Sujata Pal

Distributed Information-Based Cooperative Strategy Adaptationin Opportunistic Mobile Networks

Cooperation among nodes is a fundamental necessity in opportunistic mobile networks (OMNs), where the messages are transferred using the store-carry-and-forward mechanism, due to sporadic inter-node wireless connectivity. While multiple works have addressed this issue, they are often constrained in their assumptions on solutions (e.g., requirement of central authority, and tracing the recipient nodes for providing reward or punishment). In this work, we address this research lacuna by taking an evolutionary theory-based approach. In evolutionary theory, the players analyze alternative strategies and select the best one to survive in a population. Inspired by this, in this work, we propose a Distributed Information-Based Cooperation Ushering Scheme (DISCUSS) to promote cooperation in message forwarding between nodes. In this scheme, the nodes maintain and exchange information with one another during contacts about the messages created and delivered in the network. Based on this, the nodes evaluate their own performance and compare that with the approximated network performance to adapt the most successful forwarding strategy. Simulation results show that the message delivery ratio in the network improves upto 31 percent, when the nodes dynamically switch their strategies, as compared to the case when they do not. Furthermore, the DISCUSS scheme fared closely to its variant with the nodes having complete knowledge about the network-wide performance.

SeeR: Simulated Annealing-Based Routing in Opportunistic Mobile Networks

Opportunistic Mobile Networks (OMNs) are characterized by intermittent connectivity among nodes. In many scenarios, the nodes attempt at local decision making based on greedy approaches, which can result in getting trapped at local optimum. Moreover, for efficient routing, the nodes often collect and exchange a lot of information about others. To alleviate such issues, we present SeeR, a simulated annealing-based routing protocol for OMNs. In SeeR, each message is associated with a cost function, which is evaluated by considering its current hop-count and the average aggregated inter-contact time of the node. A node replicates a message to another node, when the latter offers a lower cost. Otherwise, the message is replicated with decreasing probability. Moreover, SeeR works based solely upon local observations. In particular, a node does not track information about other nodes, and, therefore, reduces the risk of privacy leaks unlike many other protocols. We evaluated the performance of SeeR by considering several real-life traces under plausible conditions. Experimental results show that, in the best case, SeeR can reduce the average message delivery latency by about 58 percent, when compared to other popular routing protocols.

Contact-based routing in DTNs

Multi-copy replication is an efficient approach for routing a message between a pair of source and destination nodes in a Delay Tolerant Network (DTN). However, such an approach disseminates an undesirable number of replicas of messages, which increases the overhead of the network. To restrain this, disparate routing techniques have evolved that limit the number of copies of the messages. However, in these schemes a message stays undesirably long in the buffer of a node. To address this issue, we propose a contact-based routing algorithm for DTNs that minimizes the average message buffer time of a node, while maintaining a targeted message delivery ratio compared to the existing state-of-the-art routing protocols. Simulation results show that the average message buffer time reduces upto one fourth from the existing quota-based schemes, and the message delivery ratio improves upto 18% over the well-known flooding based schemes.

Rock-Scissors-Paper cycle of cooperation strategies in Opportunistic Mobile Networks

Opportunistic Mobile Networks (OMNs) are characterized by intermittent connectivity among the nodes, which results in lack of end-to-end communication paths. The nodes depend upon the other nodes for forwarding their messages and, therefore, the intermediate nodes play the crucial role of cooperation in forwarding the messages of the others nodes. Many existing mechanisms - for example, incentive- and punishment-based schemes - are costlier in OMNs, since in both of these schemes it is required to trace the recipient nodes for providing credit/punishment. In this work, we study the problem of cooperation by considering three groups of nodes based on three strategies - cooperate, exploit, and isolate. The cooperators help the other nodes for forwarding their messages. The exploiters, on the other hand, use other nodes as free-riders without helping them in forwarding the messages. Finally, the isolators neither take help, nor provide so to the other nodes in forwarding the messages. We investigate the impact of such behaviors on the performance of message delivery using synthetic and real-life traces. The simulation results confirm the formation of a Rock-Scissors-Paper (RSP) cycle, when the sizes of the groups, and hence, the dominating strategy, varies. Further, the delivery ratio of the messages increases upto 20%-35%, when most of the nodes in the network choose to cooperate.

Cooperation in Delay Tolerant Networks

The delay tolerant networking architecture was proposed for the networks where the typical assumptions made for the Internet fails. One of the primary characteristics of such networks is the intermittent connectivity among the nodes, resulting in the lack of end-to-end communication paths. Unlike the Internet, mobile ad-hoc networks (MANETs) and other forms of traditional networks, message transfers in Delay Tolerant Networks (DTNs) follow the store-carry-and-forward paradigm. It is, therefore, crucial that the nodes in DTNs cooperate among themselves to help the messages reach their respective destinations. Such favorable environments, however, are not obtained in the presence of selfish/malicious nodes. In this chapter, we present a survey of the different schemes proposed in the literature to enforce cooperation in DTNs. We identify the different aspects on which nodes in DTNs could cooperate, and review the different schemes proposed for the same. Specifically, we explore in detail the incentive-based and game theory inspired mechanisms adopted for the same. To the best of our knowledge, no survey on cooperation in DTNs has been presented so far.

Evolutionary Game in Wireless Networks

Game theory has been widely used in wireless networks for solving problems of conflict and cooperation among rational agents. A particularly interesting branch of game theory is evolutionary game theory (EGT), where population evolves over time. In EGT, the players circumspectly adapt the most successful strategies over time. This adaptation is done by replicator dynamics. In the first part of this chapter, we take a quick tour of the fundamental concepts in classical and evolutionary game theory. Followed by this, we look at diverse applications of EGT with a focus on communication networks. Subsequently, we discuss about a particularly popular game based, called the Rock-Scissors-Paper (RSP) game. This chapter concludes with an application of the RSP game to OMNs by considering the relationship that exists among different cooperation strategies of the nodes.

Game Theoretic Analysis of Cooperative Message Forwarding in Opportunistic Mobile Networks

In cooperative communication, a set of players forming a coalition ensures communal behavior among themselves by helping one another in message forwarding. Opportunistic mobile networks (OMNs) require multihop communications for transferring messages from the source to the destination nodes. However, noncooperative nodes only forward their own messages to others, and drop others’ messages upon receiving them. So, the message delivery overhead increases in OMN. For minimizing the overhead and maximizing the delivery rate, we propose two coalition-based cooperative schemes: 1) simple coalition formation (SCF) and 2) overlapping coalition formation (OCF) game. In SCF, we consider the presence of a central information center, whereas OCF is a fully distributed scheme. In SCF, coalitions are disjoint, whereas in OCF, a node may be the member of multiple coalitions at the same time. All nodes in a coalition help each other cooperatively by forwarding group messages to the intermediate or destination nodes. The goal of the nodes is to achieve high success rate in delivering messages. The proposed SCF scheme is cohesive, in which disjoint coalitions always combine to form grand coalition. In OCF, a node reaches a stable grand coalition when all the nodes of the OMN are members of overlapping coalition of the node. No node gains by deviating from the grand coalition in SCF and OCF. Simulation results based on synthetic mobility model and real-life traces show that the message delivery ratio of OMNs increase by up to 67%, as compared to the noncooperative scenario. Moreover, the message overhead ratio using the proposed coalition-based schemes reduces by up to about (1/3)rd of that of the noncooperative communication scheme.

Enforcing Cooperation in OMNs

Nodes in OMNs usually suffer from lack of end-to-end communication paths, which makes them to depend upon other intermediate nodes for forwarding their messages. Therefore, the intermediate nodes play the crucial role of cooperation in OMNs. In this chapter, we take a close look at different types of cooperation enforcement schemes proposed for OMNs. These include credit- and reputation-based mechanisms and game theoretic approaches among others. The latter portion of this chapter presents a detailed discussion on the design of a distributed scheme for promoting cooperation in OMNs. The proposed scheme, DISCUSS, is inspired by evolutionary theory. We look at different theoretical aspects as well as the feasibility of its use in real life.

Vehicle Air Pollution Monitoring Using IoTs

Air pollution is a major cause of health problem in urban areas. Vehicles are the major sources of the current air pollution in urban cities. In this work, we proposed a pollution monitoring system for vehicles using IoTs. This system measures the real-time pollution generated by vehicles on road. This paper describes the design of the system for sensing the pollution using sensor, arduino, smart phone and mobile applications for displaying the personalize air pollution information for individual vehicle. We evaluate the proposed approach on real-data experiment and it shows some preliminary results.

Origins and Characteristics

The “traditional” model of networks that we are familiar with fails to work when certain fundamental assumptions, such as availability of end-to-end communications paths and short round-trip times, do not hold true. Delay-tolerant networks (DTNs) were proposed to enable communication in such scenarios by leveraging the store-carry-and-forward mechanism of message transfer. In this chapter, we look at the origins of DTNs, their characteristics, and different variations such as opportunistic mobile networks (OMNs). This chapter also presents a short review of some of the popular research areas in DTNs/OMNs. The chapter concludes with a brief overview of network simulations. Many of these topics would be discussed at a greater depth in the remainder of the book.