Evaluating Load Balancing in Peer-to-Peer Resource Sharing Algorithms for Wireless Mesh Networks

Wireless mesh networks are a promising area for the deployment of new wireless communication and networking technologies. In this paper, we address the problem of enabling effective peer-to-peer resource sharing in this type of networks. In particular, we consider the well-known Chord protocol for resource sharing in wired networks and the recently proposed MeshChord specialization for wireless mesh networks, and compare their performance under various network settings for what concerns total generated traffic and load balancing. Both iterative and recursive key lookup implementation in Chord/MeshChord are considered in our extensive performance evaluation. The results confirm superiority of MeshChord with respect to Chord, and show that recursive key lookup is to be preferred when considering communication overhead, while similar degree of load unbalancing is observed. However, recursive lookup implementation reduces the efficacy of MeshChord cross-layer design with respect to the original Chord algorithm. MeshChord has also the advantage of reducing load unbalancing with respect to Chord, although a moderate degree of load unbalancing is still observed, leaving room for further improvement of the MeshChord design

As farpas da história: lampejos na poesia de Giovanni Raboni

A coletânea Barlumi di storia de Giovanni Raboni aparece intimamente ligada, desde o título, com a história privada e coletiva. Porém, é uma história que não se apresenta como imediatamente legível, tudo é visto em filigrana, por lampejos, em uma perspectiva benjaminiana. Os espaços são interrogados e, na contraluz da existência, aparecem as farpas dos fatos históricos que penetram na carne do poema, transfigurados por meio da palavra poética. Esse procedimento resulta evidente desde o começo de sua trajetória, não somente poética, mas no campo da editoria e de sua atuação em duas importantes revistas: aut aut e Questo e altro. O objetivo deste trabalho é traçar esse percurso na poesia de Raboni, pondo em diálogo essas experiências editoriais com a última coletânea indicada. No específico, será analisado o poema “Ogni tanto succede”, em que o olhar do poeta atravessa a piazza Fontana, tristemente famosa por ter sido o palco do atentado à Banca Nazionale dell’Agricoltura (12 de dezembro de 1969), evento que inaugura a época do terrorismo na Itália. É por meio da descrição da praça que o poeta pode falar sobre o acontecimento histórico, que ecoa em todo o poema, sem ser propriamente nomeado. A história aparece na sombra, no ausente, nas dobras da experiência. Para desdobrar essa relação entre história, memória e palavra poética em Raboni, tentaremos um diálogo pontual com o poeta Gianni D’Elia, com quem compartilha uma visão de poesia que não pode se abster do seu papel social e político.The collection Barlumi di storia by Giovanni Raboni appears linked, since the title, with a private and collective history. However, it is a story that does not present itself as immediately readable, everything is seen in filigree, by flashes, in a Benjaminian perspective. The spaces are questioned and, in the light of existence, the splinters of historical facts penetrate the flesh of the poem, transfigured through the poetic word. This procedure has been evident since the beginning of its trajectory, also in the field of publishing and its performance in two important magazines aut aut and Questo e altro. The objective of this work is to trace a path in Raboni's poetry, putting these editorial experiences in dialogue with the indicated collection. Specifically, the poem “Ogni Tanto Succede” will be analyzed, in which the poet's gaze crosses piazza Fontana, famous for being the stage of the attack on the Banca Nazionale dell'Agricoltura (December 12, 1969), an event that commence a time of terrorism in Italy. It is through the description of the square that the poet can talk about the historical event, which echoes throughout the poem, without it being properly named. History appears in the shadow, in the absent, in the folds of experience. In order to investigate this relationship between history, memory and the poetic word in Raboni, we will seek for a specific dialogue with the poet Gianni D’Elia, with whom he shares a vision of poetry that cannot abstain itself from its social and political role.La raccolta Barlumi di storia del poeta Giovanni Raboni si mostra intimamente legata, fin dal titolo, alla storia privata e collettiva. Tuttavia, è una storia che non si presenta come immediatamente leggibile, tutto è visto in filigrana, per barlumi, in una prospettiva benjaminiana. Gli spazi sono interrogati e, in controluce all’esistenza, appaiono le schegge dei fatti storici che penetrano nella carne della poesia, trasfigurati attraverso la parola poetica. Questo procedimento risulta evidente fin dall’inizio della sua traiettoria, non soltanto poetica, ma anche nel campo dell’editoria e della sua collaborazione con due importanti riviste aut aut e Questo e altro. L’obiettivo di questo lavoro è tracciare un percorso nella poesia di Raboni, facendo dialogare queste esperienze editoriali con la raccolta citata. Nello specifico, sarà analizzata la poesia “Ogni tanto succede”, in cui lo sguardo del poeta attraversa piazza Fontana, tristemente famosa per essere stata palcoscenico dell’attentato alla Banca Nazionale dell’Agricoltura (12 dicembre 1969), evento che inaugura l’epoca del terrorismo in Italia. È attraverso della descrizione della piazza che il poeta può parlare del fatto storico, che echeggia in tutta la poesia, senza essere propriamente nominato. La storia appare nell’ombra, nell’assente, nelle pieghe dell’esperienza. Per sviluppare questa relazione fra storia, memoria e parola poetica in Raboni, tenteremo un dialogo puntuale con il poeta Gianni D’Elia, con cui condivide una visione di poesia che non si può astenere dal suo ruolo sociale e politico

Representing the War. Early Twentieth Century Maps and Models in the Fonds of the Italian War History Museum in Rovereto

Abstract. The representation of the areas in which some of the most significant events of the First World War took place has produced a wide range of materials, such as cartography, aerial and terrestrial photos, textual descriptions and field surveys. In addition, war events were also represented through three-dimensional models. Topographic maps and models constitute composite figurations, which are rich in informative data useful for the preservation of the memory of places and for increasing the knowledge of cultural heritage. Hence, these sources need to be studied, described, interpreted and used for future enhancement. The focus of this paper are archival materials from the collections kept at the Italian War History Museum of Rovereto (Museo Storico Italiano della Guerra), in the Trentino-Alto Adige region. Firstly, we will investigate the cartographic fond in order to assess the composition and origin of its materials. Secondly, we will present the Museum's collection of Early-Twentieth Century models. Such precious heritage is not yet part of an exhibition, and is kept in the Museum's warehouses. The paper constitutes the occasion to present the initial results of a still ongoing project by the Geo-Cartographic Centre for Study and Documentation (GeCo) of the University of Trento on the study and analysis of two archival complexes preserved in the abovementioned Museum. In particular, the paper focuses on the heuristic value of such representational devices, which enable an analysis of the different methods and languages through which space is planned and designed, emphasizing the complementarity between different types of visualization

Using participatory approaches with children and young people to research volitional reading

Children and young people’s volitional book reading has declined consistently over the last two decades, and research efforts to reverse this trajectory would benefit considerably from the input and insights of children and young people. Meanwhile, the expanding and intensifying role of technology in many children and young people’s daily lives makes it difficult for adult reading researchers to stay informed and up-to-date on how technology is shaping and diversifying volitional reading practices and experiences. Participatory research approaches aim to break down the traditional barriers which exist between the researcher and the researched, creating inclusive, non-hierarchical relationships which support collaborative research, and draw upon the knowledge and experience of all involved. While there is growing interest in, and use of, participatory approaches in reading research, this is the first review, to the best of our knowledge, which focuses on participatory research approaches within the context of children and young people’s reading. The aim of this review article is to a) summarise the principles, benefits, and methodological considerations associated with participatory approaches with children and young people, and b) describe different participatory reading research studies with children or young people, and reflect on how these can inform future research into volitional reading. This article aims to inform, support, and encourage the reading research community to consider adopting participatory principles and practices in their work (where appropriate), as we work collectively to enhance knowledge, thinking, and practice in relation to children and young people’s volitional reading.</p

Multihop Beaconing Forwarding Strategies in Congested IEEE 802.11p Vehicular Networks

Multi-hop propagation of situational information is a promising technique for improving beaconing performance and increasing the degree of situational awareness onboard vehicles. However, limitation on beacon size prescribed by standardization bodies implies that only<br> information about 3-4 surrounding vehicles can be piggybacked in a beacon packet. In most traffic situations, the number of vehicles within transmission range is much larger than 3-4, implying that multi-hop forwarding strategies must be devised to select which neighboring<br> vehicle\u27s information to include in a transmitted beacon. In this paper, we investigate the effectiveness of different multi-hop forwarding strategies in delivering fresh situational information to surrounding vehicles. Effectiveness is estimated in terms of both average information age<br> and probability of experiencing a situational-awareness blackout of at least 1 sec. Both metrics are estimated as a function of the hop distance from the transmitting vehicle, and in presence of different level of radio channel congestion. The investigation is based on extensive simulations<br> whose multi-hop communication performance is corroborated by real-world measurements. <br> The results show that network-coding based strategies substantially improve forwarding performance as compared to a randomized strategy, reducing the average information age of up to 60%, the blackout probability of up to two orders of magnitude.<br> We also consider the effect of multi-hop propagation of situational information on the reliability of a forward collision warning application, and show that network-coding based propagation yields a factor three improvement of reliability with respect to a randomized forwarding strategy, and even higher improvements with respect to the case of no propagatio

Beaconing Performance in IEEE 802.11p Vehicular Networks: the Effect of Radio Channel Congestion

In this paper, we study the performance of the beaconing mechanism underlying active safety vehicular applications in presence of different levels of channel congestion. The importance of this study lies in the fact that channel congestion is considered a major factor influencing communication performance in vehicular networks, and that ours is the first investigation of the effects of congestion based on extensive, real-world measurements. The results of our study reveal that congestion has a profound impact on the most important beaconing performance metric, namely, packet (beacon) inter reception time, influencing not only the average value, but also the shape of the distribution. Congestion also considerably increases the frequency of potentially dangerous situation-awareness blackouts, with a likely negative impact on the effectiveness of active safety applications. Our study also reveals that multihop propagation of beaconing information can be used as an effective means of lessening the negative impact of congestion on beaconing performance

Multihop Beaconing Forwarding Strategies in Congested IEEE 802.11p Vehicular Networks

Abstract?Multi-hop propagation of situational information is a promising technique for improving beaconing performance and increasing the degree of situational awareness onboard vehicles. A possible way of achieving this is by piggyback information on the beacon packets that are sent periodically by each vehicle in the network, as prescribed by the DSRC and ETSI standards. However, prescribed limitations on beacon size imply that only information about a very small number of surrounding vehicles can be piggybacked in a beacon packet. In most traffic situations, this number is well below the typical number of vehicles within transmission range, implying that multi-hop forwarding strategies must be devised to select which neighboring vehicle?s information to include in a transmitted beacon. In this paper, we designed different multi-hop forwarding strategies, and assessed their effectiveness in delivering fresh situational information to surrounding vehicles. Effectiveness is estimated in terms of both information age and probability of experiencing a potentially dangerous situational-awareness blackout. Both metrics are estimated as a function of the hop distance from the transmitting vehicle, and in presence of different level of radio channel congestion. The investigation is based on extensive simulations whose multi-hop communication performance is corroborated by real-world measurements. The results show that network-coding based strategies substantially improve forwarding performance as compared to a randomized strategy, reducing the average information age of up to 60%, and the blackout probability of up to two orders of magnitude.We also consider the effect of multi-hop propagation of situational information on the reliability of a forward collision warning application, and show that network-coding based propagation yields a factor three improvement of reliability with respect to arandomized forwarding strategy, and even higher improvements with respect to the case of no propagation

Measuring IEEE 802.11p Performance for Active Safety Applications in Cooperative Vehicular Systems

Abstract-In this paper, we present a measurement study of application layer performance in IEEE 802.11p vehicular networks. More specifically, our focus is on active safety applications, which are based on the exchange of beacon messages containing status information between close-by vehicles. We consider two performance metrics relevant to active safety applications: the first is application-layer goodput, which can be used to optimize congestion control techniques aimed at limiting the beaconing load on the wireless channel; the second is the beacon reception rate, which is useful to estimate the level of situation awareness achievable onboard vehicles. Our measurements were conducted using a prototypal, 802.11p compliant communication device developed by NEC, in both stationary and mobile V2V scenarios, and disclosed several useful insights on 802.11p application-level performance. To the best of our knowledge, the ones presented in this paper are the first application-level measurements of IEEE 802.11p based vehicular networks reported in the literature

The IPERMOB System for Effective Real-Time Road Travel Time Measurement and Prediction

Accurate, real-time measurement and estimation of road travel time is considered a central problem in the design of advanced Intelligent Transportation Systems. In particular, whether eective, real-time collection of travel time measurements in a urban area is possible is, to the best of our knowledge, still an open problem. In this paper, we introduce the IPERMOB system for efficient, real-time collection of travel time measurements in urban areas through vehicular networks. We demonstrate that travel time measurements can be accurately estimated onboard GPS-equipped vehicles, and delivered to a centralized server within a few seconds by sending a single message. Furthermore, in IPERMOB locations of travel time checkpoints can be dynamically changed through software reconfiguration, thus at a very limited cost as compared to the enormous costs of, say, installing and/or changing location of automatic vehicle identification equipment. We demonstrate the effectiveness of our approach through extensive travel time collection campaigns. In particular, our technique is shown to estimate travel time with an accuracy below 1%, with two-, three-orders of magnitude savings in both communication and storage resources with respect to existing techniques based on centralized collection of GPS traces. In the last part of the paper, we further show how real-time travel time measurements can be exploited to perform accurate, short range travel time predictions in situations where existing travel time prediction approaches are challenged (e.g., in presence of traffic congestion). The effects of vehicular network penetration rate on accuracy of travel time prediction are also discusse

Load Balancing Hashing for Geographic Hash Tables

In this paper, we address the problem of balancing the network traffic load generated when querying a geographic hash table. State-of-the-art approaches can be used to improve load balancing by changing the underlying geo-routing protocol used to forward queries in the geographic hash table. However, this comes at the expense of considerably complicating the routing process, which no longer occurs along (near) straightline trajectories, but requires computing complex geometric transformations. Thus, current load balancing approaches are impractical in application scenarios where the nodes composing the geographic hash table have limited computational power, such as in most wireless sensor networks. In this paper, we propose a novel approach to solve the traffic load balancing problem in geographic hash tables: instead of changing the (near) straight-line geo-routing protocol used to send a query from the node issuing the query (the source) to the node managing the queried key (the destination), we propose to "reverse engineer" the hash function so that the resulting destination density, when combined with a given source density, yields a perfectly balanced load distribution. We first formally characterize the desired destination density as a solution of a complex integral equation. We then present explicit destination density functions (taken from the family of Beta distributions) yielding quasi-perfect load balancing under the assumption of uniformly distributed sources. Our theoretical results are derived under an infinite node density model. In order to prove practicality of our approach, we have performed extensive simulations resembling realistic wireless sensor network deployments showing the effectiveness of our approach in considerably improving load balancing. Differently from previous work, the load balancing technique proposed in this paper can be readily applied in geographic hash tables composed of computationally constrained nodes, as it is typically the case in wireless sensor networks