Günter Schäfer

Exploration of adaptive beaconing for efficient intervehicle safety communication

In the future intervehicle communication will make driving safer, easier, and more comfortable. As a cornerstone of the system, vehicles need to be aware of other vehicles in the vicinity. This cooperative awareness is achieved by beaconing, the exchange of periodic single-hop broadcast messages that include data on the status of a vehicle. While the concept of beaconing has been developed in the first phase of research on VANETs, recent studies have revealed limitations with respect to network performance. Obviously, the frequency of beacon messages directly translates into accuracy of cooperative awareness and thus traffic safety. There is an indisputable trade-off between required bandwidth and achieved accuracy. In this work we analyze this trade-off from different perspectives considering the consequences for safety applications. As a solution to the problem of overloading the channel, we propose to control the offered load by adjusting the beacon frequency dynamically to the current traffic situation while maintaining appropriate accuracy. To find an optimal adaptation, we elaborate on several options that arise when determining the beacon frequency. As a result, we propose situation-adaptive beaconing. It depends on the vehicles own movement and the movement of surrounding vehicles, macroscopic aspects like the current vehicle density, or microscopic aspects.

The archaeal respiratory supercomplex SoxM from S. acidocaldarius combines features of quinole and cytochrome c oxidases.

Abstract The hyperthermoacidophilic archaeon Sulfolobus acidocaldarius has a unique respiratory system with at least two terminal oxidases. Genetic and preliminary biochemical studies suggested the existence of a unique respiratory supercomplex, SoxM. Here we show (i) that all respective genes are translated into polypeptides, and (ii) that the supercomplex can be separated from the alternative oxidase SoxABCD and in that way characterized in a catalytically competent form for the first time. It acts as a quinol oxidase and contains a total of seven metal redox centers. One of it the blue copper protein sulfocyanin functionally links two subcomplexes. One is a bb3-type terminal oxidase moiety containing CuA and CuB, whereas the other consists of a Rieske FeSprotein and a homolog to cytochrome b in this case hosting two hemes AS. Based on a 1:1 stoichiometry, 1 mol complex contains 6 mol Fe and 4 mol Cu. Its activity is completely inhibited by cyanide and strongly by aurachinC and D derivatives as inhibitors of the quinol binding site. These data suggest that the complex provides two proton pumping sites. Interestingly, subunitII reveals an unusual pH dependence and is proposed to act as a pH sensor as well as a regulator of catalytic activity via a reversible transition between two states of the CuA ligation. This is a novel hint at how S. acidocaldarius can adapt to and survive in its extreme natural environment.

Site-specific uncoupling and inhibition of energy transfer by biguanides

Abstract 1. 1. The oligomycin-like effect of biguanide derivatives, which was reported previously, has been investigated in more detail. 2. 2. Phenethylbiguanide, when used at high concentrations, not only inhibits succinate respiration but also DPNH-linked respiration in tightly coupled mitochondria. 3. 3. Evidence is given that aliphatic biguanides, which are inhibitors of energy transfer, may also act as uncoupling agents. Their coupling efficiency increases with the unpolar qualities of the molecule. n -Heptylbiguanie behaves as an uncoupler of the second phosphorylating site, whereas it is an inhibitor of the first. 4. 4. The inhibiting effects of biguanides occur after a short lag-period and the action of biguanide is highly dependent on the metabolic state of the mitochondria.

Degradation of Transmission Range in VANETs caused by Interference

ABSTRACT Reliability is one of the key requirements for inter-vehicle communication in order to improve safety in road traffic. This paper describes the difficulties of inter-vehicle communication. We focus on an analysis of the state-of-the art MAC protocol draft IEEE P802.11p and its limitations in high load situations. For our analysis we consider a particular safety scenario: An emergency vehicle is approaching a traffic jam. In a simulation experiment, we highlight that severe packet loss can occur. The reliable transmission range can be reduced by up to 90%. The main reason for this degradation is interference caused by transmissions of other vehicles within the traffic jam. In the study, we focus on the vehicle at the very end of the traffic jam. There, we measure the number of packets per second that are successfully received from the emergency vehicle. The key observation is that only a small fraction of the warning lead time remains which will also reduce the time for the driver to react on this information on an approaching emergency vehicle.

The unusual iron sulfur composition of the Acidianus ambivalens succinate dehydrogenase complex.

The succinate dehydrogenase complex of the thermoacidophilic archaeon Acidianus ambivalens was investigated kinetically and by EPR spectroscopy in its most intact form, i.e., membrane bound. Here it is shown that this respiratory complex has an unusual iron-sulfur cluster composition in respect to that of the canonical succinate dehydrogenases known. The spectroscopic studies show that center S3, the succinate responsive [3Fe-4S]1+/0 cluster of succinate dehydrogenases, is not present in membranes prepared from aerobically grown A. ambivalens, nor in partially purified complex fractions. On the other hand, EPR features associated to the remaining centers, clusters S1 ([2Fe-2S]1+/2+) and S2 ([4Fe-4S]2+/1+), could be observed. Similar findings were made in other archaea, namely Acidianus infernus and Sulfolobus solfataricus. Kinetic investigations showed that the A. ambivalens enzyme is reversible, capable of operating as a fumarate reductase - a required activity if this obligate autotroph performs CO2 fixation via a reductive citric acid cycle. Sequencing of the sdh operon confirmed the spectroscopic data. Center S3 ([3Fe-4S]) is indeed replaced by a second [4Fe-4S] center, by incorporation of an additional cysteine, at the cysteine cluster binding motif (CxxYxxCxxxC-->CxxCxxCxxxC). Genomic analysis shows that genes encoding for succinate dehydrogenases similar to the ones here outlined are also present in bacteria, which may indicate a novel family of succinate/fumarate oxidoreductases, spread among the Archaea and Bacteria domains.

Cytochrome b558/566 from the archaeon Sulfolobus acidocaldarius. A novel highly glycosylated, membrane-bound b-type hemoprotein.

In this study we re-examined the inducible cytochrome b 558/566 from the archaeonSulfolobus acidocaldarius (DSM 639), formerly thought to be a component of a terminal oxidase (Becker, M., and Schäfer, G. (1991) FEBS Lett. 291, 331–335). An improved purification method increased the yield of the protein and allowed more detailed investigations. Its molecular mass and heme content have been found to be 64,210 Da and 1 mol of heme/mol of protein, respectively. It is only detectable in cells grown at low oxygen tensions. The composition of the growth medium also exerts significant influence on the cytochromeb 558/566 content of S. acidocaldarius membranes. The cytochrome exhibits an extremely high redox potential of +400 mV and shows no CO reactivity; a ligation other than a His/His-coordination of axial ligands appears likely. It turned out to be highly glycosylated (more than 20% of its molecular mass are sugar residues) and is probably exposed to the outer surface of the plasma membrane. The sugar moiety consists of severalO-glycosidically linked mannoses and at least oneN-glycosidically linked hexasaccharide comprising two glucoses, two mannoses, and two N-acetyl-glucosamines. The gene of the cytochrome (cbsA) has been sequenced, revealing an interesting predicted secondary structure with two putative α-helical membrane anchors flanking the majority of a mainly β-pleated sheet structure containing unusually high amounts of serine and threonine. A second gene (cbsB) was found to be cotranscribed. The latter displays extreme hydrophobicity and is thought to form a functional unit with cytochromeb 558/566 in vivo, although it did not copurify with the latter. Sequence comparisons show no similarity to any entry in data banks indicating that this cytochrome is indeed a novel kind of b-type hemoprotein. A cytochromec analogous function in the pseudoperiplasmic space ofS. acidocaldarius is discussed.

Modeling Roadside Attacker Behavior in VANETs

Communication using VANETs is commonly seen as the next milestone for improving traffic safety. Vehicles will be enabled to exchange any kind of information that helps to detect and mitigate dangerous situations. Security research in the past years has shown that VANETs are endangered by a plethora of severe security risk. Subject of this work is the modeling of attackers that target active safety applications in VANETs. Through a risk analysis, this work identifies assets, threats and potential attacks in inter-vehicle communication. The risk analysis shows that the most serious threat arises from a quasi-stationary (road-side) attacker that distributed forged warning messages. This attacker is discussed more deeply. We show the degrees of freedom that are available for position forging and find thereby two attacks that demand attention: single position forging having low effort compared to sophisticated movement path forging having a potentially high influence on road traffic safety.

Optimally DoS Resistant P2P Topologies for Live Multimedia Streaming

Using a peer-to-peer approach for live multimedia streaming applications offers the promise to obtain a highly scalable, decentralized, and robust distribution service. When constructing streaming topologies, however, specific care has to be taken in order to ensure that quality of service requirements in terms of delay, jitter, packet loss, and stability against deliberate denial of service attacks are met. In this paper, we concentrate on the latter requirement of stability against denial-of-service attacks. We present an analytical model to assess the stability of overlay streaming topologies and describe attack strategies. Building on this, we describe topologies, which are optimally stable toward perfect attacks based on global knowledge, and give a mathematical proof of their optimality. The formal construction and analysis of these topologies using global knowledge lead us to strategies for distributed procedures, which are able to construct resilient topologies in scenarios, where global knowledge can not be gathered. Experimental results show that the topologies created in such a real-world scenario are close to optimally stable toward perfect denial of service attacks.

A Distributed IP Mobility Approach for 3G SAE

Future generations of mobile operator networks, based on an all-IP-based flat architecture and a multitude of different access technologies, require a proper IP-based mobility management in place. In this article, a scalable and completely distributed mobility management is presented which is based on a Distributed Hash Table data structure. The Distributed IP Mobility Approach (DIMA) remains completely compatible towards Mobile IP and its variants Hierarchical Mobile IP and Proxy Mobile IP. We examine the average service time per packet and the load caused by lookups in the system, by applying a suitable mobility model and by using a traffic model consisting of a mix of representative traffic classes (HTTP, VoIP, Audio and Video streaming). Thereby, we show that the system remains scalable allowing to serve an arbitrary amount of participants, provides a network-based route optimization and a better resilience than Mobile IP at the cost of only slightly increased signalling effort.

Evidence for a Rieske-type FeS center in the thermoacidophilic archaebacterium Sulfolobus acidocaldarius

A high‐potential iron‐sulfur cluster with characteristics similar to a Rieske‐type center was detected in the plasma membrane of Sulfolobus acidocaldarius by EPR spectroscopy. In the reduced form this center has g‐values of g z = 2.031, g y = 1.890 and g x = 1.725 (g av = 1.88, rhombicity = 0.37) and its reduction potential at pH 7.4 was determined to be +325 ± 10 mV. The archaebacterial cluster exhibits some unique properties, in comparison to eubacterial and eukaryotic Rieske‐type centers. First, the reduction potential is pH‐dependent in the range from pH 6.7 to 8.2. Second, the typical inhibitor of Rieske FeS centers, DBMIB, had no effect on the g‐values of this cluster. The center is reducible by both NADH and succinate in the presence of cyanide, an inhibitor of the terminal oxidases. The possible role of a Rieske‐type center in an organism lacking any c‐type cytochromes is discussed.