Saïd Yahiaoui

Coloring based approach for matching unrooted and/or unordered trees

We consider the problem of matching unrooted unordered labeled trees, which refers to the task of evaluating the distance between trees. One of the most famous formalizations of this problem is the computation of the edit distance defined as the minimum-cost sequence of edit operations that transform one tree into another. Unfortunately, this problem has been proved to be NP-complete. In this paper, we propose a new algorithm to measure distance between unrooted unordered labeled trees. This algorithm uses a specific graph coloring to decompose the trees into small components (stars and bistars). Then, it determines a distance between two trees by computing the edit distance between their components. We prove that the proposed distance is a pseudo-metric and we analyze its time complexity. Our experimental evaluations on large synthetic and real world datasets confirm our analytical results and suggest that the distance we propose is accurate and its algorithm is scalable.

Efficient self-stabilizing algorithms for minimal total k-dominating sets in graphs

We propose the first polynomial self-stabilizing distributed algorithm for the minimal total dominating set problem in an arbitrary graph. Then, we generalize the proposed algorithm for the minimal total k-dominating set problem. Under an unfair distributed scheduler, the proposed algorithms converge in O(mn) moves starting from any arbitrary state, and require O(logn) storage per node.

Self-stabilizing algorithms for minimal global powerful alliance sets in graphs

We propose a self-stabilizing distributed algorithm for the minimal global powerful alliance set problem in an arbitrary graph. Then, we give self-stabilizing algorithms for some generalizations of the problem. Using an unfair distributed scheduler, the proposed algorithms converge in O(mn) moves starting from an arbitrary state.

AdSIP: Decentralized SIP for Mobile Ad Hoc Networks

SIP signaling protocol relies on centralized SIP servers deployed on the infrastructure of the network to route SIP messages in order to enable user endpoints to discover each other. However, the lack of the infrastructure in ad hoc networks requires that the network nodes support the tasks of participants discovery and SIP messages routing. In this paper, we propose AdSIP protocol which is a completely distributed architecture for SIP that implements SIP servers in selected nodes. The SIP servers are selected using a distributed algorithm constructing a connected minimal global offensive alliance. AdSIP is implemented and compared under NS-2 with TCA protocol which uses a cluster based approach. The simulation results show the advantages of AdSIP and confirm that it is adapted to mobile ad hoc networks by giving low session establishment time, low control overhead and high service availability.

LifeTime-aware Backpressure - a new delay-enhanced Backpressure-based routing protocol

Dynamic backpressure is a highly desirable family of routing protocols known for their attractive mathematical properties. However, these protocols suffer from a high end-to-end delay making them inefficient for real-time traffic with strict end-to-end delay requirements. In this paper, we address this issue by proposing a new adjustable and fully distributed backpressure-based scheme with low queue management complexity, named Lifetime-Aware Backpressure (LTA-BP). The novelty in the proposed scheme consists in introducing the urgency level as a new metric for service differentiation among the competing traffic flows in the network. Our scheme not just significantly improves the quality of service provided for real-time traffic with stringent end-to-end delay constraints, but interestingly protects also the flows with softer delay requirements from being totally starved. The proposed scheme has been evaluated and compared against other state-of-the-art routing protocol, using computer simulation, and the obtained results show its superiority in terms of the achieved end-to-end delay and throughput.

Towards a dynamic evacuation system for disaster situations

Medical evacuation is one of the most important modules in the emergency plans activated during disaster situations. It aims at evacuating victims to the most appropriate health-care facilities. Evacuation plans were for a long time performed approximatively and passively rather than optimally and proactively between the disposal site and the targeted hospital and they often lacked visibility on the evolution of the events that may change data and leading to a revision of the plans. However, thanks to the proliferation of information and communication technologies (ICTs) in all aspects of life, the evacuation operations in disaster situations had known a great enhancement. In fact, critical operations such as real-time monitoring of the state of resources used during the evacuation process, detecting the occurring changes and reflecting them on the global process to provide dynamic and optimal evacuation plans become possible. In this paper, we propose a framework for dynamic evacuation operations in disaster situations. We design a system that takes into consideration the above challenges such as detecting changes and using them in an intelligent way to enable dynamic, optimal and up-to-date evacuation plans. The provided prototype is called DEvacuS (Dynamic Evacuation System).

TopCoF: A Topology Control Framework for Wireless Ad Hoc Networks

Topology Control (TC) is a well known technique used in wireless ad hoc and sensor networks to reduce energy consumption. This technique coordinates the decisions of network nodes about their transmission power to save energy, prolong network lifetime, and mitigate MAC-level medium contention, while maintaining network connectivity. In order to ease the implementation and the study in systematic way of proposed TC protocols, in terms of energy usage and network graph properties, we propose a new framework based on NS-2 simulator. The framework is named TopCoF and composed of two main parts. The first one consists of a set of NS-2 extensions to support TC, while the second is a graphical user interface for statistical analysis and visualization of simulation results traced by the first part. TopCoF is modular and generic since it implements a set of basic components used by TC protocols.