w682352838637308/, http://www.priloc.de}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {Many current location-based applications (LBA) such as friend finder services use information about the positions of mobile users. So-called location services (LSs) have been proposed to manage these mobile user positions efficiently. However, managing user positions raises privacy issues, in particular, if the providers of LSs are only partially trusted. Therefore, the concept of private position sharing for partially trusted systems was proposed in the literature. The basic idea of position sharing is to split the precise user position into a set of position shares of well-defined limited precision and distribute these shares among LSs of different providers. The main contributions of this paper are two extended position sharing approaches that improve the basic position sharing approach in two ways: Firstly, we reduce the predictability of share generation that allows an attacker to gain further information from a sub-set of shares to further increase the position precision. Secondly, we present a position sharing algorithm for constrained movement scenarios whereas the existing approach was tailored to open space environments. However, open space approaches are vulnerable to map-based attacks. Therefore, we present a share generation algorithm that takes map knowledge into account.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2012-07&engl=1} } @inproceedings {INPROC-2012-06, author = {Marius Wernke and Frank D{\"u}rr and Kurt Rothermel}, title = {{PShare: Position Sharing for Location Privacy based on Multi-Secret Sharing}}, booktitle = {Proceedings of the 10th IEEE International Conference on Pervasive Computing and Communications (PerCom 2012)}, address = {Lugano, Switzerland}, publisher = {IEEE Computer Society}, institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany}, pages = {153--161}, type = {Conference Paper}, month = {March}, year = {2012}, keywords = {Location-based applications; privacy; position sharing; location management}, language = {English}, cr-category = {C.2.4 Distributed Systems, H.3.5 Online Information Services}, ee = {ftp://ftp.informatik.uni-stuttgart.de/pub/library/ncstrl.ustuttgart_fi/INPROC-2012-06/INPROC-2012-06.pdf, http://www.priloc.de}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {Location-based applications such as Facebook Places, Foursquare, or Loopt attract millions of users by implementing point of interest finders, friend finders, geosocial networking, etc. Typically, these applications act as clients to a location service such as Google Latitude or Yahoo Fire Eagle, which manage mobile object positions and ensure the scalability to provide various clients with mobile object positions. However, exposing precise user positions raises user privacy concerns, especially if location service providers are not fully trusted, and private position information could be lost, leaked, stolen, etc. To enable the secure management of private user positions on non-trusted location servers (LSs), we present novel position sharing approaches based on the concept of multi-secret sharing. Our approaches split up a precise user position into position shares, which are distributed to different LSs of different providers such that a compromised provider only reveals user positions with degraded precision. On the other hand, clients can combine several shares queried from different LSs to increase their provided precision without the need to store precise information at a single LS. We propose two position sharing approaches: PShare-SLM is the first position sharing approach presented so far for symbolic location models. For geometric location models, we present PShare-GLM, which improves existing geometric position sharing approaches[DSR11] by considering continuous position updates and by increasing the robustness against various attacks.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2012-06&engl=1} } @inproceedings {INPROC-2012-03, author = {Stefan F{\"o}ll and Klaus Herrmann and Kurt Rothermel}, title = {{Energy-efficient Update Protocols for Mobile User Context}}, booktitle = {Proceedings of the 26th IEEE International Conference on Advanced Information Networking and Applications (AINA-2012)}, address = {Fukoka, Japan}, publisher = {IEEE}, institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany}, pages = {1--8}, type = {Conference Paper}, month = {March}, year = {2012}, keywords = {mobile users; update protocols; discrete context; energy efficiency; context accuracy}, language = {English}, cr-category = {C.2.2 Network Protocols, C.2.4 Distributed Systems}, contact = {stefan.foell@ipvs.uni-stuttgart.de}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {Nowadays, rich information about the context of mobile users is directly captured on the users' mobile phones in real-time. Especially, discrete context (e.g., the user's activity) has become highly interesting for many applications since it provides an intuitive and human-understandable description of the user's current state. However, while sensing is executed locally on the mobile device, changes of user context need to be distributed from the device to a large number of interested consumers, e.g., the friends in an online social network. This produces a large overhead for the continuous transmission of context updates and represents a serious challenge for the limited energy budget of battery-equipped mobile devices. In this paper, we propose different strategies for energy-efficient context updates. We present a number of update protocols that are characterized by an inherent trade-off between quality of context and message overhead. To this end, we investigate update criteria that allow consumers of context information to express their tolerance towards the inaccurateness of received context, and we propose update protocols that exploit this tolerance to save updates and, thus, energy. In our evaluation we analyse our update protocols based on a real-world trace of user activities and show that applications can save more than 80\% of the messages when tolerating a minor degradation of the context quality only.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2012-03&engl=1} } @inproceedings {INPROC-2012-01, author = {Patrick Baier and Frank D{\"u}rr and Kurt Rothermel}, title = {{PSense: Reducing Energy Consumption in Public Sensing Systems}}, booktitle = {Proceedings of the 26th IEEE International Conference on Advanced Information Networking and Applications (AINA-2012)}, publisher = {IEEE}, institution = {University of Stuttgart, Faculty of Computer Science, Electrical Engineering, and Information Technology, Germany}, pages = {136--143}, type = {Conference Paper}, month = {March}, year = {2012}, doi = {10.1109/AINA.2012.33}, keywords = {ad-hoc; mobile; public sensing}, language = {English}, cr-category = {C.2 Computer-Communication Networks}, ee = {ftp://ftp.informatik.uni-stuttgart.de/pub/library/ncstrl.ustuttgart_fi/INPROC-2012-01/INPROC-2012-01.pdf, http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=6184863&isnumber=6184848, http://www.comnsense.de}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {Utilizing peoples' mobile devices for gathering sensor data has attracted a lot of attention within the last few years. As a result, a great variety of systems for sensing environmental phenomena like temperature or noise have been proposed. However, most of these systems do not take into account that mobile devices have only limited energy resources. For instance, an often assumed prerequisite is that mobile devices are always aware of their position. Given the fact that a position fix is a very energy consuming operation, continuous positioning would quickly drain a device's battery. Since the owners of the mobile devices will not tolerate a significant reduction of the devices' battery lifetime, such an approach is not suitable. To address this issue we present PSense, a flexible system for efficiently gathering sensor data with mobile devices. By avoiding unnecessary position fixes, PSense reduces the energy consumption of mobile devices by up to 70\% compared to existing mobile sensing approaches. This is achieved by introducing an adaptive positioning mechanism and by utilizing energy efficient short-range communication to exchange position related information.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=INPROC-2012-01&engl=1} } @article {ART-2012-21, author = {Ralph Lange}, title = {{Scalable Management of Trajectories and Context Model Descriptions}}, journal = {PIK -- Praxis der Informationsverarbeitung und Kommunikation}, publisher = {De Gruyter}, volume = {35}, number = {4}, pages = {281--287}, type = {Article in Journal}, month = {November}, year = {2012}, doi = {10.1515/pik-2012-0041}, isbn = {ISSN 1865-8342}, keywords = {moving objects database; trajectory tracking; spatio-temporal indexing; heterogeneous information systems; defined classes}, language = {English}, cr-category = {H.2.5 Heterogeneous Databases, H.2.8 Database Applications, H.3.3 Information Search and Retrieval}, ee = {ftp://ftp.informatik.uni-stuttgart.de/pub/library/ncstrl.ustuttgart_fi/ART-2012-21/ART-2012-21.pdf}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {The ongoing proliferation of sensing technologies constitutes a huge potential for context-aware computing. It allows selecting relevant information about our physical environment from different sources and providers all over the globe. A fundamental challenge is how to provide efficient access to these immense amounts of distributed dynamic context information - particularly due to the mobility of devices and other entities. To enable such access to current and past position information about moving objects, we propose a family of protocols (CDR, GRTS) for efficiently tracking a moving object's trajectory at some remote database in real-time as well as a distributed indexing scheme (DTI) for optimized access to trajectory data that is partitioned in space to multiple database servers. For discovering context information that is relevant for the situation of an application, we propose a powerful formalism for describing context models in a concise manner and a tailored multidimensional data structure (SDC-Tree) for retrieving relevant context models out of potentially millions of descriptions.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=ART-2012-21&engl=1} } @article {ART-2012-18, author = {Kurt Rothermel and Stephan Schnitzer and Ralph Lange and Frank D{\"u}rr and Tobias Farrell}, title = {{Context-aware and quality-aware algorithms for efficient mobile object management}}, journal = {Pervasive and Mobile Computing}, publisher = {Elsevier}, volume = {8}, number = {1}, pages = {131--146}, type = {Article in Journal}, month = {February}, year = {2012}, doi = {10.1016/j.pmcj.2011.04.009}, issn = {1574-1192}, keywords = {context-awareness; location management; mobile object tracking; range queries; efficiency}, language = {English}, cr-category = {C.2 Computer-Communication Networks, H.2.8 Database Applications}, ee = {http://dx.doi.org/10.1016/j.pmcj.2011.04.009}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {The management of positions of mobile objects is an essential prerequisite for many context-aware systems such as advanced traffic management systems or personal assistance systems. In this paper, we present two approaches for the scalable tracking of mobile object trajectories and the efficient processing of continuous spatial range queries, respectively. We show in detail how both approaches utilize the basic concepts of accuracy relaxation and utilization of context information, such as movement predictions, to minimize the number of position updates, the size of trajectory data, and the number of energy-consuming position sensing operations.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=ART-2012-18&engl=1} } @article {ART-2012-17, author = {Umakishore Ramachandran and Kirak Hong and Liviu Iftode and Ramesh Jain and Rajnish Kumar and Kurt Rothermel and Junsuk Shin and Raghupathy Sivakumar}, title = {{Large-Scale Situation Awareness With Camera Networks and Multimodal Sensing}}, journal = {Proceedings of the IEEE}, publisher = {IEEE}, volume = {100}, number = {4}, pages = {878--892}, type = {Article in Journal}, month = {April}, year = {2012}, issn = {0018-9219}, doi = {10.1109/JPROC.2011.2182093}, keywords = {Cameras; Computer vision; Intelligent sensors; Large-scale systems; Real time systems; Resource management; Surveillance; Target tracking; Video recording; cameras; image sensors; multimedia communication; ubiquitous computing; video surveillance; Moore law; data-intensive nature; disaster recovery; emergency response; functional situation awareness system; health care; ill-defined research area; large-scale camera network deployment; large-scale reliable system; large-scale situation awareness; media-rich sensor-based application; multimedia algorithm; multimodal sensing; real-time analysis; resource requirement; sensing data; Large-scale distributed systems; programing model; resource management; scalability; situation awareness; video-based surveillance}, language = {German}, cr-category = {C.2 Computer-Communication Networks, I.4 Image Processing and Computer Vision, D.1 Programming Techniques}, ee = {http://dx.doi.org/10.1109/JPROC.2011.2182093}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {Sensors of various modalities and capabilities, especially cameras, have become ubiquitous in our environment. Their intended use is wide ranging and encompasses surveillance, transportation, entertainment, education, healthcare, emergency response, disaster recovery, and the like. Technological advances and the low cost of such sensors enable deployment of large-scale camera networks in large metropolises such as London and New York. Multimedia algorithms for analyzing and drawing inferences from video and audio have also matured tremendously in recent times. Despite all these advances, large-scale reliable systems for media-rich sensor-based applications, often classified as situation-awareness applications, are yet to become commonplace. Why is that? There are several forces at work here. First, the system abstractions are just not at the right level for quickly prototyping such applications on a large scale. Second, while Moore's law has held true for predicting the growth of processing power, the volume of data that applications are called upon to handle is growing similarly, if not faster. Enormous amount of sensing data is continually generated for real-time analysis in such applications. Further, due to the very nature of the application domain, there are dynamic and demanding resource requirements for such analyses. The lack of right set of abstractions for programing such applications coupled with their data-intensive nature have hitherto made realizing reliable large-scale situation-awareness applications difficult. Incidentally, situation awareness is a very popular but ill-defined research area that has attracted researchers from many different fields. In this paper, we adopt a strong systems perspective and consider the components that are essential in realizing a fully functional situation-awareness system.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=ART-2012-17&engl=1} } @article {ART-2012-04, author = {Andreas Grau and Klaus Herrmann and Kurt Rothermel}, title = {{Scalable Network Emulation - The NET Approach}}, journal = {Journal of Communications - Special Issue: Advances in Communications and Networking - II}, publisher = {Academy Publisher}, volume = {7}, number = {1}, pages = {3--16}, type = {Article in Journal}, month = {January}, year = {2012}, issn = {1796-2021}, doi = {10.4304/jcm.7.1.3-16}, keywords = {Scalable Network Emulation; Placement; Migration; Node Virtualization; Virtual Time}, language = {English}, cr-category = {C.2.4 Distributed Systems}, department = {University of Stuttgart, Institute of Parallel and Distributed Systems, Distributed Systems}, abstract = {Network emulation is an efficient method for evaluating distributed applications and communication protocols bycombining the benefits of real world experiments and networksimulation. The process of network emulation involves the executionof connected virtual nodes running the software under test ina controlled environment. Our Network Emulation Testbed (NET) achieves high scalability by combining efficient node virtualization and adaptive virtual time. In this paper, we provide an overview of our system. First, we introduce our efficient emulation architecture. Second, we present our approaches (NETplace and NETbalance) to minimize the runtime of the network experiments. The idea of NETplace is to minimize the load of the testbed by calculating an initial placement of virtual nodes onto the testbed nodes. During the runtime of the experiment NETbalance adapts this placement to changed resource requirements of the software under test. Finally, we introduce NETcaptain, a graphical user interface to setup, control and visualize network experiments.}, url = {http://www2.informatik.uni-stuttgart.de/cgi-bin/NCSTRL/NCSTRL_view.pl?id=ART-2012-04&engl=1} }