Naércio Magaia

A multi-objective routing algorithm for Wireless Multimedia Sensor Networks

Graphical abstractDisplay Omitted HighlightsA new multi-objective approach for the routing problem in Wireless Multimedia Sensor Networks (WMSNs) is proposed.Classical approximations optimize a single objective or Quality of Service (QoS) parameter.Classical approximations do not take into account the conflicting nature of QoS parameters which leads to sub-optimal solutions.The proposed approach takes into account multiple QoS requirements such as delay and the Expected Transmission Count (ETX).The case studies applying the proposed approach shows clear improvements on the QoS routing solutions. In this paper, a new multi-objective approach for the routing problem in Wireless Multimedia Sensor Networks (WMSNs) is proposed. It takes into account Quality of Service (QoS) requirements such as delay and the Expected Transmission Count (ETX). Classical approximations optimize a single objective or QoS parameter, not taking into account the conflicting nature of these parameters which leads to sub-optimal solutions. The case studies applying the proposed approach show clear improvements on the QoS routing solutions. For example, in terms of delay, the approximate mean improvement ratios obtained for scenarios 1 and 2 were of 15 and 28 times, respectively.

Betweenness centrality in Delay Tolerant Networks

Dynamic networks, in particular Delay Tolerant Networks (DTNs), are characterized by a lack of end-to-end paths at any given instant. Because of that, DTN routing protocols employ a store-carry-and-forward approach, holding messages until a suitable node to forward them is found. But, the selection of the best forwarding node poses a considerable challenge. Additional network information (static or dynamic) can be leveraged to aid routing protocols in this troublesome task. One could use centrality metrics, therefore providing means to differentiate the importance of nodes in the network. Among these metrics, betweenness centrality is one of the most prominent, as it measures the degree to which a vertex is in a position of brokerage by summing up the fraction of shortest paths between other pairs of vertices passing through it. So, in this paper, betweenness centrality is surveyed, that is, its definitions and variants in static and dynamic networks are presented. Also, a survey of standard algorithms used to compute the metric (exact and approximate) is presented. Finally, a survey and a discussion on how DTN routing protocols make use of the betweenness centrality metric and algorithms to aid message forwarding is also presented.

Bundles fragmentation in Vehicular Delay-Tolerant Networks

Vehicular Delay-Tolerant Networks use the delay-tolerant architecture and protocols to overcome the disruptions in network connectivity. These concepts help in cases where the network is sparse or with large variations in density or there is no end-to-end connectivity, by providing a communications solution for non real-time applications. This paper presents data fragmentation techniques to optimize the efficiency of data delivery for the case of the short node contacts that characterize vehicle networks. The techniques were tested in a laboratory environment with portable digital assistants and Lego Mindstorm NXT robotic cars. If no fragmentation is used, only small messages are successfully transferred. Proactive fragmentation fragments messages to a predefined size in the source node. Reactive fragmentation adjusts the fragment sizes to the real duration of the contact when it is broken. Reactive fragmentation showed a good efficiency in adapting the fragmentation in real time to the contact duration. Proactive fragmentation can perform slightly better if the fragment sizes are carefully chosen as it requires less processing. As this choice is difficult, reactive fragmentation is more practical to use.

The Vehicular Delay-Tolerant Networks (VDTN) Euro-NF joint research project

The Vehicular Delay-Tolerant Networks (VTDN) project proposed a novel architecture for VDTN. Besides positioning the bundle layer below the network layer, it employs out-of-band signaling and devises the separation of the control plane and data plane. A laboratory prototype was created to demonstrate this approach. The project also developed new applications, fragmentation mechanisms, content storage and retrieval mechanisms, dropping and scheduling policies, and routing protocols for VDTNs.

Nodes' misbehavior in Vehicular Delay-Tolerant Networks

Vehicular Delay-Tolerant Networks (VDTNs) are composed of mobile nodes that communicate wirelessly with each other to forward data despite connectivity issues. This paper focuses on the problem of some nodes trying to impair the communication of a VDTN. In the paper we study the case of nodes that delay the forwarding of messages that is a particularly difficult to detect form of misbehavior. We study the impact of this form of misbehavior on eight VDTN routing protocols using a large set of simulations and two scenarios. The results show that depending on the type of misbehavior, message replication and intelligent selection of the next hop can help routing protocols to be resilient to node misbehavior.

ePRIVO: An enhanced PRIvacy-preserVing Opportunistic routing protocol for Vehicular Delay-Tolerant Networks

This paper proposes an enhanced PRIvacy preserVing opportunistic routing protocol (ePRIVO) for vehicular delay-tolerant networks (VDTN). ePRIVO models a VDTN as a time-varying neighboring graph where edges correspond to neighboring relationship between pairs of vehicles. It addresses the problem of vehicles taking routing decision meanwhile keeping their information private, i.e., vehicles compute their similarity and/or compare their routing metrics in a private manner using the Paillier homomorphic encryption scheme. The effectiveness of ePRIVO is supported through extensive simulations with synthetic mobility models and a real mobility trace. Simulation results show that ePRIVO presents on average very low cryptographic costs in most scenarios. Additionally, ePRIVO presents on average gains of approximately 29% and 238% in terms of delivery ratio for the real and synthetic scenarios considered compared to other privacy-preserving routing protocols.

FinalComm: Leveraging Dynamic Communities to Improve Forwarding in DTNs

This article proposes a social-based routing protocol for Delay-Tolerant Networks (DTNs) known as FinalComm. FinalComm allows nodes to build a view of the existing communities in the network. With this information, nodes are able to relay messages after computing if the neighbor will most probably meet the destination or any other node from the community of the destination of the message. Simulation results shows that FinalComm is able to achieve a high delivery rate and an extremely low overhead ratio, if compared with four other routing protocols. Specifically, FinalComm presents average gains of 31.4% in terms of delivery rate in comparison with other routing protocols for the scenarios considered.

REPSYS: A Robust and Distributed Reputation System for Delay-Tolerant Networks

Distributed reputation systems can be used to foster cooperation between nodes in decentralized and self-managed systems due to the nonexistence of a central entity. In this paper, a Robust and Distributed Reputation System for Delay-Tolerant Networks (REPSYS) is proposed. REPSYS is robust because despite taking into account first- and second-hand information, it is resilient against false accusations and praise, and distributed, as the decision to interact with another node depends entirely on each node. Simulation results show that the system is capable, while evaluating each nodes participation in the network, to detect on the fly nodes that do not accept messages from other nodes and that disseminate false information even while colluding with others, and while evaluating how honest is each node in the reputation system, to classify correctly nodes in most cases.

LBHD: Drop policy for routing protocols with delivery probability estimation

Delay Tolerant Networks (DTN) are characterized by a lack of end-to-end connectivity. As such, messages (called bundles) can be stored in buffers for a long time. Network congestion can result in poor delivery rates, as bundles are dropped before having a chance of reaching their destination. Some routing protocols, such as the Probabilistic Routing Protocol using History of Encounters and Transitivity (PRoPHET), maintain estimations of delivery probabilities for each destination. In this paper, a new drop policy called Largest Bundles Hosts Deliverability (LBHD) is proposed that considers all the hosts that received a replica of the same bundle, and their respective delivery probability as estimated by PRoPHET. LBHD uses this additional information to better manage congestion. Simulation results show that LBHD achieves the best delivery probability when compared with other drop policies proposed in the literature. The LBHD policy achieved an average delivery rate 37% better than the default Drop Head (FIFO) policy at the price of a 21% increased average delay.