Dipl.-Inf.

Roscher, Karsten

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  • Publication
    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.
  • Publication
    Efficient distribution of certificate chains in VANETs
    ( 2017)
    Bittl, Sebastian
    ;
    Roscher, Karsten
    Wireless car-to-X communication technology is about to enter the mass market within the next years. Thereby, security in created vehicular ad-hoc networks depends on digital signatures managed by a multi-level certificate hierarchy. Certificate distribution is critical in regard to channel usage and delay of data reception via security caused packet loss. These issues are even more significant in case not only pseudonym certificates, but also certificate authority certificates, have to be exchanged between nodes on demand. Prior work has not treated dissemination of higher level elements from a multi-level certificate chain in detail. Thus, this work provides a study on the recently standardized algorithms. Several drawbacks of the straight forward solution taken so far are identified, which include severe denial of service weaknesses. Solutions to the distribution problem are found to be similar to the ones of the packet forwarding problem encountered in position-based routing. Hence, we study several algorithms for efficient distribution of a certificate chain in regard to channel load, which are adapted from their counterparts in position-based routing. Thereby, a combination of pseudonym certificate buffering with requester based responder selection is found to be able to completely remove the requirement for certificate chain distribution in VANETs. The introduced design avoids the found denial of service weakness, while decreasing the worst case size of the security envelope of VANET messages by more than a third at the same time.
  • Publication
    On the feasibility of multi-hop communication in a realistic city scenario
    ( 2017)
    Roscher, Karsten
    Vehicular ad hoc networks (VANETs) are about to enter the market in the upcoming years. While direct message exchange is limited to a few hundred meters and mostly line-of sight, multi-hop forwarding can significantly extend the communication range. In this paper, the influence of network density and vehicle distribution on multi-hop communication in VANETs is investigated using a model of the city of Luxembourg. Introducing an idealistic reference routing we identify the need for high penetration rates to achieve acceptable reliability independent of the selected routing protocol. A comparison with Greedy forwarding shows its weaknesses to select proper next hop candidates when the number of equipped vehicles increases.
  • Publication
    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.
  • Publication
    Protocol modeling accuracy in VANET simulators
    ( 2017)
    Bittl, Sebastian
    ;
    Roscher, Karsten
    Vehicular ad hoc networks are about to enter the mass market in upcoming years. High effort for real world field tests leads to high dependency of development and evaluation of such networks on simulations. We compare supported features of common simulation frameworks with current standards and study the performance impact of incomplete standard conformance. We find that a lack of support for data encoding schemes and security functionality may massively affect simulation results. Our findings apply to many well-known simulation frameworks. Proposals to overcome identified weaknesses are provided.
  • Publication
    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.
  • Publication
    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.
  • Publication
    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.
  • Publication
    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.
  • Publication
    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.