In opportunistic networks, selfish nodes can exploit the services provided by other nodes by downloading messages that interest them, but refusing to store and distribute messages for the benefit of other nodes. We propose a mechanism to discourage selfish behavior based on the principles of barter. We develop a game-theoretic model in which we show that the proposed approach indeed stimulates cooperation of the nodes. The results show that, in practical scenarios, the message delivery rate considerably increases, if the mobile nodes follow the Nash Equilibrium strategy in the proposed mechanism compared to the data dissemination protocol when no encouraging mechanism is present.
Abstract. In this paper, we propose two mechanisms for wormhole detection in wireless sensor networks. The proposed mechanisms are based on hypothesis testing and they provide probabilistic results. The first mechanism, called the Neighbor Number Test (NNT), detects the increase in the number of the neighbors of the sensors, which is due to the new links created by the wormhole in the network. The second mechanism, called the All Distances Test (ADT), detects the decrease of the lengths of the shortest paths between all pairs of sensors, which is due to the shortcut links created by the wormhole in the network. Both mechanisms assume that the sensors send their neighbor list to the base station, and it is the base station that runs the algorithms on the network graph that is reconstructed from the received neighborhood information. We describe these mechanisms and investigate their performance by means of simulation.
In this paper, we propose an authentication scheme that is designed to reduce the authentication delay during a WiFi handover process. We observe that the largest part of the delay is due to the remote communications between the access point and the AAA server that authorizes the access to the network. In order to eliminate remote communications, our scheme uses pre-authorization, and it pre-distributes authentication information to the access points that are the potential targets of a future handover. This ensures that only local communications (between the mobile station and the access point) take place during the handover itself. We describe the design of our scheme, as well as report on a proofof-concept implementation. Our validation results show that our scheme breaks the dependency of the authentication delay on the round-trip time between the access point and the AAA server. This makes our scheme applicable in real time applications such as telephony and video streaming for WiFi users.
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