Conference papers

titre

No-Regret Caching with Noisy Request Estimates

auteur

Younes Ben Mazziane, Francescomaria Faticanti, Giovanni Neglia, Sara Alouf

article

IEEE VCC 2023 - IEEE Virtual Conference on Communications, Nov 2023, New York (ONLINE), United States

resume

Online learning algorithms have been successfully used to design caching policies with regret guarantees. Existing algorithms assume that the cache knows the exact request sequence, but this may not be feasible in high load and/or memory-constrained scenarios, where the cache may have access only to sampled requests or to approximate requests' counters. In this paper, we propose the Noisy-Follow-the-Perturbed-Leader (NFPL) algorithm, a variant of the classic Follow-the-Perturbed-Leader (FPL) when request estimates are noisy, and we show that the proposed solution has sublinear regret under specific conditions on the requests estimator. The experimental evaluation compares the proposed solution against classic caching policies and validates the proposed approach under both synthetic and real request traces.

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titre

Computing the Hit Rate of Similarity Caching

auteur

Younes Ben Mazziane, Sara Alouf, Giovanni Neglia, Daniel Sadoc Menasche

article

IEEE Global Communications Conference (GLOBECOM), Dec 2022, Rio de Janeiro, Brazil. pp.141-146, ⟨10.1109/GLOBECOM48099.2022.10000890⟩

resume

Similarity caching allows requests for an item i to be served by a similar item i ′. Applications include recommendation systems, multimedia retrieval, and machine learning. Recently, many similarity caching policies have been proposed, but still we do not know how to compute the hit rate even for simple policies, like SIM-LRU and RND-LRU that are straightforward modifications of classic caching algorithms. This paper proposes the first algorithm to compute the hit rate of similarity caching policies under the independent reference model for the request process. In particular, we show how to extend the popular timeto-live approximation in classic caching to similarity caching. The algorithm is evaluated on both synthetic and real world traces.

DOI

DOI : 10.1109/GLOBECOM48099.2022.10000890

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titre

A Formal Analysis of the Count-Min Sketch with Conservative Updates

auteur

Younes Ben Mazziane, Sara Alouf, Giovanni Neglia

article

IEEE INFOCOM WNA 2022 - The second Workshop on Networking Algorithms (WNA), May 2022, New York, United States. ⟨10.1109/INFOCOMWKSHPS54753.2022.9798146⟩

resume

Count-Min Sketch with Conservative Updates (CMS-CU) is a popular algorithm to approximately count items' appearances in a data stream. Despite CMS-CU's widespread adoption, the theoretical analysis of its performance is still wanting because of its inherent difficulty. In this paper, we propose a novel approach to study CMS-CU and derive new upper bounds on the expected value and the CCDF of the estimation error under an i.i.d. request process. Our formulas can be successfully employed to derive improved estimates for the precision of heavy-hitter detection methods and improved configuration rules for CMS-CU. The bounds are evaluated both on synthetic and real traces.

DOI

DOI : 10.1109/INFOCOMWKSHPS54753.2022.9798146

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titre

Optimisation du préchargement dans un monde dynamique

auteur

Kausthub Keshava, Alain Jean-Marie, Sara Alouf

article

ROADEF 2022 - 23ème congrès annuel de la Société Française de Recherche Opérationnelle et d'Aide à la Décision, INSA Lyon, Feb 2022, Villeurbanne - Lyon, France

resume

Optimisation du préchargement dans un monde dynamique

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titre

Stochastic Models for Solar Power

auteur

Dimitra Politaki, Sara Alouf

article

EPEW 2017 - European Performance Engineering Workshop, Sep 2017, Berlin, Germany. pp.282--297, ⟨10.1007/978-3-319-66583-2_18⟩

resume

In this work we develop a stochastic model for the solar power at the surface of the earth. We combine a deterministic model of the clear sky irradiance with a stochastic model for the so-called clear sky index to obtain a stochastic model for the actual irradiance hitting the surface of the earth. Our clear sky index model is a 4-state semi-Markov process where state durations and clear sky index values in each state have phase-type distributions. We use per-minute solar irradiance data to tune the model, hence we are able to capture small time scales fluctuations. We compare our model with the on-off power source model developed by Miozzo et al. (2014) for the power generated by photovoltaic panels, and to a modified version that we propose. In our on-off model the output current is frequently resampled instead of being a constant during the duration of the " on " state. Computing the autocorrelation functions for all proposed models, we find that the irradiance model surpasses the on-off models and it is able to capture the multiscale correlations that are inherently present in the solar irradiance. The power spectrum density of generated trajectories matches closely that of measurements. We believe our irradiance model can be used not only in the mathematical analysis of energy harvesting systems but also in their simulation.

DOI

DOI : 10.1007/978-3-319-66583-2_18

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titre

Performance Evaluation of Train Moving-Block Control

auteur

Giovanni Neglia, Sara Alouf, Abdulhalim Dandoush, Sebastien Simoens, Pierre Dersin, Alina Tuholukova, Jérôme Billion, Pascal Derouet

article

13th International Conference on Quantitative Evaluation of SysTems (QEST) , Aug 2016, Quebec City, Quebec, Canada. pp.348-363, ⟨10.1007/978-3-319-43425-4_23⟩

resume

In moving block systems for railway transportation a central controller periodically communicates to the train how far it can safely advance. On-board automatic protection mechanisms stop the train if no message is received during a given time window. In this paper we consider as reference a typical implementation of moving-block control for metro and quantify the rate of spurious Emergency Brakes (EBs), i.e. of train stops due to communication losses and not to an actual risk of collision. Such unexpected EBs can happen at any point on the track and are a major service disturbance. Our general formula for the EB rate requires a probabilistic characterization of losses and delays. Calculations are surprisingly simple in the case of homogeneous and independent packet losses. Our approach is computationally efficient even when emergency brakes are very rare (as they should be) and can no longer be estimated via discrete-event simulations.

DOI

DOI : 10.1007/978-3-319-43425-4_23

Accès au texte intégral et bibtex

titre

ns-3 Based Framework for Simulating Communication Based Train Control (CBTC) Systems

auteur

Abdulhalim Dandoush, Alina Tuholukova, Sara Alouf, Giovanni Neglia, Sebastien Simoens, Pascal Derouet, Pierre Dersin

article

Workshop on ns-3 (WNS3 '16), Jun 2016, Seattle, WA, United States. pp.116-123, ⟨10.1145/2915371.2915378⟩

resume

In a Communication Based Train Control System (CBTC), a central zone controller server (ZC) exchanges signaling messages with on-board carborne controllers (CC) inside the trains through a wireless technology. The ZC calculates and sends periodically to each train its Limit of Movement Authority (LMA), i.e. how far the train can proceed. A CC triggers an emergency break (EB) if no message is received within a certain time interval to avoid collision. Clearly, it is not desired to have an EB due to signaling messages losses (called spurious EB) and not to real risks for the trains. Quantifying the rate of spurious EBs and predicting correctly CBTC system performance are hard tasks with important industrial relevance. This work aims at filling this gap using simulation to better predict CBTC system performance and avoid extra provisioning before deployment. A typical CBTC system implementation for metro by Alstom Transport is considered. New ns-3 modules (CBTC protocol, Video traffic generator, multi-channel scanning mechanism, 3D antennas patterns) are developed and a piece of existing code is enhanced. The simulation is also used to investigate the dimension of the radio access networks in a realistic environment (specific modems and access point antennas, radio frequencies, train and track models), another aspect also ignored in the previous literature. Last, our approach can be useful to validate some analytical works.

DOI

DOI : 10.1145/2915371.2915378

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titre

A Markovian Queueing System for Modeling a Smart Green Base Station

auteur

Ioannis Dimitriou, Sara Alouf, Alain Jean-Marie

article

EPEW: European Performance Evaluation Workshop, Aug 2015, Madrid, Spain. pp.3-18, ⟨10.1007/978-3-319-23267-6_1⟩

resume

We investigate a model to assess the performance of a base station (BS) fully powered by renewable energy sources. The BS is modeled as a three-queue system where two of them are coupled. One represents accumulated energy, the second is the data queue and the third one serves as a reserve energy queue. This smart BS is able to dynamically adjust its coverage area (thereby controlling the traffic intensity) and to generate signals to the reserve energy queue that trigger the movement of energy units to the main energy buffer. Given the randomness of renewable energy supply and the internal traffic intensity control, our queueing model is operated in a finite state random environment. Using the matrix analytic formalism we construct a five-dimensional Markovian model to study the performance of the BS. The stationary distribution of the system state is obtained and key performance metrics are calculated. A small numerical example illustrates the model and a simplified product-form approximation is proposed.

DOI

DOI : 10.1007/978-3-319-23267-6_1

Accès au texte intégral et bibtex

titre

Modeling modern DNS caches

auteur

Nicaise Choungmo Fofack, Sara Alouf

article

VALUETOOLS - 7th International Conference on Performance Evaluation Methodologies and Tools, Dec 2013, Turin, Italy. pp.184-193, ⟨10.4108/icst.valuetools.2013.254416⟩

resume

Caching is undoubtedly one of the most popular solution that easily scales up with a world-wide deployment of resources. Records in Domain Name System (DNS) caches are kept for a pre-set duration (time-to-live or TTL) to avoid becoming outdated. Modern caches are those that set locally the TTL regardless of what authoritative servers say. In this paper, we introduce analytic models to study the modern DNS cache behavior based on renewal arguments. For tree cache networks, we derive the cache performance metrics, characterize at each cache the miss process and the aggregate request process. We address the problem of the optimal caching duration and find that constant TTL is the best only if if inter-request times have a concave CDF. We validate our theoretical findings using real DNS traces (single cache case) and via event-driven simulations (network case). Our models are very robust as the relative error between empirical and analytic values stays within 1% in the former case and less than 5% in the latter case.

DOI

DOI : 10.4108/icst.valuetools.2013.254416

Accès au texte intégral et bibtex

titre

On the Minimization of Power Consumption in Base Stations using on/off Power Amplifiers

auteur

Angelos Chatzipapas, Sara Alouf, Vincenzo Mancuso

article

2011 IEEE Online Conference on Green Communications, Sep 2011, Online, France. pp.18-23, ⟨10.1109/GreenCom.2011.6082501⟩

resume

Using energy generated with fossil fuel causes global warming due to the greenhouse effect, which threatens our environment. One of the challenges for New Generation Networks (NGN) is then the reduction of energy consumption, in particular at the BSs (Base Stations) which use about 85% of the total network energy. We contribute to the research with a mathematical model that calculates the total power consumption of a BS and enlightens the way to minimize it. First, we analyze the power consumed at every different component of the BS. Second, based on the cost incurred in turning off the BS's power amplifiers, we show how to decide whether it is convenient to keep the BS idle during those intervals in which no traffic has to be sent, or to turn off the amplifiers. Our model is evaluated by means of numerical examples, and shows that interesting power gain can be obtained under a large spectrum of load conditions.

DOI

DOI : 10.1109/GreenCom.2011.6082501

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titre

Power save analysis of cellular networks with continuous connectivity

auteur

Vincenzo Mancuso, Sara Alouf

article

2011 IEEE International Symposium on a World of Wireless, Mobile and Multimedia Networks (WoWMoM), Jun 2011, Lucca, Italy. ⟨10.1109/WoWMoM.2011.5986202⟩

resume

In this paper, we analyze the power save and its impact on web traffic performance when customers adopt the continuous connectivity paradigm. To this aim, we provide a model for packet transmission and cost. We model each mobile user's traffic with a realistic web traffic profile, and study the aggregate behavior of the users attached to a base station by means of a processor-shared queueing system. In particular, we evaluate user access delay, download time and expected economy of energy in the cell. The model is validated through packet-level simulations. Our model shows that dramatic energy save can be achieved by both mobile users and base stations, e.g., as much as 70% of the energy cost due to packet transmission at the base station.

DOI

DOI : 10.1109/WoWMoM.2011.5986202

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titre

Passive Online RTT Estimation for Flow-Aware Routers Using One-Way Traffic

auteur

Damiano Carra, Konstantin Avrachenkov, Sara Alouf, Alberto Blanc, Philippe Nain, Georg Post

article

NETWORKING 2010, May 2010, Chennai, India. pp.109-121, ⟨10.1007/978-3-642-12963-6_9⟩

resume

With the introduction of new generation high speed routers, and with the help of "flow-aware" traffic management, it becomes possible to improve the Quality of Service for users as well as the network efficiency for ISPs. An example of the "flow-aware" traffic management is the Alcatel-Lucent "Semantic Networking" framework where short-lived flows are processed with high priority and long-lived flows are controlled on a per flow basis. In order to control efficiently the flows, it is useful to know an estimate of the Round Trip Time (RTT). In the present work, we provide an online RTT estimation algorithm which is passive and needs one-way traffic only. The one-way traffic requirement is essential for the application of the algorithm for "flow-aware" traffic management inside the network. To the best of our knowledge, there was no online one-way traffic RTT estimators. Tests on a controlled testbed and on the Internet demonstrate high accuracy of the proposed estimator.

DOI

DOI : 10.1007/978-3-642-12963-6_9

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titre

Optimal sampling for state change detection with application to the control of sleep mode

auteur

Amar Prakash Azad, Sara Alouf, Eitan Altman, Vivek Borkar, Georgios Paschos

article

48th IEEE Conference on Decision and Control (CDC 2009), Dec 2009, Shanghai, China. pp.1645-1650, ⟨10.1109/CDC.2009.5400669⟩

resume

This work considers systems with inactivity periods of unknown duration. We study the question of scheduling waking up instants in which a server can check whether the inactivity period is over. There is a cost proportional to the delay from the moment the inactivity period ends until the server discovers it, a (small) running cost while the server is away and also a cost for waking up. As an application to the problem, we consider the energy management in WiMax where inactive mobiles reduce their energy consumption by entering a sleep mode. Various standards exist which impose specific waking-up scheduling policies at wireless devices. We check these and identify optimal policies under various statistical assumptions. We show that periodic fixed vacation durations are optimal and derive the optimal period. We show that this structure does not hold for other inactivity distributions but manage to obtain some suboptimal solutions which perform strictly better than the periodic ones. We finally obtain structural properties for optimal policies for the case of arbitrary distribution of inactivity periods.

DOI

DOI : 10.1109/CDC.2009.5400669

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titre

Vacation policy optimization with application to IEEE 802.16e power saving mechanism

auteur

Amar Prakash Azad, Sara Alouf, Eitan Altman, Vivek Borkar, Georgios Paschos

article

2nd IFIP Wireless Days (WD 2009), Dec 2009, Paris, France. ⟨10.1109/WD.2009.5449688⟩

resume

Much research has been devoted to optimizing the power saving mechanism in wireless mobile devices. Recent advances in wireless radio technology facilitate the implementation of various possible sleep policies. One basic question that arises is: which policy performs best under a certain condition? Furthermore, what are the optimal parameters for a given policy? To answer these questions, we formulate an optimization problem, which entails cost minimization for a given parameterized policy and selection of the best policy among a class. We propose a cost function which captures the inherent tradeoff of delay and energy saving. This takes into account the cost of response time due to the extra sleep, the energy saving during the sleep, and the cost for periodic waking up (for listening). As an application, we consider IEEE 802.16e's power saving mechanism. We study various practical policies and check their performance. We show that the constant duration policy is optimal for Poisson inactivity periods, but not for hyper-exponentially distributed inactivity periods. In the policy where vacations are i.i.d. exponential random variables, we derive analytically the optimal control as a function of the expected inactivity period. This result holds for general inactivity periods. Our framework allows us to compare the performance of several optimal and suboptimal practical policies with that of the IEEE 802.16e standard.

DOI

DOI : 10.1109/WD.2009.5449688

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titre

Distributed gradient optimization for epidemic routing: A preliminary evaluation

auteur

Giovanni Neglia, Giuseppe Reina, Sara Alouf

article

2nd IFIP Wireless Days (WD 2009), Dec 2009, Paris, France. ⟨10.1109/WD.2009.5449659⟩

resume

In this paper we address the problem of designing adaptive epidemic-style forwarding mechanisms for message delivery in Delay Tolerant Networks. Our approach is based on a new analytical framework for multi-agent optimization through distributed subgradient methods. We investigate how this framework can be adapted to the considered networking problem and perform a preliminary evaluation, which shows promising results in terms of convergence speed.

DOI

DOI : 10.1109/WD.2009.5449659

Accès au texte intégral et bibtex

titre

Flow Aware Traffic Management

auteur

Alberto Blanc, Konstantin Avrachenkov, Sara Alouf, Georg Post

article

5th International Workshop on Traffic Management and Traffic Engineering for the Future Internet (EuroNFTraf '09), Dec 2009, Paris, France

resume

TCP congestion control mechanism, while simple and scalable, has several well known limitations: 1) often different flows experience synchronized losses, leading to lower link utilization, and 2) when flows with different Round Trip Times (RTT) share the same bottleneck link, the flows with a smaller RTT will receive a larger share of the capacity. Not only this allocation of capacity is non-optimal in general, but it cannot be modified as long as only drop tail queues and TCP are used. Active Queue Management algorithms aim at improving link utilization by desynchronizing packet losses for different flows, albeit without addressing the fairness issue. Many AQM algorithms have been proposed (like RED, REM, Blue, Stochastic fair blue, just to name a few), but, to the best of our knowledge, none of them is capable of addressing both issues while being easy to configure and supporting different fairness criteria. Another advantage of using AQM algorithms is that routers can use Explicit Congestion Notification, in order to inform a sender that it needs to reduce its sending rate. We propose a new flow-aware traffic management mechanism that aims at addressing the two aforementioned limitations of TCP, while being self-configuring and supporting different fairness criteria. Clearly the fairness criteria has to be

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titre

A realistic simulation model for peer-to-peer storage systems

auteur

Abdulhalim Dandoush, Sara Alouf, Philippe Nain

article

Fourth International ICST Conference on Performance Evaluation Methodologies and Tools (VALUETOOLS '09), Oct 2009, Pisa, Italy. ⟨10.4108/ICST.VALUETOOLS2009.7653⟩

resume

The peer-to-peer (P2P) paradigm have emerged as a cheap, scalable, self-repairing and fault-tolerant storage solution. This solution relies on erasure codes to generate additional redundant fragments of each "block of data" in order to increase the reliability and availability and overcome the churn. When the amount of unreachable fragments attains a predefined threshold, due to permanent departures or long disconnections of peers, a recovery process is initiated to compensate the missing fragments, requiring multiple fragments of data of a given "block" to be downloaded in parallel for an enhanced service. Recent modeling efforts that address the availability and the durability of data have assumed the recovery process to follow an exponential distribution, an assumption made mainly in the absence of studies characterizing the "real" distribution of the recovery process. This work aims at filling this gap and better understanding the behavior of these systems through simulation while taking into consideration the heterogeneity of peers, the underlying network topologies, the propagation delays and the transport protocol. To that end, the distributed storage protocol is implemented in the NS-2 network simulator. This paper describes a realistic simulation model that captures the behavior of P2P storage systems. We provide some experiments results that show how modeling the availability and durability can be impacted by the recovery times distribution which is impacted in turn by the characteristics of the the network and the context.

DOI

DOI : 10.4108/ICST.VALUETOOLS2009.7653

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titre

Simulation analysis of download and recovery processes in P2P storage systems

auteur

Abdulhalim Dandoush, Sara Alouf, Philippe Nain

article

21st International Teletraffic Congress (ITC 2009), Sep 2009, Paris, France

resume

Peer-to-peer storage systems rely on data fragmentation and distributed storage. Unreachable fragments are continuously recovered, requiring multiple fragments of data (constituting a ldquoblockrdquo) to be downloaded in parallel. Recent modeling efforts have assumed the recovery process to follow an exponential distribution, an assumption made mainly in the absence of studies characterizing the ldquorealrdquo distribution of the recovery process. This work aims at filling this gap through a simulation study. To that end, we implement the distributed storage protocol in the NS-2 network simulator and run a total of seven experiments covering a large variety of scenarios. We show that the fragment download time follows approximately an exponential distribution. We also show that the block download time and the recovery time essentially follow a hypo-exponential distribution with many distinct phases (maximum of as many exponentials). We use expectation maximization and least square estimation algorithms to fit the empirical distributions. We also provide a good approximation of the number of phases of the hypo-exponential distribution that applies in all scenarios considered. Last, we test the goodness of our fits using statistical (Kolmogorov-Smirnov test) and graphical methods.

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titre

Performance analysis of centralized versus distributed recovery schemes in P2P storage systems

auteur

Abdulhalim Dandoush, Sara Alouf, Philippe Nain

article

International IFIP-TC 6 Networking Conference : Networking 2009, May 2009, Aachen, Germany. pp.676-689, ⟨10.1007/978-3-642-01399-7_53⟩

resume

This paper studies the performance of Peer-to-Peer Storage Systems (P2PSS) in terms of data lifetime and availability. Two schemes for recovering lost data are modeled through absorbing Markov chains and their performance are evaluated and compared. The first scheme relies on a centralized controller that can recover multiple losses at once, whereas the second scheme is distributed and recovers one loss at a time. The impact of each system parameter on the performance is evaluated, and guidelines are derived on how to engineer the system and tune its key parameters in order to provide desired lifetime and/or availability of data. We find that, in stable environments such as local area or research laboratory networks where machines are usually highly available, the distributed-repair scheme offers a reliable, scalable and cheap storage/backup solution. This is in contrast with the case of highly dynamic environments, where the distributed-repair scheme is inefficient as long as the storage overhead is kept reasonable. P2PSS with centralized-repair scheme are efficient in any environment but have the disadvantage of relying on a centralized authority. Our analysis also suggests that the use of large size fragments reduces the efficiency of the recovery mechanism.

DOI

DOI : 10.1007/978-3-642-01399-7_53

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titre

Analysis of an M/G/1 Queue with Repeated Inhomogeneous Vacations with Application to IEEE 802.16e Power Saving Mechanism

auteur

Sara Alouf, Eitan Altman, Amar Prakash Azad

article

5th International Conference on Quantitative Evaluation of Systems (QEST '08), Sep 2008, Saint-Malo, France. pp.27-36, ⟨10.1109/QEST.2008.37⟩

resume

The goal of this paper is to establish a general approach for analyzing queueing models with repeated in homogeneous vacations. At the end of a vacation, the server goes on another vacation, possibly with a different probability distribution, if during the previous vacation there have been no arrivals. In case there have been one or more arrivals during a vacation then a busy period starts after a warm-up time. In order to get an insight on the influence of parameters on the performance, we choose to study a simple M/G/1 queue (Poisson arrivals and general independent service times) which has the advantage of being tractable analytically. The theoretical model is applied to the problem of power saving for mobile devices in which the sleep durations of a device correspond to the vacations of the server. Various system performance metrics such as the frame response time and the economy of energy are derived. A constrained optimization problem is formulated to maximize the economy of energy achieved in power save mode, with constraints as QoS conditions to be met. An illustration of the proposed methods is shown with a WiMAX system scenario to obtain design parameters for better performance. Our analysis allows us not only to optimize the system parameters for a given traffic intensity but also to propose parameters that provide the best performance under worst case conditions.

DOI

DOI : 10.1109/QEST.2008.37

Accès au texte intégral et bibtex

titre

M/G/1 queue with repeated inhomogeneous vacations applied to IEEE 802.16e power saving

auteur

Sara Alouf, Eitan Altman, Amar Prakash Azad

article

2008 ACM SIGMETRICS International Conference on Measurement and Modeling of Computer Systems, Jun 2008, Annapolis, Maryland, United States. pp.451-452, ⟨10.1145/1375457.1375516⟩

DOI

DOI : 10.1145/1375457.1375516

Accès au texte intégral et bibtex

titre

Embedding Evolution in Epidemic-Style Forwarding

auteur

Sara Alouf, Iacopo Carreras, Daniele Miorandi, Giovanni Neglia

article

IEEE Internatonal Conference on Mobile Adhoc and Sensor Systems (MASS 2007), Oct 2007, Pisa, Italy. ⟨10.1109/MOBHOC.2007.4428686⟩

resume

In this work, we introduce a framework to let forwarding schemes evolve in order to adapt to changing and a priori unknown environments. The framework is inspired by genetic algorithms: at each node a genotype describes the forwarding scheme used, a selection process fosters the diffusion of the fittest genotypes in the system and new genotypes are created by combining existing ones or applying random changes. A case study implementation is presented and its performance evaluated via numerical simulations.

DOI

DOI : 10.1109/MOBHOC.2007.4428686

Accès au texte intégral et bibtex

titre

Performance analysis of peer-to-peer storage systems

auteur

Sara Alouf, Abdulhalim Dandoush, Philippe Nain

article

20th international teletraffic conference on Managing traffic performance in converged networks (ITC '07), Jun 2007, Ottawa, Canada. pp.642-653, ⟨10.1007/978-3-540-72990-7_57⟩

resume

This paper evaluates the performance of two schemes for recovering lost data in a peer-to-peer (P2P) storage systems. The first scheme is centralized and relies on a server that recovers multiple losses at once, whereas the second one is distributed. By representing the state of each scheme by an absorbing Markov chain, we are able to compute their performance in terms of the delivered data lifetime and data availability. Numerical computations are provided to better illustrate the impact of each system parameter on the performance. Depending on the context considered, we provide guidelines on how to tune the system parameters in order to provide a desired data lifetime.

DOI

DOI : 10.1007/978-3-540-72990-7_57

Accès au texte intégral et bibtex

titre

Design and Analysis of an Adaptive Backoff Algorithm for IEEE 802.11 DCF Mechanism

auteur

Mouhamad Ibrahim, Sara Alouf

article

NETWORKING 2006, May 2006, Coimbra, Portugal. pp.184-196, ⟨10.1007/11753810_16⟩

resume

This paper presents an adaptive backoff algorithm for the contention-based Distributed Coordination Function (DCF) of the IEEE 802.11 standard. Relying on on-line measurements of the number of sources, the algorithm, called Adaptive BEB, judiciously sets the size of the minimal contention window to adapt to the congestion level in the shared medium. The paper also provides an extension to Adaptive BEB for enhancing its performance over noisy channels. In this extension, a simple EWMA filter is used to derive a Packet Error Rate estimator. The performance evaluation of our proposal is addressed via simulations.

DOI

DOI : 10.1007/11753810_16

Accès au texte intégral et bibtex

titre

Quasi-optimal bandwidth allocation for multi-spot MFTDMA satellites

auteur

Sara Alouf, Eitan Altman, Jérôme Galtier, Jean-François Lalande, Corinne Touati

article

INFOCOM 2005, Mar 2005, Miami, United States. pp.560-571, ⟨10.1109/INFCOM.2005.1497923⟩

resume

This paper presents an algorithm for resource allocation in satellite networks. It deals with planning a time/frequency plan for a set of terminals with a known geometric configuration under interference constraints. Our objective is to maximize the system throughput while guaranteeing that the different types of demands are satisfied, each type using a different amount of bandwidth. The proposed algorithm relies on two main techniques. The first generates admissible configurations for the interference constraints, whereas the second uses linear and integer programming with column generation. The obtained solution estimates a possible allocation plan with optimality guarantees, and highlights the frequency interferences which degrade the construction of good solutions.

DOI

DOI : 10.1109/INFCOM.2005.1497923

Accès au texte intégral et bibtex

titre

On the dynamic estimation of multicast group sizes

auteur

Sara Alouf, Eitan Altman, Chadi Barakat, Philippe Nain

article

Sixteenth International Symposium on Mathematical Theory of Networks and Systems (MTNS2004), Jul 2004, Leuven, Belgium

resume

This paper concerns multicast applications that are interested in the evolution of their membership over time. It covers optimal on-line estimation algorithms for determining the membership of a multicast group. The paper briefly reviews the related work and our own contributions to the field. Using a probabilistic acknowledgement scheme and signal processing's filtering techniques, we have derived MSE-optimal estimators under the assumptions of Poisson subscribers arrival and either exponentially or hyperexponentially distributed lifetime of receivers. Our estimators have been tested through trace-driven simulations using data from real multicast video sessions over which they exhibit very good performance.

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titre

Estimating membership in a multicast session

auteur

Sara Alouf, Eitan Altman, Chadi Barakat, Philippe Nain

article

ACM SIGMETRICS international conference on Measurement and modeling of computer systems - 2003, Jun 2003, San Diego, United States. pp.250-260, ⟨10.1145/781027.781059⟩

resume

We propose two novel on-line estimation algorithms to determine the size of a dynamic multicast group. We first use a Wiener filter to derive an optimal estimator for the membership size of the session in case the join process is Poisson and the lifetime of participants is distributed exponentially. We next develop the best first-order linear filter from which we derive an estimator that holds for any lifetime distribution. We apply this approach to the case where the lifetime distribution is hyperexponential. Both estimators hold under any traffic regime. Applying both estimators on real traces corresponding to video sessions, we find that both schemes behave well, one of which performs slightly better than the other in some cases. We further provide guidelines on how to tune the parameters involved in both schemes in order to achieve high quality estimation while simultaneously avoiding feedback implosion.

DOI

DOI : 10.1145/781027.781059

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titre

Optimal on-line estimation of the size of a dynamic multicast group

auteur

Sara Alouf, Eitan Altman, Philippe Nain

article

Twenty-First Annual Joint Conference of the IEEE Computer and Communications Societies (INFOCOM 2002), Jun 2002, New York City, New York, United States. pp.1109- 1118, ⟨10.1109/INFCOM.2002.1019359⟩

resume

In this paper we propose an efficient on-line estimation algorithm for determining the size of a dynamic multicast group. By using diffusion approximation and Kalman filter, we derive an estimator that minimizes the mean square of the estimation error. As opposed to previous studies, where the size of the multicast group is supposed to be fixed throughout the estimation procedure, we consider a dynamic estimation scheme that updates the estimation at every observation step. The robustness of our estimator to violation of the assumptions under which it has been derived is addressed via simulations. Further validations of our approach are carried out on real audio traces.

DOI

DOI : 10.1109/INFCOM.2002.1019359

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titre

Forwarders vs. centralized server: an evaluation of two approaches for locating mobile agents

auteur

Sara Alouf, Fabrice Huet, Philippe Nain

article

ACM SIGMETRICS international conference on Measurement and modeling of computer systems - 2002, Jun 2002, Marina Del Rey, California, United States. pp.278-279, ⟨10.1145/511334.511379⟩

DOI

DOI : 10.1145/511334.511379

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titre

Inferring network characteristics via moment-based estimators

auteur

Sara Alouf, Philippe Nain, Don Towsley

article

Twentieth Annual Joint Conference of the IEEE Computer and Communications Societies (INFOCOM 2001), Apr 2001, Anchorage, Alaska, United States. pp.1045-1054, ⟨10.1109/INFCOM.2001.916298⟩

resume

In this work we develop simple inference models based on finite capacity single server queues for estimating the buffer size and the intensity of cross traffic at the bottleneck link of a path between two hosts. Several pairs of moment-based estimators are proposed to estimate these two quantities. The best scheme is then identified through simulation

DOI

DOI : 10.1109/INFCOM.2001.916298

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