Abstract—A hybrid ad hoc network is a structure-based network that is extended using multihop communications. Indeed, in this kind of network, the existence of a communication link between the mobile station and the base station is not required: A mobile station that has no direct connection with a base station can use other mobile stations as relays. Compared with conventional (single-hop) structure-based networks, this new generation can lead to a better use of the available spectrum and to a reduction of infrastructure costs. However, these benefits would vanish if the mobile nodes did not properly cooperate and forward packets for other nodes. In this paper, we propose a charging and rewarding scheme to encourage the most fundamental operation, namely packet forwarding. We use “MAC layering ” to reduce the space overhead in the packets and a stream cipher encryption mechanism to provide “implicit authentication ” of the nodes involved in the communication. We analyze the robustness of our protocols against rational and malicious attacks. We show that—using our solution—collaboration is rational for selfish nodes. We also show that our protocols thwart rational attacks and detect malicious attacks. Index Terms—Network-level security and protection, wireless communication, authentication security, payment schemes. 1

This paper investigates the probabilistic connectivity

Caching is an important technique to support pervasive Internet access. Cache consistency measures the deviation between the cached data and the source data. In mobile computing environments, especially with ad hoc networks, users are in great need of the flexibility in tuning their consistency requirements, in order to make tradeoffs between the specified cache consistency and the cost incurred. Existing works have used Delta Consistency (DC) and Probabilistic Consistency (PC) which, to some extent, provide the users with such flexibility. In this paper, we propose a general consistency model called Probabilistic Delta Consistency (PDC). PDC covers all existing consistency models including DC and PC, and integrates the flexibility granted by both DC and PC. Thus, PDC enables the users to flexibly specify their consistency requirements in two orthogonal dimensions, namely the deviation in time/value and the ratio of queries gaining the specified consistency. We also propose a consistency maintenance algorithm, called Flexible Combination of Push and Pull (FCPP), which can meet users ’ consistency requirements specified under the PDC model. An analytical model is derived to achieve the optimized combination of push and pull, so as to ensure the user-specified consistency requirements, while minimizing the consistency maintenance overhead. Extensive simulations are conducted to evaluate the performance of the FCPP algorithm. Evaluation results show that, compared with the widely used Dynamic TTR algorithm, FCPP can save up to 68 % of the traffic overhead and reduce the query delay by up to 84%. 1.

Abstract—The growth in wireless communication technologies attracts a considerable amount of attention in mobile ad hoc networks. Since mobile hosts in an ad hoc network usually move freely, the topology of the network changes dynamically and disconnection occurs frequently. These characteristics make it likely for a mobile ad hoc network to be separated into several disconnected partitions, and the data accessibility is hence reduced. Several schemes are proposed to alleviate the reduction of data accessibility by replicating data items. However, little research effort was elaborated upon exploiting the group mobility where the group mobility refers to the phenomenon that several mobile nodes tend to move together. In this paper, we address the problem of replica allocation in a mobile ad hoc network by exploring group mobility. We first analyze the group mobility model and derive several theoretical results. In light of these results, we propose a replica allocation scheme to improve the data accessibility. Several experiments are conducted to evaluate the performance of the proposed scheme. The experimental results show that the proposed scheme is able to not only obtain higher data accessibility, but also produce lower network traffic than prior schemes. Index Terms—Mobile data service, replica allocation, data accessibility, mobile computing, ad hoc networks. 1

This study presents an analysis of the impact of mitigation on computer worm propagation in Mobile Ad-hoc Networks (MANETS). According to the recent DARPA BAA-Defense Against Cyber Attacks on MANETS [4], ”One of the most severe cyber threats is expected to be worms with arbitrary payload that can infect and saturate MANETbased networks on the order of seconds”. Critical to the design of effective worm counter measures in MANET environments is an understanding of the propagation mechanisms and the performance of the mitigation technologies. This work aims to advance the security of these critical systems through increased knowledge of propagation mechanisms, performance and the effect of mitigation technologies. We present both analytic and simulation analysis of

Mobility models are widely used in the simulation-based performance analysis of mobile networks. However, there is a trade-off between simple parametrization and realistic movement patterns. Synthetic models like the random waypoint and random direction model are simple to implement, but they only provide unrealistic simple user sojourn densities and traffic flows. In contrast, graph- or trip-based mobility models are complex to parameterize and their results are difficult to compare. In this paper, we propose the location-dependent parameterization of the random direction model to fill this gap. This model extension allows to setup non-homogeneous mobility scenarios, in particular based on real-world traces, while it still belongs to the class of synthetic random walk mobility models. We show that the location-dependent parametrization can accurately model arbitrary mobility patterns with very limited implementation complexity.

Performance evaluation of ad hoc routing protocols typically depends on simulation, since the deployment of ad hoc networks is still relatively rare. However, past evaluations of multicast routing protocols have utilized a single, simple mobility model with low density and often very low traffic rates. In this paper we explore the performance of multicast routing under a set of scenarios based on varying mobility patterns, density and traffic rates. We use these scenarios to uncover performance bottlenecks in both ODMRP and ADMR, resulting in significant performance degradation in some cases. By identifying the mechanisms that cause these bottlenecks, we identify general cases where ad hoc multicast routing protocols can improve their performance.

Opportunistic communication allows humans equipped with mobile devices to exchange information via a wireless link whenever they are nearby. This work examines the performance of a profile-based data dissemination scheme. We use a 2step simulation approach which combines realistic user mobility traces with synthetic mobility models. We consider different system configurations and evaluate their effects on the data dissemination scheme. In particular, we look at how different wireless networking technologies affect the system and how much can we benefit from the installation of fixed information sprinkler nodes. Furthermore, we investigate the effects of user behavior by comparing selfish and generous users. Our results clearly demonstrate that realistic user mobility patterns result in a feasible opportunistic data dissemination scheme. In most of the studies scenarios, the effectiveness of the dissemination is very high, with over 90 % of the users reached within a week of real time. Our results on user behavior show that although the effects of selfish behavior can be mitigated, they cannot be completely eliminated. I.

Abstract—Routing in a mobile ad hoc network is challenging because nodes can move at any time, invalidating a previouslydiscovered route. Multicast routing is even more challenging, because a source needs to maintain a route to potentially many group members simultaneously. Providing scalable solutions to this problem typically requires building a hierarchy or an overlay network to reduce the cost of route discovery and maintenance. In this paper, we show that a much simpler alternative is possible, by using source specific semantics and relying on the unicast routing protocol to find all routes. This separation of concerns enables the multicast routing protocol to focus on minimizing join latency, repair latency, and control overhead. We design a routing protocol based on these principles and demonstrate its effectiveness through simulations. I.

The modeling of user movements is used to investigate network performance of Mobile IP and Ad-Hoc networks. Of the several movement models which exist, one which is in common use is the Random Waypoint Model (RWP). In this presentation we summarise the movement models in use and their application, and examine their validity for Mobile IP by using a real-life trace of user movement.