International Journal Papers
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- ItemLifetime-Aware Backpressure : A New Delay-Enhanced Backpressure-Based Routing Protocol(IEEE, 2019-03) Kabou, Abdelbaset; Nouali-Taboudjemat, Nadia; Djahel, Soufiene; Yahiaoui, Saïd; Nouali, OmarDynamic 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.
- ItemFast parallel algorithms for finding elementary circuits of a directed graph: a GPU-based approach(Springer Science+Business Media, 2023-03) Benachour, Amira; Yahiaoui, Saïd; El Baz, Didier; Nouali‑Taboudjemat, Nadia; Kheddouci, HamamacheCircuits in a graph are interesting structures and identifying them is of an important relevance for many applications. However, enumerating circuits is known to be a difficult problem, since their number can grow exponentially. In this paper, we propose fast parallel approaches for enumerating elementary circuits of directed graphs based on graphics processing unit (GPU). Our algorithms are based on a massive exploration of the graph in a breadth-first search strategy. Algorithm V-FEC explores the graph starting from different vertices simultaneously. To further reduce the search space, we present T-FEC, another algorithm that uses triplets as an initial set to start exploring. To the best of our knowledge, those are the first parallel GPU-based algorithms for finding all circuits of a given graph. In addition, they find circuits of a given length and circuits with a specific vertex or edge. The evaluation results show that the proposed approaches achieve up to 190x speed-up over Johnson’s algorithm, one of the most efficient sequential algorithms for finding circuits.
- ItemColoring based approach for matching unrooted and/or unordered trees(Elsevier, 2013-04) Yahiaoui, Saïd; Haddad, Mohammed; Effantin, Brice; Kheddouci, HamamacheWe 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.
- ItemReachability in big graphs : A distributed indexing and querying approach(Elsevier, 2021-09) Hocine, Imane; Yahiaoui, Saïd; Bendjoudi, Ahcene; Nouali-Taboudjemat, NadiaThe advent of Big graphs characterized by their enormous number of nodes, with multiple edges between them makes the existing reachability query indexing approaches unable to guarantee a reasonable time for both the index construction and query steps. Therefore a novel approach that takes into account these new characteristics during the graph processing is needed. In this paper, we propose an Overlay Graph-based Distributed Reachability Indexing approach (ODRI), an indexing scheme through which the index construction and reachability query are processed in a parallel and distributed manner. The key idea of ODRI is to process a Big graph as a set of smaller subgraphs (partitions) interconnected to each other through an overlay graph. In this way, the partitions can be indexed in parallel and, at the same time, the reachability information can also be extracted. Hence, the index construction and query processing time will be reduced significantly. Therefore, ODRI ensures the scalability of Big graphs, which is a challenge for the existing reachability approaches. Besides, we formally prove that this strategy preserves the reachability properties. Using real-life data, we experimentally verify that our approach outperforms the state-of-the-art methods, and is scalable in terms of the number of partitions, regardless of how graphs are distributed.
- ItemEfficient parallel branch-and-bound approaches for exact graph edit distance problem(Elsevier, 2022-12) Dabah, Adel; Chegrane, Ibrahim; Yahiaoui, Saïd; Bendjoudi, AhceneGraph Edit Distance (GED) is a well-known measure used in the graph matching to measure the similarity/dissimilarity between two graphs by computing the minimum cost of edit operations needed to transform one graph into another. This process, Which appears to be simple, is known NP-hard and time consuming since the search space is increasing exponentially. One way to optimally solve this problem is by using Branch and Bound (B&B) algorithms, Which reduce the computation time required to explore the whole search space by performing an implicit enumeration of the search space instead of an exhaustive one based on a pruning technique. nevertheless, They remain inefficient when dealing with large problem instances due to the impractical running time needed to explore the whole search space. To overcome this issue, We propose in this paper three parallel B&B approaches based on shared memory to exploit the multi-core CPU processors: First, a work-stealing approach where several instances of the B&B algorithm explore a single search tree concurrently achieving speedups up to 24 faster than the sequential version. Second, a tree-based approach where multiple parts of the search tree are explored simultaneously by independent B&B instances achieving speedups up to 28. Finally, Due to the irregular nature of the GED problem, two load-balancing strategies are proposed to ensure a fair workload between parallel processes achieving impressive speedups up to 300. all experiments have been carried out on well-known datasets