Mascotteis a joint team between INRIA Sophia Antipolis  Méditerranée and the laboratory I3S (Informatique Signaux et Systèmes Sophia Antipolis) which itself belongs to CNRS (Centre National de la Recherche Scientifique) and UNS (University of NiceSophia Antipolis).
Mascotteis a joint team between INRIA Sophia Antipolis Méditerranée and the laboratory I3S (Informatique Signaux et Systèmes de Sophia Antipolis) which itself belongs to CNRS (Centre National de la Recherche Scientifique) and UNS (University of Nice Sophia Antipolis). Its research fields are Algorithmics, Discrete Mathematics, Combinatorial Optimization and Simulation, with applications to telecommunication networks.
The objectives of the Mascotteprojectteam are to design networks or communication algorithms. In order to meet these objectives, the team studies various theoretical tools, such as Discrete Mathematics, Graph Theory, or Algorithmics and develops applied techniques and tools, especially for Combinatorial optimization and Computer simulation. In particular Mascotteused in the last year both these theoretical and applied tools for the design of various networks, such as WDM, wireless (radio), satellites, overlay, and peertopeer networks. This research has been done within various industrial and international collaborations.
This results also in the production of advanced softwares such as the Mascoptlibrary ( Mascotteoptimization), and ambitious software projects such as the OSA computer Simulation Architecture.
Last year Mascotte has strongly increased both its international and industrial collaborations.
International Collaborations:besides its long standing European collaboration (inside the IST/FET europeean project AEOLUS or bilateral ones), and the associated team with S.F.U. (Canada), a new associated team EWIN with the Universidade Federal do Ceará (Fortaleza, Brazil) has been started.
Industrial collaborations:Mascottehas joined the common laboratory INRIA / AlcatelLucent BellLabs (participation in the ADR HiMa on autonomous dynamic management of virtual topologies). Mascottehas also got a contract with AlcatelLucent BellLabs on dynamic compact routing. Mascottegot a financial support of the région PACAto work with two SME's (3Roam and Avisto) on wireless IP backhaul networks (project RAISOM).
ANR:Four new ANR have been accepted in 2009: AGAPE (on parametrized and exact algorithms); DIMAGREEN (on design and management of green networks), ECOSCells (on efficient cooperating small cells) and GraTel with Taiwan (on graphs for telecommunications).
The project develops tools and theory in the following domains: Discrete Mathematics (in particular Graph Theory), Algorithmics, Combinatorial optimization and Simulation.
Typically, a telecommunication network (or an interconnection network) is modeled by a graph. A vertex may represent either a processor or a router or any of the following: a switch, a radio
device, a site or a person. An edge (or arc) corresponds to a connection between the elements represented by the vertices (logical or physical connection). We can associate more information
both to the vertices (for example what kind of switch is used, optical or not, number of ports, equipment cost) and to the edges (weights which might correspond to length, cost, bandwidth,
capacity) or colors (modeling either wavelengths or frequencies or failures) etc. Depending on the application, various models can be defined and have to be specified. This modeling part is an
important task. To solve the problems, we manage, when possible, to find polynomial algorithms. For example, a maximum set of disjoint paths between two given vertices is by Menger's theorem
equal to the minimum cardinality of a cut. This problem can be solved in polynomial time using graph theoretic tools or flow theory or linear programming. On the contrary, determining whether
in a directed graph there exists a pair of disjoint paths, one from
s_{1}to
t_{1}and the other from
s_{2}to
t_{2}, is an NPcomplete problem, and so are all the problems which aim at minimizing the cost of a network which can satisfy certain traffic requirements. In addition to deterministic
hypothesis (for example if a connection fails it is considered as definitely down and not intermittently), the project started recently to consider probabilistic ones.
Graph coloring is an example of tool which appears in various contexts: WDM networks where colors represent wavelengths, radio networks where colors represent frequencies, fault tolerance where colors represent shared risk resource groups, and scheduling problems. Another tool concerns the development of new algorithmic aspects like parametrized algorithms. A school has been organized on this topic and the research will be conducted under the ANR project AGAPE.
Theoretical results are described after, with more emphasis on those of Graph Theory (Section ) and algorithmic aspects (Section ).
For the last year the main application domain of the project remained Telecommunications. Within this domain, we consider applications that follow the needs and interests of our industrial partners, in particular Orange Labsor AlcatelLucent BellLabs, but also SME's like UbiStorageor 3Roam.
Mascotteis mainly interested in the design of heterogeneous networks. The project has kept working on the design of backbone networks in particular optical ones (see Section ) but also on wireless access networks (see Section ) and on overlay (Peer to peer) networks (see Section ), in particular inside the European FET project AEOLUS.
Part of these research is done within the join laboratory INRIAAlcatelLucent BellLabs, (participation in the ADR HiMa on autonomous dynamic management of virtual topologies and within the ANR ECOSCells leaded by AlcatelLucent BellLabs). Mascottehas also a contract with AlcatelLucent BellLabs, on dynamic compact routing. An emphasis is put on green networks with low power consumption financed with the ANR DIMAGREEN. We have also developed two cooperations with SMEs. The first one is on data storage in peertopeer networks with the SME UbiStoragewithin the ANR SPREADS (Safe P2P reliable Architecture for Data Storage). The second one is on backhaul networks with the SME 3Roam,and is funded by the région PACAproject RAISOM (Wireless IP Service Deployment optimization and monitoring)
MascoptandopenGVE(
http://
Mascopt
is a free Java library distributed under the terms of the LGPL
license which is dedicated to graph and network processing.
Mascoptincludes a collection of Java interfaces and classes that implement fundamental data structures and algorithms. The forthcoming public
distribution of
Mascoptwill appear in january 2010 under the name of the
openGVEproject,
Mascoptbeing one implementation of the bridge graph interface [R. Correa,
http://
The main objective of Mascopt( MascotteOptimization) project is to ease software development in the field of network optimization. Examples of problems include routing, grooming, survivability, and virtual network design. Mascopthelps implementing a solution to such problems by providing a data model of the network and the demands, classes to handle data and ready to use implementation of existing algorithms or linear programs (e.g. shortest paths or integral multicommodity flow).
A generic linear programming interface allows users to program the same way whether the target solver is IBM ILOG CPLEX, GLPK (GNU Linear Programming Kit) or CLP/CBC (accessed through JNI).
Mascopthas intensively been used within Mascotteindustrial cooperation programs for experimentation and validation purposes: with Alcatel Space Technologies on the design of faulttolerant onboard network satellites, on the optimization of the access layer and planning of satellite communication and with Orange Labs on the design of telecommunication backbone networks.
Another cooperation at INRIA Sophia Antipolis Méditerranée is the use of Mascoptby the Aoste team.
OSA: an Open Componentbased Architecture for DiscreteEvent Simulations. (
http://
Componentbased modeling has many wellknown good properties. One of these properties is the ability to distribute the modeling effort amongst several experts, each having his/her own area of system expertise. Clearly, the less experts have to care about areas of expertise of others, the more efficient they are in modeling subsystems in their own area. Furthermore, the process of studying complex systems using discreteevent computer simulations involves several areas of nonsystem expertise, such as discreteevent techniques or experiment planning.
The Open Simulation Architecture (OSA) is designed to enforce a strong separation of the enduser roles and therefore, ensure a successful cooperation of all the experts involved in the process of simulating complex systems.
The OSA architecture is also intended to meet the expectations of a large part of the discreteevent simulation community: it provides an open platform intended to support researchers in a wide range of their simulation activities, and allows the reuse and sharing of system models in the simulation community by means of a flexible and generic component model (Fractal).
Many discreteevent simulators are developed concurrently, but with identical or similar purpose. Another goal of OSA is to favor the reuse and integration of simulation software components and models. To favor reuse, OSA uses a layered approach to combine the modeling, simulation, and related concerns, such as instrumentation or deployment. This ability is demonstrated by the successful integration and reuse of thirdparty components, such as Scave, the analysis module of Omnet++, or a large number of the James II plugins developped by the University of Rostock. OSA is both a testbed for experimenting new simulation techniques and a tool for real case studies.
OSA is Open Source (LGPL) and is available for download on the INRIA forge server
http://
Dipergrafs(
http://
The Dipergrafs project proposes a Java framework for the manipulation of directed hypergraphs. Briefly, a directed hypergraph consists in a set of directed links, each link connecting a set of vertices to another set of vertices. In other words, a directed hypergraph is a graph in P(E). Hypergraphs are used into the fields of network modeling, rational databases, semantic web, expert systems, route planning. In particular, the design objectives of Dipergrafs are to make it particularly useful in the context of network simulation.
Briefly Dipergrafs: has a vertexoriented design (in opposite to nodeoriented design), that is the graph is seen as a collection of relations between nodes; imposes no constraint on the type of nodes and vertices (in opposite to frameworks which oblige to follow a certain structure, leading tp a lack of flexibility); provides implementations for common graph operations : navigation (paths, connected components, shortest paths, hopexploring, etc), graph queries, graph metrics (radius, density, degrees, distance/adjacency/incidence matrices, etc), distributions of vertex metrics; is mostly usable through a small set of Java classes (in opposite to frameworks whose utilization requires the knowledge of numerous classes); features graph input/output mechanisms, allowing persistence, serialization, etc; does not feature any graph rendering tool. Instead bridges to external products dedicated to rendering are provided; comes with a set of composeable topology generator allowing to quickly instantiate the desired topology.
Dipergrafs is extensively used in the DRMSim project, in which it enables the modeling and simulation of large backbone networks.
DRMSim: (
http://
The expansion of the Internet routing system results in a number of research challenges, in particular, the Border Gateway Protocol (BGP) starts to show its limits amongst others in terms of the number of routing table entries it can dynamically process and control. Dynamic routing protocols showing better scaling properties are thus under investigation. However, because deploying underdevelopment routing protocols on the Internet is not practicable at a largescale (due to the size of the Internet topology), simulation is an unavoidable step to validate the properties of a newly proposed routing scheme. Unfortunately, the simulation of interdomain routing protocols over large networks (order of tens of thousands of nodes) poses real challenges due to the limited memory and computational power that computers impose. Existing simulation tools exhibit limitations in terms of the number of nodes they can handle and in the models they propose. This motivated us for conceiving and developing an adequate network simulator call DRMSim (Dynamic Routing Model simulator) which addresses the specific problem of largescale simulations of (interdomain) routing models on large networks.
DRMSim relies on a discreteevent simulation engine. It proposes a general routing model which accommodates any network configuration. Aside to this, it includes specific models for GLP, and Kchordal network topologies, as well as implementations of routing protocols, including the NSR routing protocol and lightweight versions of BGP. More features will be further incorporated into the simulator. In particular, they address the challenge of simulation of larger networks (order of 10k nodes), the next step is to propose new routing algorithms, including stateoftheart ones, to enhance the code, and to go further with distributed simulation campaigns.
DRMSim is developped in cooperation with LaBRI (Laboratoire Bordelais de Recherche en Informatique, Bordeaux, France).
Network design is a very wide subject that concerns all kinds of networks. For telecommunications networks it can be either physical networks (backbone, access, wireless, ...) or virtual (logical) ones. The objective is to design a network able to route a (given, estimated, dynamic, ...) traffic under some constraints (e.g. capacity) and with some quality of service (QoS) requirements. Usually the traffic is expressed as a family of requests with parameters attached to them. In order to satisfy these requests, we need to find one (or many) path(s) between their end nodes. The set of paths is chosen according to the technology, the protocol or the QoS constraints. For instance, optical backbones use the WDM technology to take better advantage of the capacity of the optical fibers often already installed. This is achieved through the multiplexing of several wavelength channels onto the same fiber. In that case a resource allocation is an optical channel, which consists of a path and a wavelength assigned on each link along the path, and is called a lightpath. If wavelength translation is performed in optical switching, then to each channel may be assigned different wavelengths on each link along the path; otherwise the wavelength continuity constraint must be satisfied on all links along the path. Of course, two lightpaths sharing a link must use different wavelengths on that link. The design can be done at the conception of the network (i.e. when conceiving a virtual network in MPLSwhere we have to establish virtual paths) or to adapt the network to changes (failures, new link, updates of routers, variation of traffic, ...). Finally there are various optimization criteria which differ according to the point of view: for a network user they are related to his/her satisfaction (minimizing delays, increasing available bandwidth, ...), while for a network operator, economics criteria like minimizing deployment and operating costs are more important.
This very wide topic is considered by a lot of academic and industrial teams in the world. Our approach is to attack these problems with tools from Discrete Mathematics and to consider mainly telecommunications networks. This approach is shared by other teams in Europe, most of them being part of European projects IST FET AEOLUS (where Mascotteis leader of subproject SP2 Resource management) and COST 293 Graal (where Mascotteis leader of working group WGA broadband and optical networks). Outside Europe, many teams have also this approach and sometimes we have direct collaborations with them: Vancouver (EA RESEAUXCOM), Montréal, Fortaleza (EA EWIN),...
In a WDM network, routing a connection request consists in assigning it a route in the physical network and a wavelength. When each request uses at most
1/
Cof the bandwidth of the wavelength, we say that the grooming factor is
C. That means that on a given edge of the network we can groom at most
Crequests on the same wavelength. With this constraint the objective can be either to minimize the number of wavelengths (related to the transmission cost) or minimize the number of
Add/Drop Multiplexers (ADM) used in the network (related to the cost of the nodes).
We have first addressed the problem of traffic grooming in WDM rings or paths with AlltoAll uniform unitary traffic. The goal is to minimize the total number of ADMs required. We have
shown that this problem corresponds to a partition of the edges of the complete graph into subgraphs, where each subgraph has at most
Cedges (where
Cis the grooming factor) and where the total number of vertices has to be minimized. Using tools of graph and design theory, we optimally solved the problem for practical values and
infinite congruence classes of values for a given
C. We give optimal constructions on unidirectional rings when
CN(
N1)/6and when
C= 3, 4, 5, 6, 12, on paths when
C= 2, and bidirectional rings when
C= 1, 2, 3and
C=
k(
k+ 1)/2(
k1) for infinite congruence classes
, and propose an approximate construction for alltoall traffic
on unidirectional rings for any value of
C, and on bidirectional rings for
C= 2, 3
. We also showed how to improve lower bounds by using refined
counting techniques, and how to determine the maximum number of connections which can be established in a path of size
Nor in a DAG.
Then, we have also studied the alltoall traffic grooming on unidirectional rings with grooming factor
Cand with the extra constraints that the traffic between a subset of vertices must be served with grooming factor
C^{'}. We provided optimal constructions for
C= 4and
C^{'}= 1, 2, 3
.
Furthermore, we refined the complexity analysis of the problem for general traffic requirement and established the first inapproximability result on traffic grooming using a study of the
complexity (including parametrized complexity)
. We have provided an approximation algorithm for ring and path
networks with approximation factor of
O(
n^{1/3}log
^{2}n), independent of the grooming factor. Moreover, we have proposed an
a prioriplacement of ADMs in unidirectional WDM rings allowing to satisfy any set of requests with bounded degree
d(a node is source or destination of at most
drequests)
.
Moreover, we studied the traffic grooming on the path with online traffic and distributed routing algorithm. We have shown how to design the best possible virtual topologies (assignment of ADMs to wavelengths), independently of the routing algorithm and for any bounded degree traffic instances. We have in particular analyzed the performances of distributed greedy routing algorithms .
We also studied the placement of optical add/drop multiplexers (OADM) that allows adding or dropping wavelengths from/to an optical fiber. For this problem, we provided a 4approximation algorithm for general instances on unidirectional path, and improved approximation factors for particular instances .
In production networks, traffic evolution, failures and maintenance operations force to adapt regularly the current configuration of the network (virtual topology, routing of connections). In this context, we have developed tools to switch connections one after the other from a precomputed routing to another with limited service disruptions. We thus concentrated on the reoptimization phase of the network, or migrationof the routing. We have modeled this problem as a scheduling problem in a dependency digraph that may contains cycles, the process number, and then established some similarities and differences with two other known problems: the pathwidthand a particular graph searching problem. Dependency cycles are broken through the use of temporary routes or temporary disruptions (called “agents” in the model) that have to be minimized. We have proved that the problem is NPcomplete and difficult to approximate in general, characterized the classes of (di)graphs that can be processed with at most two agents, and proposed distributed algorithms for computing this parameter and other graph invariants in trees. We proposed a heuristic algorithm that performs better and faster than previous proposals, and investigated the problem with the extra constraints that some connections should never be interrupted (particular service level agreement) , . We also studied tradeoffs between the total number of interruptions and the maximum number of concurrent interruptions, proving in particular that the knowledge of one parameter does not help to optimize the other .
We have extended our study to the case in which connections use only a fraction of the bandwidth of a link. In , we proved that deciding whether it exists a scheduling of the rerouting of connection requests without traffic interruption is NPcomplete even if requests use the third of the bandwidth of a link.
AllOptical Label Switching (AOLS) is a promising technology that performs packet forwarding without any opticalelectricaloptical conversions, thus speeding up the forwarding. However, the cost of this technology requires limiting the number of labels needed to ensure the forwarding when routing a set of requests using GMPLStechnology. In particular, this prevents the usage of label swapping techniques.
We have studied the routing problem in this context using label stacking techniques. We have formalized the problem by associating to each routing strategy a logical hypergraph, called a
hypergraph layout, whose hyperarcs are dipaths of the physical graph, called tunnels in
GMPLSterminology. We defined a cost function for the hypergraph layout, depending on its total length plus its total hop count. Minimizing the cost
of the design of an AOLS network can then be expressed as finding a minimum cost hypergraph layout. In
,
, we prove hardness results for the problem, namely for general
directed networks we prove that it is NPhard to find a
Clog
napproximation, where
Cis a positive constant and
nis the number of nodes of the network. For symmetric directed networks, we prove that the problem is APXhard. These hardness results hold even if the traffic instance is a partial
broadcast. On the other hand, we provide approximation algorithms, in particular an
O(log
n)approximation for symmetric directed networks. We focussed on the case where the physical network is a directed path, providing a polynomialtime dynamic
programming algorithm first for one source
,
, and then for a fixed number
kof sources running in time
O(
n^{k+ 2})
.
We have also considered labelstripping techniques that allow reducing further the overall number of labels but at the cost of increasing the stack size and so waste bandwidth. We proposed a heuristic algorithm performing tradeoffs between the stack size and the waste of bandwidth .
The transmission of an optical signal in a fiber causes small phase shifting and power loss forcing to regenerate the signal after a certain distance (e.g. 1000km). We have investigated the problem of minimizing the number of locations to place the regenerators in a WDM network in various settings: limited or unlimited number of regenerators per site, routing given or not, general and particular topologies. In each setting, we established the complexity and inapproximability of the problem, and provided approximation algorithms and exact polynomial time algorithms whenever possible.
Mascottehas conducted an intense research effort on wireless access networks. From the technological and architectural point of view, the field is broad, from mesh (or multihop cellular) networks to adhocand sensor networks. Nevertheless, many questions and approaches are generic from an algorithmic and structural viewpoint.
In particular, we have studied three of the more prominent performance metrics for radio networks. Using combinatorial optimization and centralized algorithmic with a network design flavor, transport capacity and energy consumption of the networks have been studied. Using distributed algorithmic with a protocol flavor, fast data gathering and call scheduling are investigated. Our approach is complementary with those developed in other INRIA projectteams such as Planete, Maestro, Swing(ex Ares) or Pops. The complementarity has been exploited through an ARC collaboration with Aresand Pops, a joint Ph.D. between Maestroand Mascotteand, recently, an ANR VERSO project in which Maestro, Mascotteand Swingare involved.
At the international level, our researches are comparable and collaborative with some groups in renowned research centers such as CTI of Patras in Greece, Universities of Roma or Salerno in Italy, the Technion Institute in Israël, SFU in Vancouver, Canada, UFC, Universidade Federal do Ceará, Fortaleza, Brazil, or the University of Sao Paulo in Brazil.
We studied a wide range of issues of wireless networks, from the design of efficient crosslayer medium access, call scheduling and routing techniques and energy efficient optimization, to the development of theoretical tools for analyzing and evaluating dynamic networks. Some graph coloring problems motivated by channel assignment in wireless networks are detailed in Section and the optimization techniques and wireless simulation tools that we have developed are also cited in Section .
The specific challenges of multihop wireless networks lead to a strong research effort on efficient protocols design where the offered capacity is a key objective. More specifically, the routing strategy largely impacts the network capacity, i.e. the throughput offered to each flow.
, investigate the problem of determining feasible radio configurations in fixed broadband wireless networks, focusing on power efficiency. Under this scenario, a powerefficient configuration can be characterized by a modulation constellation size and a transmission power level. Every link holds a set of powerefficient configurations, each of them associating a capacity with its energy cost. We introduce a joint optimization of data routing and radio configuration that minimizes the total energy consumption while handling all the traffic requirements simultaneously. An exact mathematical formulation of the problem is presented. It relies on a minimum cost multicommodity flow with step increasing cost functions, which is very hard to optimize. We then propose a piecewise linear convex function, obtained by linear interpolation of powerefficient points, that provides a good approximation of the energy consumption on the links, and present a relaxation of the previous formulation that exploits the convexity of the cost functions. This yields lower bounds on the total energy expenditure, and finally heuristic algorithms based on the fractional optimum are employed to produce feasible configuration solutions. Our models are validated through extensive experiments, and the results testify the potentialities behind this novel approach.
, focuses on the energy consumption of adhocand sensor networks through the viewpoint of congestion. Congestion not only causes packet loss and increases queueing delay, but also leads to unnecessary energy consumption. Two types of congestion can occur: nodelevel congestion, which is caused by buffer overflow in the node, or linklevel congestion, when wireless channels are shared by several nodes arising in collisions. A measure of linklevel congestion in static wireless adhoc and sensor networks randomly deployed over an area is studied. The measure of congestion considered is the inverse of the greatest eigenvalue of the adjacency matrix of the random graph. This measure gives an approximation of the average quantity of wireless links of a certain length on the network. We survey the results to find this measure in Bernoulli random graphs. We use tools from random graph and random matrix theory to extend this measure on Geometric random graphs.
Several works of Mascottehave dealt with gathering (data collection) in wireless multi hop networks when interferences constraints are present.
, , suppose that the time is slotted and that during one time slot (step) each node can transmit to one of its neighbor at most one data item. Each device is equipped with a half duplex interface; so a node cannot both receive and transmit simultaneously. During a step only non interfering transmissions can be done. In other words, the non interfering calls done during a step will form a matching. Under these settings, the best known algorithm, in terms of the makespan or completion time, in grid networks was a multiplicative 1.5approximation algorithm. In such topologies, we give a very simple +2 approximation algorithm and then a more involved +1 approximation algorithm. Moreover, our algorithms work when no buffering is allowed in intermediary nodes, i.e., when a node receives a message at some step, it must transmit it during the next step.
Distributed call scheduling in wireless networks is a challenging problem to tackle. Indeed, even when interferences are not considered, computing an optimal call scheduling with local information is still an open question.
In , we have investigated the problem of distributed transmission scheduling in wireless networks. Due to interference constraints, "neighboring links" cannot be simultaneously activated, otherwise transmissions will fail. Here, we consider any binary model of interference. We assume that traffic is singlehop and that time is slotted. We suppose also random arrivals on each link during each slot. We design a fully distributed local algorithm with the following properties: it works for any arbitrary binary interference model; it has a constant overhead (independent of the size of the network and the values of the queues); and it needs no knowledge. Indeed contrary to other existing algorithms, we do not need to know the values of the queues of the “neighboring links”, which are difficult to obtain in a wireless network with interference. We also give sufficient conditions for stability under Markovian assumptions. The performance of our algorithm (throughput, stability) have been investigated and compared via simulations to that of previously proposed schemes.
The assessment of routing protocols for mobile wireless networks is a difficult task, because of the networks dynamic behavior and the absence of benchmarks. However, some of these networks, such as intermittent wireless sensors networks, periodic or cyclic networks, and some delay tolerant networks (DTNs), have more predictable dynamics, as the temporal variations in the network topology can be considered as deterministic, which may make them easier to study. Recently, a graph theoretic model, the evolving graphs was proposed to help capture the dynamic behavior of such networks, in view of the construction of least cost routing and other algorithms. The algorithms and insights obtained through this model are theoretically very efficient and intriguing. However, there were no study about the use of such theoretical results into practical situations.
Providing a continous connection with a terrestrial backbone network from a vehicle moving at high speeds is still an open issue. Various options have already been considered and still being studied such as UMTS, WiMax, LEO Satellites, and so on. Despite some of these having already been implemented and commercially exploited (eg. satellite connexions on trains), most fail to offer a sufficiently reliable service to their customers over long periods of travel time (UMTS/3G) or suffer from a limited ability to support a large number of simultaneous users (satellites). Let's consider the case of trains. Ideally, onboard customers want a fulltime connection of their laptop to a regular WiFi network, such that they don't need an additional device, and they want that network to provide a continuous and reliable connection to the Internet. Furthermore, many other devices onboard trains could benefit of such a continuous and reliable connection (eg. security cameras, broadcasting service, etc.), but these devices do not necessarily rely on TCP/IP. In , , we introduce a new system that allows fast handover between an onboard, fast moving IEEE 802.11 device and a series of 802.11 Access Points regularly placed along the road or track. This new device, called Spiderman, seamlessly alternates connections on two radio channels in order to hide the standard WiFi scanning and association delays. Another noticeable property of this new system is that it is fully implemented withen the OSI layer 2, which means that it does not depend on upper layers mobility mechanisms (in particular TCP/IP). A prototype of this system is currently under testing.
Traditional means to store data are dedicated servers or magnetic tapes. These solutions are reliable but expensive. Recently, hard disks and bandwidth have become cheaper and widely available, allowing new forms of data storage on distributed, peertopeer (P2P) architectures. To achieve high durability, such P2P systems encode the user data in a set of redundant fragments and distribute them among the peers. These systems are cheap to operate, but their highly distributed nature raises questions about reliability, durability, availability, confidentiality, and routing of the data. An abundant literature exists on the topic of P2P storage systems. Several efforts to build largescale selfmanaging distributed systems have been done, among others, Intermemory, Ocean Store, Freenet, PASTRY, CFS, Total Recall. However, few analytical models have been proposed to estimate the behavior of the system (the data durability, resource usage, e.g., bandwidth) and understand the tradeoffs between the system parameters. Furthermore, in almost all these models, the behavior of a single block is modeled and the block failures are considered independent. We showed that this assumption can lead to severe errors of estimation on the behavior of a system subject to peer failures . Therefore the need of new more complex analytical models to describe the systems. Part of Mascotte's work on this topic is done inside the ANR SPREADS project.
In P2P storage systems, peers fail continuously, hence, the necessity of selfrepairing mechanisms to achieve high durability. In , , we propose and study analytical models that assess the bandwidth consumption and the probability to lose data of storage systems that use erasure coded redundancy. We show by simulations that the classical stochastic approach found in the literature, that models each block independently, gives a correct approximation of the system average behavior, but fails to capture its variations over time. These variations are caused by the simultaneous loss of multiple data blocks that results from a peer failing (or leaving the system). We then propose a new stochastic model based on a fluid approximation that better captures the system behavior. In addition to its expectation, it gives a correct estimation of its standard deviation. This new model is validated by simulations.
In , , we study the impact of different data placement strategies on the system performance when using erasure codes redundancy schemes. We compare three policies: two of them local, in which the data are stored in logical neighbors, and the other one global, in which the data are spread randomly in the whole system. We focus on the study of the probability to lose a data block and the bandwidth consumption to maintain enough redundancy. We use simulations to show that, without resource constraints, the average values are the same no matter which placement policy is used. However, the variations in the use of bandwidth are much more bursty under the local policies. When the bandwidth is limited, these bursty variations induce longer maintenance time and henceforth a higher risk of data loss. Finally, we propose a new external reconstruction strategy and a suitable degree of locality that could be introduced in order to combine the efficiency of the global policy with the practical advantages of a local placement.
Besides the complexity in time or in number of messages, a common approach for analyzing distributed algorithms is to look at their assumptions on the underlying network. In , we focus on the study of such assumptions in dynamic networks, where the connectivity is expected to change, predictably or not, during the execution. Our main contribution is a theoretical framework dedicated to such analysis. By combining several existing components (local computations, graph relabellings, and evolving graphs), this framework allows to express detailed properties on the network dynamics and to prove that a given property is necessary, or sufficient, for the success of an algorithm. Consequences of this work include (i) the possibility to compare distributed algorithms on the basis of their topological requirements, (ii) the elaboration of a formal classification of dynamic networks with respect to these properties, and (iii) the possibility to check automatically whether a network trace belongs to one of the classes, and consequently to know which algorithm should run on it.
In collaboration with Intel Research Berkeley, Mascotteworked on methods for providing security to end hosts in typical enterprise environments. The research is focused on making end host security customizable and adaptable by exploring design profiles based on the end host's communication traffic and using these for anomaly detection.
Estimating the number of distinct flows in a data stream has many applications in network monitoring and network security. For instance, one can count the number of distinct flows on a traffic to detect Denial of Service attacks. In , a new class of algorithms to estimate the cardinality of very large multisets using constant memory and doing only one pass on the data is introduced. It is based on order statistics rather than on bit patterns in binary representations of numbers. Three families of estimators are analyzed. They attain a standard error of using M units of storage, which places them in the same class as the best known algorithms so far. The algorithms have a very simple internal loop, which gives them an advantage in terms of processing speed. For instance, a memory of only 12 kB and only few seconds are sufficient to process a multiset with several million elements and to build an estimate with accuracy of order 2 percent. The algorithms are validated both by mathematical analysis and by experimentation on real Internet traffic.
In order to cope with the constant evolution and ever growing complexity and size of networks, new tools and modeling techniques are regularly developed within Mascotte. These tools are first developed to answer the internal needs of the team, but we also pay attention to the visibility and the dissemination of these tools in the scientific community.
In the domain of discreteevent simulation, our development efforts on the Open Simulation Architecture (OSA) are going on
(See Section
and
http://
Since OSA is still in early ages, we have also been using and contributing to other simulation software. This includes in particular significant contributions to the Omnet++ simulator , . These contributions were mainly motivated by our work on the design and prototyping of a new wireless system, called Spiderman, that provides a continuous and highspeed wireless connection onboard fast moving vehicles like trains .
We also designed and developed a Dynamic Routing Model Simulator (DRMSim) (see Section ), which addresses the specific problem of largescale simulations of (interdomain) routing models on large networks. DRMSim is a discreteevent simulator that comes with a generic routing models and implementations of BGP as well as of StateoftheArt compact routing protocols. It relies on the Dipergrafs library, which allows efficient operations on large graphs (see Section ). This simulator is designed in particular to address the limitations found in other simulators in terms of the number of nodes they can handle and in the models they propose.
Mobility issues in MANETs have also been studied using simulations. In we have studied the impact of mobility on MANET topology. More precisely, we consider a network composed of a finite number of stations which move into a closed environment. The mobility is defined by the Random Waypointmobility model. Thus, the aim of these works is to determine the impact of the mobility on the network connectivity. The result is an empirical formulation of two bounds on the number of connected components into the network.
The
Mascoptlibrary has reached maturity and is intensively used inside the team for testing and evaluation of optimization programs (see Section
and
http://
Mascotteprincipally investigates applications in telecommunications via Graph Theory (see other objectives). However it also studies a number of theoretical problems of general interest. Our research mainly focused on three important topics: graph colouring, width parameters and random graphs.
Graph colouring is a hot topic in Graph Theory. It is one of the oldest problem in combinatorics (with the 4colour problem), has a central position in Discrete Mathematics and a huge number of applications. Lots of new results have been obtained the last ten years with the fast development of new techniques (structural and probabilistic). In Mascottewe studied graph colouring problems via these new methods (probabilistic method, discharging method,...).
The theory of width parameters (treewidth, branchwidth, ...) is a deep and algorithmically useful structure theory. Therefore it is now widely studied and used. In particular, it is strongly related to graph searching problems (see ).
Since the seminal paper of Erdös and Rényi, the theory of random graphs has now grown a very active field with an extensive literature. There are many beautiful results in the theory of random graphs as well as various applications in computer science, biology, ... In Mascotte, we study random graphs for their own sake but as well as tools to solve some graphtheoretic questions which have nothing to do with randomness.
Colouring and edgecolouring are two central concepts in Graph Theory. There are many important and long standing conjectures in these areas. We are trying to make advances towards such conjectures, in particular Hadwiger's conjecture, the List Colouring Conjecture and the Acyclic EdgeColouring Conjecture. We also investigated the relation between the chromatic number and the crossing number of a graph.
We are also interested in colouring problems arising from some practical problems: improper colouring,
L(
p,
q)labelling, directed star arboricity and good edgelabelling. The first two are both motivated by channel assignment and the last two are motivated by problems
arising in WDM networks. In
, some of these problems are summarized.
We also studied some other variants of colouring like circular colouring, nonrepetitive colouring and frugal colouring.
Hadwiger's conjecture: The famous Hadwiger's conjecture asserts that every graph with no
K_{t}minor is
(
t1)colourable. The case
t= 5is known to be equivalent to the Four Colour Theorem by Wagner, and the case
t= 6is settled by Robertson, Seymour and Thomas. So far the cases
t7are wide open. In
, we prove the following two theorems: There is an
O(
n^{2})algorithm to decide whether or not a given graph
Gsatisfies Hadwiger's conjecture for the case
t. Every minimal counterexample to Hadwiger's conjecture for the case
thas at most
f(
t)vertices for some explicit bound
f(
t).
Edgecolouring: The most celebrated conjecture on edgecolouring is the List Colouring Conjecture asserting that the chromatic index is always equal to the list
chromatic index. Together with Vizing's Theorem it implies the following conjecture : For any graph
Gwith maximum degree
, the list chromatic index is at most
+ 1. In
, we give a short proof of a result of Borodin showing that this
later conjecture holds for planar graphs of maximum degree at least 9.
We also investigate the algorithmic issue of edgecolouring. For any
c>1, we describe
a linear time algorithm for fractionally edge colouring simple
graphs with maximum degree at least

V/
c.
A proper edgecolouring with the property that every cycle contains edges of at least three distinct colours is called an
acyclic edgecolouring. The
acyclic chromatic indexof a graph
G, denoted
_{a}^{'}(
G)is the minimum
ksuch that
Gadmits an
acyclic edgecolouringwith
kcolours. The Acyclic Colouring Conjecture states that
_{a}^{'}(
G) =
(
G) + 2for every graph
G. In
,
, we conjecture that if
Gis planar and
(
G)is large enough then
_{a}^{'}(
G) =
(
G). We settle this conjecture for planar graphs with girth at least 5 and outerplanar graphs. We also show that
_{a}^{'}(
G)
(
G) + 25for all planar graph
G.
Crossing and colouring: The crossing number of a graph
G, denoted by
cro(
G), is the minimum number of crossings in any drawing of
Gin the plane.
The Four Colour Theorem states that if a graph has crossing number zero then it is 4colourable. It is then natural to find upper bounds on the chromatic number in terms of its crossing
number. Oporowski and Zhao showed that a graph with crossing number at most 3 is 5colourable unless it contains a
K_{6}. They conjecture that this result could be extended to graphs with crossing number at most 5. In
, we disprove this conjecture but show that every graph with
crossing number at most 4 and containing no
K_{6}is 5colourable. We also show some colourability results on graphs that can be made planar by removing few edges. In particular, we show that if there exists three edges whose removal
leaves the graph planar then it is 5colourable.
Improper colouring: A
kimproper
colouringis a mapping
cfrom its vertex set into a set of colours such that every vertex has at most
kneighbours with the same colour. A result of Lovász states that for any graph
G, such a partition exists if
. When
k= 0, this bound can be reduced by Brooks' Theorem, unless
Gis complete or an odd cycle. In
, we study the following question, which can be seen as a
generalisation of the celebrated Brooks' Theorem to improper colouring: does there exist a polynomialtime algorithm that decides whether a graph
Gof maximum degree
has
kimproper chromatic number at most
? We show that the answer is no, unless P = NP, when
=
(
k+ 1),
k1and
. We also show that, if
Gis planar,
k= 1or
k= 2,
= 2
k+ 2, and
= 2, then the answer is still no, unless P = NP. These results answer some
questions of Cowen et al. [Journal of Graph Theory 24(3):205219, 1997].
L(
p,
q)labelling: An
L(
p,
q)labelling of
Gis an integer assignment
fto the vertex set
V(
G)such that

f(
u)
f(
v)
p, if
uand
vare adjacent, and

f(
u)
f(
v)
q, if
uand
vhave a common neighbour. Such a concept is a modeling of a simple channel assignment, in which the separation between channels depends on the distance. More precisely, it has to be at
least
pif they are very close and
qif they are close (but not very close). The goal is to find an
L(
p,
q)labelling
fof
Gwith minimum
span(i.e.
max{
f(
u)
f(
v),
u,
v
V(
G)}). It is well known that deciding if a graph has an
L(
p, 1)labelling with minimum span
kis NPcomplete. We show that it remains NPcomplete when restricted to planar graphs
or vertexedge incidence graphs
which form a small class of bipartite graphs. We also give
some upper bouns for the span of an
L(1, 1)labelling of a planar graph with large girth.
Directed star arboricity: A
staris an arborescence in which the root dominates all the other vertices. A
galaxyis a vertexdisjoint union of stars. The
directed star arboricityof a digraph
D, denoted by
dst(
D), is the minimum number of galaxies needed to cover
A(
D). In
, we show that
dst(
D)
(
D) + 1and that if
Dis acyclic then
dst(
D)
(
D). These results are proved by considering the existence of spanning galaxies in digraphs. Thus, we study the problem of deciding whether a digraph
Dhas a spanning galaxy or not. We show that it is NPcomplete (even when restricted to acyclic digraphs) but that it becomes polynomialtime solvable when restricted to strongly
connected digraphs.
Good edgelabelling: Let
be a family of dipaths of a DAG (Directed Acyclic Graph)
G. The
loadof an arc is the number of dipaths containing this arc. Let
be the maximum of the load of all the arcs and let
be the minimum number of wavelengths (colours) needed to colour the dipaths of
in such a way that two dipaths with the same wavelength are arcdisjoint. There exist DAGs such that the ratio between
and
cannot be bounded. An
internal cycleis an oriented cycle such that all the vertices have at least one predecessor and one successor in
G(said otherwise every cycle contain neither a source nor a sink of
G). We prove
that, for any family of dipaths
,
if and only if
Ghas no internal cycle. We also consider a new class of DAGs, which is of interest in itself, those for which there is at most one dipath from a vertex to another. We call these
digraphs UPPDAGs. For these UPPDAGs we show that the load is equal to the maximum size of a clique of the conflict graph. We prove that the ratio between
and
cannot be bounded. For that we introduce
good edgelabellingsof the conflict graph, namely edgelabellings such that for any ordered pair of vertices
(
x,
y)there do not exist two paths from
xto
ywith increasing labels. In
,
, we aim at characterizing the class of graphs that admit a good
edgelabelling. First, we exhibit infinite families of graphs for which no such edgelabelling can be found. We then show that deciding if a graph admits a good edgelabelling is NPcomplete.
Finally, we give large classes of graphs admitting a good edgelabelling:
C_{3}free outerplanar graphs, planar graphs of girth at least 6, subcubic
{
C
_{3},
K
_{2, 3}}free graphs.
We also study nonrepetitive colouring. A sequence
such that
r_{i}=
r_{n+
i}for all
1
i
n, is called a
repetition. A sequence
Sis called
nonrepetitiveif no
block(i.e. subsequence of consecutive terms of
S) is a repetition. Let
Gbe a graph whose edges are coloured. A trail is called
nonrepetitiveif the sequence of colours of its edges is nonrepetitive. If
Gis a plane graph, a
facial nonrepetitive edgecolouringof
Gis an edgecolouring such that any
facial trail(i.e. trail of consecutive edges on the boundary walk of a face) is nonrepetitive. We denote
_{f}^{'}(
G)the minimum number of colours of a facial nonrepetitive edgecolouring of
G. In
, we show that
_{f}^{'}(
G)
8for any plane graph
G. We also get better upper bounds for
_{f}^{'}(
G)in the cases when
Gis a tree, a plane triangulation, a simple 3connected plane graph, a hamiltonian plane graph, an outerplanar graph or a Halin graph. The bound 4 for trees is tight.
We also worked on frugal colouring. In
, we prove that every graph with maximum degree
can be properly
(
+ 1)coloured so that no colour appears more than
O(log
/loglog
)times in the neighbourhood of any vertex. This is best possible up
to the constant factor in the O(–) term. We also provide an efficient algorithm to produce such a colouring.
A key notion in the treewidth theory is the duality between the bramblenumber of a graph and its treewidth. Adapting the method introduced in Graph Minors x [Robertson and Seymour, Journal of Combinatorial Theory B 52(2): 153190 (1991)], we propose a new proof of it . Our approach is based on a new definition of submodularity on partition functions which naturally extends the usual one on set functions. The proof does not rely on Menger's theorem, and thus greatly generalises the original one. It thus provides a dual for matroid treewidth. One can also derive all known dual notions of other classical widthparameters from it.
On the algorithmic point of view, lots of polynomial time algorithms based on treewidth use a related duality fact: if a graph has no
r×
rgrid minor then its treewidth is bounded by
2
^{20
r
5}. This huge upper bound is far from being tight (a polynomial in
rbound is conjectured) and implies the existence of large constant in the actual timecomplexity of the algorithms and thus make the algorithms not efficient practically. Hence an issue
is to find the tight upper bound or at least lower the actual upper bound. In
, we show that a graph with no
3×3grid minor has treewidth at most 7. This is tight and improves the best known upper bound which was 2942.
In
, we present a result concerning the relation between the
pathwidth of a planar graph and the pathwidth of its topological dual. More precisely, we prove that for a 3connected planar graph
G,
pw(
G)
3
pw(
G^{*}) + 2. For 4connected planar graphs, and more generally for Hamiltonian planar graphs, we prove a stronger bound
pw(
G^{*})
2
pw(
G) +
c. The best previously known bound was obtained by Fomin and Thilikos who proved that
pw(
G^{*})
6
pw(
G) +
cte. The proof is based on an algorithm which, given a fixed spanning tree of
G, transforms any given decomposition of
Ginto one of
G^{*}. The ratio of the corresponding parameters is bounded by the maximum degree of the spanning tree. In
, we present a result concerning the relation between the
branchwith of a graph embedded in a surface of Euler genus
gand the branchwidth of its topological dual. We prove that
for any graph
Gembedded in a surface of Euler genus
g.
We studied various parameters of random graphs and random walks.
Given a branching random walk, let
M_{n}be the minimum position of any member of the
nth generation. In
, we calculate
to within
O(1)and prove exponential tail bounds for
, under quite general conditions on the branching random walk. In particular, together with work by Bramson [Z. Wahrsch. Verw. Gebiete 45 (1978) 89108], our results fully characterise
the possible behaviour of
when the branching random walk has bounded branching and step size.
A
circuitin a simple undirected graph
G= (
V,
E)is a sequence of vertices
{
v
_{1},
v
_{2}, ...,
v
_{k+ 1}}such that
v_{1}=
v_{k+ 1}and
{
v
_{i},
v
_{i+
i}}
Efor
i= 1, ...,
k. A circuit
Cis said to be
edgesimpleif no edge of
Gis used twice in
C. In
,
, we study the following problem: which is the largest integer
ksuch that, given any subset of
kordered vertices of an infinite square grid, there exists an edgesimple circuit visiting the
kvertices in the prescribed order? We prove that
k= 10. To this end, we first provide a counterexample implying that
k<11. To show that
k10, we introduce a methodology, based on the notion of core graph, to reduce
drastically the number of possible vertex configurations, and then we test each one of the resulting configurations with an
ILPsolver.
Mascotteis also interested in the algorithmic aspects of Graph Theory. In general we try to find the most efficient algorithms to solve various problems of Graph Theory and telecommunication networks either with exact algorithms or approximation ones. We are mainly focused on four important topics:
The routing problems plays an essential role in communication networks. It involves how to transfer data from some origins to some destinations within a reasonable amount of time. In Mascotte, we consider this problem in centralized and distributed environments. We also consider the routing problem in particular graph classes and in general graphs.
Graph searching gathers an active research community (see, e.g., the first three editions of the "Workshop on Graph Searching, Theory and Applications" took place in Crete (2006), Brazil (2008) and Czech Republic (2009)). In particular, the graph searching problem has been widely studied for its close relationship with graph decompositions (see Section ). Note that this problem has also a practical impact in the area of optical network reconfiguration which is dealt with in Section .
The field of algorithmic game theory combines computer science concepts of complexity and algorithm design with game theory and economic theory. Algorithmic game theory is considered as the most powerful tool dealing with noncooperative systems in which the lack of coordination among the players produces inefficient solutions in the optimization of systems requirements. There are a lot of situations occurring in real life in which we seek the maximization of our own benefit and very often the final outcome of our efforts also depends on the behavior of other people we have no control on. In Mascotte, we are interested in considering communication problems arising in networks with noncooperative users.
Parameterized complexity is a recent approach to deal with intractable computational problems having some parameters that can be relatively small with respect to the
input size. This area has been developed extensively during the last decade. More precisely, a parameter
Pis any function mapping graphs to nonnegative integers. The parameterized problem associated with parameter
Pasks, for some fixed
k, whether
P(
G)
kfor a given graph
G. For decision problems with input size
nand parameter
k, the goal is to design an algorithm with running time
f(
k).
n, where
fdepends only on
k. Problems having such an algorithm are said to be fixedparameter tractable (FPT).
We consider the routing problem through three different approaches: compact routing, the
(
,
k)routing problem and the disjoint paths problem. First two studies consider specific classes of graphs while the third one considers general graphs.
Compact routing:
In any distributed communication network it is important to deliver messages between pairs of nodes. Routing schemes consist in the design of a routing table in each node (node's local memory where the routing information is stored) together with a protocol that allow each node to decide toward which port (incident edge) it must transmit a message knowing the message's destination. Compact routing consider the tradeoffs between the length of the computed routes and the size of routing tables (the local knowledge of each node about the network's topology). Antoher issue of interest is the computation of routing table.
In general, it is difficult to establish good tradeoffs between the length of computed routes and the size of the routing tables. Efficient algorithms for computing routing tables should take advantage of the particular properties arising in large scale networks. We consider two properties: low (logarithmic) diameter and high clustering coefficient (implying the existence of few large induced cycles). We propose a routing scheme that computes short routes in the class of kchordal graphs, i.e., graphs with no chordless cycles of length more than k . This algorithm has been implemented using DRMSim .
(
,
k)routing problem:
In the
(
,
k)routing problem, each node can send at most
packets and receive at most
kpackets. In this setting, the goal is to minimize the number of time steps required to route all packets to their respective destinations, under the constraint that each link can be
crossed simultaneously by no more than one packet. Permutation routing is the particular case
=
k= 1. In the
rcentral routing problem, all nodes at distance at most
rfrom a fixed node
vwant to send a packet to
v. In
, we study the permutation routing, the
rcentral routing and the general
(
,
k)routing problems on plane grids, that is square grids, triangular grids and hexagonal grids. We use the
storeandforward
port model, and we consider both full and halfduplex networks. The main contributions are the following: (1) tight permutation routing algorithms on fullduplex hexagonal grids, and
half duplex triangular and hexagonal grids, (2) tight
rcentral routing algorithms on triangular and hexagonal grids, (3) tight
(
k,
k)routing algorithms on square, triangular and hexagonal grids, and (4) good approximation algorithms (in terms of running time) for
(
,
k)routing on square, triangular and hexagonal grids, together with new lower bounds on the running time of any algorithm using shortest path routing. All these
algorithms are completely distributed, i.e. can be implemented independently at each node. Finally, we also formulate the
(
,
k)routing problem as a
Weighted Edge Coloringproblem on bipartite graphs. We provide a survey on above problems in
.
Disjoint paths problems:
Given a number of requests (pair of vertices), the disjoint paths problem asks whether there exist pairwise disjoint paths to be assigned to all requests. We investigate several variants of this widely studied problem.
A graph
Gis
klinked if
Ghas at least
2
kvertices
, such that
Gcontains
kpairwise disjoint paths between
x_{i}and
y_{i}(
i= 1to
k). We say that
Gis parity
klinked if
Gis
klinked and, in addition, the paths can be chosen such that the parities of their length are prescribed. Thomassen was the first to prove the existence of a function
f(
k)such that every
f(
k)connected graph is parity
klinked if the deletion of any
4
k3vertices leaves a nonbipartite graph. In
, we show that the above statement is still valid for
50
kconnected graphs. This is the first result that connectivity which is a linear function of
kguarantees the ErdösPósa type result for parity
klinked graphs. In
, we consider a similar problem where each vertex is on at most
two of these paths. We present an
O(
m(
m,
n)
logn)algorithm for fixed
k, where
n,
mare the number of vertices and the number of edges, respectively, and the function
(
m,
n)is the inverse of the Ackermann function. This is the first polynomial time algorithm for this problem, and generalizes polynomial time algorithms by Kleinberg,
and Kawarabayashi and Reed, respectively, for the half integral disjoint paths packing problem, i.e., without the parity requirement. We also have algorithms running in
O(
m(1 +
))time for any
>0for this problem, if
kis up to
o(
logloglogn)for general graphs, up to
o(
loglogn) for planar graphs, and up to
o(
loglogn/
g)for graphs on the surface, where
gis Euler genus. Furthermore, if
kis fixed, then we have linear time algorithms for the planar case and for the bounded genus case.
Graph Searching encompasses a wide variety of combinatorial problems related to the capture of an arbitrary fast fugitive residing in a network by a team of searchers. The goal consists in minimizing the number of searchers required to capture the fugitive in a network and in computing the corresponding capture strategy. We mainly investigate three variants of graph searching: visible graph searching, connected graph searching and distributed graph searching. The first study is motivated by the relationship between graph searching and graph decompositions, while the main motivation for both other studies is the design of distributed protocols allowing searchers to compute a capture strategy.
Roughly, if the fugitive is visible (i.e., the searchers are permanently aware of the position of the fugitive) then graph searching is equivalent to treewidth, while it is equivalent to pathwidth otherwise. In , we introduce nondeterministic graph searching where the fugitive is visible a limited number of steps. We prove the NPhardness of this problem and design an exponential exact algorithm for solving it. This new variant leads to the unified view of graph decompositions in terms of partition functions and partitioningtrees .
A strategy is called connected if the clear part (the part where the fugitive cannot stand) always induces a connected subgraph. In particular, when the strategy has to be computed online,
this property ensures safe communications between the searchers during the whole strategy. In
, we investigate the cost of the connectedness of a strategy. We
design an algorithm that computes a connected capture strategy using at most
O(
tw(
G)*
k)times the search number of
G, in any
kchordal graph
Gwith treewidth
tw(
G).
We then propose a polynomialtime distributed algorithm for clearing any network using the optimal number of searchers assuming that the searchers have some knowledge about the network
they are clearing. More precisely, we prove that the amount of information necessary to clear any
nnode network in a monotone distributed way is
(
nlogn)bits
. When the network is unknown a priori, we propose a
polynomialtime distributed algorithm for clearing any
nnode network using
times the optimal number of searchers and we prove this is optimal
.
In highly distributed systems, it might be too strong or unrealistic to assume that the resources of the system are directly accessible and controllable by a centralized authority. Therefore, we consider communication problems arising in networks with autonomous or noncooperative users. In such a scenario, users pursue an own often selfish strategy and the system evolves as a consequence of the interactions among them. The interesting arising scenario is thus characterized by the conflicting needs of the users aiming to maximize their personal profit and of the system wishing to compute a socially efficient solution.
The uncoordinated users' behavior, addressing communication primitives in an individualistic and selfish manner, poses several intriguing questions ranging from the definition of reasonable and practical models, to the quantification of the efficiency loss due to the lack of users' cooperation. We survey several results lately achievied in this research area and propose interesting future research directions .
We consider the pure Nash equilibrium as the outcome of the game and in turn as the concept capturing the notion of stable solution of the system. We make different progresses on the understanding of a variety of problems in communication networks. We study the performances of Nash equilibria in isolation games, a class of competitive location games recently introduced by Zhao et al. For all the cases in which the existence of Nash equilibria has been shown, we give tight or asymptotically tight bounds on the prices of anarchy and stability under the two classical social functions mostly investigated in the scientific literature, namely, the minimum utility per player and the sum of the players' utilities. Moreover, we prove that the convergence to Nash equilibria is not guaranteed in some of the not yet analyzed cases .
We design FPTalgorithms for four NPcomplete problems: the BoundedDegree Connected Subgraph Problems on Planar Graphs, the Bounded leaves Subtree Problem, the Fractional Path Coloring Problem and the Spanning Galaxies Problem.
In
,
, we present subexponential parameterized algorithms on planar
graphs for a family of problems that consist in, given a graph
G, finding a connected subgraph
Hwith bounded maximum degree, while maximizing the number of edges (or vertices) of
H. These problems are natural generalisations of the
Longest Pathproblem. Our approach uses bidimensionality theory to obtain combinatorial bounds, combined with dynamic programming techniques over a
branch decomposition of the input graph. These techniques need to be able to keep track of the connected components of the partial solutions over the branch decomposition, and can be seen as
an
algorithmic tensorthat can be applied to a wide family of problems that deal with finding connected subgraphs under certain constraints.
An outtree
Tis an oriented tree with exactly one vertex of indegree zero and a vertex
xof
Tis called internal if its outdegree is positive. In
, we design randomized and deterministic algorithms for deciding
whether an input digraph contains a subgraph isomorphic to a given outtree with
kvertices. Both algorithms run in
O^{*}(5.704
^{k})time. We apply the deterministic algorithm to obtain an algorithm of runtime
O^{*}(
c^{k}), where
cis a constant, for deciding whether an input digraph contains a spanning outtree with at least
kinternal vertices. This answers in the affirmative a question of Gutin, Razgon and Kim (Proc. AAIM'08).
In
, we study the natural linear programming relaxation of the path
coloring problem. We prove constructively that finding an optimal fractional path coloring is FPT with the degree of the tree as parameter: the fractional coloring of paths in a bounded
degree trees can be done in a time which is linear in the size of the tree, quadratic in the load of the set of paths, while exponential in the degree of the tree. We give an algorithm based
on the generation of an efficient polynomial size linear program. Our algorithm is able to explore in polynomial time the exponential number of different fractional colorings, thanks to the
notion of trace of a coloring that we introduce. We further give an upper bound on the cost of such a coloring in binary trees and extend this algorithm to bounded degree graphs with bounded
treewidth. Finally, we also show some relationships between the integral and fractional problems, and derive a
(1 + 5/3
e)approximation algorithm for the path coloring problem in bounded degree trees, improving on existing results. This classic combinatorial problem finds
applications in the minimization of the number of wavelengths in wavelength division multiplexing (WDM) optical networks. In
, we describe a linear time algorithm for fractionally edge
colouring simple graphs with maximum degree at least

V/
c(
c>1).
In , we prove that the parametrized version of the Spanning Galaxies Problem (see Section ) has a linear kernel.
On Dynamic Compact Routing Schemes in collaboration with LABRI (Bordeaux)
Mascotteis part of the join laboratory INRIA / AlcatelLucent Belllabs France within the ADR HiMa (research action on High Manageability) and works on autonomous dynamic management of virtual topologies (the ADR finances a Ph.D. student).
(
http://
Grant for a Ph.D. student (N. Nepomuceno) cofinanced by the SME 3Roam and the région PACAon optimization and dynamic routing in wireless backhaul networks.
On Wireless IP Service Deployment optimization and monitoring.
The objectives of the project DIMAGREEN (DesIgn and MAnagement of GREEN networks with low power consumption) are to introduce and analyze energyaware network designs and managements in order to increase the lifespan of telecommunication hardware and to reduce the energy consumption together with the electricity bill.
(
http://
The project AGAPE (Parametrized and exact graph algorithms) is led by Mascotteand implies also LIRMM (Montpellier) and LIFO (Orléans).
(
http://
The project SPREADS (Safe P2pbased REliable Architecture for Data Storage) is leaded by the SME UbiStorage; other partners are the INRIA teams Mascotteand REGAL in Rocquencourt and Eurecom and LACL Paris XII. It concerns the evaluation and optimization of a peertopeer based reliable storage system for which simulations of very large peertopeer systems will be done using OSA. It has got the approbation and label of the “pôle de compétitivité” SCS.
The ECOSCells (Efficient Cooperating Small Cells) project aims at developing the algorithms and solutions required to allow Small Cells Network (SCN) deployment. The consortium gathers industrial groups, together with 3 SME and 6 research institutes: AlcatelLucent Bell Labs (leader), Orange Labs, 3ROAM, Sequans, Siradel, INRIA teams Maestro, Mascotteand Swing, Université d'Avignon et des Pays de Vaucluse, Laboratoire des Signaux et Systèmes / Supelec, LAAS and Eurecom.
(
http://
ARC BROCCOLI (Building instRumenting and deplOying Componentbased arChitecture fOr Largescale applIcations) involves the INRIA teams Mascotte, Adamin Lille Nord Europe and Télécom SudParis  ACMES team in Evry. The topic is the very large scale deployment and instrumentation of OSA distributed simulations on Gridcomputing facilities (e.g. on Grid 5000).
Réseaux de communications, working group of GDR ASR, CNRS. (
http://
Action Graphes, working group of GDR IM, CNRS. (
http://
On Algorithmic Principles for Building Efficient Overlay Computers (AEOLUS), in collaboration with 21 European universities and coordinated by University of Patras, Greece.
The recent explosive growth of the Internet gives rise to the possibility of a global computer of grandscale consisting of Internetconnected computing entities (possibly mobile, with varying computational capabilities, connected among them with different communication media), globally available and able to provide to its users a rich menu of highlevel integrated services that make use of its aggregated computational power, storage space, and information resources. Achieving this efficiently and transparently is a major challenge that can be overcome by introducing an intermediate layer, the overlay computer.
The goal of AEOLUS is to investigate the principles and develop the algorithmic methods for building such an overlay computer that enables this efficient and transparent access to the resources of an Internetbased global computer.
Mascotteis the leader of SubProject 2 on resource management.
The work within this subproject focuses on the study of fundamental issues for accessing and managing communication resources in an overlay computer. Our research addresses novel and challenging algorithmic issues for efficient resource discovery and querying like construction of overlay networks, query routing and execution, and for sharing critical resources like bandwidth.
Responsable: Frédéric Havet.
On Graph colouring: theoretical and algorithmic aspects.
Responsable: Frédéric Havet.
On Graph colouring: theoretical and algorithmic aspects.
Responsable: JeanClaude Bermond.
Joint team with the Network Modeling Group (S.F.U., Vancouver, Canada). One of the main objectives is to strengthen our collaboration with S.F.U. Many reciprocal visits have been performed.
(
http://
Responsable: Frédéric Havet.
Joint team EWIN (Efficient algorithms in WIreless Networks) with the Departamento de Computação of Universidade Federal do Ceará of Fortaleza (Brazil).
(
http://
University of Southern Denmark, Odensee, Denmark, October 329, 2009 (4 weeks)
Universidade Federal do Ceará, Fortaleza, Brasil, November 23December 6, 2009 (2 weeks)
Universidade Federal do Ceará, Fortaleza, Brazil, November 28 December 12, 2009 (2 weeks)
Salerno Italy, July 1August 31, 2009 (2 months)
University of Ljubljana, Slovenia, June 2127, 2009 (1 week)
Simon Fraser University, Vancouver, Canada, October 1529, 2009 (2 weeks)
University Rostock, Rostock, Germany, May 23 June 6, 2009 (2 weeks)
AlcatelLucent BellLabs, Holmdel, USA, December 11, 2009 (1 day)
Charles University, Pragues, Czech Republic, June 2127, 2009 (1 week)
Universidade Federal do Ceará, Fortaleza, Brasil, October 110, 2009 (10 days)
University of Bordeaux (LaBRi) France, October 57, 2009 (3 days)
RWTH Aachen University, Aachen, Germany. September 20October 3, 2009 (2 weeks)
Charles University, Pragues, Czech Republic, June 2127, 2009 (1 week)
EPI Swing, CITI, INSA Lyon, France, April 2030, 2009 (10 days)
Alcatel Lucent BellLabs, Antwerpen, Belgium, January 1516, 2009 (2 days)
Weizmann Institute of Science, Rehovot, Istael, October 1317, 2009 (4 days)
National and Kapodistrian University of Athens, Grece, June 1723, 2009 (1 week)
Salerno Italy, July 1August 31, 2009 (2 months)
Carleton University, Ottawa, Canada, June 115, 2009 (2 weeks)
S.F.U. Vancouver, Canada, February 24 May 22, 2009 (3 months)
Visit to LMD, Marseille, France (February 24, 2009);
Visit to GSCOP, Grenoble, France (September 1618, 2009); Visit to the University of Ljubljana, Slovenia, (October 25 – November 11, 2009);
LIAFA, Paris, France (January 14, 2009); AlcatelLucent Bell labs, Antwerpeen, Belgium, (October 2223, 2009);
Visit to VSIM at Carleton University, Ottawa, Canada (July, 21  July 31, 2009; August 9  August 20, 2009); Visit to SFU, Vancouver, Canada (August 19, 2009); Visit to INRIA/ Adam, Lille (June 912, 2009); Visit to DAATLE, Gardanne (Nov 24, 2009).
Visit to LIAFA, Paris, France (February 1720, 2009); Visit to GSCOP, Grenoble, France (September 1618, 2009); Visit to LIA, Federal University of Ceará, Brasil, (November 7–13, 2009);
Visit to VSIM at Carleton Univeristy, Ottawa, Canada (August, 320, 2009);
Visit to UFC (Universidade Federal do Ceará), Fortaleza, Brazil (July 29  September 2, 2009);
Visit to the Department of Electrical and Computer Engineering, University of Waterloo, Ontario, Canada (January 7February 7, 2009);
Visit to Carleton University, Ottawa, Canada, (July 20  Aug 09, 2009);
Visit to Universidade Federal do Ceará, Fortaleza, Brazil, (July 9  September 1st 2009);
Visit to LaBRI, Bordeaux, France (March 913, 2009, and November 26 December 5, 2009); Visit to LIFL, EPI Pops, Lille, France (March 5, 2009); Many short visits to LIF, Marseille, France;
Visit to Simon Fraser Univ., School of Computer sciences, Vancouver, Canada (November 323, 2009)
Visit to ACMES, Evry, France (January 1923, 2009); Visit to LACL, Créteil, France (April 20May 1); Visit to Carleton University, Ottawa, Canada (July 27August 14); Visit to ACMES, Evry, France (September 14October 2, 2009);
Many short visits to CITI lab (INSA Lyon/INRIA) and long stay (September  December);
Visit to the Algorithms Research Group of University of Bergen. Bergen, Norway (May 1421, 2009); Visit to the Research Group on Graph Theory and Combinatorics of UPC, Barcelona, Spain (February 18, 2009 and August, 2009).
expert for DRTT, AERES, ANRT and various projects outside France (Canada,...); member of the comité de sélectionof 61 ^{e}section of UNS; responsible of the Pôle ComRedof I3S; member of the recruiting committee of an ingeneer for the Pôle ComRedof I3S; member of the Ph.D. committee of the University of Marseille.
expert for the National Sciences and Engineering Research Council of Canada (NSERC) and the ANR; Member of committee 525 (Applied mathematics) of the fonds québécois de la recherche sur la nature et les technologies(FQNRT), research in team program, 2009; International expert for the Ministry of Education, Youth and Sports of the Czech Republic under the priority axis 2 "Regional R &D centres" of Operational Programme Research and Development for Innovation, a major research programme cofunded from the EU Structural Funds, 2009; Member of the comité du suivi doctoralof INRIA Sophia Antipolis (since 01/2009); Member of comité de sélectionof 61 ^{e}section for UNS, 2009.
member of I3S laboratory committee.
elected member of I3S laboratory committee.
responsible of a new international master of science at University of Nice Sophia Antipolis (
http://
elected member of the CNRS National Committee, nominated member of I3S laboratory committee (  September), nominated member of CITI laboratory committee (October  ).
member of the comité de sélectionof 27 ^{e}section of the IUT, Univ. of Nice Sophia; director of the Licence LP SIL degree at IUT.
Combinatorics Probability and Computing, Computer Science Reviews, Discrete Mathematics, Discrete Applied Mathematics, Journal of Graph Theory, Journal Of Interconnection Networks (Advisory Board), Mathématiques et Sciences Humaines, Networks, Parallel Processing Letters and the Siambook series on Discrete Mathematics, Transactions on Network Optimization and Control (2009), Discrete Mathematics, Algorithms and Applications (2009).
Journal of Parallel and Distributed Computing (Academic Press), Parallel Processing Letters (World Scientific), Journal of Interconnection Networks (World Scientific), Wireless Networks (Springer).
ICST International Conference on Simulation Tools and Techniques (SIMUTools 2009), Rome, February 2009 .
Journal of Combinatorial Theory, Series B (Elsevier). Journal of Graph Theory.
Member of the Advisory Committee of ISPAN 2009 The 10th International Symposium on Pervasive Systems, Algorithms and Networks December 1416, 2009 Kaohsiung, Taiwan, R.O.C;
Pôle ResCom du GDR ASR du CNRS (since 2005); Rencontres francophones sur les aspects algorithmiques des télécommunications, AlgoTel;
ICST International Conference on Simulation Tools and Techniques (SIMUTools 2009), Rome, February 2009;
Journées Combinatoire et Algorithmes du Littoral Méditerranéen (JCALM);
3rd edition of the International workshop on Mobility, Algorithms, Graph Theory In dynamic Networks (IMAGINE 2009) that was held in conjonction with SIROCCO 2009  Piran, Slovenia  May 28th, 2009;
Member of the Pacific Institute for Mathematical Sciences Scientific Review Committee until June 30 2009.
one week, March 2009, Bellairs Research Institute, Barbados. B. Reed coorganizer
one week, May 2009, CRM in Montreal, Canada. B. Reed coorganizer
May 2009, CRM in Montreal, Canada. B. Reed coorganizer
Lozari, France, May 2529 2009 (70 participants).
F. Havet organizing chair
3rd International workshop on Mobility, Algorithms, Graph Theory In dynamic NEtworks. Piran, Slovenia, May 28th, 2009. I. SauValls cochair
one week, August 2009, BIRS in Banff, Alberta, Canada. B. Reed coorganizer
Sept. 2125, 2009, Puyloubier, France.
F. Havet organizing chair.
Invited session, Pisa, Italy, Sept 22, 2009.
O. Dalle organizing chair
Sophia Antipolis, France, October 1920 2009 (25 participants).
F. Havet organizing chair.
ACM Mobility 2009.
11th rencontres francophones sur les aspects algorithmiques des télécommunications(Algotel 2009), CarryleRouet, France, June 1619, 2009.
International Workshop on Network Simulation Tools (NSTOOLS 2009), Pisa, Italy, October 19, 2009; High Performance Computing &Simulation (HPCS 2009) Conference, Leipzig, Germany, June 2124 2009.
5th LatinAmerican Algorithms, Graphs and Optimization Symposium (LAGOS 2009), Gramado, Brazil, November 37, 2009.
11th Journées Graphes et Algorithmes(JGA 2009), Montpellier, France November 56, 2009.
ACM Mobility 2009.
Radio Mesh Networks and the Round Weighting Problem. Ph.D. thesis, Université de Nice Sophia Antipolis, 2009.
Structures combinatoires et simulation des réseaux radio maillés. Ph.D. thesis, Université de Nice Sophia Antipolis, 2009.
Optimisation d'algorithmes de traitement de signal sur les nouvelles architectures modernes de calculateur parallèle embarqué. Ph.D. thesis, Université de Nice Sophia Antipolis, 2009.
Optimisation et simulation pour l'étude des réseaux ambiants. Ph.D. thesis, Université de Nice Sophia Antipolis, 2009.
Optimization in graphs under degree constraints. Application to telecommunication networks. Ph.D. thesis, Université de Nice Sophia Antipolis, 2009.
Dynamic network routing, since December 2009.
Allocation de fréquences et coloration des Lgraphes, since October 2008.
Méthodes et outils pour la modélisation et la simulation centrées réseau à base de composants Fractal, since February 2008.
Conception et analyse d'algorithmes distribués d'ordonnancement dans les réseaux sansfil, since October 2008.
Modélisation et analyse de réseaux pairàpair utilisés pour le stockage fiable de données, since October 2007.
Optimisation et routage dynamique dans les réseaux sans fil, since December 2007.
Design and management of networks with low power consumption, since October 2009.
Modélisation et simulation à événements discrets à base de composants Fractal, since January 2008.
Algorithmic aspects of graph colourings, since November 2009.
Optimisation dans les réseaux de collecte IP sans fils, since November 2009.
Ph.D. committee member of P. Reyes (UNS, Nice, France, August 5 2009), I. SauValls (UNS, Nice, France, October 16, 2009), C. Molle (UNS, October 29, 2009), C. Gomes (UNS, Nice, France, December 1, 2009). HDR committee of R. Klasing: referee and member, Bordeaux, November 16, 2009)
Ph.D. referee of G. Monaco, (U. L'Aquilla, Italy, December 7 2009); Ph.D. committee of I. SauValls, (UNS, Nice, France, October 16, 2009.
Ph.D. committee member of P. Reyes (UNS, Nice, France, August 5, 2009), C. Molle (UNS, October 29, 2009), C. Gomes (UNS, Nice, France, December 1, 2009). HDR committee of R. Klasing: referee and member (Bordeaux, November 16, 2009)
Ph.D. committee member of P. Reyes (UNS, Nice, France, August 5, 2009) Ph.D. committee member of C. Molle (UNS, Nice, France, October 29, 2009)
reviewer and Ph.D. committee member of G. Quercini (Univ. di Genova / DISI, Italy May 8th, 2009).
supervised the internship of Julio Araujo (UFC Foraleza, Brazil) on good edgelabelling of graphs, March 2009 (1 month).
supervised the internship of Issam Tahiri (PFE INPT Rabat, Morocco) on the design of a simulation tool for dynamic routing schemes in the Internet, MarchSeptember 2009 (6 months).
supervised the internship of Christian Delettre (PFE EPU 3, UNS, France) on the dynamic management of virtual topologies in multilayer networks, MarchSeptember 2009 (6 months).
supervised the internship of Ronan Soares (UFC Foraleza, Brazil) on routing reconfiguration in WDM networks, MarchMay 2009 (3 months).
supervised the internship of Saber Ben Nejma (PFE Sup'Com Tunis, Tunisia) on Routing reconfiguration in WDM networks, SeptemberDecember 2009 (4 months).
supervised the internship of Paula Uribe on Extending the INET Framework for Directional and Asymmetric wireless Comunications, AprilOctober 2009 (7 months).
supervised the internship of Stéphane Caron (ENS Ulm) on the study of placement policies in P2P storage systems, JuneAugust 2009 (3 months).
supervised the internship of Sandeep Kumar Gupta (IIT Delhi) on the algorithmics of P2P storage systems, MayJuly 2009 (10 weeks).
supervised the internship of Nikhil Arora (IIT Delhi / India) on Implementation and evaluation of a peertopeer storage system over the AEOLUS (Algorithmic Principles for Building Efficient Overlay Computers / European project) testbed, MayJuly 2009 (3 months).
Mascottehas widely contributed to the launching and success of UBINET: a new international master of science at University of Nice Sophia Antipolis (
http://
At the graduate level, members of Mascotteare also involved in teaching in other Masters like the master MDFI of University of Marseille or in the 3rd year of engineering schools.
The members of Mascotteare heavily involved in teaching activities at undergraduate levels (Licence, IUT, Master 1, ENS program, Engineering Schools like Polytech'Nice). Some members are also involved in administrative duties related to teaching. For example, M. Syska is director of the Licence LP SIL degree at IUT. The teaching is carried out by members of the University as part of their teaching duties, and for INRIA CNRS or Ph.D.'s as extra work.
Altogether that represents more than 1000 hours per year.
The members of Mascottealso supervise several student projects and internships at all levels (Master 1 and 2, Engineering Schools).
at DIMACS/DyDAn Workshop on Approximation Algorithms in Wireless Ad Hoc and Sensor Networks, DIMACS, Rutgers University, NJ USA April 22  24, 2009. Journées Graphes et Optimisation en l'honneur de Charles Delorme, Orsay, June 26, 2009
Paris, France, January 1516, 2009.
Attended by JC. Bermond and D. Coudert.
Sophia Antipolis, France, January 16, 2009.
Attended by D. Coudert, L. Hogie, F. Giroire, J. Moulierac, N. Nisse and S. Pérennes.
CITI, Lyon (with AlcatelLucent BellLabs), February 11, 2009.
Attended by N. Nepomuceno and H. Rivano.
Mascotte Team meeting, March 1113 2009, Le Boréon, France.
Attended by almost all members of Mascotte.
Paris, France, March 2627, 2009.
Attended by D. Coudert and C. Molle (speaker).
Pretty Structure, Existential Polytime and Polyhedral Combinatorics, April 79, 2009, Paris, France.
Attended by N. Cohen.
6th Journées Combinatoire et Algorithmes du Littoral Méditerranéen. Programmation linéaire pour l'algorithmique et la combinatoire, May 7th, 2009, LIF, Marseille France.
Attended by N. Cohen, C. Gomes, F. Giroire, F. Havet, D. Mazauric, C. Molle, N. Nepomuceno, N. Nisse, H. Rivano and I. SauValls.
Rencontre DGARecherche et Innovation Scientifique, May 14, 2009, Paris, France.
Attended by C. Molle (poster).
BellLabs, Murray Hill, NJ, USA, June 13, 2009.
Attended by D. Coudert (speaker) and H. Rivano (speaker).
3rd Meeting of the ALADDIN Project, June 1112, 2009, La Rochelle, France.
Attended by P. Reyes (speaker).
Journées simulation de grands systèmes distribués/P2P, August 30September 1, 2009, INRIA Sophia Antipolis, France.
Attended by O. Dalle, F. Giroire, L. Hogie, J. Monteiro, J. Ribault.
(Operational Programme Research and Development for Innovation), Prague, Czech Republic, August 31  September 4, 2009.
Attended by D. Coudert.
Paris, France, September 18, 2009.
Attended by D. Coudert and N. Nisse.
Athens, Greece, September 2122, 2009.
Attended by JC. Bermond and D. Coudert.
September 2125, 2009, Puyloubier, France.
Attended by N. Cohen and F. Havet.
AlcatelLucent / INRIA Joint lab, Paris, France, October 12, 2009.
Attended by JC. Bermond, F. Giroire and D. Coudert.
3rd Workshop on Graph Searching, October 59, 2009, Valtice, Czech Republic.
Attended by N. Nisse and I. SauValls.
October 7, 2009.
Attended by H. Rivano.
7th Journées Combinatoire et Algorithmes du Littoral Méditerranéen, October 1920 2009, Sophia Antipolis, France.
Attended by N. Cohen (speaker), F. Giroire, F. Havet (speaker), D. Mazauric, J. Moulierac, N. Nepomuceno, N. Nisse (speaker), B. Onfroy, B. Reed (speaker) L. Sampaio and I. SauValls.
Paris Rocquencourt, France, October 2021, 2009.
Attended by D. Coudert (speaker), N. Nisse and H. Rivano.
11th Journées Graphes et Algorithmes2009, November 56, 2009, Montpellier, France.
Attended by D. Coudert, D. Mazauric (speaker), C. Molle (speaker), N. Nisse and L. Sampaio.
Avignon, France, November 9, 2009.
Attended by D. Coudert, N. Nepomuceno, N. Nisse and H. Rivano.
Bordeaux, France, November 2627, 2009.
Attended by N. Nisse (speaker).
Bordeaux, France, December 34, 2009.
Attended by D. Coudert, L. Hogie and N. Nisse.
10th journées doctorales en informatique et réseaux, Belfort, France, February 24, 2009.
Attended by D. Mazauric (speaker).
13th Conference on Optical Design and Modeling, Braunschweig, Germany, February 1820, 2009.
Attended by D. Coudert (speaker).
2nd International Conference on Simulation Tools and Techniques, Rome, Italy, March 26 2009.
Attended by O. Dalle, JC. Maureira (speaker), J. Monteiro (speaker), J. Ribault (speaker).
2th International Workshop on OMNeT++, March 6th, 2009, Rome, Italy.
Attended by JC. Maureira (speaker).
DIMAP Workshop on Algorithmic Graph Theory, March 2325, 2009, Warwick, UK.
Attended by D. Coudert, N. Nisse (speaker) and I. SauValls (speaker)
Paris, France, April 12, 2009.
Attended by J. Ribault (speaker).
69th IEEE Vehicular Technology Conference, Barcelona, Spain, April 2629, 2009.
Attended by C. Molle (speaker).
16th International Colloquium on Structural Information and Communication Complexity, Piran, Slovenia, May 2527, 2009.
Attended by I. SauValls (speaker).
8th Cologne Twente Workshop on Graphs and Combinatorial Optimization, Paris, France, June 24, 2009.
Attended by I. SauValls (speaker).
1st IEEE WoWMoM Workshop on Hot Topics in Mesh Networking, June 1519, 2009, Kos, Greece.
Attended by N. Nepomuceno (speaker).
11th rencontres francophones sur les aspects algorithmiques des télécommunications, CarryleRouet, France, June 1619, 2009.
Attended by D. Coudert, F. Giroire, D. Mazauric (speaker), J. Monteiro (speaker), J. Moulierac, N. Nisse, S. Pérennes, P. Reyes (speaker), H. Rivano (speaker), and I. Tahiri.
35th International Workshop on GraphTheoretic Concepts in Computer Science, Montpellier, France, June 2426, 2009.
Attended by I. SauValls (speaker).
20th International Workshop on Combinatorial Algorithms, Hradec nad Moravicí, Czech Republic, June 28July 2, 2009.
Attended F. Giroire (speaker).
European Conference on Combinatorics, Graph Theory and Applications, September 711, 2009, Bordeaux, France.
Attended by F. Havet (speaker).
9th IEEE International Conference on PeertoPeer Computing, Seattle, US, September 911, 2009.
Attended by F. Giroire and J. Monteiro (speaker).
8th International Conference on ADHOC Networks &Wireless, Murcia, Spain, September 2325, 2009.
Attended by C. Gomes (speaker) and P. Reyes (speaker).
12th International Symposium on Recent Advances in Intrusion Detection, Saint Malo, France, Septemper 2325, 2009.
Attended by F. Giroire.
Colloque francophone sur l'ingénierie des protocoles2009, October 1215, 2009, Strasbourg, France.
Attended by C. Molle.
Fourth workshop on Graph Classes, Optimization, and Width Parameters, October 1517, 2009, Bergen, Norway.
Attended by F. Havet (speaker).
34th IEEE Conference on Local Computer Networks, Zurich, Switzerland, October 2023, 2009.
Attended by J. Monteiro (speaker).
9th International Conference on ITS Telecomunication, October 2123, 2009, Lille, France.
Attended by JC. Maureira (speaker) and P. Uribe.
V LatinAmerican Algorithms, Graphs and Optimization Symposium, November 37, 2009, Gramado, Brasil.
Attended by F. Havet (speaker).
Winter Simulation Conference, Austin, Texas, USA, December 1316, 2009.
Attended by O. Dalle and J. Ribault (speaker).
Joint ARRIVAL/AEOLUS Workshop &School (EC FP6 IST/FET projects ARRIVAL and AEOLUS)LargeScale Optimization: Robustness, Online and Offline Issues, May 1315, 2009, Patras, Greece.
Attended by C. Gomes and N. Nepomuceno.
Spring School on Fixed Parameter and Exact Algorithms May 2529 2009, Lozari, Corsica (France).
Attended by JC. Bermond, N. Cohen and F. Havet.
école d'hiver 'Hot Topics in Distributed Computing', La Plagne, France, March 1520, 2009.
Attended by F. Giroire, J. Monteiro (speaker), S. Pérennes, J. Ribault.
Several members of
Mascottewere involved in the "Fête de la Science": in particular, a video describing the research activities of
Mascottehas been made (
http://
JC. Bermond has given lectures about Sudoku in classes of "seconde" (June 18, 2009).