1,721,083 research outputs found
Providing reliable and fault-tolerant broadcast delivery in mobile ad hoc networks
No full textMobile ad-hoc networks are making a new class of mobile applications feasible. They benefit from the fast deployment and reconfiguration of the networks, are mainly characterized by the need to support many-to-many interaction schema within groups of cooperating mobile hosts and are likely to use replication of data objects to achieve performances and high data availability. This strong group orientation requires specialized solutions that combine adaptation to the fully mobile environment and provide the adequate level of fault tolerance. In this paper, we present the reliable broadcast protocol that has been purposely designed for mobile ad-hoc networks. The reliable broadcast service ensures that all the hosts in the network deliver the same set of messages to the upper layer. It represents the building block to obtain higher broadcast and multicast services with stronger guarantees and is an efficient and reliable alternative to flooding. The protocol is constructed on top of the wireless MAC protocol, which in turn sits over the clustering protocol. It provides an exactly once message delivery semantics and tolerates communication failures and host mobility. Temporary disconnections and network partitions are also tolerated under the assumption that they are eventually repaired, as specified by a Liveness property. The termination of the protocol is proved and complexity and performance analyses are also provided
Epidemic Diffusion of Data in Opportunistic Networks
No full textOpportunistic networks have interesting communication behavior that could enable to bring ad hoc networks to people's everyday life. To allow this to happen, several efforts are still required to provide routing strategies capable to efficiently cope with the highly variable network topology and the need to tolerate temporary network partitions. This paper focuses on this argument and proposes the use of epidemic algorithms to provide best effort data delivery to all nodes in an opportunistic scenario. The main contribution of the paper is to show that the approach actually has the ability to deal with the mentioned constraints and outperforms flooding to diffuse packets over the network. The paper presents the first set of simulation results and highlights the parameters that influence the performances of the protocol. These results represent a sort of worst case analysis of the approach and are the starting point to design an adaptive diffusion protocol which is capable to adapt to both the dynamics of the network and the mobility conditions
ORION - Ontology-based queRy routIng in Overlay Networks
No full textCurrent search engines are rapidly changing to embrace more powerful mechanisms that are capable of reasoning on semantic attributes of contents in a distributed repository. Formalisms have been proposed to represent the semantic attributes. Yet, traditional approaches for content sharing in peer-to-peer systems cannot be adapted to use semantic information. Some novel proposals in the literature consider semantic aspects in P2P systems. However, they either make strong assumptions on the semantic model, or have high communication and computation overhead.
In this work, we propose a completely distributed infrastructure, where peers self-organize in an overlay network that mirrors the semantic relations among contents held by peers, in order to support semantic routing of queries. No assumption is needed about peers’ knowledge. Simulations show that the rate of successful content retrieval is higher than for other solutions with equally null assumptions on the system, with lower costs
Self-adaptive and Stateless Broadcast in Delay and Disruption Tolerant Networks
No full textIn delay and disruption tolerant networks, DTNs,
the broadcast communications have been so far disregarded
under the conviction that their cost is unaffordable in the
presence of highly sparse and mobile nodes. This paper defines
the problem of a topology-independent broadcast in DTNs in
terms of effectiveness and efficiency, and provides some interesting
contribution to understand broadcast in the DTN scenario.
Firstly, the paper shows that it is possible to design simple self-
adaptive control mechanisms that keep the broadcast overhead
surprisingly low, while ensuring high node coverage. Secondly, the
paper throws the attention onto the fact that, despite the effective
control mechanism, a sender-based broadcast has a cost to reach
the last 10% of nodes much higher than the cost of reaching
the first 90%. Finally, it shows that, under certain simplified
constraints, a weak reliable broadcast service can be achieved
without relevant extra costs over the best effort service. All the
above points are discussed with the support of simulation results
Adaptive Retransmission Policy for Reliable Warning Diffusion in Vehicular Networks
No full textUse of wireless technologies is becoming pervasive in everyday life. Recently, research began analyzing their use on board of vehicles for several kinds of applications, ranging from traffic safety to fleet management and cooperative work, to entertainment and Internet browsing. In this work, we focus on safety applications and in particular on the approach proposed in the framework of the PATH project [1] for reliable diffusion of warnings to advertise problems in vehicular traffic. The approach in [1] is based on static parameters describing the environment. Unfortunately, in real environments those parameters may dynamically change over time. In this work we present performance measurements obtained by varying the parameters, to evaluate how the performance of the approach depends on environmental conditions
Extracting human mobility and social behavior from location-aware traces
No full textThe concepts of location and community are rapidly becoming key points in the design of new communication paradigms and in deploying emerging mobile computing services. The need of reliable and quantitative knowledge and predictions of some relevant information, such as which locations are enjoyed by people in their daily lives and how people aggregate within communities, advocates a realistic mobility model able to describe both the human mobility throughout locations and the human attitude to socialize within communities. Unfortunately, so far, neither the concept of location nor the concept of community has been univocally defined. In this paper, we approach the problem from the most basic of starting points, namely by analyzing the real Global Positioning System datasets of human mobility traces. On this elementary basis, the paper provides a few relevant contributions. We firstly derive a deep understanding of the term “location” and at the same time of the notion of community strictly related to it. Secondly, we merge the two concepts into what we call geo-community. By proceeding from real spatial data rather than from a priori reasonings, we are able to quantitatively describe geo-communities and infer the probability distributions of all the features of human behavior. Finally, not to lose social implications, we present the method to derive people sociality from geo-communities
Utility-based forwarding: a comparison in different mobility scenarios
No full textSeveral proposals are available in the literature that deal with the problem of message forwarding in Opportunistic Networks (ONs). These proposals attempt to derive the path from source to destination that minimizes delivery latency and traveled hops, and maximizes the probability of successful delivery, while saving the overall system resources through a limitation of the number of message copies. Utilitybased forwarding achieves these goals through the use of functions that discriminate among nodes in terms of their utility to reach a destination. Although the approach is very promising, so far, there is no understanding about the tight relationship between utility functions and the mobility scenario in which they operate and, as a consequence, we are unable to design efficient solutions for practical ONs. In this work, we focus on this point by analysing five well known utility functions in five different scenarios. We establish relationships between the mechanisms adopted by the utility functions to discriminate among candidate relays, and the characteristics of the environment in terms of people mobility and the structure of their communities. The results can be useful to select an appropriate forwarding mechanism when deploying an experimental Opportunistic Network, and to design a novel utility function able to adapt to variable mobility patterns
Content dissemination on location-based communities : a comparative analysis
No full textThis paper focuses on content dissemination in location-centered communities and provides the first comparative analysis of two forwarding algorithms on real scenario, namely, ProfileCast - which has been on purposely designed for this environment - and InterestCast - which by contrast addresses more general settings. The paper provides quantitative evaluation of relevant metrics (i.e. community coverage, delivery delay, energy/message efficiency) to be considered whenever attempting to spread contents to the persons that are used to visit the same location. Moreover, the experiment allows to give an insight on the problems arising when deploying these protocols on real settings and an empirical evaluation of two different approaches. ProfileCast leverages mechanisms to automatically extract the intrinsic characteristics of the users from their behavior pattern; a content generated by a node is implicitly addressed to users with similar behavior as the source. InterestCast matches content tags against interests explicitly expressed by the users
Context sensing for autonomic forwarding in opportunistic networks
No full textRank-based policies represent a promising approach for designing message forwarding algorithms that meet the needs of opportunistic networks. In fact, they combine low computation and communication costs with good performance in terms of both latency and delivery rates. Nonetheless, they highly depend on the mobility scenario relevant to the user, and a forwarding policy with good performances in heterogeneous settings has yet to be designed. In this paper, we propose to provide each mobile device with novel autonomic observation and reasoning components according to the following objectives: enable the device (i) to achieve awareness about the behavior of the mobility scenario it is moving in, and (ii) to identify the role played by the device within the set of other moving devices. These components are combined into a self-configuring forwarding algorithm that uses them to locally install both the utility function and the relevant settings suitable for the sensed configuration. Through of extensive simulations, this paper shows that by properly discriminating between roles it is possible to derive a self-configuring forwarding mechanism that constantly performs well in different mobility settings
Reasoning about multicast in opportunistic networks
No full textMobile computing services are becoming highly
personalized and influenced by user location, social attitudes and interests. This trend is often synthesized with the term behavior-awareness. Behavioral services characterize most of the applications of Opportunistic Networks and advocate a single communication paradigm: multicast. Despite that, multicast is
less studied than unicast and broadcast. We believe that there is not correspondence between problem relevance and research
attention. This paper focuses on the multicast best effort service in opportunistic networks with the aim of better understanding the problem and defining the guidelines for the design of a novel multicast protocol
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