Section: New Results

Peer-to-peer wireless autonomic networked systems

Low stretch and small state geographic routing in sensor networks

Participants : Marin Bertier, Anne-Marie Kermarrec, Guang Tan.

This work addresses a central problem in ad hoc sensor (and more generally wireless) networks: that of finding (asymptotically) shortest paths using minimum possible per-node state. Assuming the availability of location information (hence geographic) to each node, and that a source node knows the location of a destination node, we explore this problem in two approaches. In the first approach, we abstract the network into a highly compact global structure, known as visibility graph in computational geometry, that produces constant-stretch paths while getting rid of the notorious reliance on O(n) per-node state. To our knowledge this is the first geographic routing protocol that offers provably optimal performance with per-node state independent of network size. In the context of a more general location-free (or virtual coordinate) environment, our second approach uses the idea of divide-and-conquer, whereby the network is partitioned to convex pieces that are amenable to greedy routing. Based on new insights into the performance pitfalls of previous work, the notion of convexity results in a significantly better tradeoff between stretch and state size than existing solutions.

Adaptive data forwarding in delay-tolerant networks

Participants : Marin Bertier, Anne-Marie Kermarrec, Aline Carneiro Viana.

We conducted studies in information dissemination in mobile networks where a contemporaneous path may never exist between two nodes (a source and a destination) in the network, known as delay-tolerant networks (DTNs). These networks are further challenged by strict resource constraints (e.g., memory, CPU and energy limitations). Our goal in this domain was to support intelligent and adaptive forwarding, which allows a good trade-off between reliability and resource-efficiency. We then design a new protocol, called Seeker, which empowers nodes with the ability to estimate favorable contact opportunities by taking advantage of any information they can locally infer. Hence, nodes are able to adapt and self-organize in dynamic environments with minimal control overhead. This work has been performed in collaboration with researcher Roy Friedman (from Technion - Israel Institute of Technology). The general idea was published in the ExtremeCom workshop [67] , which, although at its first edition, gave us the opportunity to meet other active researchers and practitioners in areas related to delay tolerant networks. The complete description of the protocol can also be found in [92] .

Reliable data dissemination in cognitive radio networks

Participants : Mubashir Husain Rehmani, Aline Carneiro Viana.

Recent advances in cognitive radio technology have enabled opportunistic wireless cognitive radio (CR) nodes to efficiently locate and exploit spectrum under-utilized by licensed primary radio (PR) nodes. Nevertheless, CR transmissions should not degrade the reception quality of PR nodes and should be immediately interrupted whenever a neighboring PR activity is detected. The main problem we tackle here is the channel assortment in multi-hop cognitive radio networks and concerns how to increase the transmission coverage of CR nodes by selecting good qualified channels for communicating . Our channel assortment strategy , named `SURF', provides to CR nodes a strategy to assort channels according to their availabilities, giving to nodes the possibility of selecting the best classified one for transmission and/or overhearing. Finally, our strategy improves network reliability – since less PR-occupied channels will be selected – and receivers coverage – since an acceptable number of CR neighbors in terms of space sharing will compete for the selected channel.

This work has been done in collaboration with Hicham Khalife from LaBRI/Université Sciences et Technologies - Bordeaux I.

A content-based network coding to match social interest similarities in delay tolerant networks

Participants : Golnaz Karbaschi, Aline Carneiro Viana.

Considering users' social characteristics leads to better use of network coding in delay tolerant networks. We present a content-based network coding that aims to match the social interests similarities (i.e., same profession, hobbies, interests, etc.) of people in a community. We aim to provide a more adaptive-to-social-network coding and lower decoding delay for the users that are interested in different contents . This work was published in the ExtremeCom 2009 Workshop [53] . Additionally, adaptive-to-social-network coding requires to deal with the unfairness issues of network coding in multi-hop wireless networks. The reason for this unfairness is that by mixing different flows, packets destined to one destination in order to be decoded need to wait for the reception of the whole mixed set of encoded packets that may be totally independent in terms of final destination. This may lead to highly unfair delay for small block data. To mitigate this unfairness, relay nodes may mix only packets going to the same destination. We call this strategy FairMix and it was published in the IEEE PIMRC 2009 conference [54] . This work was performed in collaboration with Khaldoun Al Agha and Steven Martin from LRI/University of Paris-Sud. More details about the idea can be also found in [85] .

Cryptographic protocols to fight sinkhole attacks on tree-based routing in wireless sensor networks

Participants : Aline Carneiro Viana, Fabrice Le Fessant.

Wireless Sensor Networks (WSN) are penetrating more and more in our daily life. As a consequence, security has become an important matter for these networks. We introduce two new cryptographic protocols of different complexity and strength in limiting network degradation caused by sinkhole attacks on tree-based routing topologies in Wireless Sensor Networks (WSNs). The main goal of both protocols is to provide continuous operation by improving resilience against, rather than detection of, these attacks. The main benefit of providing resilience is that it allows operating (or graceful degradation) in the presence of attacks. Furthermore, while resilience mechanisms do not dismiss detection mechanisms, detection mechanisms often introduce more complexity and so, more weaknesses to the system, which might not justify their benefits. More specifically our two RESIlient and Simple Topology-based reconfiguration protocols are: RESIST-1 and RESIST-0. RESIST-1 prevents a malicious node from modifying its advertised distance to the sink by more than one hop, while RESIST-0 does not allow such lying at the cost of additional complexity. This work was firstly published in the NPSec Workshop  [102] held in conjunction with ICNP 2009.

Self-management: Virtual coordinates for autonomous networked system

Participants : Anne-Marie Kermarrec, Achour Mostefaoui, Michel Raynal, Gilles Trédan, Aline Carneiro Viana.

The motivation behind this research work comes from the lack in the literature, of an autonomous system able (1) to permanently evolve and self-organize under dynamic changing conditions (due either to the environment or technological issues), and (2) to provide various networking functionalities over the same underlying support system. Our answer to those demands was an autonomous system able not only to be adaptable to environment changing conditions, but also, that provides variety to network functionalities. Thus, we have designed an autonomous and lightweight self-organizing networked system that, by imposing a bounded overhead to wireless devices, constructs a base network structure for supporting network functionalities, commonly required in WSNs. We have only exploited local connectivity information and per-neighbor communication. This work has been performed in collaboration with researcher Roy Friedman (from Technion - Israel Institute of Technology) and is currently in submission. The research related to this subject has been published at the ICDCN conference [58] .

Data organization in wireless sensor networks

Participants : Massimo Vecchio, Aline Carneiro Viana.

We have been working on how to make the sensed monitored data available to the mobile sink in a robust, adaptive, and efficient way. In this context, we have proposed, in collaboration with researchers Artur Ziviani (from the National Laboratory for Scientific Computing (LNCC), Brazil) and Roy Friedman (from the Technion - Israel Institute of Technology) an efficient data dissemination approach (in terms of overhead and representativeness) to allow a mobile sink to gather a representative view of the monitored region covered by n sensor nodes by visiting anym nodes, where . This work was firstly published in the journal IEEE Communication Letter [14] . Then, the Post-Doc Massimo Vecchio started working on other probabilistic techniques in order to decrease the overhead incurred by this previous approach. This work is currently in submission to a journal. We have received the first reviewers' comments and resubmit the paper again.

Additionally, with researchers from the LRI/University of Paris-Sud (Fatiha Zaidi, Thomas Herault, Thomas Largillier, and Sylvain Peyronnet) the protocol Supple was also proposed for proactive data dissemination in wireless sensor networks. In Supple, sensor nodes use a simple tree-based structure, constructed during the neighborhood discovery phase, which allows weight distribution among nodes. Weights are based on predefined criterion of selection as well as distribution law, and are used by sensors at the data dissemination phase. At this phase, sensors then make on the fly forwarding and data storing decisions based on their own weights and the weights of their neighbors. Supple takes thus advantage of the bias among different sensors' weights for good data dissemination. The resulting work is currently in submission at the IEEE Percom 2010 Conference.

With researchers Fatiha Zaidi from LRI/University of Paris-Sud and Stephane Maag from TELECOM & Management SudParis, the paper "One step forward: Linking Wireless Self-Organising Networks Validation Techniques with Formal Testing approaches" was accepted for publication in one of the main ACM Journals in Computer Science, the ACM Computing Surveys [13] .

Energy-efficient route discovery in sensor networks

Participant : Aline Carneiro Viana.

The vast literature on the wireless sensor research community contains many valuable proposals for managing energy consumption, the most important factor that determines sensor lifetime. The goal of this work is to extend the network lifetime. We aim at determining good energy-efficient routes in the network by using the energy level of nodes as a criterion to select good links in the route. In collaboration with Khaldoun Al Agha and PhD student Joseph Rahme (who is co-advised for 30% by Aline) both from LRI/Universite Paris-Sud, our first contribution in this context was the proposal of cost functions to choose energy efficient routes. The originality of the proposed cost functions lies in their completely decentralized and adaptive behavior in considering energy consumption, remaining energy of nodes, and the number of transmissions a node can make before its energy depletion.

Adaptive infrastructure deployment for data gathering in intermittently connected networks

Participant : Aline Carneiro Viana.

A collaboration with Marcelo Dias de Amorim from CNRS/LIP6 focuses on applications of wireless sensor networks that require periodic readings. This means that these readings should be performed following some predefined parameter f_min that denotes the minimum frequency at which the whole target area must be sensed. We consider mobile sensor network and focus on how sensors should move, in order to guarantee the coverage of all targets in the network in a timely and efficient way. To answer this issue, we proposed a mobility strategy that consists in making nodes follow a Hilbert space-filling curve and use opportunistic contacts to reduce the data delivery's delay.

Additionally, a joint work with researchers from EPI POPS of INRIA Lille (Tahiry Razafindralambo, Nathalie Mitton), Marcelo Dias de Amorim, and Katia Obraczka from UC Santa Cruz, CA, USA started, where the protocol COVER was proposed. COVER is an adaptive strategy for placement and trajectory control of infrastructure nodes in intermittently connected networks, where data-producing nodes (targets) have to report data on a regular basis. The goal is to cover mobile targets whose mobility patterns are unknown. The main issue is how to deploy and manage the infrastructure nodes in order to adaptively guarantee network availability, to respect required data gathering latency, to balance load and still to limit deployment cost. The first results are currently in submission at the IEEE Percom 2010 conference.

Building secured links is sensor networks

Participants : Marin Bertier, Achour Mostefaoui, Gilles Trédan.

This work deals with malicious behaviors in the context of sensor networks. Such a behavior can be due to an adversary that has some sensors under control or more generally to a problem of the sensor itself. Effectively, as sensors are small devices that are industrially built, many of them may be defective. Moreover, it is known that when a sensor is running out of energy, it can enter a state where it behaves abnormally. Malicious behaviors in sensor networks are less hard to handle as the power of the adversary is lower. Indeed a sensor has a limited energy. The more it is active the less it will survive and thus even its computation power is bounded. In the case of a sensor network with static sensors, we try to build secured links between sensors. The objective is to avoid the case of an adversary that collects the whole information exchanged among the sensors.