In recent years, wireless Internet service providers (WISPs) have established thousands of WiFi hot spots in cafes, hotels and airports in order to offer to travelling Internet users access to email, web or other Internet service. However, two major problems still slow down the deployment of this kind of networks: the lack of a seamless roaming scheme and the variable quality of service experienced by the users. This paper provides a response to these two problems: We present a solution that, on the one hand, allows a mobile node to connect to a foreign WISP in a secure way while preserving its anonymity and, on the other hand, encourages the WISPs to provide the users with good QoS. We analyse the robustness of our solution against various attacks and we prove by means of simulations that our reputation model indeed encourages the WISPs to behave correctly.

Wireless Mesh Networks (WMNs) represent a new and promising paradigm that uses multi-hop communications to extend WiFi networks: By deploying only one hot spot (directly connected to the Internet) and several transient access points (TAPs), an Internet Service Provider (ISP) can extend its coverage and serve a large number of clients using a single broadband connection. Unfortunately, if the medium access protocol is poorly designed or inadequate, it can lead to severe unfairness and low bandwidth utilization. In this paper, we propose a fair scheduling mechanism that optimizes the bandwidth utilization in the mesh network. Our solution assigns transmission rights to the links in the WMN and maximizes thespatial reuse(i.e., the possibility for links that do not contend to be activated at the same time). We show that our solution is fair and collision-free, and we evaluate its efficiency by means of simulations.

The rapid growth of WiFi over the past two years reveals the willingness of the Wireless Internet Service Providers (WISPs) to develop this technology and the interest of the users in this new service. However, the lack of unified roaming slows down the deployment of this kind of networks. In this paper, we present a simple solution that allows a mobile node to connect to a hot spot managed by a WISP in a secure way while preserving its anonymity. We use a reputation-based system to discourage the WISPs from providing a bad quality of service to the mobile nodes. We will show that all the parties are motivated to behave correctly, that our solution thwarts rational attacks, that it is possible to detect malicious attacks and, in some case, identify the attackers.

In multi-hop cellular networks, data packets have to be relayed hop by hop from a given mobile station to a base station and vice-versa. This means that the mobile stations must accept to forward information for the benefit of other stations. In this paper, we propose an incentive mechanism that is based on a charging/rewarding scheme and that makes collaboration rational for selfish nodes. We base our solution on symmetric cryptography to cope with the limited resources of the mobile stations. We provide a set of protocols and study their robustness with respect to various attacks. By leveraging on the relative stability of the routes, our solution leads to a very moderate overhead.

In multi-hop cellular networks, 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) cellular networks, this new generation can lead to a better usage of the available spectrum and to a reduction of infrastructure costs. However, these benefits would vanish if the mobile nodes do 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 analyse the robustness of our protocols against rational and malicious attacks. We show that our protocols thwart rational attacks and detect malicious attacks. We also show that our solution makes collaboration rational for selfish nodes.

In multi-hop cellular networks, 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) cellular networks, this new generation can lead to a better usage 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 analyse the robustness of our protocols against rational and malicious attacks. We show that our protocols thwart rational attacks and detect malicious attacks. We also show that our solution makes collaboration rational for selfish nodes.

In multi-hop wireless networks, data packets are relayed in several wireless hops from their source to their destination. Based on whether a fixed infrastructure is used or not, we can distinguish two types of multi-hop wireless networks: pure ad hoc and multi-hop cellular networks. Pure ad hoc networks do not rely on any fixed infrastructure; hence, the packet relaying service has to be provided solely by the end user devices. Multi-hop cellular networks rely on a set of base stations that are connected to a high speed backbone network; here, data packets have to be relayed by end user devices from the source to the backbone and from the backbone to the destination. Multi-hop cellular networks are a potential evolution of both voice-centric networks such as GSM and data-centric networks such as CDPD or IEEE 802.11... In this paper, we present our ongoing work on the design of mechanisms that stimulate collaboration of end users in both pure ad hoc and multi-hop cellular networks. We put the emphasis on stimulating packet forwarding, as this is one of the most fundamental services that end users should provide to each other.

Naouel Ben Salem, Levente Buttyan, Jean-Pierre Hubaux and Markus Jakobsson abstract: In multi-hop cellular networks, 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) cellular networks, this new generation can lead to a better usage 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 analyse the robustness of our protocols against rational and malicious attacks. We show that our protocols thwart rational attacks and detect malicious attacks. We also show that our solution makes collaboration rational for selfish nodes.