Stephan Eidenbenz

Parametric probabilistic sensor network routing

Motivated by realistic sensor network scenarios that have misinformed nodes and variable network topologies, we propose a fundamentally different approach to routing that combines the best features of limited-flooding and information-sensitive path-finding protocols into a reliable, low-power method that can make delivery guarantees independent of parameter values or information noise levels. We introduce Parametric Probabilistic Sensor Network Routing Protocols, a family of light-weight and robust multi-path routing protocols for sensor networks in which an intermediate sensor decides to forward a message with a probability that depends on various parameters, such as the distance of the sensor to the destination, the distance of the source sensor to the destination, or the number of hops a packet has already traveled. We propose two protocol variants of this family and compare the new methods to other probabilistic and deterministic protocols, namely constant-probability gossiping, uncontrolled flooding, random wandering, shortest path routing (and a variation), and a load-spreading shortest-path protocol inspired by [Servetto, Barrenechea, 2002]. We consider sensor networks where a sensors knowledge of the local or global information is uncertain (parametrically noised) due to sensor mobility, and investigate the trade-off between robustness of the protocol as measured by quality of service (in particular, successful delivery rate and delivery lag) and use of resources (total network load). Our results show that the multi-path protocols are less sensitive to misinformation, and suggest that in the presence of noisy data, a limited flooding strategy will actually perform better and use fewer resources than an attempted single-path routing strategy, with the Parametric Probabilistic Sensor Network Routing Protocols outperforming other protocols. Our results also suggest that protocols using network information perform better than protocols that do not, even in the presence of strong noise.

OURS: optimal unicast routing systems in non-cooperative wireless networks

We propose novel solutions for unicast routing in wireless networks consisted of selfish terminals: in order to alleviate the inevitable over-payment problem (and thus economic inefficiency) of the VCG (Vickrey-Clark-Groves) mechanism, we design a mechanism that results in Nash equilibria rather than the traditional strate-gyproofness (using weakly dominant strategy). In addition, we systematically study the unicast routing system in which both the relay terminals and the service requestor (either the source or the destination nodes or both) could be selfish. To the best of our knowledge, this is the first paper that presents social efficient unicast routing systems with proved performance guarantee. Thus, we call the proposed systems: Optimal Unicast Routing Systems (OURS).Our main contributions of OURS are as follows. (1) For the principal model where the service requestor is not selfish, we propose a mechanism that provably creates incentives for intermediate terminals to cooperate in forwarding packets for others. Our mechanism substantially reduces the overpayment by using Nash equilibrium solutions as opposed to strategyproof solutions. We then study a more realistic case where the service requestor can act selfishly. (2) We first show that if we insist on the requirement of strategyproofness for the relay terminals, then no system can guarantee that the central authority can retrieve at least 1overn of the total payment. (3) We then present a strategyproof unicast system that collects 1over2n of the total payment, which is thus asymptotically optimum. (4) By only requiring Nash Equilibrium solutions, we propose a system that creates incentives for the service requestor and intermediate terminals to correctly follow the prescribed protocol. More importantly, the central authority can retrieve at least half the total payment. We verify the economic efficiency of our systems through simulations that are based on very realistic terminal distributions.

COMMIT: a sender-centric truthful and energy-efficient routing protocol for ad hoc networks with selfish nodes

We consider the problem of establishing a route and sending packets between a source/destination pair in ad hoc networks composed of rational selfish nodes, whose purpose is to maximize their own utility. In order to motivate nodes to follow the protocol specification, we use side payments that are made to the forwarding nodes. Our goal is to design a fully distributed algorithm such that: (i) a node is always better off participating in the protocol execution (individual rationality), (ii) a node is always better off behaving according to the protocol specification (truthfulness), (iii) messages are routed along the most energy-efficient path, and (iv) the message complexity is reasonably low. We introduce the COMMIT protocol for individually rational, truthful, and energy-efficient routing in ad-hoc networks. To the best of our knowledge, this is the first ad hoc routing protocol with these features. COMMIT is based on the VCG payment scheme, in conjunction with a novel game-theoretic technique to achieve truthfulness for the sender node. By means of simulation, we show that the inevitable economic inefficiency is small. As an aside, our work demonstrates the advantage of using a cross-layer approach to solving problems: leveraging the existence of an underlying topology control protocol, we are able to simplify the design and analysis of our routing protocol, and to reduce its message complexity. On the other hand, our investigation of the routing problem in presence of selfish nodes disclosed a new metric under which topology control protocols can be evaluated: the cost of cooperation.

Containment of misinformation spread in online social networks

With their blistering expansions in recent years, popular on-line social sites such as Twitter, Facebook and Bebo, have become some of the major news sources as well as the most effective channels for viral marketing nowadays. However, alongside these promising features comes the threat of misinformation propagation which can lead to undesirable effects, such as the widespread panic in the general public due to faulty swine flu tweets on Twitter in 2009. Due to the huge magnitude of online social network (OSN) users and the highly clustered structures commonly observed in these kinds of networks, it poses a substantial challenge to efficiently contain viral spread of misinformation in large-scale social networks. In this paper, we focus on how to limit viral propagation of misinformation in OSNs. Particularly, we study a set of problems, namely the β1T -- Node Protectors, which aims to find the smallest set of highly influential nodes whose decontamination with good information helps to contain the viral spread of misinformation, initiated from the set I, to a desired ratio (1 − β) in T time steps. In this family set, we analyze and present solutions including inapproximability result, greedy algorithms that provide better lower bounds on the number of selected nodes, and a community-based heuristic method for the Node Protector problems. To verify our suggested solutions, we conduct experiments on real world traces including NetHEPT, NetHEPT_WC and Facebook networks. Empirical results indicate that our methods are among the best ones for hinting out those important nodes in comparison with other available methods.

The COMMIT Protocol for Truthful and Cost-Efficient Routing in Ad Hoc Networks with Selfish Nodes

We consider the problem of establishing a route and sending packets between a source/destination pair in ad hoc networks composed of rational selfish nodes whose purpose is to maximize their own utility. In order to motivate nodes to follow the protocol specification, we use side payments that are made to the forwarding nodes. Our goal is to design a fully distributed algorithm such that (1) a node is always better off participating in the protocol execution (individual rationality), (2) a node is always better off behaving according to the protocol specification (truthfulness), (3) messages are routed along the most energy-efficient (least cost) path, and (4) the message complexity is reasonably low. We introduce the COMMIT protocol for individually rational, truthful, and energy-efficient routing in ad hoc networks. To the best of our knowledge, this is the first ad hoc routing protocol with these features. COMMIT is based on the VCG payment scheme in conjunction with a novel game-theoretic technique to achieve truthfulness for the sender node. By means of simulation, we show that the inevitable economic inefficiency is small. As an aside, our work demonstrates the advantage of using a cross-layer approach to solving problems: Leveraging the existence of an underlying topology control protocol, we are able to simplify the design and analysis of our routing protocol and reduce its message complexity. On the other hand, our investigation of the routing problem in the presence of selfish nodes disclosed a new metric under which topology control protocols can be evaluated: the cost of cooperation.

Bluetooth worm propagation: mobility pattern matters!

The alarm that worms start to spread on increasingly popular mobile devices calls for an in-depth investigation of their propagation dynamics. In this paper, we study how mobility patterns affect Bluetooth worm spreading speeds. We find that the impact of mobility patterns is substantial over a large set of of changing Bluetooth and worm parameters. For instance, a mobility model under which devices move among a fixed set of activity locations can result in worm propagation speeds four times faster than a classical mobility model such as the random walk model. Our investigation reveals that the key factors affecting Bluetooth worm propagation speeds include spatial distributions of nodes, link duration distributions, degrees to which devices are mixed together, and even the burstiness of successive links.

Modeling Propagation Dynamics of Bluetooth Worms (Extended Version)

In the last few years, the growing popularity of mobile devices has made them attractive to virus and worm writers. One communication channel often exploited by mobile malware is the Bluetooth interface. In this paper, we present a detailed analytical model that characterizes the propagation dynamics of Bluetooth worms. Our model captures not only the behavior of the Bluetooth protocol but also the impact of mobility patterns on the Bluetooth worm propagation. Validation experiments against a detailed discrete-event Bluetooth worm simulator reveal that our model predicts the propagation dynamics of Bluetooth worms with high accuracy. We further use our model to efficiently predict the propagation curve of Bluetooth worms in big cities such as Los Angeles. Our model not only sheds light on the propagation dynamics of Bluetooth worms, but also allows to predict spreading curves of Bluetooth worm propagation in large areas without the high computational cost of discrete-event simulation.

Equilibria in topology control games for ad hoc networks

We study topology control problems in ad hoc networks, where network nodes get to choose their power levels in order to ensure desired connectivity properties. Unlike most other work on this topic, we assume that the network nodes are owned by different entities, whose only goal is to maximize their own utility that they get out of the network without considering the overall performance of the network. Game theory is the appropriate tool to study such selfish nodes: we define several topology control games in which the nodes need to choose power levels in order to connect to other nodes in the network to reach their communication partners while at the same time minimizing their costs. We study Nash equilibria and show that -- among the games we define -- these can only be guaranteed to exist if all network nodes are required to be connected to all other nodes (we call this the Strong Connectivity Game). We give asymptotically tight bounds for the worst case quality of a Nash equilibrium in the Strong Connectivity Game and we improve these bounds for randomly distributed nodes. We then study the computational complexity of finding Nash equilibria and show that a polynomial-time algorithm finds Nash equilibria whose costs are at most a factor 2 off the minimum cost possible; for a variation called Connectivity Game, where each node is only required to be connected (possibly via intermediate nodes) to a given set of nodes, we show that answering the question, if a Nash equilibrium exists, is NP-hard, if the network graph satisfies the triangle inequality. For a second game called Reachability Game, where each node tries to reach as many other nodes as possible, while minimizing its radius, we show that 1+o(1)-approximate Nash equilibria exist for randomly distributed nodes. Our work is a first step towards game-theoretic analyses of ad hoc networks.

Inapproximability Results for Guarding Polygons without Holes

The three art gallery problems VERTEX GUARD, EDGE GUARD and POINT GUARD are known to be NP-hard [8]. Approximation algorithms for VERTEX GUARD and EDGE GUARD with a logarithmic ratio were proposed in [7]. We prove that for each of these problems, there exists a constant Ɛ > 0, such that no polynomial time algorithm can guarantee an approximation ratio of 1 + Ɛ unless P = NP. We obtain our results by proposing gap-preserving reductions, based on reductions from [8]. Our results are the first inapproximability results for these problems.

Modeling Propagation Dynamics of Bluetooth Worms

The growing popularity of mobile devices in the last few years has made them attractive to virus and worm writers. One communication channel exploited by mobile malware is the Bluetooth interface. In this paper, we present a detailed analytical model that characterizes the propagation dynamics of Bluetooth worms. Our model captures not only the behavior of the Bluetooth protocol but also the impact of mobility patterns on the Bluetooth worm propagation. Validation experiments against a detailed discrete-event Bluetooth worm simulator reveal that our model predicts the propagation dynamics of Bluetooth worms with high accuracy.