[Show abstract][Hide abstract] ABSTRACT: Distributed Online Social Networks (DOSNs) do not rely on a central repository for storing social data so that the users can keep control of their private data and do not depend on the social network provider. The ego network, i.e. the network made up of an individual, the ego, along with all the social ties she has with other people, the alters, may be exploited to define distributed social overlays and dis-semination protocols. In this paper we propose a new epidemic protocol able to spread social updates in DOSN overlays where the links between nodes are defined by considering the social interactions between users. Our approach is based on the notion of Weighted Ego Betweenness Cen-trality (WEBC) which is an egocentric social measure approximating the Betweenness Centrality. The computation of the WEBC exploits a weighted graph where the weights correspond to the tie strengths be-tween the users so that nodes having a higher number of interactions are characterized by a higher value of the WEBC. A set of experimental results proving the effectiveness of our approach is presented.
Second Workshop on Large Scale Distributed Virtual Environments on Clouds and P2P, LSDVE 2014, EUROPAR 2014,, Porto; 08/2014
[Show abstract][Hide abstract] ABSTRACT: The IPv6 Routing Protocol for Low Power and Lossy Networks (RPL) has been recently standardised by the IETF ROLL working group to support IPv6 routing for resource constrained devices in industrial, home and urban environments. However, several studies have shown that RPL may experience (very) low delivery rates, particularly in large-scale deployments. In this paper we provide an in-depth analysis of the protocol attributes and design choices that generate such unreliability issues. Then, we describe and evaluate a new implementation of the RPL standard for the Contiki OS to improve data delivery reliability. The salient feature of our RPL implementation is to adopt a flexible cross-layering design that provides simple routing optimisations, enhanced link estimation capabilities and efficient management of neighbour tables. In order to verify the effectiveness of our RPL implementation we use an Advanced Metering Infrastructure (AMI) as case study. Results obtained using Cooja emulator in two sets of experiments, differentiated by the presence or lack of duty cycling, indicate that our RPL implementation outperforms the one provided in Contiki in terms of average packet delivery rates by up to 200% in networks with 100 nodes.
IEEE Transactions on Industrial Informatics 08/2014; · 8.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Future Internet scenario will be characterised by a very large amount of information circulating in large scale content-centric networks. One primary concern is clearly to replicate and disseminate content efficiently, such that – ideally – it is replicated and spread only in those portions of the network where there are interested users. As centralised data dissemination solutions are unlikely to be feasible due to the sheer amount of content expected to circulate, nodes themselves must locally take data dissemination decisions, taking into account contextual information about users interests. In this paper, we consider a mobile opportunistic networking environment where mobile nodes exploit contacts among each other to replicate and disseminate content without central control. In this environment, we see nodes as proxies of their human users in the cyber world made up by mobile devices. Accordingly, we want nodes to act as much as possible as their users would do if they had to disseminate information among each other. We thus propose a new solution based on cognitive heuristics. Cognitive heuristics are functional models of the human mental processes, studied in the cognitive psychology field. They describe the judgement process the brain performs when subject to temporal constraints or partial information. We illustrate how these cognitive processes can be fruitfully implemented into a feasible and working ICT solution, in which decisions about the dissemination process are based on aggregated information built up from observations of the encountered nodes and successively exploited through a stochastic mechanism to decide what content to replicate. These two features allow the proposed solution to drastically limit the state kept by each node, and to dynamically adapt to the dynamics of content diffusion, the dynamically changing node interests and the presence of churning of nodes participation to the data dissemination process. The performance of our solution is evaluated through simulations and compared with reference solutions in the literature.
Pervasive and Mobile Computing 05/2014; in press. · 1.63 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Online Social Networks (OSNs) usually exploit a logically centralized infrastructure which has several drawbacks including scalability, privacy, and dependence on a provider. In contrast to centralized OSNs, a Distributed Online Social Network helps to lower the cost of the provider drastically, and allows better control of user privacy. A distributed approach introduces new problems to address, as data availability or information diffusion, which require the definition of methods for the analysis of the social graph. This paper focuses the problem of the evaluation of the centrality of a node in a Distributed Online Social Network and proposes a distributed approach for the computation of the Ego Betweenness Centrality, which is an ego-centric method to approximate the Betweenness Centrality. We propose a set of algorithms to compute the betweenness centrality in static and dynamic graphs, which can be directed or undirected. We propose both a broadcast and a gossip protocol to compute the Ego Betweenness Centrality. A set of experimental results proving the effectiveness of our approach are presented.
PerCol'14: The Fifth IEEE Workshop on Pervasive Collaboration and Social Networking, Budapest; 03/2014
[Show abstract][Hide abstract] ABSTRACT: In last couple of decades, cellular networks have revolutionized the way users access communication networks but they required a huge effort to operators for the development of a wireless infrastructure which has been designed considering deployment ...
[Show abstract][Hide abstract] ABSTRACT: Foundational work in the area of opportunistic networks has shown that the distribution of intercontact times between pairs of nodes has a key impact on the network properties, for example, in terms of convergence of forwarding protocols. Specifically, forwarding protocols may yield infinite expected delay if the intercontact time distributions present a particularly heavy tail. While these results hold for the distributions of intercontact times between individual pairs, most of the literature uses the aggregate distribution, i.e., the distribution obtained by considering the samples from all pairs together, to characterize the properties of opportunistic networks. In this paper, we provide an analytical framework that can be used to check when this approach is correct and when it is not, and we apply it to a number of relevant cases. We show that the aggregate distribution can be way different from the distributions of individual pair intercontact times. Therefore, using the former to characterize properties that depend on the latter is not correct in general, although this is correct in some cases. We substantiate this finding by analyzing the most representative distributions characterizing real opportunistic networks that can be obtained from reference traces. We review key cases for opportunistic networking, where the aggregate intercontact time distribution presents a heavy tail with or without exponential cutoff. We show that, when individual pairs follow Pareto distributions, the aggregate distribution consistently presents a heavy tail. However, heavy tail aggregate distributions can also emerge in networks where individual pair intercontact times are not heavy tailed, for example, exponential or Pareto with exponential cutoff distributions. We show that an exponential cutoff in the aggregate appears when the average intercontact times of individual pairs are finite. Finally, we discuss how to use our analytical model to know whether collecting aggregate - nformation about intercontact times is sufficient or not, to decideâin practiceâwhich type of routing protocols to use.
IEEE Transactions on Mobile Computing 12/2013; 12(12):2483-2495. · 2.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Opportunistic Networks (OppNets) offer a very volatile and dynamic networking environment. Several applications proposed for OppNets - such as social networking, emergency management, pervasive and urban sensing - involve the problem of sharing content amongst interested users. Despite the fact that nodes have limited resources, existing solutions for content sharing require that the nodes maintain and exchange large amount of status information, but this limits the system scalability. In order to cope with this problem, in this paper we present and evaluate a solution based on cognitive heuristics. Cognitive heuristics are functional models of the mental processes, studied in the cognitive psychology field. They describe the behavior of the brain when decisions have to be taken quickly, in spite of incomplete information. In our solution, nodes maintain an aggregated information built up from observations of the encountered nodes. The aggregate status and a probabilistic decision process is the basis on which nodes apply cognitive heuristics to decide how to disseminate content items upon meeting with each other. These two features allow the proposed solution to drastically limit the state kept by each node, and to dynamically adapt to both the dynamics of item diffusion and the dynamically changing node interests. The performance of our solution is evaluated through simulation and compared with other solutions in the literature.
[Show abstract][Hide abstract] ABSTRACT: Opportunistic networking is one of the key paradigms to support direct communication between devices in a mobile scenario. In this context, the high volatility and dynamicity of information and the fact that mobile nodes have to make decisions in condition of partial or incomplete knowledge, makes the development of effective and efficient data dissemination schemes very challenging. In this paper we present algorithms based on well-established models in cognitive sciences, in order to disseminate both data items, and semantic information associated with them. In our approach, semantic information represents both meta-data associated to data items (e.g., tags associated to them), and meta-data describing the interests of the users (e.g., topics for which they would like to receive data items). Our solution exploits dissemination of semantic data about the users’ interests to guide the dissemination of the corresponding data items. Both dissemination processes are based on models coming from the cognitive sciences field, named cognitive heuristics, which describe how humans organise information in their memory and exchange it during interactions based on partial and incomplete information. We exploit a model describing how semantic data can be organised in each node in a semantic network, based on how humans organise information in their memory. Then, we define algorithms based on cognitive heuris- tics to disseminate both semantic data and data items between nodes upon encounters. Finally, we provide initial performance results about the diffusion of interests among users, and the corresponding diffusion of data items.
[Show abstract][Hide abstract] ABSTRACT: In this paper we present DroidOppPathFinder, a Mobile Social Network application designed to generate and share contents about paths for fitness activity in a city. The application is able to recommend the best path in a specific area by analyzing the user’s preferences and real- time environmental characteristics collected by heterogeneous sensing devices and services through opportunistic sensing mechanisms. To this aim, DroidOppPathFinder is developed on top of our middleware CAMEO, which provides context- and social-aware functionalities to improve both the application’s performances and the user experience. This work represents a real example of opportunistic sensing service as additional support to the development ofMSN applications. In addition, it demonstrates an efficient management of heterogeneous sensing data and services on mobile devices in order to further enrich the context of both local and remote nodes.
IEEE International Symposium on a World of Wireless Mobile and Multimedia Networks; 01/2013
[Show abstract][Hide abstract] ABSTRACT: WiFi Direct introduces new opportunities to deploy real opportunistic networks through users' mobile devices. However, its original specification does not take into account all the parameters that can emerge from an opportunistic network scenario, not only in terms of technical requirements (e.g., available resources and connectivities) but also of users characteristics and profiles, which can heavily influence the system's performances and devices' interactions. In this work we investigate the feasibility of creating opportunistic networks on top of WiFi Direct framework by analyzing the protocol's performances in real scenarios with a variable number of mobile devices. Experimental results show the times required to form a group of variable size and the best configurations to support opportunistic networking operations and upper layer applications.
[Show abstract][Hide abstract] ABSTRACT: Low-Power and Lossy Networks (LLNs) are an enabling technology for many Internet of Things (IoT) applications. To allow LLNs to interoperate with the Internet the IETF is specifying IP-compatible standards that are specifically designed for embedded devices with small memory and limited computing capabilities. The purpose of this paper is to investigate the interplay between the recently proposed IETF standard for IPv6 routing in LLNs, called RPL, with state-of-the-art autoconfiguration algorithms that assign network addresses in a hierarchical manner. To this end, we have extended the default RPL implementation available in Contiki operating system to support T-DAAP, LISAA and DAAM addressing schemes. Our experimental results clearly show that the mechanisms used by RPL to configure and maintain a tree-based network topology frequently break address hierarchy, limiting the opportunities for route aggregation. Furthermore, classical techniques used to reduce network instability significantly increase the network set-up times and, in same cases, degrade path qualities.
Wireless Communications and Mobile Computing Conference (IWCMC), 2013 9th International; 01/2013
[Show abstract][Hide abstract] ABSTRACT: The proliferation of smartphones as complex sensing systems represents today the basis to further stimulate the active participation of mobile users in opportunistic sensing services. However, single sensing devices (either independent network com- ponents or integrated inmore powerful devices) generally present different capabilities and implement proprietary standards. This highlights the necessity of defining a common standard for sensing data encoding in order to guarantee the interoperability of heterogeneous devices and personal mobile systems. In this paper we present Sensor Mobile Enablement (SME), a light- weight standard for efficiently identifying, coding and decoding heterogeneous sensing information on mobile devices. After a detailed analysis of SME features and advantages, we present its performances derived from real experiments on Android smartphones. Results highlight that SME does not heavily impact on mobile system’s performances while efficiently supporting opportunistic sensing services.
International Workshop on the Impact of Human Mobility in Pervasive Systems and Applications; 01/2013
[Show abstract][Hide abstract] ABSTRACT: Advanced communication/networking technologies should be integrated in next-generation power systems (a.k.a. smart grids) to improve their resilience, efficiency, adaptability, and sustainability. Many believe that the smart grid communication infrastructure will emerge from the interconnection of a large number of small-scale networks organized into a hierarchical architecture covering larger geographic areas. In this article, first we carry out a thorough analysis of the key components of the smart grid communication architecture, discussing the different network topologies and communication technologies that could be employed. Special emphasis is given to the advanced metering infrastructure, which will be used to interconnect the smart meters deployed at customers' premises with data aggregators and control centers. The design of scalable, reliable, and efficient networking solutions for AMI systems is an important research problem because these networks are composed of thousands of resource-constrained embedded devices usually interconnected with communication technologies that can provide only low-bandwidth and unreliable links. The IPv6 Routing Protocol for Low Power and Lossy Networks was recently standardized by the IETF to specifically meet the requirements of typical AMI applications. In this article we present a thorough overview of the protocol, and we critically analyze its advantages and potential limits in AMI applications. We also conduct a performance evaluation of RPL using a Contiki-based prototype of the RPL standard and a network emulator. Our results indicate that although average performance may appear reasonable for AMI networks, a few RPL nodes may suffer from severe unreliability issues and experience high packet loss rates due to the selection of suboptimal paths with highly unreliable links.
[Show abstract][Hide abstract] ABSTRACT: The vast proliferation of Online Social Networks (OSN) is generating many new ways to interact and create social relationships with others. While substantial results have been obtained in anthropology literature describing the properties of human social networks, a clear understanding of the properties of social networks built using OSN is still to be achieved. The presence of a huge amount of records containing users’ communication history, provided by OSN, represents a new opportunity to analyse and better understand the human social behaviour. In this paper we present ego-net digger, a novel Facebook application for the analysis of ego networks in OSN. Ego-net digger collects users’ social data and gives a representation of their personal social networks according to the Dunbar’s circles model. To show the potential of our application we analyse a sample data set collected during a data acquisition campaign, finding interesting similarities between the structure of Facebook ego networks and the properties found in the anthropology literature. Specifically, we find that, in our sample, there is a clear evidence of the presence of the same ego network structure - i.e., the Dunbar’s circles - as found in human social networks formed offline.
HotSocial '12 Proceedings of the First ACM International Workshop on Hot Topics on Interdisciplinary Social Networks Research; 08/2012
[Show abstract][Hide abstract] ABSTRACT: The physical environment is becoming more and more saturated with computing and communication entities that interact among themselves, as well as with users: virtually everything will be enabled to source information and respond to appropriate stimuli. In this technology-rich scenario, real-world components interact with cyberspace via sensing, computing and communication elements, thus driving towards what is called the Cyber–Physical World (CPW) convergence. Information flows from the physical to the cyber world, and vice-versa, adapting the converged world to human behavior and social dynamics. Indeed humans are at the center of this converged world since information about the context in which they operate is the key element to adapt the CPW applications and services. Alongside, a new wave of (human) social networks and structures are emerging as important drivers for the development of novel communication and computing paradigms. In this article we present some of the research issues, challenges and opportunities in the convergence between the cyber and physical worlds. This article is not a comprehensive survey of all aspects of the CPW convergence. Instead, it presents some exciting research challenges and opportunities identified by members of the journal’s editorial board with a goal to stimulate new research activities in the emerging areas of CPW convergence.
Pervasive and Mobile Computing 02/2012; 8(1):2-21. · 1.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To allow pervasive and distributed monitoring and control of grid devices and resources, the next-generation electricity grid needs a scalable and reliable two-way communication infrastructure, known as Advanced Metering Infrastructure (AMI). In such communication system, characterized by the interconnection of thousands of resource-constrained embedded devices, such as smart meters and intelligent electric devices (IEDs), the routing protocol plays an essential role to guarantee a timely and reliable communication service. In this paper we investigate the performance of RPL, the IPv6 routing protocol recently standardized by IETF to meet the requirements of such networks. Special emphasis is given to the analysis of route-level attributes, such as path stretch, route lifetimes, dominance, and flapping, which are used to estimate the quality and stability of the RPL routes. Our results show that RPL nodes may suffer from severe unreliability problems, mainly because RPL often selects sub-optimal paths with low quality links. Furthermore, RPL routes are strongly dominated by a single route, and this may prevent RPL from quickly adapt to link quality variations. We believe that the findings of this study may facilitate the design of new mechanisms to improve the reliability and adaptability of RPL.
Sustainable Internet and ICT for Sustainability (SustainIT), 2012; 01/2012
[Show abstract][Hide abstract] ABSTRACT: BitTorrent is currently a very popular protocol for P2P file sharing, and most of BitTorrent users access the Internet from residential networks. In this paper we compare the legacy BitTorrent protocol with EE-BitTorrent, a proxy-based version recently proposed for energy efficiency, in a residential scenario. We show that the performance achieved by users is strongly influenced by the uplink throughput allowed by the access network. When the available uplink rate is low, the legacy BitTorrent protocol performs poorly and EE-BitTorrent outperforms it, in terms of average download time and energy consumption at the user's PC. The opposite occurs when the uplink rate is good. Motivated by these results, we designed and implemented AdaBT, an adaptive algorithm that dynamically selects the most efficient BitTorrent option (i.e., legacy or proxy-based), depending on the operating conditions experienced by the user. Our experimental results show that AdaBT is able to reduce significantly the download time provided by either the legacy BitTorrent or EE-BitTorrent.
Computers and Communications (ISCC), 2012 IEEE Symposium on; 01/2012
[Show abstract][Hide abstract] ABSTRACT: Wireless Sensor Networks (WSNs) are emerging as an effective solution for a wide range of real-life applications. In scenarios where a fine-grain sensing is not required, sensor nodes can be sparsely deployed in strategic locations and special Mobile Elements (MEs) can be used for data collection. Since communication between a sensor node and a ME can occur only when they are in the transmission range of each other, one of the main challenges in the design of a WSN with MEs is the energy-efficient and timely discovery of MEs. In this paper, we consider a hierarchical ME discovery protocol, namely Dual beacon Discovery (2BD) protocol, based on two different beacon messages emitted by the ME (i.e., Long-Range Beacons and Short-Range Beacons). We develop a detailed analytical model of 2BD assuming a sparse network scenario, and derive the optimal parameter values that minimize the energy consumption at sensor nodes, while guaranteeing the minimum throughput required by the application. Finally, we compare the energy efficiency and performance of 2BD with those of a traditional discovery protocol based on a single beacon. Our results show that 2BD can provide significant energy savings, especially when the discovery phase is relatively long.
World of Wireless, Mobile and Multimedia Networks (WoWMoM), 2012 IEEE International Symposium on a; 01/2012