Rainer Baumann

An evaluation of inter-vehicle ad hoc networks based on realistic vehicular traces

Vehicular ad hoc networks (VANETs) using WLAN tech-nology have recently received considerable attention. The evaluation of VANET routing protocols often involves simulators since management and operation of a large number of real vehicular nodes is expensive. We study the behavior of routing protocols in VANETs by using mobility information obtained from a microscopic vehicular traffic simulator that is based on the on the real road maps of Switzerland. The performance of AODV and GPSR is significantly in uenced by the choice of mobility model, and we observe a significantly reduced packet delivery ratio when employing the realistic traffic simulator to control mobility of nodes. To address the performance limitations of communication pro-tocols in VANETs, we investigate two improvements that increase the packet delivery ratio and reduce the delay until the first packet arrives. The traces used in this study are available for public download.

Generic mobility simulation framework (GMSF)

Vehicular ad-hoc networks with inter-vehicular communications are a prospective technology which contributes to safer and more efficient roads and offers information and entertainment services to mobile users. Since large real-world testbeds are not feasible, research on vehicular ad-hoc networks depends mainly on simulations. Therefore, it is crucial that realistic mobility models are employed. We propose a generic and modular mobility simulation framework (GMSF). GMSF simplifies the design of new mobility models and their evaluation. Besides, new functionalities can be easily added. GMSF also propose new vehicular mobility models, GIS-based mobility models. These models are based on highly detailed road maps from a geographic information system (GIS) and realistic microscopic behaviors (car-following and traffic lights management). We perform an extensive comparison of our new GIS-based mobility models with popular mobility models (Random Waypoint, Manhattan) and realistic vehicular traces from a proprietary traffic simulator. Our findings leverages important issues the networking community still has to address.

Towards Realistic Mobility Models for Vehicular Ad-hoc Networks

In performance studies of vehicular ad hoc networks, the underlying mobility model plays a major role. In this paper, we investigate the influence of three mobility models on the performance of ad hoc network routing protocols (AODV and GPSR). As a benchmark, we use the popular random waypoint mobility model. Our second model is based on a vehicular traffic simulator that we proposed in earlier work. Finally, as third model, we propose a novel mobility model based on vectorized street maps and speed limit information extracted from a geographic information system. With the two considered routing protocols, the random waypoint mobility model tends to lead to substantially higher performance than with our own, presumably more realistic mobility models.

HEAT: Scalable Routing in Wireless Mesh Networks Using Temperature Fields

Existing unicast routing protocols are not suited well for wireless mesh networks as in such networks, most traffic flows between a large number of mobile nodes and a few access points with Internet connectivity. In this paper, we propose HEAT, an anycast routing protocol for this type of communication that is designed to scale to the network size and to be robust to node mobility. HEAT relies on a temperature field to route data packets towards the Internet gateways, as follows. Every node is assigned a temperature value, and packets are routed along increasing temperature values until they reach any of the Internet gateways, which are modeled as heat sources. Our major contribution is a distributed protocol to establish such temperature fields. The distinguishing feature of our protocol is that it does not require flooding of control messages. Rather, every node in the network determines its temperature considering only the temperature of its direct neighbors, which renders our protocol particularly scalable to the network size. We analyze our approach and compare its performance with OLSR through simulations with Glomosim. We use realistic mobility patterns extracted from geographical data of large Swiss cities. Our results clearly show the benefit of HEAT versus OLSR in terms of scalability to the number of nodes and robustness to node mobility. The packet delivery ratio with HEAT is more than two times higher than OLSR in large mobile scenarios and we conclude that HEAT is a suitable routing protocol for city-wide wireless mesh networks.

Routing Packets into Wireless Mesh Networks

Wireless mesh networks are a promising way to provide Internet access to fixed and mobile wireless devices. In mesh networks, traffic between mesh nodes and the Internet is routed over mesh gateways. On the forward path, i.e., from mesh nodes to Internet nodes, for all mesh nodes only route information for one destination, the gateways, needs to be maintained. However, on the backward path from the Internet to mesh nodes, an individual route for every mesh node is required. In this paper we investigate protocols for backward path routing in wireless mesh networks. Using simulation experiments with realistic mobility patterns of pedestrians and cars in cities, we compare three protocols, each of which represents a routing protocol family: (i) AODV with an extension for mesh networks, a reactive routing protocol, (ii) FBR, a proactive routing protocol, and (iii) GSR, a source routing protocol. Our results indicate that FBR has the highest packet delivery ratio but is not scalable to the network size. The extended AODV seems to be neither scalable nor does it achieve a high packet delivery ratio. A good compromise is provided by GSR, which is the most scalable to the network size and still achieves a high packet delivery ratio.

Routing Metrics for Wireless Mesh Networks

Routing in wireless mesh networks has been an active area of research for many years, with many proposed routing protocols selecting shortest paths that minimize the path hop count. Whereas minimum hop count is the most popular metric in wired networks, in wireless networks interference- and energy- related considerations give rise to more complex trade-offs. Therefore, a variety of routing metrics has been proposed especially for wireless mesh networks providing routing algorithms with high flexibility in the selection of best path as a compromise among throughput, end-to-end delay, and energy consumption. In this paper, we present a detailed survey and taxonomy of routing metrics. These metrics may have broadly different optimization objectives (e.g., optimize application performance, maximize battery lifetime, maximize network throughput), different methods to collect the required information to produce metric values, and different ways to derive the end-to-end route quality out of the individual link quality metrics. The presentation of the metrics is highly comparative, with emphasis on their strengths and weaknesses and their application to various types of network scenarios. We also discuss the main implications for practitioners and identify open issues for further research in the area.

Routing in Large-Scale Wireless Mesh Networks Using Temperature Fields

Many wireless mesh networks are based on unicast routing protocols even though those protocols do not provide a particularly good fit for such scenarios. In this article, we report about an alternative routing paradigm, tailor-made for large multihop wireless mesh networks: field-based anycast routing. In particular, we present HEAT, a routing protocol based on this paradigm. In contrast to previous protocols, HEAT requires communication only between neighboring nodes. The underlying routing concept is a field similar to a temperature field in thermal physics. In extensive simulation experiments, we found that HEAT has excellent scalability properties due to a fully distributed implementation, and it provides much more robust routes than the unicast protocols, AODV and OLSR. As a consequence, in large-scale mobile scenarios, the packet delivery ratio with HEAT is more than two times higher, compared to AODV or OLSR. These promising results indicate that HEAT is suitable for large-scale wireless mesh networks that cover entire cities.

Link-Diversity Routing: A Robust Routing Paradigm for Mobile Ad Hoc Networks

We present link-diversity routing, a routing paradigm that achieves high path resilience in mobile ad hoc networks. Link-diversity routing chooses each hop of a packets route, so that the choice reflects the amount of outgoing links towards the destination at the intermediate hops. This choice maximizes the opportunities to make progress at every hop in the presence of unpredictable link failures caused by mobility or fading effects. As a result, link diversity routing takes paths which are less prone to fail due to individual link failures than traditional routing. We develop a loop-free and distributed link-diversity routing algorithm. The algorithm is based on an analogy from the heat theory which consists of routing packets along the steepest gradient of a temperature field. We perform simulations of our algorithm with a DSDV-based implementation. Our simulations show that link-diversity routing increases the end-to-end packet delivery ratio to a factor of up to four without any additional protocol overhead compared to the traditional minimum hop- count based DSDV.

The Transport Layer Revisited

End-to-end transport protocols such as TCP perform poorly in mobile environments, primarily due to their inability to cope with the dynamics incurred by node mobility. We re-consider the design decisions that lead to the end-to-end design of the transport layer. To this end, we present a framework for reliable hop-by-hop transport protocols. Based on this framework, we design and evaluate such a protocol and compare its performance to TCP. Overall, our hop-by-hop protocol achieves up to 3 times faster delivery of messages in our experiments with mobile networks. We conclude that hop-by-hop protocols might be more suitable for reliable communication in mobile networks than end-to-end protocols.

SaFT: Reliable Transport in Mobile Networks

End-to-end transport protocols perform poorly in mobile environments, primarily due to the frequent route breaks induced by node mobility. We present a framework for hop-by-hop transport protocols and propose a new reliable transport protocol: SaFT (store-and-forward transport). We evaluate its performance in mobile ad hoc networks vis-a-vis TCP. Overall, SaFT achieves up to 3 times faster delivery of messages in such networks. We conclude that store-and-forward protocols are suited well to provide reliable communication in mobile ad hoc networks