An increasing demand for ubiquitous connectivity has motivated the integration of various wireless technologies such as cellular systems, WLANs, and MANETS. The multi-hop connectivity paradigm is gaining importance as it increases the coverage and capacity of infrastructure networks by integrating with ad-hoc type of networks. In multi-hop wireless networks two fundamental questions are, can multi-hop networks provide uninterrupted connectivity due to the mobility of the intermediate relay

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... and how to determine the service quality in a multi-hop network for a given network scenario. In this article we develop an analytical model to evaluate the performance of multi-hop networks and analyze the performance of multi-hop networks under different network scenarios." "The capacity of CDMA cellular networks is interference limited. Multi-hop cellular communication promises to reduce interference, hence increasing the capacity. However, such capacity gains depend on the actual interference. The location of a call determines its interference effect on the network. In this paper, we study the effect of call distribution on the capacity of multi-hop CDMA cellular networks. The capacity of multi-hop is compared to that of the single hop case. The effect of non-uniform call distribution inside a cell is studied. It is shown that in the multi-hop case call distribution in a cell affects the capacity of this cell but hardly the capacity of its neighboring cells. The case is reversed in the single-hop case. Call distribution in a cell has no effect on the capacity of this cell, but it can have a significant effect on the capacity of surrounding cells. It is shown that if calls tend to originate near the border of one cell, this can seriously degrade the capacity of the whole network. This scenario is alleviated in the multi-hop case due to the shorter distances signals have to travel, hence resulting in lower interference. This paper also highlights the scenarios where multi-hop communication is deeply needed." "Many methods for end-to-end bandwidth estimation on wired networks assume that link capacities are constant and that all cross-traffic interaction occurs through queuing delays at node buffers. Wireless ad hoc networks do not conform to these assumptions due to the shared and unreliable nature of the transmission medium. In this paper we show that the end-to-end bandwidth is a random variable distributed within some range, which depends on the packet length, among other factors. After developing a simple theoretical framework to compare with, we devise a simple and effective dispersion-based method to estimate the mean of the end-to-end bandwidth as a function of packet length. The method is shown to converge quickly to an accurate estimate for any packet length, to be robust against cross-traffic, and to timely track bandwidth variations. All this is accomplished with high efficiency." "This paper analyses the implementation of best-effort services over mobile ad hoc networks considering that, if no special transport protocols are used, a mobile ad hoc may be rendered useless to conventional applications. The paper develops an analytical model for the capacity of mobile ad hoc networks, which is able to indicate when the ad hoc network is effectively unusable. It was verified by a large scale simulation study. The simulation study also provides empirical rules that can be used to implement algorithms for real-time operation of mobile ad hoc networks. After validating our model, we provide a set of engineering rules for capacity management in such networks." "Mobile Ad-hoc Networks (MANETs) are particularly difficult to manage due to the highly dynamic nature of its traffic, caused by variations on the number of users, their locations and the type of applications they use. This paper proposes a new modeling framework for mobile ad-hoc networks that integrates all important functional characteristics of a MANET and is able to predict network Quality of Service (QoS) based only on traffic measurements (or simulations), without requiring any information on the network structure, traffic routing or users' mobility. The application of the proposed framework to a specific modeling problem involves two phases: first, the network model is built from a set of (past) measurements of the gateways inbound/outbound traffic and the corresponding network QoS metrics, then, the constructed model can be used to predict (future) values of the QoS metrics based only on the inbound/outbound traffic. This framework does not impose any restrictions to the type of metrics that are selected to characterise QoS. Our results show that this approach can achieve excellent performance in terms of predicting QoS at multiple gateways, even when there are significant changes in the number of network users." back to top "Application Layer Multicast (ALM) was proposed as a practical alternative to overcome the difficulty of large scale deployment of IP multicast. An important number of solutions were yet proposed for constructing overlay networks, however only a limited effort was given to security issues in ALM. In this paper we propose an efficient key management protocol, called Transition Key Scheme (TKS), that can be applied within any ALM solution. Our scheme reduces the key management overhead in case of highly dynamic membership sessions. Simulation results confirm that TKS reduces significantly key management overhead, compared to other existing ALM key management protocols." "This work presents the design of real-time application for wireless sensor networks (WSNs) using an algorithm based on data stream. The proposed algorithm is based on sampling techniques applied to data histograms created from original data streams acquired by sensor nodes. As a result, the algorithm provides a sample of only log n items that represents the original data stream of n elements. In this work, we show how to use the data reduction algorithm in real-time WSN design." "There are many applications of ad hoc sensor networks that have to ensure immunity to adversaries. One challenge is how to bootstrap secure communication among nodes. Several schemes for the pre-distribution of keys have been proposed, however, they usually have high memory requirements or large communication overhead if sensor network is large. In this paper we propose a novel key pre-distribution scheme based on polynomials. The properties of our scheme are the same as a scheme presented by Blom, but we propose to use a different technique that can be easily extended if we get rid of a node's computation constrains (e.g. in ad hoc networks). By using polynomial-based key pre-distribution, we can reduce the storage needed at receivers down to $O(t)$ where $t$ is a system and security parameter. Moreover using only this information, pairwise keys can be established efficiently for each pair of nodes. Using pairwise keys, nodes are able to establish group and routing keys and construct the communication tree securely." "In this paper we analyze how to reduce the time dedicated to network access control operations in mobile ad hoc networks (MANET) with Internet connectivity. This topic is interesting in many scenarios where operators deploy the MANET as an access network to their infrastructure. The objective is to provide a mechanism allowin Internet gateways to accepts only authorized traffic without decreasing the overall performance of network and ad-hoc nodes. We propose a solution based on pre-autheication which uses utillity-based optimal control to choose with which gateways to pre-authenticate over time. We prove through simulation results that the proposed scheme improves traidtional schemes in different scenarios." back to top ; Paulo Mendes (DoCoMo Eurolabs, Germany); "It is expected that next generation of networks will handle new types of services which are destined to large audiences and have different QoS requirements. From the transport point of view, multicast is the most suitable technology for the required group communication services, since it avoids packets duplication and saves network resources. However, QoS-aware multicast content deliver raises several problems, such as the control of QoS trees in environments with asymmetric routing. This paper presents Multi-servIce Resource Allocation (MIRA), a multicast-aware resource reservation protocol for class-based networks that consider routing asymmetries. MIRA controls the resources of network classes associated to multicast sessions considering the QoS characteristics of the latter and network conditions of the available classes in the source-to-receivers path. A detailed description of the functionalities of MIRA and a conceptual analysis against RSVP and RMD-QoSM are presented. Finally, the session setup time, and the signalling and state overheard in comparison with RSVP are analyzed based on simulations."