Associate Professor Version française

Address :

Département informatique
20, Av. des buttes de Coësmes
F-35043 Rennes Cedex, France
Tel : +33 (0) 2 23 23 86 79
Fax : +33 (0) 2 23 23 84 53

Campus de Beaulieu,
F-35042 Rennes Cedex, France
Tel : +33 (0) 2 99 84 74 42
Fax : +33 (0) 2 99 84 71 71

email :          molnar@irisa.fr


in the Computer Science (INFO) Department of Insa

Research Interests  

 Examples of my Research Activities

Steiner Problem in Graphs and Related Works
From the topology point of view, the lower cost multicast diffusion in a network corresponds to a partial minimum spanning tree (named also minimal Steiner tree). The construction of such a tree being NP-complete, in our research, we give some scalable heuristic algorithms. In our proposition, the connections are simple minimum Steiner trees between the already existing sub-trees of the partial spanning tree. Our first proposition is the modification of the well known Kruskal's heuristic. The same idea can also be applied on the Takahashi-Matsuyama's heuristic. Our heuristics raise the following question: when we are improving an existing partial spanning tree by addition of a (more advantageous) partial subtree, which part of the original tree can be removed in order to eliminate the introduced cycles?  Generally, the structure which can be removed is a forest. We give a method of reduction for the arising problem as well as the algorithmic solution to identify the maximum removal forest .

Multicast Communication with QoS
In certain cases in packet switched communication networks when there is no available exact link state
information more sophisticated multicast routing algorithms are needed. We develop new algorithms for QoS routing. In our propositions, the multicast routing with bandwidth and cost requirement in the case of incomplete information is reduced to a deterministic Steiner tree problem. 

Often, the QoS requirement is based on several additive metrics. The corresponding QoS routing is a hard problem. We propose several algorithms to compute multicast routes under multiple constraints.

Multicast Communication in All Optical WDM Networks
The multicast communication becomes a particular and interesting problem in all optical WDM networks. Different physical constraints exist in these networks. The multicast routing (the partial spanning tree construction) should respect the physical constraints of the links and nodes.

Dependable networking needs redundancies of the applied routes. One of the most efficient methods to provide dependability is the protection of the routes which can be a global protection with the help of pre-configured cycles or a system of individual protections.

Generally, the here mentioned problems rise hard optimization questions.

Ph.D. Students

Alia Bellabas

Fen Zhou

Alexandre Poquet

Hamza Drid

Hanen Idoudi

Joanna Moulierac

Alexandre Guitton

Students in Research Master's Degree

Alexandre Poquet (Université de Rennes 1) : “Réseaux ad hoc et sécurité” (2006, co-encadrement avec Bernard Cousin)

Emilie Lambert (Université de Rennes 1) : “Contrôle de la QoS pour flux multimédia” (2005, co-encadrement avec Bernard Cousin)

Yazid Mohand Saidi (Université de Lille) : “Protection d’arbres multicast” (2005, co-encadrement avec Bernard Cousin)

Thomas Holey (University of Newcastle) : “Topology control in wireless ad hoc networks” (2005)

Aymen Belghith (ENSI, Tunisie) : “PSM in 801.11 infrastructure networks” (2005)

Andrew Wildrige (University of Newcastle): "Heuristics for the Steiner Problem" (1999)

Patrick Cathiard, Alain Jouanno (St Cyr, COETQUIDAN Rennes) : "Optimisation des systèmes de VP dans les réseaux ATM" (1998, co-encadrement avec R. Marie)

Alexander Alexandrov Alexandrov, Milen Dimitrov Stoianov (University of Sofia): "Traffic Management on ATM Networks" (1997)



Recent Publications

Mémoire to obtain French HDR scientific degree: