Sandrine Vial

Indexing in-network trajectory flows

Indexing moving objects (MO) is a hot topic in the field of moving objects databases since many years. An impressive number of access methods have been proposed to optimize the processing of MO-related queries. Several methods have focused on spatio-temporal range queries, which represent the foundation of MO trajectory queries. Surprisingly, only a few of them consider that the objects movements are constrained. This is an important aspect for several reasons ranging from better capturing the relationship between the trajectory and the network space to more accurate trajectory representation with lower storage requirements. In this paper, we propose T-PARINET, an access method to efficiently retrieve the trajectories of objects moving in networks. T-PARINET is designed for continuous indexing of trajectory data flows. The cornerstone of T-PARINET is PARINET, an efficient index for historical trajectory data. The structure of PARINET is based on a combination of graph partitioning and a set of composite B+-tree local indexes. Because the network can be modeled using graphs, the partitioning of the trajectory data makes use of graph partitioning theory and can be tuned for a given query load and a given data distribution in the network space. The tuning process is built on a good quality cost model that is supplied with PARINET. The advantage of having a cost model is twofold; it allows a better integration of the index into the query optimizer of any DBMS, and it permits tuning the index structure for better performance. The tuning process can be performed before the index creation in the case of historical data or online in the case of indexing data flows. In fact, massive online updates can degrade the index quality, which can be measured by the cost model. We propose a specific maintenance process that results into T-PARINET. We study different types of queries and provide an optimized configuration for several scenarios. T-PARINET can easily be integrated into any RDBMS, which is an essential asset particularly for industrial or commercial applications. The experimental evaluation under an off-the-shelf DBMS shows that our method is robust. It also significantly outperforms the reference R-tree-based access methods for in-network trajectory databases.

Distributed Chasing of Network Intruders by Mobile Agents

This paper addresses the graph searching problem in a distributed setting. We describe a distributed protocol that enables searchers with logarithmic size memory to clear any network, in a fully decentralized manner. The search strategy for the network in which the searchers are launched is computed online by the searchers themselves without knowing the topology of the network in advance. It performs in an asynchronous environment, i.e., it implements the necessary synchronization mechanism in a decentralized manner. In every network, our protocol performs a connected strategy using at most k + 1 searchers, where k is the minimum number of searchers required to clear the network in a monotone connected way, computed in the centralized and synchronous setting

Research article: Automated prediction of three-way junction topological families in RNA secondary structures

We present an algorithm for automatically predicting the topological family of any RNA three-way junction, given only the information from the secondary structure: the sequence and the Watson-Crick pairings. The parameters of the algorithm have been determined on a data set of 33 three-way junctions whose 3D conformation is known. We applied the algorithm on 53 other junctions and compared the predictions to the real shape of those junctions. We show that the correct answer is selected out of nine possible configurations 64% of the time. Additionally, these results are noticeably improved if homology information is used. The resulting software, Cartaj, is available online and downloadable (with source) at: http://cartaj.lri.fr.

An Algorithmic Game-Theory Approach for Coarse-Grain Prediction of RNA 3D Structure

We present a new approach for the prediction of the coarse-grain 3D structure of RNA molecules. We model a molecule as being made of helices and junctions. Those junctions are classified into topological families that determine their preferred 3D shapes. All the parts of the molecule are then allowed to establish long-distance contacts that induce a 3D folding of the molecule. An algorithm relying on game theory is proposed to discover such long-distance contacts that allow the molecule to reach a Nash equilibrium. As reported by our experiments, this approach allows one to predict the global shape of large molecules of several hundreds of nucleotides that are out of reach of the state-of-the-art methods.

Distributed cost management in a selfish multi-operators BGP network

In this paper we deal with inter-domain routing management from an economical point of view. We present a game theory based costing model that maps BGP peers (autonomous systems belonging to different operators) into a strategic (selfish) agents competing for transit traffic as a service provided and charged to their peers. Indeed, in our model each operator fixes a price to each neighbor for each transit traffic unit. Then, BGP routing choice is made based on a minimum cost criterion where the goal of each operator is to minimize its costs. We investigate some particular strategies of updating prices that operators can use locally in order to minimize their costs. We focus on BGP stabilization properties related to such strategies from a simulation point of view.

A Mixed Deflection and Convergence Routing Algorithm: Design and Performance

All-optical packets networks represent a challenging and attractive technology to provide a large bandwidth for future networks. The motivations for an all-optical network and a description of the ROM project may be found in [5]. With current optical technology, optical switches do not have large buffers or even buffers at all. Delay loops allow some computation time for the routing algorithms but they are not designed to store a large amount of packets. Therefore routing algorithms are quite different from the algorithms designed for store and forward networks based on electronic buffering. In this paper, we study packet routing strategies without intermediate storage of data packets (hereafter simply called packets) [8], such as deflection routing [3,10] and Eulerian routing [2,6,1]. These routing strategies do not allow packet loss. Thus the performance guarantee in terms of packets loss is just the physical loss rate which is very low for optical fibers. However these strategies keep the packets inside the network and reduce the bandwidth. The usable bandwidth (i.e., the goodput) of the network and the routing protocol is therefore a major measure of interest. In this paper, we focus on two performance criteria: the goodput of the network, and the ending guarantee. First let us define them more precisely.

Virtual circuit allocation with QoS guarantees in the ECOFRAME optical ring

We present the ECOFRAME metro ring network and how we can provide virtual circuit emulation with QoS guarantee at a subwavelegth level. The architecture is based on a centralized HUB and reservations. The scheduler in the HUB reserves a set of rectangles, called a pattern to describe the slots allocated to a node. We study the tradeoff between the complexity of the reservation at the HUB level and the performance of the network: distribution of the end to end delay and utilization of the ring.

PARINET: A tunable access method for in-network trajectories

In this paper we propose PARINET, a new access method to efficiently retrieve the trajectories of objects moving in networks. The structure of PARINET is based on a combination of graph partitioning and a set of composite B+-tree local indexes. PARINET is designed for historical data and relies on the distribution of the data over the network as for historical data, the data distribution is known in advance. Because the network can be modeled using graphs, the partitioning of the trajectory data is based on graph partitioning theory and can be tuned for a given query load. The data in each partition is indexed on the time component using B+-trees. We study different types of queries, and provide an optimal configuration for several scenarios. PARINET can easily be integrated into any RDBMS, which is an essential asset particularly for industrial or commercial applications. The experimental evaluation under an off-the-shelf DBMS shows that PARINET is robust. It also significantly outperforms both MON-tree and another R-tree based access method which are the reference indexing techniques for in-network trajectory databases.

Virtualization and allocation of network service resources using graph embedding

Recent developments in optical communications have led to the creation of large scale optical networks allowing users to run distributed applications with high QoS requirements. The virtualization and the efficient allocation of network resources and application services is one key element of these new applications management. In this paper, we study this problem from a graph embedding point of view. After defining and motivating the main problems we focus on, we give results on NP-completeness and inapproximability of these problems. Then, we propose an online heuristic approach to solve them and we evaluate its performances by simulation.

Efficient Generation of Stable Planar Cages for Chemistry

In this paper we describe an algorithm which generates all colored planar maps with a good minimum sparsity from simple motifs and rules to connect them. An implementation of this algorithm is available and is used by chemists who want to quickly generate all sound molecules they can obtain by mixing some basic components.