Dominique Barth

Uniform emulations of Cartesian-product and Cayley graphs

In this paper, we consider graphs modeling interconnection networks of parallel systems and we deal with network simulations. More specifically, we focus on simulations involving Cartesian-product graphs and some subclasses of Cayley graphs. We study emulations based on graph homomorphisms and iso-retractions. In particular, we give necessary and sufficient conditions for the existence of an iso-retraction of a Cartesian product graph G□H onto graph G. Furthermore, we show that each uniform (in terms of the load of the vertices in the target graph) emulation of the hypercube Hn onto the hypercube Hn−1 is an iso-retraction. Finally, we deal with iso-retractions of transposition Cayley graphs.

Transit prices negotiation: combined repeated game and distributed algorithmic approach

We present both a game theoretic and a distributed algorithmic approach for the transit price negotiation problem in the interdomain routing framework. The analysis of the centralized transit price negotiation problem shows that the only one non cooperative equilibrium is when the lowest cost provider takes all the market. The perspective of the game being repeated makes cooperation possible while maintaining higher prices. We consider then the system under a realistic distributed framework and simulate its behaviour under a simple price adjustment strategy and analyse whether it matches the theoretical results.

Mobile users assignment control strategies for LTE networks

Actual mobile operators are facing capacity issues of their networks and the growth of their energy consumption. This paper presents two strategies to control the assignment of mobile users in heterogeneous LTE networks. The objective of controlling is to improve the offered QoS while reducing the energy consumption of serving base stations. The control proposed in these strategies is local; both strategies aim at selecting the femtocell or macrocell that will serve a mobile user making a handover request. Moreover, as the femtocells can be switched off and the macrocells have to remain always on, both strategies offload mobile users to/from the selected femtocell/macrocell, that is, the mobile user may be moved from a femtocell to a macrocell or the other way around. The move is legitimate if the power consumption is lower and the QoS offered to the mobile user is not sacrified. Using real network data, simulations are done to evaluate these strategies in terms of power consumption and energy intensity of the network, the percentage of served mobile users, allocated capacity, and deactivated femtocells.

Scattering and multi-scattering in trees and meshes, with local routing and without buffering

In interconnection networks, messages must go through a sequence of intermediate nodes before reaching their final destinations. In general, these intermediate nodes have the possibility to store a message during several rounds. This allows the node to wait for a link that gets the message closer to its destination to be free. This is the store-and-forward model. However, intermediate storage is often difficult to realize. In this paper, we consider a communication model in which intermediate nodes do not need store the in-transit messages. The messages must leave the router immediately. Under this model, we study communication operations that involve many messages, such as scattering and multi-scattering. This allows us to give optimal or near-optimal scattering and algorithms. In addition, we use shortest-paths local routing functions in the networks under consideration. This is a realistic hypothesis when dealing with parallel systems. These features are significant of what we do: provide general powerful and efficient algorithms that can be adapted in real machines.