MAC design for WiFi infrastructure networks: a game-theoretic approach

In WiFi networks, mobile nodes compete for accessing a shared channel by means of a random access protocol called Distributed Coordination Function (DCF). Although this protocol is in principle fair, since all the stations have the same probability to transmit on the channel, it has been shown that unfair behaviors may emerge in actual networking scenarios because of non-standard configurations of the nodes. Due to the proliferation of open source drivers and programmable cards, enabling an easy customization of the channel access policies, we propose a game-theoretic analysis of random access schemes. Assuming that each node is rational and implements a best response strategy, we show that efficient equilibria conditions can be reached when stations are interested in both uploading and downloading traffic. More interesting, these equilibria are reached when all the stations play the same strategy, thus guaranteeing a fair resource sharing. When stations are interested in upload traffic only, we also propose a mechanism design, based on an artificial dropping of layer-2 acknowledgments, to force desired equilibria. Finally, we propose and evaluate some simple DCF extensions for practically implementing our theoretical findings.Comment: under review on IEEE Transaction on wireless communication

Distributed Weight Selection in Consensus Protocols by Schatten Norm Minimization

In average consensus protocols, nodes in a network perform an iterative weighted average of their estimates and those of their neighbors. The protocol converges to the average of initial estimates of all nodes found in the network. The speed of convergence of average consensus protocols depends on the weights selected on links (to neighbors). We address in this paper how to select the weights in a given network in order to have a fast speed of convergence for these protocols. We approximate the problem of optimal weight selection by the minimization of the Schatten p-norm of a matrix with some constraints related to the connectivity of the underlying network. We then provide a totally distributed gradient method to solve the Schatten norm optimization problem. By tuning the parameter p in our proposed minimization, we can simply trade-off the quality of the solution (i.e. the speed of convergence) for communication/computation requirements (in terms of number of messages exchanged and volume of data processed). Simulation results show that our approach provides very good performance already for values of p that only needs limited information exchange. The weight optimization iterative procedure can also run in parallel with the consensus protocol and form a joint consensus-optimization procedure.Comment: N° RR-8078 (2012

How to Network in Online Social Networks

In this paper, we consider how to maximize users' influence in Online Social Networks (OSNs) by exploiting social relationships only. Our first contribution is to extend to OSNs the model of Kempe et al. [1] on the propagation of information in a social network and to show that a greedy algorithm is a good approximation of the optimal algorithm that is NP-hard. However, the greedy algorithm requires global knowledge, which is hardly practical. Our second contribution is to show on simulations on the full Twitter social graph that simple and practical strategies perform close to the greedy algorithm.Comment: NetSciCom 2014 - The Sixth IEEE International Workshop on Network Science for Communication Networks (2014

Processes of Formation of Ottoman Damascus

Cet article s’appuie sur une analyse de la morphologie urbaine de la ville à partir des cartes de Damas dressées au cours du Mandat français. Il a pour but l’étude du processus de fabrique urbaine de la période médiévale sur les traces de la cité préislamique – jusqu’à la période ottomane, en portant une attention plus particulière aux cours des maisons damascènes. Il ne s’agit pas ici de donner une description exhaustive de toutes les étapes et de tous les processus de formation de la Damas ottomane mais plutôt de fournir une analyse de la ville intra muros, de loin la plus complexe étant donné la stratigraphie accumulée au cours de l’histoire, en essayant de décrire les principales transformations qui ont présidé à la mise en place de la structure de la ville ottomane.This study is based on an interpretation of Damascus urban morphology based on French cadastral maps. It focuses on the processes of urban fabric from medieval times (on the remains of the pre-Islamic city) to the Ottoman period, paying particular attention to the processes of formation of courtyard houses and their role in the urban fabric. The aim of this study is not to give an extensive description of all the stages and formation processes of Ottoman Damascus; but rather to analyze the most complex urban areas within the walls. It is also an attempt to describe most important transformation processes that were at the origin of the Ottoman urban structure.تستند هذه المقالة على تحليل الشكلانية العمرانية لدمشق انطلاقاً من خرائط للمدينة تمّ إعدادها أثناء الانتداب الفرنسي. وتهدف إلى دراسة السيرورة التدريجية للصناعة العمرانية خلال العصر الوسيط – متتبعين أثر المدينة ما قبل الإسلام – وحتى العصر العثماني، وذلك بمنح اهتمام أكبر بباحات البيوت الدمشقية. وليس المقصود هنا إعطاء وصف متكامل لكل المراحل ولكل أنواع السيرورة في تشكيل دمشق العثمانية، إنما المقصود بالأحرى تقديم تحليل للمدينة داخل السور، وهو الأكثر تعقيداً بسبب الطبقات التي تراكمت على مرّ التاريخ، محاولين وصف التحولات الرئيسية التي كانت في مقدمة إرساء بنية المدينة العثمانية

Bullying prevention and intervention in education through the visual arts: an instrumental case study

According to the American Educational Research Association (AERA) (2013) bullying is one of the greatest health risks to children and young adults in the United States. It is harmful in its impact to the victim, the bystander, and the bully and is often less visible and less identifiable than other public health concerns. The effects on victims, offenders, and bystanders can be long lasting and can affect an individual’s development (AERA, 2013). The impact of bullying on education is profound. As a result of bullying, a child’s academic achievement can be greatly affected (Petrosino, Guckenburg, & DeVoe, 2010). As mandated by law, school districts have implemented the required intervention programs that stimulate conversation but do not provide a lasting effect. While there are currently many intervention programs in schools, the arts must be included and be an active part of any program. The purpose of this instrumental case study is to understand, explore, and provide insight into the interventions used in conventional districts where art education is not used as well as those districts that do employ the visual arts as interventions for bullies, victims, and bystanders. I will also examine the differences and similarities between the two disciplines, art education, and art therapy and will explore the role of each

The Role of Demographics: Who Engages in and Who Benefits from Family Supportive Supervisor Behavior?

Organizations have traditionally instituted formal workplace benefits to help employees alleviate the stress of work-family conflict. However, largely due to implementation difficulties, the effectiveness of formal work-family benefits is questionable. Informal workplace supports, such as family supportive supervisor behavior (FSSB) provide a better explanation for employee well-being. However, we know little about what predicts FSSB or about which employees benefit from it the most. Thus, the purpose of this study is to empirically examine demographic predictors of FSSB and of which employees benefit most from FSSB. Drawing on social identity theory, a research model is proposed to examine whether an individual’s demographic characteristics, operationalized as gender identity, marital status and parental status predicts FSSB. In addition, this study explores whether FSSB relates to employee task performance and whether this relationship is mediated by work-family conflict. From an academic perspective, this model may contribute to the literature by expanding the nomological network of FSSB to include potential predictors. From a practitioner perspective, this study will provide insight regarding existing supervisor work-family related competencies as well as, opportunities for development and training

Timely Data Delivery in a Realistic Bus Network

Abstract—WiFi-enabled buses and stops may form the backbone of a metropolitan delay tolerant network, that exploits nearby communications, temporary storage at stops, and predictable bus mobility to deliver non-real time information. This paper studies the problem of how to route data from its source to its destination in order to maximize the delivery probability by a given deadline. We assume to know the bus schedule, but we take into account that randomness, due to road traffic conditions or passengers boarding and alighting, affects bus mobility. We propose a simple stochastic model for bus arrivals at stops, supported by a study of real-life traces collected in a large urban network. A succinct graph representation of this model allows us to devise an optimal (under our model) single-copy routing algorithm and then extend it to cases where several copies of the same data are permitted. Through an extensive simulation study, we compare the optimal routing algorithm with three other approaches: minimizing the expected traversal time over our graph, minimizing the number of hops a packet can travel, and a recently-proposed heuristic based on bus frequencies. Our optimal algorithm outperforms all of them, but most of the times it essentially reduces to minimizing the expected traversal time. For values of deadlines close to the expected delivery time, the multi-copy extension requires only 10 copies to reach almost the performance of the costly flooding approach. I