Position-Based Multicast for Mobile Ad-hoc Networks

In general, routing protocols for mobile ad-hoc networks (MANETs) can be classified into topology-based protocols and position-based protocols. While for unicast routing many proposals for both classes exist, the existing approaches to multicast routing basically implement topology-based algorithms and only a few of them make use of the geographic positions of the network nodes. These have in common that the sending node has to precalculate the multicast tree over which the packets are distributed and store it in each packet header. This involves two main issues: (a) These approaches are not very flexible with regard to topological changes which abandons the advantages that position-based routing has against topology-based routing, and (b) they do not scale with the number of receivers, since every one of them has to be named in the packet header. This thesis solves these issues and further advances position-based multicast routing. Position-Based Multicast (PBM) enhances the flexibility of position-based multicast routing by following the forwarding principle of position-based unicast routing. It transfers the choice of the next hops in the tree from the sender to the forwarding nodes. Based on the positions of their neighboring nodes, these are able to determine the most suitable next hop(s) at the moment when the packet is being forwarded. The scalability with respect to the number of receiving nodes in a group is solved by Scalable Position-Based Multicast (SPBM). It includes a membership management fulfilling different tasks at once. First, it administers group memberships in order to provide multicast sources with information on whether nodes are subscribed to a specific group. Second, it implements a location service providing the multicast sources with the positions of the subscribed receiver nodes. And third, it geographically aggregates membership data in order to achieve the desired scalability. The group management features two modes of operation: The proactive variant produces a bounded overhead scaling well with the size of the network. The reactive alternative, in contrast, reaches low worst-case join delays but does not limit the overhead. Contention-Based Multicast Forwarding (CBMF) addresses the problems that appear in highly mobile networks induced by outdated position information. Instead of basing forwarding decisions on a perception that may no longer be up to date, the packets are addressed only to the final destination; no explicit next hops are specified. The receiving nodes, which are candidate next hops, then decide by means of contention which of them are the most suitable next hop(s) for a packet. Not only is the decision made based on the most currently available data, but this procedure also saves the regular sending of beacon messages, thus reducing the overhead. The lack of multicast congestion control is another unsolved problem obstructing high-bandwidth data transmission. Sending out more and more packets to a multicast group lets the performance decrease. Backpressure Multicast Congestion Control (BMCC) takes care that the network does not need to handle more packets than it is able to. It achieves this by limiting the packet queues on the intermediate hops. A forwarder may not forward the next packet of a stream before it has noticed---by overhearing the transmission of the next hop---that the previous packet has succeeded. If there is congestion in an area, backpressure is implicitly built up towards the source, which then stops sending out packets until the congestion is released. BMCC takes care that every receiving node will receive packets at the same rate. An alternative mode of operation, BMCC with Backpressure Pruning (BMCC-BP) allows the cutting of congested branches for single packets, permitting a higher rate for uncongested receivers. Besides presenting protocols for multicast communication in MANETs, this thesis also describes implementations of two of the above-mentioned protocols. The first one is an implementation of SPBM for the Linux kernel that allows IP applications to send data via UDP to a group of receivers in an ad-hoc network. The implementation resides between the MAC layer and the network/IP layer of the network stack. It is compatible with unmodified standard kernels of versions 2.4 and 2.6, and may be compiled for x86 or ARM processor architectures. The second implementation is an implementation of CBMF for the ScatterWeb MSB430 sensor nodes. Due to their low-level programmability they allow an integration of the routing protocol with the medium access control. The absence of periodic beacon messages makes the protocol especially suitable for energy-constrained sensor networks. Furthermore, other constraints like limited memory and computational power demand special consideration as well

Unicast Ad-Hoc Routing in Vehicular City Scenarios

Within Vehicular Ad-Hoc Networking (VANET), i.e., networking between radio-equipped vehicles, unicast packet forwarding can be separated into the one-dimensional highway case and the two-dimensional city case. In this report, we survey the routing methods developed in the FleetNet and Network-on-Wheels projects plus a novel combination of two wellknown methods called PBR-DV or Position-Based Routing with Distance-Vector recovery. On the quest for a city-capable candidate routing algorithm as a possible standard, we discuss the usability and performance of the protocols in city scenarios. Finally, we conclude proposing PBR-DV as a candidate protocol for small-hop-count unicast VANET scenarios

A Hierarchical Approach to Position-Based Multicast for Mobile Ad-hoc Networks

In this paper we present Scalable Position-Based Multicast (SPBM), a multicast routing protocol for ad-hoc networks. SPBM uses the geographic position of nodes to provide a highly scalable group membership scheme and to forward data packets in a way that is very robust to changes in the topology of the network. SPBM bases the forwarding decision on whether there are group members located in a given direction or not, allowing for a hierarchical aggregation of membership information: the further away a region is from an intermediate node the higher the level of aggregation should be for this region. Because of aggregation, the overhead for group membership management scales logarithmically with the number of nodes and is independent of the number of multicast senders for a given multicast group. Furthermore, we show that group management overhead is bounded by a constant if the frequency of membership updates is scaled down with the aggregation level. This scaling of the update frequency is reasonable since the higher the level of aggregation the lower the number of membership changes for the aggregate. The performance of SPBM is investigated by means of simulation, including a comparison with ODMRP, and through mathematical analysis. We also describe an open source kernel implementation of SPBM that has been successfully deployed on hand-held computers

Huginn: A 3D Visualizer for Wireless ns-2 Traces

Discrete-event network simulation is a major tool for the research and development of mobile ad-hoc networks (MANETs). These simulations are used for debugging, teaching, understanding, and performance-evaluating MANET protocols. For the first three tasks, visualization of the processes occurring in the simulated network is crucial for verification and credibility of the generated results. Working with the popular network simulator ns-2, we have not yet found a visualization toolkit capable of reading native ns-2 trace files and providing means to change the evaluated parameters without changing the visualization software. Thus, we developed Huginn, a software providing an intuitive way to visualize simulation properties and to determine how they should be displayed without the need of programming. In addition, Huginn has a 3D interface allowing a high exploitation of the (human) user’s perceptive system. It helps to handle the significant cognitive load associated with the mental reconstruction of simulated network processes. Besides presenting the software interface and architecture, we describe algorithmic solutions that might be of a more general interest for similar problems

Scalable position-based multicast for mobile ad-hoc networks

In this paper we present Scalable Position-Based Multicast (SPBM), a multicast routing protocol for ad-hoc networks. SPBM uses the geographic position of nodes to provide a highly scalable group membership scheme and to forward data packets with a very low overhead. SPBM bases its multicast forwarding decision on whether there are group members located in a given direction or not, allowing for a hierarchical aggregation of group members contained in geographic regions: the larger the distance between a region containing group members and an intermediate node, the larger can this region be without having a significant impact on the accuracy of the direction from the intermediate node to that region. Because of aggregation, the overhead for group membership management is bounded by a small constant while it is independent of the number of multicast senders for a given multicast group. We investigate the performance of SPBM by means of simulation, including a comparison with ODMRP

Statistical Analysis of the FleetNet Highway Movement Patterns

The major objective of the FleetNet project [5, 2] was to develop a platform for inter-vehicle communication based on the principles of ad-hoc communication. In its process, unicast datagram routing served as one of the research focuses to identify and conquer the challenges of data forwarding in vehicular scenarios. Among others, car movement on highways was a scenario we paid attention to. To serve as a basis for network simulation, DaimlerChrysler provided realistic highway movement traces resulting from their own vehicular movement research [3]. This document is the complement to the Technical Report [4] where we describe the work done on the DaimlerChrysler traces in order to: a) model bidirectional scenarios, b) obtain Tcl scenarios compatible with the ns-2 simulator, and c) understand the vehicle distribution and movement of the resulting scenarios from a connectivity point of view. This report consists of the whole statistical evaluation of the basic set of scenarios listed in [4] and available to the VANET (Vehicular Ad-Hoc Network) community at [1]. We highly recommend the reading of [4], which describes the structure of this document and all parameters being analyzed

Studying Vehicle Movements on Highways and their Impact on Ad-Hoc Connectivity

While Mobile Ad-Hoc Networks are generally studied using a randomized node movement model such as the Random Way-Point model [8], Vehicular Ad-Hoc Networks deal with street-bound vehicles following a completely different movement pattern. This results - among other things - in a completely different connectivity situation and new challenges for data dissemination or routing/forwarding algorithms. Thus, researchers need a) suitable movement patterns for simulation, and b) a solid statistical understanding of the connectivity situation independent of the protocols utilized. In this work, we present a set of movement traces derived from typical situations on German Autobahns and an elaborate statistical analysis with respect to movement and connectivity relevant parameters. In addition, we present HWGui, a visualization, transformation, and evaluation package developed to study these scenarios. Beside the analysis capabilities HWGui is able, among other things, to generate movement files suitable for simulation with ns-2 [10]