Although far from optimal, flooding is an indispensable message dissemination technique for network-wide broadcast within mobile ad hoc networks (MANETs). As such, the plain flooding algorithm provokes a high number of unnecessary packet rebroadcasts, causing contention, packet collisions and ultimately wasting precious limited bandwidth. Studies have been undertaken to optimize flooding using a deterministic approach. Because of the highly dynamic and mobile characteristics of MANETs, probabilistic algorithms may be better suited. We explore the phase transition phenomenon observed in percolation theory and random graphs as a basis for defining probabilistic flooding algorithms. We consider models with and without packet collisions to better understand when phase transition occurs. We show through simulation that in cases of no collision control, probabilistic flooding greatly enhances network performance while significantly reducing broadcast packets in dense networks, although phase transition is not observed.

Traditionally, reliable multicast protocols are deterministic in nature. It is precisely this determinism that tends to become their limiting factor when aiming at reliability and scalability, particularly in highly dynamic networks, e.g., ad hoc networks. As probabilistic protocols, gossip-based multicast protocols, recently (re-)discovered in wired networks, appear to be a viable means to “fight fire with fire ” by exploiting the nondeterministic nature of ad hoc networks. This paper presents a protocol that is designed to meet a more practical specification of probabilistic reliability; this gossipbased multicast protocol, called Route Driven Gossip (RDG), can be deployed on any basic on-demand routing protocol. RDG is custom-tailored to ad hoc networks, achieving a high level of reliability without relying on any inherent multicast primitive. We illustrate our RDG protocol by layering it on top of the “bare” DSR protocol. We prove the reliability and scalability of RDG through both analysis and simulation.

We propose a distributed on-demand power-management protocol for collecting data in sensor networks. The protocol aims to reduce power consumption while supporting fluctuating demand in the network and provide local routing information and synchronicity without global control. Energy savings are achieved by powering down nodes during idle times identified through dynamic scheduling. We present a real implementation on wireless sensor nodes based on a novel, two-level architecture. We evaluate our approach through measurements and simulation, and show how the protocol allows adaptive scheduling and enables a smooth trade-off between energy savings and latency. An example current measurement shows an energy savings of 83 % on an intermediate node.

This paper studies the problem of updates in decentralised and self-organising P2P systems in which peers have low online probabilities and only local knowledge. The update strategy we propose for this environment is based on a hybrid push/pull rumor spreading algorithm and provides a fully decentralised, efficient and robust communication scheme which offers probabilistic guarantees rather than ensuring strict consistency. We describe a generic analytical model to investigate the utility of our hybrid update propagation scheme from the perspective of communication overhead.

Some forms of ad-hoc networks need to operate in extremely performance-challenged environments where end-to-end connectivity is rare. Such environments can be found for example in very sparse mobile networks where nodes ”meet ” only occasionally and are able to exchange information, or in wireless sensor networks where nodes sleep most of the time to conserve energy. Forwarding mechanisms in such networks usually resort to some form of intelligent flooding, as for example in probabilistic routing. We propose a communication algorithm that significantly reduces the overhead of probabilistic routing algorithms, making it a suitable building block for a delay-tolerant network architecture. Our forwarding scheme is based on network coding. Nodes do not simply forward packets they overhear but may send out information that is coded over the contents of several packets they received. We show by simulation that this algorithm achieves the reliability and robustness of flooding at a small fraction of the overhead.

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We propose a generic framework for distributed broadcasting in ad hoc wireless networks. The approach is based on selecting a small subset of nodes (also called nodes) to form a forward node set to carry out a broadcast process. The status of each node, forward or non-forward, is determined either by the node itself or by other nodes. Node status can be de-termined at different snapshots of network state along time (called views) without causing problems in broadcast coverage. Therefore, the forward node set can be constructed and main-tained through either a proactive process (i.e., “up-to-date”) before the broadcast process or a reactive process (i.e., “on-the-fly”) during the broadcast process. A sufficient condition, called coverage condition, is given for a node to take the non-forward status. Such a condition can be easily checked locally around the node. Several existing broadcast algorithms can be viewed as special cases of the generic framework with k-hop neighborhood information. A compre-hensive comparison among existing algorithms is conducted. Simulation results show that new algorithms, which are more efficient than existing ones, can be derived from the generic framework.

We show that network coding allows to realize energy savings in a wireless ad-hoc network, when each node of the network is a source that wants to transmit information to all other nodes. Energy efficiency directly affects battery life and thus is a critical design parameter for wireless networks. We propose an implementable method for performing network coding in such a setting. We analyze theoretical cases in detail, and use the insights gained to propose a practical, fully distributed method for realistic wireless ad-hoc scenarios. We address practical issues such as setting the forwarding factor, managing generations, and impact of transmission range. We use theoretical analysis and packet level simulation.

Mainstream approaches to content-based distributed publish-subscribe typically route events deterministically based on information collected from subscribers, and do so by relying on a tree-shaped overlay network. While this solution achieves scalability in fixed, large-scale settings, it is less appealing in scenarios characterized by high dynamicity, e.g., mobile ad hoc networks or peer-to-peer systems. At the other extreme, researchers in the related fields of multicast and group communication have successfully exploited probabilistic techniques that provide increased fault tolerance, resilience to changes, and yet are scalable. In this paper, we propose a novel approach where event routing relies on deterministic decisions driven by a limited view on the subscription information and, when this is not sufficient, resorts to probabilistic decisions performed by selecting links at random. Simulations show that the particular mix of deterministic and probabilistic decisions we put forth in this work is very effective at providing high event delivery and low overhead in highly dynamic scenarios, without sacrificing scalability. 1.

We study an efficient broadcast scheme in mobile ad hoc networks (MANETs). The objective is to determine a small set of forward nodes to ensure full coverage. We first study several methods to select a small forward node set assuming that the neighborhood information can be updated in a timely manner. Then we consider a general case, where each node updates its neighborhood information based asynchronously on a pre-defined frequency and node move even during the broadcast process. The virtual network constructed from local views of nodes may not be connected, its links may not exist in the physical network, and the global view constructed from collection of local views may not be consistent. In this paper, we first give a sufficient condition for connectivity at the physical network to ensure the connectivity at the virtual network. We then propose a solution using two transmission ranges to address the link availability issue. The neighborhood information as well as the forward node set are determined based on a short transmission range while the broadcast process is done on a long transmission range. The difference between these two ranges is based on the update frequency and the speed of node movement. Finally, we propose a mechanism called aggregated local view to ensure consistency of the global view. By these, we extend Wu and Dai’s coverage condition for broadcasting in a network with mobile nodes. The simulation study is conducted to evaluate the coverage of the proposed scheme.