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Showing papers by "Hannes Hartenstein published in 2006"


Proceedings ArticleDOI
01 Jan 2006
TL;DR: A fully distributed and localized algorithm called D-FPAV (distributed fair power adjustment for vehicular networks) for adaptive transmit power adjustment which is formally proven to achieve max-min fairness is proposed.
Abstract: Improving the safety of drivers and passengers by wirelessly exchanging information between vehicles represents a major driving force for the design of vehicular ad hoc networks. In a heavy loaded 802.11-based network, however, safety-related packets might collide frequently and cannot be decoded by a receiver, thus they might not be effective in increasing the safety level on the roads. In this paper, we propose to use transmit power control in order to reduce packet collisions, while taking into account the major design goal of vehicular ad hoc networks, i.e. increasing safety. While previous work has addressed the issue of power control primarily for optimizing network capacity and/or connectivity, the optimization criterion for improving safety has to be built upon the concept of fairness: a higher transmit power of a sender should not be selected at the expense of preventing other vehicles to send/receive their required amount of safety information. In this paper, we propose a fully distributed and localized algorithm called D-FPAV (distributed fair power adjustment for vehicular networks) for adaptive transmit power adjustment which is formally proven to achieve max-min fairness. Furthermore, we investigate the effectiveness and robustness of D-FPAV through extensive simulations based on a realistic highway scenario and different radio propagation models

209 citations


Proceedings ArticleDOI
20 Apr 2006
TL;DR: This work proposes an identity registration procedure called self-registration that makes use of the inherent distribution mechanisms of a P2P network, as a starting point for a quantitative analysis of time-stability of P 2P networks under Sybil attacks.
Abstract: The robustness of peer-to-peer (P2P) networks, in particular of DHT-based overlay networks, suffers significantly when a Sybil attack is performed. We tackle the issue of Sybil attacks from two sides. First, we clarify, analyze, and classify the P2P identifier assignment process. By clearly separating network participants from network nodes, two challenges of P2P networks under a Sybil attack become obvious: i) stability over time, and ii) identity differentiation. Second, as a starting point for a quantitative analysis of time-stability of P2P networks under Sybil attacks and under some assumptions with respect to identity differentiation, we propose an identity registration procedure called self-registration that makes use of the inherent distribution mechanisms of a P2P network.

144 citations


Proceedings ArticleDOI
07 Oct 2006
TL;DR: In order to understand the effects of different radio propagation environments on packet level incoordination, a detailed simulation study is provided measuring six transmission success/failure categories and five performance metrics.
Abstract: In wireless one-hop broadcast communications, each node broadcasts messages to inform all neighbors within an intended communication range. Clearly, the packet transmission of the various nodes might interfere with each other due to the overlapping communication ranges. IEEE 802.11 Distributed Coordination Function (DCF) provides some basic mechanisms for coordination of these transmissions. However, due to its distributed nature, DCF suffers from coordination failures, e.g., due to the very well-known hidden terminal problem. When considering realistic radio propagation phenomena to various degrees, these 'incoordination problems' can drastically increase. On the other hand, transceivers with packet capturing capability might be able to deal with some of the uncoordinated packets. In order to understand the effects of different radio propagation environments on packet level incoordination, we provide a detailed simulation study measuring six transmission success/failure categories and five performance metrics. We report quantitative results w.r.t. probability of incoordination and the effects of power-setting and packet retransmission strategies.

111 citations



Journal ArticleDOI
TL;DR: In this paper, the authors use the Random Way-Point Model (RWP) as a "worst case assumption" of node mobility concerning communication protocol performance in the sense that a positive correlation between performance in an RWP scenario and an arbitrary scenario exists.
Abstract: The mobility of the nodes in a Mobile Ad-Hoc Network (MANET) is a crucial factor in the performance studies of communication protocols for these kind of networks. For this reason, researchers usually use a randomized node movement model, such as the Random Way-Point Model [6], in the process of designing or analyzing the behavior of their protocols. Since movement is not very predictable in these scenarios, they generally serve as a "worst case assumption" of node mobility concerning communication protocol performance in the sense that a positive correlation between performance in an RWP scenario and an arbitrary scenario exists. Additionally, RWP is an analytically well-understood mobility scheme and the movements can be generated very easily with tools complementary to most of the common network simulators.

66 citations


Proceedings ArticleDOI
03 Apr 2006
TL;DR: It is shown that for contention-based forwarding (CBF) techniques, realistic channel characteristics provide a positive impact in terms of an increased average hop distance, and an analytical derivation of the expected hop distance for CBF provides a basis to optimally adjust CBF parameters.
Abstract: The discrepancy between real-world radio channel behavior and its standard modeling in simulations (unit disk graph) is a major reason for protocols to perform differently - often worse - than predicted when deployed in a real-world setup. As researchers having to deal with real ad hoc networks are aware of, assuming a fixed border for a node's communication range might not only lead to inaccurate results but also to a wrong judgment on the comparison between different protocols. We have set up a simulation study to investigate the effects of realistic channel characteristics on packet forwarding strategies for vehicular ad hoc networks. The contributions of this paper are threefold: i) we provide a performance evaluation of various routing/forwarding strategies under the realistic non-deterministic Nakagami radio propagation model and compare the results with the ones obtained using the standard two-ray-ground model. Validated German highway movement patterns are used to model node mobility. ii) We demonstrate that realistic channel conditions present an opportunity and not only a drawback for some forwarding strategies. More specifically, we show that for contention-based forwarding (CBF) techniques, realistic channel characteristics provide a positive impact in terms of an increased average hop distance. iii) We provide an analytical derivation of the expected hop distance for CBF that provides a basis to optimally adjust CBF parameters

64 citations


01 Jan 2006
TL;DR: This paper addresses data forwarding as a key responsibility of a VANET’s (Vehicular Ad hoc NETwork) communication device, and discusses two different approaches, packet-centric forwarding (PCF) and information-centric Forwarding (ICF), both aimed to disseminate information in aVANET environment.
Abstract: In the architectural design of a communication technology the assignment of responsibilities to its different modules or layers is a key issue. The modularization and assignment of functions to modules has a strong impact on the system performance. In this paper, we address data forwarding as a key responsibility of a VANET’s (Vehicular Ad hoc NETwork) communication device. More specifically, we discuss two different approaches, packet-centric forwarding (PCF) and information-centric forwarding (ICF), both aimed to disseminate information in a VANET environment. Basically, assuming a layered protocol design adapted to VANETs, it is argued where and how functions related to node connectivity and data transport could be implemented. Discussing pros and cons of ICF and PCF, we define amodular information-based architecture with a hybrid approach for dissemination of safety information where: i) information forwarding responsibilities reside in the application protocol layer(s) and exploit the applications’ capability of information modification, aggregation, and invalidation, ii) packet forwarding functionalities are implemented in the network protocol layer to rapidly disseminate information of very high priority (safety-of-life), and iii) low-cost nodes incapable of processing safety-related information, can be used to increase network connectivity.

38 citations


DOI
01 Jan 2006
TL;DR: The result of an extensive analysis of both the IEEE 802.11 DCF specification and the ns-2 module describes the different behavior corresponding to the physical layer capture model that current wireless interfaces present.
Abstract: The Network Simulator 2 (ns-2) is largely the most used simulator in the Ad Hoc research community. However, the 802.11 DCF module implemented in the default distribution of ns-2 presents some bugs, i.e., discordances with the IEEE 802.11 Standard specifications. We present in this Technical Report the result of an extensive analysis of both the IEEE 802.11 DCF specification and the ns-2 module. We first describe the discordances found with respect to the different DCF.s procedures. Second, we describe the different behavior corresponding to the physical layer capture model that current wireless interfaces present. Finally we provide in the Appendix all source code modified in the different ns-2.28 files. All modified source code files can be found for download at http://dsn.tm.uni-karlsruhe.de/ns-2.28-DCF-PHY-UKA.php.

29 citations


DOI
01 Jan 2006
TL;DR: It is demonstrated that for contention-based forwarding (CBF) techniques, realistic channel characteristics provide a positive impact in terms of an increased average hop distance and an analytical derivation of the expected hop distance for CBF that provides a basis to optimally adjust CBF parameters.
Abstract: The discrepancy between real-world radio channel behavior and its standard modeling in simulations (Unit Disk Graph) is a major reason for protocols to perform different - often worse - than predicted when deployed in a real-world setup. As researchers having to deal with real ad hoc networks are aware of, assuming a fixed border for a node's communication range might not only lead to inaccurate results but also to a wrong judgment on the comparison between different protocols. We have set up a simulation study to investigate the effects of realistic channel characteristics on packet forwarding strategies for vehicular ad hoc networks. The contributions of this technical report are threefold: i) We provide a performance evaluation of various routing/forwarding strategies under the realistic non-deterministic Nakagami radio propagation model and compare the results with the ones obtained using the standard Two-Ray-Ground model. Validated German highway movement patterns are used to model node mobility. ii) We demonstrate that realistic channel conditions present an opportunity and not only a drawback for some forwarding strategies. More specifically, we show that for contention-based forwarding (CBF) techniques, realistic channel characteristics provide a positive impact in terms of an increased average hop distance. iii) We provide an analytical derivation of the expected hop distance for CBF that provides a basis to optimally adjust CBF parameters.

24 citations


Proceedings Article
29 Sep 2006
TL;DR: The goal of this workshop is to present and discuss recent advances in the developing area of wireless vehicular ad hoc networking (VANET) and to bring experts from different parts of the world together to exchange ideas and to discuss exciting challenges and their solutions in this very active VANET community.
Abstract: Welcome to VANET 2006, the Third ACM International Workshop on Vehicular Ad Hoc Networks! After the success of the first two VANET workshops in 2004 and 2005, 2006 is a great year to continue this exciting workshop. The application of short- to medium-range vehicle communication systems (vehicle-to-vehicle as well as vehicle-to-roadside) technologies is closer to reality than ever before, and the widespread deployment of a communications infrastructure on the roadways and in production vehicles has the potential to improve transportation and the quality of life in ways not imagined a generation ago. VANET technology is entering a critical phase, where academia, industry, and governments worldwide are investing significant time and resources to either prepare for a larger scale deployment decision or to already deploy this technology so that its many benefits in the areas of safety, improvement of traffic flow, and convenience can be leveraged: In the United States, the Vehicle Infrastructure Integration Initiative (VII) works toward deployment of advanced vehicle-vehicle and vehicle-infrastructure communications based on 5.9 Ghz Dedicated Short Range Communication Technology (DSRC). The VII Consortium, established in 2004, is working to determine the feasibility of widespread deployment and to establish an implementation strategy. The consortium consists of most major vehicle manufacturers, many State Departments of Transportation, and the US Department of Transportation. Furthermore, the Vehicle Safety Communication Consortium (VSC), a group of OEMs partnering with the US Department of Transportation, is working on next generation communication-based vehicle safety applications such as a Cooperative Intersection Collision Avoidance Systems (CICAS). In Japan, Vehicle to Infrastructure Communication for Safety and Mobility is developed in the Smartway project. Among others, one of the goals of Smartway is to enable the realization of services related to "safety and safe driving" via communication technology. Vehicle-to-Vehicle Communication for Safety is also looked at in the Advanced Safety Vehicle (ASV) program sponsored by the Japanese Ministry of Land, Infrastructure and Transport (MLIT). In Europe, the COMeSafety program started its work within the 6th Framework Program on January 1, 2006. The project supports the eSafety Forum with respect to all issues related to vehicle-to-vehicle and vehicle-to-infrastructure communications as the basis for cooperative intelligent road transport systems. The Car2Car Communication Consortium is a non-profit organization initiated by European vehicle manufacturers, which is open for suppliers, research organizations, and other partners. The Car2Car Communication Consortium is dedicated to the objective of further increasing road traffic safety and efficiency by means of inter-vehicle communications. .The goal of this workshop is to present and discuss recent advances in the developing area of wireless vehicular ad hoc networking (VANET) and to bring experts from different parts of the world together to exchange ideas and to discuss exciting challenges and their solutions in this very active VANET community.

18 citations


DOI
01 Jan 2006
TL;DR: The modifications realized in ns-2 are described in order to model more accurately future wireless communications in vehicular environments to reflect the behavior described in the current draft of IEEE 802.11p.
Abstract: The network simulator ns-2 is a widely used tool in the field of wired and wireless communications research. Although the ns-2 implementation is in constant evolution, it fails, for obvious reasons, to reflect all aspects related to the newest communication technologies. One example of such technology is 5.9GHz Direct Short Range Communications (DSRC) for vehicular environments, which is currently attracting attention due to its promises to reduce the amount of road fatalities and improve vehicular traffic efficiency on public roads. The IEEE 802.11p group is currently developing a standard to enable future 5.9GHz DSRC based inter-vehicle communications. In this report, we describe the modifications realized in ns-2 in order to model more accurately future wireless communications in vehicular environments. Section 2 reports the extensions performed to the PHY and MAC modules in order to include cumulative noise capabilities. Note that vehicular environments are specially sensible to the way interferences are modeled since safety related information will be commonly transmitted in a broadcast fashion. Section 3 describes the adjustments required to the MAC and PHY modules to reflect the behavior described in the current draft of IEEE 802.11p.

Proceedings ArticleDOI
01 Nov 2006
TL;DR: This paper provides a classification of the most relevant European directives, laws, and legal opinions on electronic communication systems and presents developer/operator guidelines with their corresponding legal consequences for various P2P systems.
Abstract: Currently, the topic of `Bandwidth on Demand' is actively discussed in the US (eg with respect to `network neutrality') not only from a technological point of view, but also from an economic and legal perspective Technically, bandwidth and resulting throughput can be controlled by ISPs on OSI layers 1-3, but additionally `bandwidth on demand' can also be provided by means of the application layer utilizing peer-to-peer (P2P) systems (eg BitTorrent) In this paper we analyze from a European perspective legal status and legal consequences (rights and obligations) of using and operating such overlay networks We first provide a classification of the most relevant European directives, laws, and legal opinions on electronic communication systems Afterwards, we categorize P2P systems and their involved components from the legal point of view Based on this categorization, we present developer/operator guidelines with their corresponding legal consequences for various P2P systems

Proceedings Article
01 Jan 2006
TL;DR: A formalization of a metric able to characterize the effect of different propagation models on IEEE 802.11 networks, and its evaluation (using the ns-2.28 simulator) with respect to packet reception rates is provided, based on the CSMA/CA principle, which can assist researchers to understand the details of wireless communications.
Abstract: Assume a communication scenario in wireless ad hoc and sensor networks where each node periodically sends out status information as a 1-hop broadcast to inform neighboring nodes. These scenarios are typical for monitoring and safety related applications where each node needs information about its neighborhood, e.g., in vehicular ad hoc networks. In IEEE 802.11 based ad hoc networks, one reason not to receive a packet is due to collisions caused by the well known hidden terminal problem (stressed in the addressed scenario where RTS/CTS mechanism is not applicable). It is also well known that wireless communication protocols may achieve different performance results when assuming different radio propagation models and implementations [1]. While the effect of the hidden terminal problem is well understood when utilizing a deterministic1 radio propagation model, it has a new ‘flavor’ with the utilization of more realistic2 ones, which do not experience a fixed Carrier Sense range (CS). Our contribution in this document is a formalization of a metric able to characterize the effect of different propagation models on IEEE 802.11 networks, and its evaluation (using the ns-2.28 simulator) with respect to packet reception rates. The new metric, which we name Packet Level Incoordination (PLI), is based on the CSMA/CA principle and measures the inability of CSMA/CA of correctly coordinate the nodes on a network from a specific node’s perspective (see Fig. 1). This new metric can assist researchers to understand the details of wireless communications, and thus, in the process to find the best strategies (e.g., power control) when designing optimal protocols. The reminder of the paper is the following: Section II briefly presents radio propagation principles, and the way they and the physical layer are implemented in the used simulator. In Section III, we provide the general definition of PLI and the simulation results. Section IV concludes the paper.

DOI
08 Dec 2006
TL;DR: Peer-to-Peer (P2P-) Netze bilden logische bzw. virtuelle Netze auf Basis existierender Netze wie dem Internet.
Abstract: Peer-to-Peer- (P2P-) Netze bilden logische bzw. virtuelle Netze auf Basis existierender Netze wie dem Internet. P2P-Netze zeichnen sich insbesondere durch ih- re dezentrale Struktur und selbstorganisierende Mechanismen aus, welche im Gegen- satz zu Client-Server Architekturen die Last auf alle teilnehmenden Knoten gleichm¨ a- sig verteilen. Durch die dezentrale Struktur in Kombination mit selbstorganisierenden Mechanismen ist es daher m¨ oglich, hoch skalierbare P2P-Netze zu konstruieren. Zudem erhdieVerteilungauf viele Knoten dieRobustheit des Netzes gegen¨ uber Ausf¨ allen einzelner Knoten. P2P-Netze sind meist so gestaltet, dass beim Ausfall ein- zelner Knoten deren Aufgaben von einem anderen wahrgenommen werden. Dennoch sind P2P-Netze nicht per se robust, da neben dem vereinzelten Ausfall von Knoten auch gezielte Attacken m¨ oglich sind. Dieser Beitrag gibt einen ¨ Uberblick ¨ uber Atta- cken auf P2P-Netze. Auserdem wird die so genannte Sybil Attacke vertieft diskutiert und ihre Auswirkungen auf die Robustheit aufgezeigt. Abschliesend wird ein neuer Ansatz pr¨ asentiert, um die Wahrscheinlichkeit einer solchen Attacke zu verringern.


01 Jan 2006
TL;DR: Die Architektur unterstützt universitätsweite Prozesse bei einer losen Kopplung von weiterhin autarken Organisationseinheiten, deren lokalen Geschäftsprozesse auch durch die Integration in einen föderativen Verbund weitgehend erhalten bleiben.
Abstract: IT-gestützte Prozesse und Dienste in Lehre, Forschung und Weiterbildung durchdringen zunehmend die Universität im Inneren und verbinden sie mit der Außenwelt. Als Basis für einrichtungsübergreifende Geschäftsprozesse einer solchen Pervasive University wird ein flexibles Identitätsmanagement benötigt, welches eine lebendige Dienstevielfalt unterstützt. Hierfür schlagen wir eine dienstorientierte Identitätsmanagementarchitektur vor. Fundament der vorgestellten Architektur ist die Betrachtung der Universität als föderativer Verbund ihrer organisatorischen Einheiten. Die Architektur unterstützt universitätsweite Prozesse bei einer losen Kopplung von weiterhin autarken Organisationseinheiten, deren lokalen Geschäftsprozesse auch durch die Integration in einen föderativen Verbund weitgehend erhalten bleiben. Wir beschreiben die Entwurfsprinzipien und die Architektur des bereits prototypisch umgesetzten Systems. Einleitung und Motivation Aktuelle Entwicklungen erfordern von Universitäten den autorisierten Zugriff auf personenbezogene und kontextsensitive Dienste überall und jederzeit. Zudem muss sich eine moderne Universität durch die Fähigkeit auszeichnen, dem stetigen Wandel, getrieben durch strategische und politische Vorgaben, neue Kooperationen im nationalen und internationalen Umfeld sowie durch wissenschaftliche Weiterentwicklungen, gewachsen zu sein. Ein Ansatz sich dieser Herausforderung zu stellen, ist ein integriertes, dienstorientiertes Informationsmanagement, das ein Fundament für eine Pervasive University darstellt und damit eine Durchdringung sowohl nach außen über Universitätsgrenzen hinaus als auch nach innen innerhalb der Universität erzielt [Ju03]. Um dies zu erreichen, ist es notwendig, durchgängige Geschäftsprozesse auf heterogenen Organisationsund IT-Infrastrukturen zu realisieren. Dabei gilt es, bereits bestehende Dienstleistungen, die sich unabhängig voneinander entwickelt haben und in der Regel zueinander inkompatibel sind, zusammenzuführen. Da integrierte Geschäftsprozesse über verschiedene Dienstanbieter und deren Zugriffskontrolle hinwegreichen, ist es notwendig, ein sich über Organisationsstrukturen erstreckendes Identitätsmanagement mit entsprechender Benutzerund Rechteverwaltung zur Verfügung zu stellen.

DOI
08 Dec 2006
TL;DR: Drei evolutionäre Phasen im lokalen Kontext eines einzelnen Betreibers and zwei in Bezug auf den universitätsweiten Kon Text identifizieren kann.
Abstract: Die effiziente Verwaltung und Bereitstellung von Identitätsdaten in heterogenen Systemumgebungen ist nach wie vor eine intensiv diskutierte Thematik. Verschärft wird die Diskussion durch den Einsatz von IuK-Diensten die institutionsübergreifend agieren und somit eine institutionsübergreifende Authentisierung und Autorisierung benötigen. Bisherige Umsetzungen im fakultativen, d.h. lokalen Kontext der ATIS (Abteilung Technische Infrastruktur), als Betreiber der Dienste für die Fakultät für Informatik, und Arbeiten im KIMProjekt (Karlsruher Integriertes InformationsManagement, [KIM]) haben ergeben, dass man diesbezüglich drei evolutionäre Phasen im lokalen Kontext eines einzelnen Betreibers und zwei in Bezug auf den universitätsweiten Kontext identifizieren kann. Diese Phasen werden vorgestellt und die Motivation für diese Phasen diskutiert.

DOI
08 Dec 2006
TL;DR: In this article, the authors present a policy-based management-verfahrens für the Einrichtung von filterregeln in Campus-netz der Universitat Karlsruhe vorgestellt.
Abstract: In diesem Beitrag wird die Konzeption und Umsetzung eines Policy- basierten Managementverfahrens fur die Einrichtung von Filterregeln im Campus- netz der Universitat Karlsruhe vorgestellt. Hierbei war das Ziel, eine Sicherheits- stufe zwischen dem einfachen "Verstecken" durch Verwendung privater IP- Adressen einerseits ("Stufe 1") und einer aufwendigen Firewall-Losung anderer- seits ("Stufe 3") anzubieten. Dieses so genannte "Stufe 2"-Sicherheitsniveau bietet fur eine grose Mehrheit der Universitatseinrichtungen und Teilnetze eine ausrei- chende Netzsicherheit bei einem deutlichen Gewinn an Flexibilitat durch dezentra- le Administrierbarkeit im Vergleich zu einer "Stufe 3" Losung. Wir beschreiben in diesem Beitrag die grundsatzlichen Uberlegungen zu den An- forderungen, die Architektur hinsichtlich der Einbettung in das Netzwerk sowie die Benutzeroberflache, das XML-basierte Policyschema und die Policy-Ubersetzung in eine "Access Control List" (ACL) und in IPTables. Erste Erfahrungen mit der vorgeschlagenen und umgesetzten Losung im produktiven Einsatz bestatigen die Leistungsfahigkeit und den Flexibilitatsgewinn.