Showing papers by "Hannes Hartenstein published in 2003"

A routing strategy for vehicular ad hoc networks in city environments

Abstract: Routing of data in a vehicular ad hoc network is a challenging task due to the high dynamics of such a network. Recently, it was shown for the case of highway traffic that position-based routing approaches can very well deal with the high mobility of network nodes. However, baseline position-based routing has difficulties to handle two-dimensional scenarios with obstacles (buildings) and voids as it is the case for city scenarios. In this paper we analyze a position-based routing approach that makes use of the navigational systems of vehicles. By means of simulation we compare this approach with non-position-based ad hoc routing strategies (dynamic source routing and ad-hoc on-demand distance vector routing). The simulation makes use of highly realistic vehicle movement patterns derived from Daimler-Chrysler's Videlio traffic simulator. While DSR's performance is limited due to problems with scalability and handling mobility, both AODV and the position-based approach show good performances with the position-based approach outperforming AODV.

Contention-based forwarding for mobile ad-hoc networks

Abstract: Existing position-based unicast routing algorithms which forward packets in the geographic direction of the destination require that the forwarding node knows the positions of all neighbors in its transmission range. This information on direct neighbors is gained by observing beacon messages each node sends out periodically. Due to mobility, the information that a node receives about its neighbors becomes outdated, leading either to a significant decrease in the packet delivery rate or to a steep increase in load on the wireless channel as node mobility increases. In this paper, we propose a mechanism to perform position-based unicast forwarding without the help of beacons. In our contention-based forwarding scheme (CBF) the next hop is selected through a distributed contention process based on the actual positions of all current neighbors. For the contention process, CBF makes use of biased timers. To avoid packet duplication, the first node that is selected suppresses the selection of further nodes. We propose three suppression strategies which vary with respect to forwarding efficiency and suppression characteristics. We analyze the behavior of CBF with all three suppression strategies and compare it to an existing greedy position-based routing approach by means of simulation with ns-2. Our results show that CBF significantly reduces the load on the wireless channel required to achieve a specific delivery rate compared to the load a beacon-based greedy forwarding strategy generates.

A performance comparison of Mobile IPv6, Hierarchical Mobile IPv6, fast handovers for Mobile IPv6 and their combination

Abstract: Mobile IP, the current IETF proposal for IP mobility support, represents a key element for future All-IP wireless networks to provide service continuity while on the move within a multi-access environment. We conducted a performance evaluation of Mobile IPv6 and its proposed enhancements, i.e., Fast Handovers for Mobile IPv6, Hierarchical Mobile IPv6 and our proposed combination of them, using the network simulator ns-2 for the case of a 'hot spot' deployment scenario. The simulation scenario comprises four access routers and up to 50 mobile nodes that communicate in accordance with the IEEE 802.11 wireless LAN standard. The study provides quantitative results of the performance improvements obtained by the proposed enhancements as observed by a single mobile user with respect to handoff latency, packet loss rate and achieved bandwidth per station. As a complementary part of the study, the signaling load costs associated with the performance improvements provided by the enhancements has been analyzed. The simulation environment allowed us also to investigate the behavior of the protocol in extreme cases, e.g., under channel saturation conditions and considering different traffic sources: CBR, VoIP, Video and TCP transfers. While some simulation results corroborate the intention of the protocols specifications, other results give insights not easily gained without performing simulations. This study provides a deep understanding of the overall performance of the various protocols and supports the design process of a Mobile IPv6-based network when a decision of whether it is appropriate to implement any of the proposed Mobile IPv6 enhancements has to be made.

Location-based routing for vehicular ad hoc networks

Abstract: Communication between vehicles is likely to be one key area where mobile ad-hoc networks will be used in the near future. Currently there are several projects ([1, 3]) that investigate this application area, while car manufacturers and their suppliers aim at the development of products within the next few years. This raises the question what kind of routing algorithm is suited for communication between vehicles. Existing performance studies for various ad-hoc routing protocols do not use movement patterns which resemble the movement of cars and are thus not well suited to answer this question. We have conducted an extensive simulation study based on realistic vehicle movement patterns. Our main aim was to investigate how a topology-based approach compares to a location-based routing scheme when applied to vehicular networks. As representatives we have chosen DSR [4] as a topology-based approach and GPSR [5] complemented with a simple location service as a location-based scheme. For a general discussion of topology-based and location-based ad-hoc routing please refer to [2] and [6]. Vehicular ad-hoc networks have several unique characteristics. The main challenge is the high speed with which nodes move in respect to each other. If oncoming traffic is included in the forwarding of packets, then relative speeds of 250 km/h to 300 km/h are common. This implies a very high rate of topology changes. Also it is not clear if one single partition spans sufficient distance to enable meaningful applications such as emergency warnings or vehicle-to-vehicle entertainment. On the other hand it is safe to assume that battery power is not an issue for vehicular ad-hoc networks. Location-based approaches further benefit from the fact that vehicles are aware of their geographical positions through the use of on-board navigation systems.

A novel forwarding paradigm for position-based routing (with implicit addressing)

Abstract: Existing position-based unicast routing algorithms, which forward packets in the geographic direction of the destination, require that the forwarding node knows the positions of all neighbors in its transmission range. This information on direct neighbors is gained by observing beacon messages each node sends out periodically. Due to mobility, the information that a node receives about its neighbors becomes outdated, leading either to a significant decrease in the packet delivery rate or to a steep increase in load on the wireless channel as node mobility increases. We describe a mechanism to perform position-based unicast forwarding without the help of beacons. In our contention-based forwarding (CBF) scheme, the next hop is selected through a distributed contention process based on the actual positions of all current neighbors. For the contention process, CBF makes use of biased timers. To avoid packet duplication, the first node that is selected suppresses the selection of further nodes. Since the basic scheme can lead to packet duplication, we describe alternative ways of suppressing those. In addition to that, we compare the CBF schemes and standard greedy forwarding by means of simulation with ns-2.

Position-based routing in ad hoc wireless networks

Abstract: In ad hoc networks, autonomous nodes collaborate to route information through the network. Commonly, nodes are end-systems and routers at the same time. In cases in which nodes have a notion of their geographic position, position-based routing protocols can be used; these protocols' properties of statelessness and fast adaptability to changes in the topology match very well with the characteristics of ad hoc networks.Position-based routing does not require the maintenance of routes; instead, forwarding decisions are made locally, based only on the node's own position, the positions of its neighbors, and the position of the destination. The routing algorithms are complemented by location services through which a node can obtain the position of a packet's destination.We will introduce the main components of position-based routing, discuss position-based routing algorithms as well as location services, and present an application scenario where position-based routing can be used for intervehicle communication.

Beaconless Position-Based Routing for Mobile Ad-Hoc Networks

Abstract: Existing position-based unicast routing algorithms, where packets are forwarded in the geographic direction of the destination, require that the forwarding node knows the positions of all neighbors in its transmission range. This information on direct neighbors is gained by observing beacon messages each node sends out periodically. The transmission of beacons and the storage of neighbor information consumes resources. Due to mobility, collected neighbor information can quickly get outdated which in turn can lead to packet drops. In this paper, we propose a mechanism to perform position-based forwarding without the help of beacons or the maintenance of neighbor tables. In our contention-based forwarding scheme(CBF) the next hop is selected through a distributed contention process using biased timers. To avoid packet duplication, the first node that is selected suppresses the selection of further nodes. We propose three suppression strategies which vary with respect to forwarding efficiency and suppression characteristics. We analyze the behavior of CBF with all three suppression strategies and compare it to an existing greedy routing approach by means of simulation with ns-2. Our results demonstrate that CBF is a promising strategy for position-based routing.

Toward a mobility metric for comparable & reproducible results in ad hoc networks research

Abstract: The performance of a mobile ad hoc network depends on its ability to adapt to changes in the network topology. It is therefore important to understand the relation between node mobility and topology dynamics. While the input parameters of a mobility model allow for generating different simulation scenarios (e.g., by selecting the speed, pause time, system area, and number of nodes), the relation to the actually generated degree of topology dynamics is usually not immediate. Thus, a translation of the mobility model to the resulting topology dynamics is required. A natural way to do this is to introduce the topology change rate (TCR), defined as the number of link changes per time unit as observed by a single node. If we measure the network performance versus the TCR instead of versus ‘incidental’ input parameters of a mobility model, a higher level of abstraction of the results will be achieved, and the reproducability and comparability of the results will be enhanced. This short paper derives in an analytical manner the TCR in a scenario where nodes move according to the random waypoint (RWP) model [5], being the most heavily used mobility model in reseach on ad hoc networks. Recent insights into RWP mobility have shown some unexpected behavior, e.g., with respect to the spatial node distribution [2] and the average velocity over time [8]. These results do not mean that RWP as a mobility model is ‘invalid’, but show the importance of proper use due to thorough understanding of the model. This contribution now provides the link between RWP mobility and the corresponding TCR. We • derive in an analytical manner the TCR as observed by a static node located at the center of a circular area in which mobile nodes move according to RWP model. • show via simulation that our expression takes over to the TCR as observed by a moving node and to other shapes of the system area. We see this result as a step towards establishing TCR as a ‘generic’ mobility metric that can help to improve the reproducability and comparability of simulation results on ad hoc networking.

Simulation Results and a Proof-of-Concept Implementation of the FleetNet Position-Based Router

Abstract: The FleetNet project1 [1,2,3] develops a platform for inter-vehicle communications based on ad hoc networking principles.With an ad hoc network established by moving vehicles, a realm of applications – ranging from exchange of emergency warnings or sensor data to unicast communication between passengers of different vehicles and to integration of the vehicular ad hoc network with the Internet through static or mobile FleetNet gateways – could be enabled in a low-latency, robust and low-cost fashion.

A simulation study on the performance of hierarchical mobile IPv6

Abstract: We performed a simulative evaluation of Hierarchical MIPv6 in comparison with standard MIPv6 using the network simulator ns-2 for a ‘hot spot deployment’ scenario. The simulation scenario comprises four access routers and up to 50 mobile nodes that move randomly and communicate in accordance with the IEEE 802.11 wireless LAN standard. The study provides quantitative results of the improvements provided by HMIPv6 with respect to handoff latency, packet loss, signaling load and bandwidth per station. The simulation environment allowed us also to investigate the behavior of the protocol in extreme cases, e.g., under channel saturation conditions, and considering different traffic sources: CBR, Video, VoIP and TCP.

Simulation Results and a Proof-of-Concept Implementation of the FleetNet Position-Based Router: Extended Abstract.

Abstract: The FleetNet project1 [1,2,3] develops a platform for inter-vehicle communications based on ad hoc networking principles.With an ad hoc network established by moving vehicles, a realm of applications – ranging from exchange of emergency warnings or sensor data to unicast communication between passengers of different vehicles and to integration of the vehicular ad hoc network with the Internet through static or mobile FleetNet gateways – could be enabled in a low-latency, robust and low-cost fashion.