1,721,058 research outputs found
Joint Routing and Energy Optimization for Integrated Access and Backhaul with Open RAN
No full textEnergy consumption represents a major part of the operating expenses of mobile network operators. With the densification foreseen with 5G and beyond, energy optimization has become a problem of crucial importance. While energy optimization is widely studied in the literature, there are limited insights and algorithms for energy-saving techniques for Integrated Access and Backhaul (IAB), a self-backhauling architecture that ease deployment of dense cellular networks reducing the number of fiber drops. This paper proposes a novel optimization model for dynamic joint routing and energy optimization in IAB networks. We leverage the closed-loop control framework introduced by the Open Radio Access Network (O-RAN) architecture to minimize the number of active IAB nodes while maintaining a minimum capacity per User Equipment (UE). The proposed approach formulates the problem as a binary nonlinear program, which is transformed into an equivalent binary linear program and solved using the Gurobi solver. The approach is evaluated on a scenario built upon open data of two months of traffic collected by network operators in the city of Milan, Italy. Results show that the proposed optimization model reduces the RAN energy consumption by 47%, while guaranteeing a minimum capacity for each UE
Agrégations pour garantir la QoS des réseaux complexes
No full textNational audienceAujourd'hui, les réseaux sont de plus en plus complexes en termes de nombre de noeuds et de diversité de flux (débits, tailles des paquets, variabilité du trafic). La garantie de la QoS (Quality of Service) demeure un problème important et difficile à résoudre. Deux aspects importants ayant un impact sur la QoS sont présentés dans cet ouvrage : la gestion du trafic, et les méthodes d'évaluation des performances basées sur les bornes stochastiques afin de dimensionner le réseau. On étudie des mécanismes d'agrégation dans deux contextes différents : le trafic et les chaînes de Markov. Dans le cas de l'agrégation de trafic, la description du trafic agrégé est simplifiée : le profil est souvent lissé et les paquets peuvent avoir des tailles identiques. Pour ce qui est des chaînes de Markov, on définit une chaine agrégée de taille réduite, plus facile à analyser
Modelling Smart Buildings Using Fault Maintenance Trees
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197697.pdf (Publisher’s version ) (Open Access)Computer Performance Engineering: 15th European Workshop, EPEW 2018, Paris, France, October 29-30, 201
Stochastic comparisons: a methodology for the performance evaluation of fixed and mobile
No full textWe propose to use a mathematical method based on stochastic comparisons of Markov chains in order to derive performance indices bounds. The main objective is to find Markovian bounding models with reduced state spaces, which are easier to solve. We apply the methodology to performance evaluation of complex telecommunication systems modelled by large size Markov chains which cannot be solved by exact methods. This methodology can be applied for continuous- or discrete-time Markov chains. In the first study, we consider an MPLS switch represented by two stages of buffers. Various kinds of traffic with different QoS levels enter the first stage, and transit in the second stage. The goal is to compute packet loss rates in the second stage. In the other study, we define a CAC scheme in a mobile network which gives the priority to the handover over the new calls. Performance evaluation of the CAC scheme consists in the computation of the dropping handover and call blocking probabilities. For the two studies, systems are represented by large state Markov chains whose resolution is difficult. We propose to define intuitively bounding systems in order to compute performance measures bounds. Using stochastic comparisons methods, we prove that the new systems represent bounds for the exact ones. Different methods can be used. For the MPLS switch, we use the coupling equivalent to the sample-path ordering, allowing the comparison of the loss rates. In the case of the CAC scheme, we apply the increasing sets formalism used to define weaker orderings, enabling the comparison of the dropping handovers and blocking probabilities. We validate stochastic comparison method by presenting some numerical results illustrating the interest of the approach.ou
On the choice of the stochastic comparison method for multidimensional Markov chains analysis
No full textInternational audienceThe stochastic comparison of multidimensional Continuous Time Markov Chains (CTMC)s is an efficient but a complex method for the performability evaluation of computer systems. Different techniques can be applied for the stochastic comparison of Markov chains. The coupling is an intuitive method, and may be applied by comparing the evolution of sample paths due to events to establish the strong ordering. The increasing set method is based on the comparison of transition rates for a family of increasing sets. It is a more general formalism as it can be applied for all stochastic orderings (strong and weak). The goal of this paper is to identify the relationships between these orderings, in order to determine the method to apply for establishing comparisons between models. Although the strong ordering between random variables implies weak orderings, this result could not be generalized to the comparison of stochastic processes. However even the strong ordering does not exist between processes, the weak constraints could be satisfied. In this paper, we aim to give the intuition to choose the most suitable method with respect to the underlying performability stud
Strong and weak stochastic bounds for multidimensional Markov chains
No full textInternational audienceWe study queueing networks similar to Jackson networks, modelled by a multidimensional Markov chain. The performance analysis may be very difficult or intractable, if there is no specific solution form. We explain how stochastic comparisons of Markov chains can be used to overcome this problem. We build new queueing which are easier to analyse and providing stochastic bounds (upper or lower) for the original model. In this paper, we propose different queueing systems in the sense of the strong and weak stochastic ordering for a general queueing network model in order to compute performance measure bounds as blocking probabilities. We discuss the accuracy of the bounds under different input parameter value
Stochastic Ordering based Markov process aggregations: applications to tandem queues
No full textWe present a general algorithm based on the stochastic ordering theory to provide a bounding aggregation for
a given Markov process. Our main goal is to provide bounds
on the performance measures of interest by considering the
aggregated process without computing the exact values which
are in general numerically difficult or intractable due to the
well-known state space explosion. The stochastic comparison has
been largely applied in performance evaluation however the state
space is generally assumed to be totally ordered which provides
less accurate bounds for multidimensional Markov processes. The
algorithm is proposed by assuming a preorder on the state space,
and it is applied in this paper to an open tandem queues system,
in order to compute loss probabilities bounds.ou
An algorithm approach to bounding aggregations of multidimensional Markov chains
No full textAbstractWe analyze transient and stationary behaviors of multidimensional Markov chains defined on large state spaces. In this paper, we apply stochastic comparisons on partially ordered state which could be very interesting for performance evaluation of computer networks. We propose an algorithm for bounding aggregations in order to derive upper and lower performance measure bounds on a reduced state space. We study different queueing networks with rejection in order to compute blocking probability and end to end mean delay bounds. Parametric aggregation schemes are studied in order to propose an attractive solution: given a performance measure threshold, we vary the parameter values to obtain a trade-off between the accuracy of bounds and the computation complexity
Comparaisons de méthodes de calcul de seuils pour minimiser la consommation énergétique d’un cloud
No full textNational audienceContexte: La généralisation des offres de Cloud a remis en lumière le problème crucial de la consommation électrique des centres de données qui sont généralement sur-dimensionnés pour assurer la qualité de service des applications hébergées. Cela implique une sous utilisation des serveurs qui entraîne des pertes électriques très importantes car la consommation électrique d’un serveur allumé mais qui ne traite pas de tâches peut aller jusqu’à environ la moitié de sa consommation maximale. Pour améliorer le taux d’utilisation des serveurs, les centres de données ont déployé des systèmes permettant l’adaptation dynamique des ressources en fonction de la charge. Ces mécanismes appelés “autoscaling” [2] sont basés sur l’activation et la désactivation des ma-chines [3]. L’objectif consiste à gérer les activations et désactivations des serveurs de façon à garantir à la fois Qualité de Service (QoS) et consommation énergétique. Parmi l’ensemble des politiques dynamiques possibles les politiques à hysteresis [7, 8] font partie des plus répandues(c’est notamment une des politiques de la plateforme de gestion des ressources [2]). Ce sont des politiques dans lesquelles des seuils différents et dépendant de la charge du système indiquent la nécessité d’activer ou de désactiver des machines virtuelles. L’optimalité de telles politiques est discutée dans [6] mais l’objectif ici est de travailler sur le calcul effectif des seuils. Notre but est de calculer efficacement les seuils optimaux d’activation et désactivation en fonction des coûts, en considérant à la fois des aspects d’évaluation de performances ainsi que des aspects énergétiques
Model checking of performance measures using bounding aggregations
No full textInternational audienceThis paper presents an algorithm based on stochastic comparisons in order to check formulas with rewards on multidimensional continuous time Markov chains (CTMC). These formulas are expressed in continuous stochastic logic (CSL) which includes means to express transient, steady-state and path performance measures. However, using simulations or analytical methods, computation of transient and steady state distribution are limited to relatively small sizes because of the state space explosion problem. We propose a model checking algorithm based on aggregated bounding Markov processes in order to perform the verification on the bounds values instead of the exact one. The stochastic comparison has been largely applied in performance evaluation however the state space is generally assumed to be totally ordered which induces less accurate bounds for multidimensional Markov processes. We use the increasing set theory and the comparison by mapping functions in order to derive performance measures bounds on reduced state spaces. The relevance of the proposed checking algorithm is the possibility of a parametric aggregation scheme in order to improve the accuracy of the bounds and in the same time the precision of the checking, but in return with an increasing of the complexity. We apply the algorithm to the performance evaluation of a tandem queueing network in order to verify if loss probabilities are included or not in an interva
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