In this paper, we propose a lightweight mechanism for revoking security certificates that is appropriate for the limited bandwidth and hardware cost constraints of a VANET. A Certificate Authority (CA) issues certificates to trusted nodes, i.e., vehicles. If the CA looses trust in a vehicle (e.g., due to evidence of malfunction or malicious behavior), the CA must promptly revoke the certificates of the distrusted vehicle. To distribute revocation information quickly even during incremental deployment, we propose that CAs use Certificate Revocation Lists (CRLs). The CRL should be composed in a secure manner, and it should be exchanged in a way such that the CRL is both quickly and widely distributed. We previously proposed a mechanism for the quick distribution of CRL updates that also covers a wide area by using vehicle-to-vehicle (V2V) communication . In this paper, we additionally investigate the performance of V2V communication in partial deployment scenarios, that is, where only a certain percentage of vehicles are equipped with VANET radios. We provide simulation results that show our V2V exchange mechanism is quicker than distributing CRLs or CRL updates through road-side units (RSUs) alone. However, this revocation process, which involves both the CA and vehicles, must conform to the aforementioned bandwidth and hardware restrictions. In this paper, we present mechanisms that achieve the goals of reduced CRL size, a computationally efficient mechanism for determining if a certificate is on the CRL, and a lightweight mechanism for exchanging CRL updates. Additionally, we expand on our previous work to provide privacy to revoked vehicles prior to their revocation.

In the US, the Dedicated Short Range Communications (DSRC) spectrum is organized into several channels. IEEE 1609.4 [2] defines an alternating-access channel switching scheme to enable a DSRC device to support applications concurrently on different channels. The default channel for Vehicle-to-Vehicle (V2V) safety messages is the Control Channel (CCH), but previous research has identified performance issues with this safety communication model. This paper proposes three alternative approaches for DSRC V2V safety communication in a multi-channel environment, all of which improve performance compared to the basic IEEE 1609.4 approach, while requiring only minor changes to the standards. The alternative approaches and the basic IEEE 1609.4 approach are evaluated via ns-2 simulations.

Abstract There are two underlying principles that guide how a vehicular ad hoc network (VANET) is built: there will be misbehavior and the extent to which vehicles can misbehave should be bounded. Additionally, the main use for VANETs currently is to enable safety applications where vehicles' position, velocity, and acceleration are broadcast to other vehicles in the VANET. Combining these guiding principles with this application results in the privacy of vehicles and users being an important concern for VANET design. Safety application messages are signed using keys and therefore linked to vehicles. In this work, we investigate how to assign keys to vehicles in order to preserve privacy and maintain our guiding VANET design principles. Specifically, we investigate the design space where individual keys may be given to multiple vehicles and vehicles may have multiple keys. Through a simple security analysis, we eliminate the case where all keys are common. Through mathematical and logical analysis, we conclude that keys should not be owned by multiple vehicles, that is, keys should be unique to vehicles and vehicles should be given multiple keys. Specifically, we show that it is impossible to provide good privacy and fast revocation when keys are shared among vehicles. Copyright © 2009 John Wiley & Sons, Ltd.

Many results have been published in the literature based on performance measurements obtained from simulations of vehicular networks (VANETs). These simulations use as input traces of vehicle movements that have been generated by traffic simulators which are based on traffic theory models. To our knowledge, no one has published any work based on actual large-scale recordings of vehicle movements. We use recordings of actual vehicle movements on various roadways. In order to enable analysis on this scale, we have developed a new VANET simulator, which can handle many more vehicles than NS-2. To enable us to use our own simulator, we present results of a cross-validation between NS-2 and our simulator, showing that both simulators produce results that are statistically the same. We use our simulator to analyze the proposed authentication mechanism, which relies on ECDSA signatures, comparing it to broadcast authentication using TESLA. We perform our evaluations using real vehicle mobility, which we believe to be the first simulations using real vehicle mobility. Our comparison shows strengths and weaknesses for each of these authentication schemes in terms of the resulting reception rates and latency of broadcast packets.

We present a GPS-enabled channel sounding platform for measuring both vehicle-to-vehicle and vehicle-to- roadside wireless channels. This platform was used to conduct an extensive field measurement campaign involving vehicular wireless channels across a wide variety of speeds and line-of-sight conditions. From the data, we present statistical characterizations of several classes of these channels at 5.9 GHz. This analysis suggests that while the proposed DSRC standard may account for Doppler and delay spreads in vehicular channels, large packets may face higher error rates due to time-varying channels.

This paper examines congestion control for explicit rate data networks. The available bit rate (ABR) service category of asynchronous transfer mode (ATM) networks serves as an example system for this paper, however the results of this paper are applicable to other explicit rate systems as well. After a plant model is established, an adaptive control strategy is presented and compared to other strategies. Two algorithm enhancements are then introduced. These enhancements reduce the convergence time and improve queue depth management. This work differentiates itself from the other contributions in the area of rate-based congestion control in its balanced approach of retaining enough complexity as to afford attractive performance properties, but not so much complexity as to make implementation prohibitively expensive.

One of the more challenging and yet unresolved issues which is paramount to the success of ATM networks is that of congestion control for available bit rate (ABR) traffic. Unlike other ATM service categories, ABR provides a feedback mechanism, allowing interior nodes to dictate source rates. Previous work has demonstrated how linear adaptive control theory can be utilized to create a stable and efficient control system for the purposes of ATM ABR congestion control. This paper investigates our previously proposed adaptive controller that uses a finite impulse response (FIR) filter to approximately invert the FIR plant. Specifically, convergence issues are addressed in depth. In doing so, a proof is provided for the convergence of the normalized least mean square (NLMS) adaptive algorithm employing a DC tap (drift tap), allowing the proof to extend beyond the (often-assumed) zero-mean case. Using a set of reasonable assumptions, parameter convergence in the mean and mean square is proven. Other issues pertaining to the stability of this controller are presented.

This paper proposes an approach to Traffic Engineering that uses differentiated services (diffserv) and multi-protocol label switching (MPLS) to provide quantitative QoS guarantees over an IP network. An algorithm that determines QoS-constrained routes is proposed and a framework that uses such an algorithm is outlined. This framework removes the responsibility of QoS guarantees from the core nodes, thereby reducing their complexity.