Ad hoc networks consist of a set of identical nodes that move freely and independently and communicate with other node via wireless links. Such networks may be logically represented as a set of clusters by grouping together nodes that are in close proximity with one another. Clusterheads form a virtual backbone and may be used to route packets for nodes in their cluster. Nodes are assumed to have non-deterministic mobility pattern. Clusters are formed by diffusing node identities along the wireless links. Different heuristics employ different policies to elect clusterheads. Several of these policies are biased in favor of some nodes. As a result, these nodes shoulder greater responsibility and may deplete their energy faster, causing them to drop out of the network. Therefore, there is a need for load-balancing among clusterheads to allow all nodes the opportunity to serve as a clusterhead. We propose a loadbalancing heuristic to extend the life of a clusterhead to the maximum budget b...

A newly deployed multi-hop radio network is unstructured and lacks a reliable and e#cient communication scheme. In this paper, we take a step towards analyzing the problems existing during the initialization phase of ad hoc and sensor networks. Particularly, we model the network as a multihop quasi unit disk graph and allow nodes to wake up asynchronously at any time. Further, nodes do not feature a reliable collision detection mechanism, and they have only limited knowledge about the network topology. We show that even for this restricted model, a good clustering can be computed e#ciently. Our algorithm e#ciently computes an asymptotically optimal clustering. Based on this algorithm, we describe a protocol for quickly establishing synchronized sleep and listen schedule between nodes within a cluster. Additionally, we provide simulation results in a variety of settings.

This paper presents a novel framework for dynamically organizing mobile nodes in wireless ad-hoc networks into clusters in which the probability of path availability can be bounded. The purpose of the (ff; t)\GammaCluster is to help minimize the far-reaching effects of topological changes while balancing the need to support more optimal routing. A mobility model for ad-hoc networks is developed and is used to derive expressions for the probability of path availability as a function of time. It is shown how this model provides the basis for dynamically grouping nodes into clusters using an efficient distributed clustering algorithm. Since the criteria for cluster organization depends directly upon path availability, the structure of the cluster topology is adaptive with respect to node mobility. Consequently, this framework supports an adaptive hybrid routing architecture that can be more responsive and effective when mobility rates are low and more efficient when mobility rates are hig...

A fault-tolerant distributed mutual exclusion algorithm which adjusts to node mobility is presented, along with proof of correctness and simulation results. The algorithm requires nodes to communicate with only their current neighbors, making it well-suited to the ad hoc environment. Experimental results indicate that adaptation to mobility can improve performance over that of similar non-adaptive algorithms when nodes are mobile.

A taxonomy of broadcast protocols in mobile ad hoc networks (MANETs) is given where protocols are classified into four groups: global, quasi-global, quasi-local, and local. The taxonomy also divides protocols based on the nature of algorithms: probabilistic and deterministic. The locality of maintenance also plays an important role in evaluating the protocol. An important objective in designing a broadcast protocol is to reduce broadcast redundancy to save scarce resources such as energy and bandwidth and to avoid the broadcast storm problem. This objective should be achieved without introducing excessive overhead and time delay, measured by the sequential rounds of information exchanges. This is done by choosing a small forward node set that forms a connected dominating set (CDS) to carry out a broadcast process. In this paper, a clustered network model is proposed in which each node is a clusterhead in the clustered architecture. Clusterheads are connected by carefully selecting non-clusterhead nodes locally at each clusterhead to connect clusterheads within 2.5 hops, a novel notion proposed in this paper. Information of neighbor clusterheads are piggybacked with the broadcast packet to further reduce each forward node set. It is shown that this approach is quasi-local with locality of maintenance. In addition, this approach has a constant approximation ratio to the minimum connected dominating set (MCDS) and generates a small forward node set in the average case. Comparisons are also done through simulation with representative protocols from each of the four groups of protocols based on the proposed taxonomy.

Shared Tree multicast is a well established concept used in several multicast protocols for wireline networks (eg. Core Base Tree, PIM sparse mode etc). In this paper, we extend the Shared Tree concept to wireless, mobile, multihop networks for applications ranging from ad hoc networking to disaster recovery and battlefield. The main challenge in wireless, mobile networks is the rapidly changing environment. We address this issue in our design by: (a) using "soft state"; (b) assigning different roles to nodes depending on their mobility (two level mobility model); (c) proposing an adaptive scheme which combines shared tree and source tree benefits. A detailed wireless simulation model is used to evaluate the proposed schemes and compare them with source based tree (as opposed to shared tree) multicast. Both uniform and 2-level mobility models are used in the comparison. The results show that shared tree protocols have low overhead and are very robust to mobility. In particular, the Ada...

The efficiency of a communication network depends not only on its control protocols, but also on its topology. We propose a distributed topology management algorithm that constructs and maintains a backbone topology based on a minimal dominating set (MDS) of the network. According to this algorithm, each node determines the membership in the MDS for itself and its one-hop neighbors based on two-hop neighbor information that is disseminated among neighboring nodes. The algorithm then ensures that the members of the MDS are connected into a connected dominating set (CDS), which can be used to form the backbone infrastructure of the communication network for such purposes as routing. The correctness of the algorithm is proven, and the efficiency is compared with other topology management heuristics using simulations. Our algorithm shows better behavior and higher stability in ad hoc networks than prior algorithms.

In this paper we present a multicast protocol which builds upon a cluster based wireless network infrastructure. First, we introduce the network infrastructure which includes several innovative features such as: minimum change cluster formation; dynamic priority token access protocol, and; distributed hierarchical routing. Then, for this infrastructure we propose a multicast protocol which is inspired by the Core Based Tree approach developed for the internet. We show that the multicast protocol is robust to mobility, has low bandwidth overhead and latency, scales well with membership group size, and can be generalized to other wireless infrastructure. I. Introduction Wireless networks provide mobile users with ubiquitous communicating capability and information access regardless of location. In this paper we address a particular type of wireless networks called "multihop" networks. As a difference from "single hop" (i.e. cellular) networks [12] which require fixed base stations inte...

In this paper we propose an "on demand" multicast routing protocol for a wireless, mobile, multihop network. The proposed scheme has two key features: (a) it is based on the forwarding group concept (i.e., a subset of nodes is in charge of forwarding the multicast packets via scoped flooding) rather than on the conventional multicast tree scheme; (b) it dynamically refreshes the forward group members using a procedure akin to on demand routing (hence the name). "On Demand" multicast is well suited to operate in an On Demand routing environment where routes are selectively computed as needed between communicating node pairs instead of being maintained and updated globally by a routing "infrastructure" (like in Distance Vector or Link State, for example). On Demand Multicast is particularly attractive in mobile, rapidly changing networks, where the traffic overhead caused by routing updates and tree reconfigurations may become prohibitive beyond a critical speed; and, in large networks w...

In this paper we evaluate several routing protocols for mobile, wireless, ad hoc networks via packet level simulations. The ad hoc networks are multi-hop wireless networks with dynamically changing network connectivity owing to mobility. In the protocol suite includes several routing protocols specifically designed for ad hoc routing, as well as more traditional protocols, such as link state and distance vector, used for dynamic networks. Performance is evaluated with respect to fraction of packets delivered, end-to-end delay and routing load for a given traffic and mobility model. Both small (30 nodes) and medium sized (60 nodes) networks are used. It is observed that the new generation of on-demand routing protocols use much lower routing load, especially with small number of peer-to-peer conversations. However, the traditional link state and distance vector protocols provide, in general, better packet delivery and end-to-end delay performance. 1 Introduction A mobile, ad hoc networ...