Dipl.-Inf.

Roscher, Karsten

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Time-controlled neighborhood-driven policy-based network selection algorithm for message dissemination in hybrid vehicular networks

2018 , Oleinichenko, Oleg , Sevilmis, Yagmur , Roscher, Karsten , Jiru, Josef

In vehicular ad hoc networks (VANETs), successful delivery of GeoUnicast and GeoBroadcast packets depends on scenario-specific aspects like vehicle density, distribution of vehicles on the road and type of the environment (e.g., urban, rural). These aspects can significantly influence the reliability of the connection between communication parties making traditional ITS-G5 based ad hoc networks unreliable. The absence of communication partners in range, long transmission distances, non-line-of-sight (NLOS) conditions are just a few examples that could hinder ITS-G5 transmissions. In this paper, we propose a Hybrid Policy-based Network Selection Algorithm that uses LTE to strengthen and complement ITS-G5 under critical conditions in which successful transmission over the ad hoc network is highly unlikely. The main objective is to use as less LTE transmissions as possible whilst maintaining high Packet Delivery Ratio (PDR) within defined delay constraints. The results, which are derived from extensive simulation campaigns, show a clear advantage of using the hybrid scheme over solely ITS-G5 or LTE.

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Feasibility of Verify-on-Demand in VANETs

2016 , Bittl, Sebastian , Roscher, Karsten

Wireless ad hoc networks are an important topic in the automotive domain. Thereby, strict security requirements lead to high effort for verification of digital signatures used to secure message exchange. A popular approach to limit such effort is to apply verify-on-demand schemes. However, we show that verify-on-demand requires much more cross layer dependencies than identified before. Moreover, a massive denial of service weakness of this kind of verification mechanism is found. Thus, we recommend to prefer verify-all schemes over their verify-on-demand counterparts.

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Efficient authorization authority certificate distribution in VANETs

2016 , Bittl, Sebastian , Roscher, Karsten

Car-to-X communication systems are about to enter the mass market in upcoming years. Security in these networks depends on digital signatures managed by a multi-level certificate hierarchy. Thereby, certificate distribution is critical in regard to channel utilization and data reception delay via security caused packet loss. These issues are even more significant in case not only pseudonym certificates but also authorization authority certificates have to be exchanged between nodes in the VANET. Prior work has not studied distribution of the elements of a multi-levelcertificate chain in detail. Hence, this work provides an analysis of the currently standardized mechanisms and identifies several drawbacks of the straight forward solution proposed so far. Thereby, we find a severe denial of service attack on that solution. Moreover, the distribution problem is found to be similar to the packet forwarding problem encountered in position-based routing. Thus, we study several strategies for efficient distribution of a certificate chain in regard to channel lad, which are adapted from their counterparts in position-based routing. Thereby, we find that by combining pseudonym certificate buffering with requester based responder selection the requirement for certificate chain distribution in VANETs can be removed completely. Hence, the proposed design avoids the identified denial of service weakness and reduces the worst case size of the security envelope of VANET messages by more than a third.

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Distribution of pseudonym certificates via bursts for VANETs with low and medium mobility

2015 , Bittl, Sebastian , Aydinli, Berke , Roscher, Karsten

Wireless intelligent transport systems based on Car-to-X communication technology are about to enter the massmarket in upcoming years. Thereby, efficient and reliable security systems are a core point of concern in system design. Currently regarded digital signature schemes using pseudonym certificates can introduce significant overhead into the highly bandwidth restricted system. Thus, mechanisms to optimize the efficiency of the security mechanisms in regard to authentication delay and channel load are required. Prior work has focused on scenarios with high node mobility, e.g., freeways. However, bandwidth conserving mechanisms are also required for urban low and medium mobility scenarios to enable foreseen extension of the wireless network for the many other volatile road users like pedestrians. Hence, an approach for efficient pseudonym certificate distribution in urban scenarios is provided in this work. The given simulation based environment shows that it can enhance cooperative awareness while limiting used bandwidth. Thus, it can be regarded as well suitable for future urban intelligent transport systems.

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Know thy neighbor - a data-driven approach to neighborhood estimation in VANETs

2017 , Roscher, Karsten , Nitsche, Thomas , Knorr, Rudi

Current advances in vehicular ad-hoc networks (VANETs) point out the importance of multi-hop message dissemination. For this type of communication, the selection of neighboring nodes with stable links is vital. In this work, we address the neighbor selection problem with a data-driven approach. To this aim, we apply machine learning techniques to a massive data-set of ETSI ITS message exchange samples, obtained from simulated traffic in the highly detailed Luxembourg SUMO Traffic (LuST) Scenario. As a result, we present classification methods that increase neighbor selection accuracy by up to 43% compared to the state of the art.

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Reliable message forwarding in VANETs for delay-sensitive applications

2016 , Roscher, Karsten , Maierbacher, Gerhard

Multi-hop forwarding in VANETs remains a challenging task. Existing protocols either focus on high packet delivery ratios or low latencies. In this paper, we propose Low-Delay Forwarding with Multiple Candidates (LDMC), a novel geographic routing approach using a combination of sender-based forwarder selection and receiver-based coordination of multiple contenders. Candidates are rated based on a combination of position and relative speed information. Contention among forwarders is realized with priority-dependent timers. Our evaluation shows substantial improvement of the forwarding delay while maintaining high packet deliver ratios comparable to contention-based algorithms for different scenarios. Hence, the proposed concept is well suited for delay-sensitive applications like cooperative positioning or coordinated driving.

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Adaptive decision algorithms for data aggregation in VANETs with defined channel load limits

2015 , Jiru, Josef , Mammu, Aboobeker Sidhik Koyamparambil , Roscher, Karsten

The main challenges when realizing safety related applications based on vehicle-to-x communication are scalability and reliability. With an increasing number of vehicles, the communication channel must not get congested especially if a large amount of information has to be transmitted over multiple hops to a destination. This challenge can be solved by reducing the data load through data aggregation. In this paper, we present a decentralized congestion control using the channel busy ratio (CBR) on the application layer for an adaptive control of aggregation levels in real time. Adaptive decision algorithms decide which data is aggregated in real time. Two different approaches are compared: One approach relies on two CBR thresholds (min/max) only and one that allows a higher number of CBR thresholds. In both cases, the adaptive aggregation control increases and decreases the data aggregation levels based on these thresholds. Our simulation results show that both approaches are able to adjust the aggregation levels to given channel load thresholds within seconds resulting in improved data quality even in heavy congested situations. Adaptive decision algorithms result in less error introduced by aggregation. The impact of the two aggregation level control approaches is discussed regarding channel load and resulting data precision.

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Mutual influence of certificate distribution and pseudonym change strategies in vehicular ad-hoc networks

2017 , Bittl, Sebastian , Roscher, Karsten

Vehicular ad-hoc networks (VANETs) are subject to high interest from both the automotive industry as well as government bodies owing to their prospect of increasing safety of driving. Wireless data exchange within VANETs requires rigid security mechanisms to enable its usage in safety critical driver assistance systems. Requirements include not only authenticity and integrity of messages, but also privacy of drivers. We find that much research has been conducted on certificate dissemination and on privacy enhancing certificate (i.e., pseudonym) change. However, mutual influence of techniques from both domains has not been studied in prior work. Hence, we provide an analysis of such cross influence. We show that certificate change massively increases channel load under currently standardised certificate distribution mechanisms. Thus, we propose to use explicit signalling of certificate changes among nodes to limit the found overhead. The conducted evaluation shows that this approach overcomes the identified problems.

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Low-Delay Forwarding with Multiple Candidates for VANETs Using Multi-Criteria Decision Making

2016 , Roscher, Karsten , Jiru, Josef , Knorr, Rudi

Vehicular ad hoc networks (VANETs) are envisioned to support driver assistance and automated driving posing strict requirements on communication reliability and delay. To support these applications, we propose Low Delay Forwarding with Multiple Candidates (LDMC), a geographic routing approach combining the advantages of sender-based control and opportunistic forwarding. Candidates are ranked based on position, time since the last status update and neighborhood information using multi-criteria decision making. Priority-dependent timers reduce the contention among forwarders. Our evaluation for freeway and grid scenarios shows substantial improvement over existing protocols for real-time applications requiring 100 ms or less end-to-end delay.

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Security overhead and its impact in VANETs

2015 , Bittl, Sebastian , Roscher, Karsten , Gonzalez, Arturo A.

Vehicular ad hoc networks (VANETs), often called Car2X communication systems, are about to enter the mass market in upcoming years. They are intended to increase traffic safety by enabling new safety critical driver assistance systems. This also means that strong security mechanisms are required to safeguard communication within VANETs. However, standardized security mechanisms lead to significant overhead in terms of bandwidth requirement and delay. Prior work has focused on reducing the overhead by advanced strategies for pseudonym and authorization authority certificate exchange. However, we find that this is not enough to enable reliable message exchange in VANETs. Various other sources of overhead caused by security mechanisms in VANETs are identified in the provided analysis. Thereby, we find cross layer and cross message dependencies. In combination with the non-fragmentation property of VANET messages, such dependencies are discovered to lead to massive dropping of packets due to maximum size violations at low protocol layers. Thus, we develop a method for cross layer on demand content assembling for VANET messages, which can avoid the size limit violations without preventing individual layers from disseminating their variable length data sets.

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