Abstract. Inter-vehicle communication is regarded as one of the major applications of mobile ad hoc networks (MANETs). In these so called vehicular ad hoc networks (VANETs) security and privacy are crucial factors for successful deployment. In a scenario, where each vehicle would have a unique identifier, eavesdroppers could easily accumulate location profiles. As a solution approach, several authors suggest using changeable pseudonyms as temporary vehicle identifiers. If a vehicle changes its pseudonym from time to time, long-term tracking can be avoided. However, as we show in this paper, changing identifiers has detrimental effects on routing efficiency and increases packet loss. So, designers of VANET systems need to aim for a balance between privacy protection on the one and performance on the other hand. The results of this paper provide advise on how to achieve this balance. 1

There has been a lot of effort in the research on routing in mobile ad hoc networks in the last years. Promising applications of MANETs, e.g. in the automotive domain, are the drive for the design of inter-vehicle networks. So far, several projects in this field have chosen geographic routing approaches because of their outstanding performance and the possibility to support location-based applications like traffic warning functions. Having reached a reasonable functional level, a next step will be a deeper study of safety and security issues. With this paper, we dive into that area by assuming defective or malicious nodes that disseminate wrong position data. First, we have a look at the local problems that may arise from falsified position data, then we show the global effects on the routing performance by simulating malicious nodes. Simulation results show that the overall ratio of successfully delivered messages decreases, depending on the number of maliciously acting nodes, even up to approximately 30%. We conclude from this result that future work should take these threats into account in order to design more robust routing protocols.

Abstract — Inter-vehicle communication is regarded as one of the major applications of mobile ad hoc networks (MANETs). Compared to MANETs, these so called vehicular ad hoc networks (VANETs) have special requirements in terms of node mobility and position-dependent applications, which are well met by geographic routing protocols. Functional research on geographic routing has already reached a considerable level, whereas security aspects have been vastly neglected so far. Since position dissemination is crucial for geographic routing, forged position information has severe impact regarding both performance and security. In this work, we first analyze the problems that may arise from falsified position data. Then, in order to lessen these problems, we propose detection mechanisms that are capable of recognizing nodes cheating about their location in position beacons. In contrast to other position verification approaches, our solution does not rely on special hardware or dedicated infrastructure. Evaluation based on simulations shows that our position verification system successfully discloses nodes disseminating false positions and thereby widely prevents attacks using position cheating. I.

This paper deals with the design and implementation of a location-based protocol for service discovery in mobile ad hoc environments. Our approach is based on geocast addressing of control messages. Moreover, it combines a reactive method -- propagating discovery requests -- with a proactive method -- disseminating service advertisements -- into a hybrid approach. For the evaluation of the protocol an experimental environment was set up. This paper presents the design of the protocol and results of experimental evaluations.

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

In this paper, we propose to apply Contention-Based Forwarding (CBF) to Vehicular Ad Hoc Networks (VANETs). CBF is a greedy positionbased forwarding algorithm that does not require proactive transmission of beacon messages. CBF performance is analyzed using realistic movement patterns of vehicles on a highway. We show by means of simulation that CBF as well as traditional position-based routing (PBR) achieve a delivery rate of almost 100% given that connectivity exists. However, CBF has a much lower forwarding overhead than PBR since PBR can achieve high delivery ratios only by implicitly using a trial-and-error next-hop selection strategy. With CBF, a better total throughput can be achieved. We further discuss several optimizations of CBF for its use in VANETs, in particular a new position-encoding scheme that naturally allows for communication paradigms such as `street geocast' and `street flooding'. The discussions show that CBF can be viewed as a concept for convergence of intelligent flooding, geocast, and multihop forwarding in the area of inter-vehicle communication.

Abstract — In comparison to other communication networks, Vehicular Ad-hoc Networks (VANETs) have unique requirements with respect to applications, types of communication, self-organization and other issues. In order to meet these requirements, the structuring of functionalities into protocols and their interaction must be re-thought. The traditional approach of decomposition of functionality into protocol layers (layered approach) and a protocol design specifically tailored to the needs of VANETs (un-layered approach) leads to two extreme and opposed manifestations of a potential VANET protocol architecture. From these two extreme approaches we derive a stack-based VANET protocol architecture that combines the strengths of both. Among the key features of this protocol architecture are VANET-specific protocol layers, a staircase approach for interaction among layers, and the use of an information connector for the exchange of cross-layer information using the publisher/subscriber pattern. This protocol architecture provides a clear modular structure with flexibility for protocol interaction and information exchange at a reasonable complexity. I.

Vehicular ad-hoc networks is an emerging research area focussing on communication infrastructures that support vehicles and road-signs in distributing roadstate data such as information about hazardous road conditions ahead, approaching emergency vehicles, and traffic delays. Vehicular ad-hoc networks combine the areas of sensor networks (data acquisition) with mobile ad-hoc networks (highly dynamic topology and lack of pre-existing infrastructure). One of the main challenges of vehicular ad-hoc networks is the data dissemination protocols capable of distributing road-state information among vehicles. This paper presents two candidates for dissemination protocols: a zone flooding protocol and a zone diffusion protocol. The two protocols combine ideas from sensor networks and geocasting to ensure that data is aggregated and distributed only in a bounded geographical area. We present a comparative simulation study of the two protocols evaluating their relative performance using conventional metrics (such as network load) as well as application-specific metrics (such as awareness). The simulation study has been conducted using the Network Simulator 2 (NS-2) and has highlighted key properties of the two protocols that can be used as a basis for selecting the most appropriate protocol. 1

(WAVE) system is developed for enhancing the driving safety and comfort of automotive users. However, owing to the nature of contention based channel access scheme, the WAVE system suffers from Quality of Service (QoS) degradation for safety applications caused by the channel congestion in scenarios with high vehicle. In this paper we study the performance of the Emergency Electronic Brake Light with Forwarding (EEBL-F) application as an example of the safety application in congested scenarios, and propose a congestion control architecture for Vehicular Ad-Hoc Networks (VANET). Concentrated on Medium Access Control (MAC) layer, two concrete congestion control approaches through manipulating MAC transmission queues are introduced. The effectiveness of the proposed congestion control approaches is evaluated through stochastic simulations. Besides, the impact of adaptive transmit power level on congestion control in VANET is also discussed with simulation results.

Host mobility patterns have an important effect on performance of ad hoc networks. For this reason, many evaluation studies involve analytical or simulation models to synthesize the movement of mobile hosts. The growing interest in investigating the use of ad hoc networks in inter-vehicle communication demands a vehicle mobility model that is capable of creating realistic movements. In fact, there exists a cellular automata (CA) model that is known for its ability to produce such movements. This paper describes a traffic microsimulator, RoadSim, which implements the basic CA model and extends it in order to generate traffic patterns suitable for use in ad hoc network research. RoadSim is capable of producing traffic that exhibits free flow characteristics, as well as start-stop waves caused by traffic jams. It can also simulate traffic in closed-loop roads or at intersections controlled by traffic signs. We intend to use this tool to evaluate ad hoc protocols in road conditions that, otherwise, cannot be reproduced without more complex and expensive traffic simulators.