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Opportunistic networks are self-organizing dynamic networks that use the communication opportunities presented by node movement to enable data delivery. Due to the indirect nature of inter-node connections and dynamic topology, opportunistic networks are vulnerable to malicious attacks, which poses a great challenge to their security. In this paper, we first propose a trust-based model for the secure routing of opportunistic networks (TBMOR), which incorporates forwarding positive degree (FP) and node activity degree (NA) into the calculation of trust value, evaluates nodes in the network by a dynamic combination of direct trust and indirect trust, and then optimizes the next node list using trust values and pruning strategies. Secondly, this paper extends the network life cycle by dynamically setting up energy thresholds to reduce network redundancy by dynamically partitioning the number of replicas using trust values.Simulation results show that compared to other routers, TBMOR can effectively resist malicious attacks, has a higher message delivery rate and lower transmission latency than other routers. [ABSTRACT FROM AUTHOR]

The intermittent network connectivity and unawareness of global network knowledge are remarkable challenges when designing efficient Position-based Opportunistic Routing (POR) for Delay Tolerant Networks (DTNs). The best progress set selection of POR effectively handles the intermittent connectivity issue and improves the reliable performance of DTNs. Hence, the optimal progress set selection and catching capacity decide the routing reliability of DTN-POR. This paper proposes a context-aware DTN-POR protocol STAP to ensure reliable DTN routing with minimum overhead STAP design is divided into three folds: application diversity and network failures, context-aware best progress set selection, and enhanced caching management. The application diversity and network failure switch the nodes in harsh environments to DTN mode for transmitting the data packets successfully to the destination. Selecting context-aware relay nodes ensures highly successful data transmissions in the absence of end-to-end connectivity. The probability estimation maximizes the data reachability by considering unique node and application-level context attributes in the best progressive set. Finally, the enhanced catching management strategy limits the number of data copies with effective catch invalidation, resulting in minimum overhead. The proposed STAP accomplishes better results in different scenarios and improves the packet delivery ratio with a minimum duplication rate. [ABSTRACT FROM AUTHOR]

Named Data Networking is a consumer-driven network that supports content consumer mobility due to the nature of in-network catching. The catching suppressed unnecessary Interest packets losses by providing an immediate copy of the data and consumer-driven nature influencedthe mobile consumer to resend unsatisfied Interest packet immediately after the handoff. Once the producer moves to a new location, the name prefix changed automatically after handoff to the new router or point of attachment. The entire network lacks the knowledge of producer movement unless if the producer announces its new prefix to update the FIBs of intermediate routers. Lack of producer's movement knowledge causes an increase of handoff latency, signaling overhead cost, Interests packets losses, poor utilization of bandwidth and packets delivery. Therefore, there is needs to provide substantial producer mobility support to minimize the handoff latency, handoff signaling overhead cost, reduce the unnecessary Interest packets loss to improve data packets delivery once a content producer relocated. In this paper, broadcasting strategy is introduced to facilitate the handoff procedures and update the intermediate routers about the producer movement. Hence, analytical investigation result of this paper addresses the deficiency of Kite scheme by minimizing handoff signaling cost and provides data path optimization after the handoff. [ABSTRACT FROM AUTHOR]

Efficient space delay-tolerant network (DTN) routing algorithms have been a hot issue in space network-related research. In this paper, for the problems of high algorithm complexity and high network overhead in space DTN routing algorithms, we introduce a node clustering algorithm and satellite node social attributes in the space DTN routing process and design a spatial delay-tolerant network routing algorithm (CD-SDTN) based on node clustering and social attributes. The algorithm designs the social attributes of the satellite nodes based on the connection frequency of the satellite nodes with the ground station and divides the community using the Circle-k-means algorithm. In the routing process, the center satellite node with the highest activity in the community manages the messages received by the satellite nodes located in the community and plans the forwarding of messages within and between communities. Simulation results show that the CD-SDTN routing algorithm has some advantages in terms of delivery rate, average delay and network overhead compared with Epidemic and Prophet, especially when the number of nodes in the satellite network is large. • CD-SDTN combines satellite node social attributes into routing algorithm. • CD-SDTN uses an improved circle-k-means clustering algorithm. • CD-SDTN proposes a novel definition of social attributes for satellite nodes. • CD-SDTN was significantly more effective compared to Epidemic and Prophet. [ABSTRACT FROM AUTHOR]

In opportunistic networks, opportunistic routing protocols are used for nodes to forward messages, which are the core technology to realize various opportunistic network applications. However, the existing opportunistic routing protocols generally have three problems: Key nodes forwarded too many messages, resulting in unbalanced energy consumption; Delivered message still occupies the cache space of nodes, resulting in the loss of undelivered message; Nodes constantly sense their surroundings and forward messages, resulting in rapid energy depletion. To better solve these problems, this paper proposes HP-ECD: heuristic Prophet routing protocol based on energy balance, cache optimization, and asynchronous dormancy. Based on Prophet, First, the HP-ECD defines the message forwarding benefits based on multiple node attributes and message importance, to realize the energy balance mechanism of nodes. Then, the HP-ECD designs the message delivery list based on the node history information, to realize the cache optimization mechanism of nodes. Finally, the HP-ECD determines whether a node is in dormancy based on the node running status, to realize the asynchronous dormancy mechanism of nodes. Simulation results show that, compared with Epidemic, Prophet, and EC-CW, HP-ECD greatly improves the message delivery rate and average remaining energy, and reduces the routing overhead rate and average storage time. [ABSTRACT FROM AUTHOR]

The maximum flow problem based on a contact graph in Delay-Tolerant Networking (DTN) is very important for routing and data planning. Common deterministic algorithms employing topological graphs with non-time varying to solve the maximum flow between two nodes include Dinic and Improved Shortest Augmenting Path (ISAP). However, these algorithms cannot be directly applied to topological networks with time series changes. Iosifidis.G gave a solution to this problem based on the time expansion graph, but his method requires high storage space, and an increase in the number of nodes results in increasing complexity. In this paper, we propose a method of dismantling and reconstructing the graph to solve the maximum flow problem in a continuously changing network. Compared with the Storage Policy (SP) algorithm of Iosifidis.G, this method does not require equal time slot splitting of each node, but instead uses discretization to reduce the scale of the graph. Finally, we add this algorithm to Contact Graph Routing (CGR) to optimize DTN data transmission, improve data delivery rate, and reduce unnecessary link occupation. Experimental results show that the optimized CGR can increase average delivery rate by 3% and reduce link usage by 4% compared to CGR. [ABSTRACT FROM AUTHOR]

Disasters could cause communication systems to partially or completely down. In such a case, relief operations need a rapidly deployed communication system to save lives. Exchanging information among the rescue team is a vital factor to make important decisions. Communication system required to be robust to failures, rapidly deployable, easily maintainable to provide better services. Wireless ad-hoc networks could be the choice of establishing communication with the aid of existing infrastructure in a post-disaster case. To optimize mobile ad-hoc network performance, address the challenges that could lead to unreliable performance is required. One and the most crucial key challenge is routing information from a sender to a receiver. Due to the characteristics of a disaster environment such as signal attenuation, communication links exist between rescue crew is short-lived, suffer from frequent route breakage, and may result in unreliable end-to-end services. Many routing protocols have been proposed and evaluated in different network environments. This paper presents the basic taxonomy of Mobile Ad Hoc Networks and the state of the art in routing categorizes (Proactive, Reactive, Geographic-aware and Delay tolerant Networks (DTN)). The comparison of existing routing protocols in Mobile Ad-Hoc Networks indicates that overhead in Proactive and Geographic is competitive with delay in Reactive and DTN routing. [ABSTRACT FROM AUTHOR]

Rural networking connectivity is a very dynamic and attractive research field. Nowadays big IT companies and many governments are working to help connect all these rural, disconnected people to Internet. This paper introduces a new routing algorithm that can bring non-real-time Internet connectivity to rural users. This solution is based on previously tested ideas, especially on Delay/Disruption Tolerant Networking technologies, since they can be used to transmit messages to and from difficult to access sites. It introduces the rural connectivity problem and its context. Then, it shows the proposed solution with its mathematical model used to describe the problem, its proposed heuristic, and its results. The advantage of our solution is that it is a low-cost technology that uses locally available infrastructure to reach even the most remote towns. The mathematical model describes the problem of transmitting messages from a rural, usually disconnected user, to an Internet connected node, through a non-reliable network using estimated delivery probabilities varying through time. The forwarding algorithm uses local knowledge gathered from interactions with other nodes, and it learns which nodes are more likely to connect in the future, and which nodes are more likely to deliver the messages to the destination. Our algorithm achieves an equal or better performance in delivery rate and delay than other well-known routing protocols for the rural scenarios tested. This paper adds more simulation results for the proposed rural scenarios, and it also extends the explanation of the mathematical model and the heuristic algorithm from the conference paper "Delay/Disruption Tolerant Networks Based Message Forwarding Algorithm for Rural Internet Connectivity Applications" [1] (doi: 10.1109/ICCCC. 2016.7496732). [ABSTRACT FROM AUTHOR]

Satellite communication networks have been widely used to provide essential communication services, including voice communication, global positioning, message communication, etc. However, sorts of network attacks are easy to be launched in these networks due to the limited computation capability and communication width, long communication delay, and intermittent link connection. In this paper, we first propose a new [E]ncryption-based [M]utual [A]uthentication and [K]ey [U]pdate (EMAKU) protocol in satellite communication networks. Next we analyze the security of the EMAKU protocol under two classic network attacks which are replay attack and man-in-the-middle attack. Finally, experiments show that the EMAKU protocol is 21.5% faster than the traditional encryption-based authentication protocols, and the average time of key update of the EMAKU protocol is about 450.01 ms. [ABSTRACT FROM AUTHOR]

In search and rescue mission, micro aerial vehicles (MAVs) are typically used to capture image and video from an aerial perspective and transfer the data to the ground station. Because of the power limitation, a cluster of MAVs are required for a large search area, hence an ad-hoc wireless network must be maintained to transfer data more conveniently and fast. However, the unstable link and the intermittent connectivity between the MAVs caused by MAVs’ movement may challenge the packet forwarding. This paper proposes a delay tolerant packet forwarding algorithm based on location estimation for MAV networks, called DTNest algorithm. In the algorithm, ferrying MAVs are used to transmit data between MAVs and the ground station, and the locations of both searching MAVs and ferrying MAVs are estimated to compute the distances between the MAVs and destination. The MAV that is closest to the destination is selected greedy to forward packet. If a MAV cannot find the next hop MAV using the greedy strategy, the packets will be stored and re-forwarded once again in the next time slot. The experiment results show that the proposed DTNest algorithm outperforms the typical DTNgeo algorithm in terms of packet delivery ratio and average routing hops. [ABSTRACT FROM AUTHOR]

Locally aware routing protocols base their next-hop selection on information about their immediate neighborhood, gathered by means of a beaconing mechanism. In general, beacons may be proactively broadcasted from nodes to their neighbors (‘receiver-initiated’ beaconing) or may be solicited by the node carrying the routed message (‘on-demand’ beaconing). On-demand beaconing is of growing importance, mainly in more dynamic and sparse environments (e.g., delay tolerant networks), and is addressed in this paper. A generic analysis is provided for the case of periodically issued beacons, linking the beacon period to the trade-off between the quality of neighborhood perception (determining the routing effectiveness) and the required amount of signaling (related to energy expenditure at the nodes). The analysis leads to upper and lower bounds for the length of the beacon period, expressed in terms of mobility characteristics. The paper also investigates policies where the inter-beacon intervals vary adapting to the environment, an approach most beneficial when routing is based on metrics bearing some relevance to time. This is the case with the MAD routing protocol, which incorporates the notion of ‘retaining time’, an estimate of the time that the carrying node will retain the message. It is shown that linking the beacon intervals to the each time applicable retaining time leads to an effective and efficient beacon policy. The paper provides simulation-based evaluation results, validating the beacon period bounds and demonstrating that, for the case of MAD, adaptive beaconing is capable of providing even better performance. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we present a broadcast dissemination protocol for messages in opportunistic networks (OppNet) that is efficient in terms of energy consumption and network capacity usage, while not increasing the number of excluded nodes (nodes not receiving messages). The majority of the OppNet broadcast delivery schemes proposed in the literature, do not take into consideration that reducing energy and buffer usage is of paramount importance in these wireless networks normally consisting of small devices. In our protocol, broadcast messages are limited by carefully selecting their prospective forwarders (storers). The keystone of our protocol is the use of Optimal Stopping Theory, which selects the best message storers at every stage of the algorithm, while holding back broad message dissemination until convenient conditions are met. The broadcast efficiency of the proposed protocol out competes other OppNet broadcast proposals in four well-known scenarios. Furthermore, the protocol reduces the number of both dropped messages and nodes not receiving messages, thus maximising network capacity usage, and the span of the message delivery. [ABSTRACT FROM AUTHOR]

Named Data Networking (NDN) performs its routing and forwarding decisions using name prefixes. This removes some of the issues affecting addresses in our traditional IP architecture such as limitation in address allocation and management, and even NAT translations etcetera. Another positivity of NDN is its ability to use the conventional routing like the link state and distance vector algorithm. In route announcement, NDN node broadcasts its name prefix which consists of the knowledge of the next communicating node. In this paper, we evaluate the performance of mobility management models used in forwarding NDN contents to a next hop. This makes it crucial to select an approach of mobility model that translates the nature of movement of the NDN mobile routers. A detailed analysis of the famous mobility model such as the Random Waypoint mobility and Constant Velocity were computed to determine the mobility rate of the NDN mobile router. Simulation analysis was carried out using ndnSIM 2.1 on Linux Version 16.1. we build and compile with modules and libraries in NS-3.29. The sample of movement of the mobile router is illustrated and our result present the viability of the Constant Velocity model as compared with the Random Way point. [ABSTRACT FROM AUTHOR]

Abstract It has been proved that, in networks with co-existing delay sensitive and delay tolerant traffic flows, the overall network utility can be significantly improved by putting off (or storing) delay tolerant flows until off-peak hours. In our previous work, we proposed Time-Shifted Multilayer Graph (TS-MLG), a routing framework for Store-and-Forward (SnF) optical circuit switched (OCS) networks. With TS-MLG, the scheduling of delay tolerant traffic flows can be determined through a single routing computation. TS-MLG has been shown to be useful in SnF OCS networks of medium size, but the computing time required per traffic flow increases quickly as the network size increases and the number of active requests grows. To control the computational complexity, the number of layers used in routing must be limited, resulting in degradation of network performance. Although the delay caused by computing the end-to-end spatial/temporal path is negligible compared to the overall end-to-end transmission delay, it decides the scalability of the control plane. This prevents TS-MLG from being used in large-scale networks. In this paper, we aim to increase the scalability of the TS-MLG, by taking into account the graph sparsity. Instead of running Dijkstra Algorithm on adjacency matrices, we propose to use adjacency list to represent the graph, and Breadth-First Search Algorithm to compute shortest paths. This reduces the computational complexity from O(N 2 × L 2 ) to O(N × L + E), in which N is the number of network nodes, L is the number of layers used in routing and E is the number of edges, with a slightly increased overhead in graph update. We verify the effectiveness of the proposed algorithm by performing a large number of computations on the same hardware platform. In a network containing 30 nodes, and when the number of layers is limited to 20, the average time needed to complete 1000 routing computations with the proposed solution is 1.597 s, while that for the original one is 244 s. The proposed solution effectively scales up TS-MLG and make it suitable for large-scale networks. [ABSTRACT FROM AUTHOR]

Abstract Delay Tolerant Networks (DTNs) have attracted much research interest recently due to its adaptability in areas without infrastructures. In such scenarios, moving data from one place (landmark) to another place (landmark) is essential for data communication between different areas. However, current DTN routing algorithms either fail to fully utilize node mobility or have additional requirements that cannot be satisfied easily in DTNs. Therefore, in this paper, we propose a distributed greedy routing algorithm, namely GreedyFlow, for efficient packet routing between landmarks in DTNs. GreedyFlow builds a local traffic map and a global landmark map on each node. The local traffic map indicates the node's knowledge about the amount of traffic (node transition) between landmarks in the area where it primarily visits. The global landmark map shows the distribution of landmarks in the system and is built offline. In packet routing, the global landmark map shows the general packet forwarding direction, while the local traffic map helps determine the next-hop landmark on the fastest path in the forwarding direction. As a result, packets are greedily forwarded toward their destination landmarks. We also propose advanced components to enhance the consistency of local traffic maps and exploit node-based forwarding, both of which help improve the packet routing efficiency. Extensive real trace driven experiments demonstrate the high efficiency of GreedyFlow. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a performance evaluation through simulations and a comparative study of main routing protocols dedicated to Vehicular Delay-Tolerant Networks. The assessment is conducted under small- and large-scale scenarios with realistic vehicle mobility patterns as defined in the TAPAS Cologne simulation scenario. Through the literature, several evaluations have been conducted on routing for Vehicular Networks, but with an abstraction or a simplification regarding the delay tolerant aspect. Furthermore, considered scenarios were relatively small and too idealistic compared to the real-world environment and its multiples challenges. Moreover, to the best of our knowledge, this is the first extensive study that compares, in the same realistic simulation environment, the main flag-carriers of various categories of VDTN routing protocols, namely Epidemic, Direct Delivery, Prophet and GeoSpray protocols. Simulation results reveal better performance for the geographical approach advocated by GeoSpray compared to the predictive one of Prophet, under all considered scenarios. Moreover, they highlight the possibility for a minimalist and naive protocol such as Direct Delivery to perform well, under specific network conditions, as when considering an anycast communication scheme. Finally, deeper analysis was undertaken on both GeoSpray and Prophet. The studies reveal the potentialities to increase the performances of GeoSpray to some extent and highlight the difficulties of adapting Prophet settings for optimal performance in realistic scenarios. [ABSTRACT FROM AUTHOR]

Abstract Delay or Disruption tolerant networks (DTNs) are mobile networks with inherent limitations on network connectivity and topology. There are a number of applications where such networks can be deployed. In extreme situations of lack of connectivity, DTNs nodes stores the messages to the destination and carry it, till it finds and suitable relay node to forward. Most of the existing researchers focused on developing smart relay selection strategies for DTNs. However, the security aspects, such as confidentiality and integrity of the messages being transmitted have been grossly overlooked in the existing DTN routing literature. Hence in this paper, we have addressed the security issues in DTN message forwarding and developed a secure method for message forwarding in DTN. Experimental results show that by incorporating the security features, DTN performance metrics, such as delivery ratio, overhead ratio and delivery delay have been improved compared to traditional routing strategies. [ABSTRACT FROM AUTHOR]

This paper considers mobility control to improve packet delivery in delay-tolerant networks (DTNs) under group mobility. Based on the group structure in group mobility, we propose two mobility control techniques; group formation enforcement and group purposeful movement. Both techniques can be used to increase the contact opportunities between groups by extending the group's reachability. In addition, they can be easily integrated into some existing DTN routing schemes under group mobility to effectively expedite the packet delivery. This paper is divided into 2 parts. First, we study how our proposed mobility control schemes reduce the packet delivery delay in DTNs by integrating them into one simple routing scheme called group-epidemic routing (G-ER). For each scheme, we analytically derive the cumulative density function of the packet delivery delay to show how it can effectively reduce the packet delivery delay. Then, based on our second proposed technique, the group purposeful movement, we design a new DTN routing scheme, called purposeful movement assisted routing (PMAR), to further reduce the packet delay. Extensive simulations in NS2 have been conducted to show the significant improvement of PMAR over G-ER under different practical network conditions. [ABSTRACT FROM AUTHOR]

The Near Field Communication (NFC) is designed for sending small data, which size does not exceed the several dozen bytes, for distance not higher than two inches. The NFC can be used in store-carry-forward scenarios which are bases for Disruptive Tolerant Networks (DTN). The aim of this paper is proposal how to use NFC in transmission of large data in DTN. We propose an algorithm of fragmenting, sending and receiving data. We described software which was used in our prototype and discussed about implementation. Finally we showed results of tests performed on our model. Obtained results presents well characteristics of our solution. [ABSTRACT FROM AUTHOR]

The Internet of Things (IoT) has successfully revolutionized our society and all aspects of our daily lives. Wake-up radio (WuR) technology on its part has contributed to the success of IoT by significantly reducing latency and power consumption. Moreover, emerging mission critical Industrial IoT (IIoT) applications are time sensitive and generate more stringent delay and reliability constraints. Therefore, WuR-based MAC protocols must be carefully designed to meet these requirements. In this paper, a Dual-Mode MAC protocol (D2MAC) is proposed to fulfill QoS requirements of both delay-tolerant and real-time IoT applications by using service differentiation in the context of WuR-based IoT networks. Our protocol adopts two operation modes: normal mode, used in the case of normal traffic conditions, and priority mode for time–critical data. A Markov chain model is used to evaluate the performance of D2MAC. A simulation model based on MiXiM/ OMNet++ framework is also proposed to validate this analytical model. We illustrate the benefits of using the priority mode (PCA-WuR) to fulfill the requirements of IIoT applications. We also demonstrate that the Performance of PCA-WuR strongly depends on the acceptable delay limit for packet transmission. [ABSTRACT FROM AUTHOR]

Due to the uncertain of connections in Delay Tolerant Networks (DTNs), most routing algorithms in DTNs need nodes to forward the message to others based on the opportunistic contact. The contact is related with the beaconing rate. In particular, nodes have more chances to encounter with each other with bigger beaconing rate, but more energy will be used. On the other hand, if the nodes forward the message to every node all the time, the efficiency of the routing algorithm is better, but it needs more energy, too. This paper tries to exploit the optimal beaconing rate and forwarding rate when the total energy is constraint. First, a theoretical framework is proposed, which can be used to evaluate the performance with different forwarding rate and beaconing rate. Then, this paper formulates a joint optimization problem based on the framework. Through Pontryagin's Maximal Principle, this paper obtains the optimal policy and proves that both the optimal forwarding and beaconing rates conform to threshold form. Simulation results show the accuracy of the theoretical framework. Extensive numerical results show that the optimal policy obtained in this paper is the best. [ABSTRACT FROM AUTHOR]

This paper investigates the use of unmanned aerial vehicles (UAVs)/drones for providing high data rates to mobile relays (MRs) placed on top of high speed train wagons, thus introducing the concept of Travel Hopping Enabled Resource Allocation (THEResA). The objective is to provide high data rate connectivity to train passengers in 5G+/6G networks. With the drone flying at the same train speed, highly directive beams can be formed and steered between the drone and each of the MRs. The simulation results in the paper show that this leads to high data rate connectivity, which will be reflected in the indoor links between the MRs and the train passengers inside the wagons. The drones maintain the connectivity to the cellular infrastructure by using high speed links with the cellular base stations (BSs) deployed along the rail track, e.g., through free space optics (FSO). The drones use the BS sites for recharging and resuming their operation. Therefore, a separate set of drones, or the same drones when they are not flying over trains, can be used to provide connectivity to remote rural areas. In fact, high speed trains might travel through rural areas with low population density. Although it is practical to lay fiber optic cables along the rail track, villages and small rural population agglomerations far from the railroad might not have access to the internet backhaul. UAVs can provide this connectivity in a delay tolerant fashion, by heading from the BSs/train station sites towards remote areas, collecting/transferring data from/to these areas, then returning to the sites along the rail track to recharge their batteries. This paper presents an analysis that shows the feasibility of this approach. [ABSTRACT FROM AUTHOR]

With the advance of Massively Parallel Computers usage, the interconnect technology overcomes the limitations of communication as a new concept. One of the most significant challenges in this concept is suitable architecture for these networks’ applications. Recently, x-Folded TM architecture was introduced as a desirable design in interconnection networks. The attractive features for x-Folded TM are less number of links and nodes compared with other architectures. This paper proposes a new mathematical model of x-Folded TM architecture to predict the average network delay under the transpose traffic pattern. Besides the mathematical model derivation for x-Folded TM architecture, we discuss the simulation experiment in x-Folded TM using the same assumptions for the purpose of validation. The mathematical results indicate that the average network delay for x-Folded TM architecture is reduced when compared with other topologies under transpose traffic pattern. The implementation of x-Folded TM architecture relies on simulations to evaluate the performance impact of the architecture as well. Consequently, all results yield the superiority of the x-Folded TM performance compared to the other networks. [ABSTRACT FROM AUTHOR]

Delay-tolerant networks (DTNs) (e.g., Internet, satellite networks, sensor networks, ad hoc networks) have attracted considerable attentions in both academia and industry. As a fundamental problem, the maximum flow is of vital importance for routing and service scheduling in networks. For solving the maximum flow problem of the DTN, an appropriate model should be built first. Compared to the conventional snapshot approach to model the DTN topology, the time aggregated graph (TAG) is capable of accurately characterizing the intermittent connectivity and time-varying capacity for each edge, and thus has been acted as a suitable model for modeling DTNs. However, existing TAG-related works only focus on solving the shortest path problem, and neither the correlation between time intervals nor nodes storage of a DTN are described in TAG, resulting in a non-trivial maximum flow problem in TAG. In this paper, we study the maximum flow problem through our proposed storage time aggregated graph (STAG) for DTNs. First, an intermediate quantity named bidirectional storage transfer series is introduced to each node in STAG, and the corresponding transfer rule is also designed for this series to model the correlation between time intervals. Next, on the basis of the storage transfer series, a STAG-based algorithm is proposed and described in detail to maximize the network flow. In addition, we analyze the effectiveness of the proposed algorithm by giving an illustrative example. [ABSTRACT FROM AUTHOR]

Delay-tolerant Network is rapidly developed as one of the challenged networks. Currently, only a few studies focus on the flexibility of replicas distribution strategy and the existing routing protocols adapted to changing workload are only qualitatively adjusted. In this paper, we present a novel routing protocol in which the replicas can be both quantitatively and qualitatively adjusted, called Adaptable Quota-Stretchy Routing protocol (AQSR). To let the delivery ratio fall in the pre-set range under constraints of given deadline and limited buffer capacity, this work presents two strategies: 1) adapting the state of message copies to the changing work load; 2) Establish a mechanism to recycle the messages in minor state. Moreover, we propose a buffer management strategy accordingly. Experiment results demonstrate that our protocol has better performance in delivery ratio and network adaptation. [ABSTRACT FROM AUTHOR]

Opportunistic routing (OR) paradigms in vehicular networks via opportunistic candidate set selection have a better performance over the pre-defined next-hop node in terms of packet delivery rate. Nevertheless, uneven vehicle distribution, highly dynamic topology, varying link interference, and bandwidth restrictions impose drastic challenges for satisfying applications requirements in static prioritizing candidate set selection policies. Besides, fulfilling quality of service (QoS) requirements of heterogeneous applications, due to the limited local topology perspective and many involving conflicting routing criteria, will be further compromised. Considering the candidate set selection policy as a Multi-Criteria Decision Making (MCDM) task, an adaptive two-hop cooperative forwarding set selection strategy called APFS is proposed in this paper. By developing a local topology perspective to the two-hop neighbor information, the APFS scheme jointly considers indicators of link stability, delay assessment, and link good-put as routing criteria. Analytical Hierarchy Process (AHP) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) methods are employed in two different scenarios in prioritizing candidate forwarding sets. First, classical AHP-TOPSIS technique with a mutable pair-wise comparison matrix is applied, and then Neutrosophic Set (NS) is combined with the classical AHP-TOPSIS method to handle ambiguous vehicular environments. The simulation results show that the APFS strategy using both prioritization policies have significantly improved the performance of packet delivery ratio, average end-to-end delay, throughput, and hop counts as compared to other schemes. [ABSTRACT FROM AUTHOR]

In urban areas, the population density is still growing (the population density starts exceeding 20.000 inhabitants per km 2 ), and so, the density of mobile users becomes very important. People are moving from home to work, from work to active places. One can take benefit of the mobility and the density to justify DTN (Delay Tolerant Network) approach protocol to convey sms (or alternative messaging services) traffic. Indeed, the mobility of users, especially during the day, create an ad hoc mobile network where the nodes are the smartphones hold by mobile clients. In this paper, their performance evaluations are based on a measurement and analysis of sms traces coming from a nationwide cellular telecommunication operator during a two month period, we propose several DTN like basic network protocols for delivering sms . We perform a temporal and spatial analysis of the Mexico City cellular network considering geolocalized sms to characterize the traffic. Such key characterization allows us to answer the question: is it possible to transmit sms using phones as relay in a large city such as Mexico City? We define four network protocols to transmit sms from a source to a destination. We study a mobile dataset including 8 Million users living in Mexico city. This gives us a precise estimation of the average transmission time and the global performance of our approach. Our analysis shows that after 30 min, half of the sms are delivered successfully to destination. On the contrary to the cellular networks, we explain how much the potentiality of the mobile users network can take benefit from complementary properties such as the locality of sms , the density of phones in Mexico City and the mobility of phone users. Moreover, we show that in a realistic scenario, our approach induces reasonable storage cost. [ABSTRACT FROM AUTHOR]

Controlling congestion is critical to ensure adequate network operation and performance. That is especially the case in networks operating in challenged- or extreme environments where episodic connectivity is part of the network’s normal operation. Consequently, the “pure” end-to-end congestion control model employed by the Internet is not adequate. Our goal is to study congestion control mechanisms that have been proposed for these so-called disruption tolerant networks, or DTNs. In this paper, we conduct a performance study comparing existing DTN congestion control mechanisms for two main application domains, namely: inter-planetary (IPN) and terrestrial networking applications. Our results confirm that congestion control helps increase message delivery ratio, even in highly congested network scenarios. Furthermore, the results show that existing DTN congestion control mechanisms do not perform well in IPN scenarios. Our study also suggests that good design principles for congestion control in DTN scenarios include: combining reactive and proactive control, using local information instead of global knowledge, and employing mechanisms that are routing protocol independent. One important conclusion from our quantitative study is that there is currently no universal congestion control mechanism that fits all DTN scenarios and applications. [ABSTRACT FROM AUTHOR]

This paper proposes a proactive fragmentation mechanism for an optimal DTN message transfer. DTN message transfer is presented to give coverage to a terrestrial sensor network by using a nanosatellite communications link. Satellite communication is modeled with a multi-access mechanism with priority in downlink traffic (ALOHAGP). This new multiple access protocol is based on unslotted ALOHA extended with an adaptive contention mechanism. It uses satellite feedback to implement the congestion control, and to dynamically adapt the channel effective throughput in an optimal way. The effective throughput has been optimized by adapting the protocol parameters as a function of the current number of active sensors received from satellite. Also, regarding the optimal size of a bundle, there is a lack of standard negotiation methods of bundle sizes that can be accepted by a bundle agent in satellite communications. Thus, too large bundles are dropped and too small messages are inefficient. We have characterized this kind of scenario obtaining a probability distribution for frame arrivals to nanosatellite and visibility time distribution providing an optimal proactive fragmentation of DTN bundles. We have found that the proactive effective throughput (goodput) reaches in some cases almost 97% of the reactive fragmentation approach. [ABSTRACT FROM AUTHOR]

How to deliver data to, or collect data from the hundreds of thousands of sensors and actuators integrated in “things” spread across virtually every smart city streets (garbage cans, storm drains, advertising panels, etc.)? The answer to the question is neither straightforward nor unique, given the scale of the issue, the lack of a single administrative entity for such tiny devices (arguably run by a multiplicity of distinct and independent service providers), and the cost and power concerns that their direct connectivity to the cellular network might pose. This paper posits that one possible alternative consists in connecting such devices to their data collection gateways using “oblivious data mules”, namely transport fleets such as taxi cabs which (unlike most data mules considered in past work) have no relation whatsoever with the smart city service providers, nor are required to follow any pre-established or optimized path, nor are willing to share their LTE connectivity. We experimentally evaluate data collection and delivery performance using real world traces gathered over a six month period in the city of Rome. Results suggest that even relatively small fleets, such as an average of about 120 vehicles, operating in parallel in a very large and irregular city such as Rome, can achieve an 80% coverage of the downtown area in less than 24 h. [ABSTRACT FROM AUTHOR]

Campus networks are featured by intermittent connection and dynamically changing topology. Due to these factors, a campus network becomes a typical scenario of delay-tolerant network (DTN). In order to ensure routing efficiency in a campus DTN, in this paper, we record the movement paths and mutual encounter numbers of the nodes and regard the quantified social characteristic as the weight of the edges between node pairs, and then a weighted graph of the network topology is obtained. Clusters including nodes with high intimacy between each other are extracted utilizing a topological cutting method. Subsequently, messages are forwarded according to the nodes' degrees of cohesion and outreach. As a result, we propose a clustering routing method based on social characteristic in DTN. Simulations based on the synthetic mobility pattern and real trace are conducted in ONE. The results show that the method can achieve about 10% higher delivery ratio and 200s less average delay than the other routing protocols. In other words, the method improves the delivery ratio and reduces the average delay in DTN. [ABSTRACT FROM AUTHOR]

One of the applications of Delay Tolerant Networking (DTN) is rural networks. For this application researchers have argued benefits on lowering costs and overcoming challenging conditions under which, for instance, protocols such as TCP/IP cannot work because their underlying requisites are not satisfied. New responses are required in order to understand the true adoption opportunities of this technology. Constraints in service level agreements and viable alternative pricing schemes are some of the new issues that arise as a consequence of the particular operation mode. In this paper, we propose a novel model for pricing delay tolerant services, which adjusts prices to demand variability subject to constraints imposed by the DTN operation. With this model we also show how important parameters such as channel rental costs, cycle times of providers, and market sensitivities affect business opportunities of operators. [ABSTRACT FROM AUTHOR]

Delay Tolerant Networks (DTNs) often suffer from intermittent disruption due to factors such as mobility and energy. Though lots of routing algorithms in DTNs have been proposed in the last few years, the routing security problems have not attracted enough attention. DTNs are still facing the threats from different kinds of routing attacks. In this paper, a general purpose defense mechanism is proposed against various routing attacks on DTNs. The defense mechanism is based on the routing path information acquired from the forwarded messages and the acknowledgment (ACK), and it is suitable for different routing schemes. Evolutionary game theory is applied with the defense mechanism to analyze and facilitate the strategy changes of the nodes in the networks. Simulation results show that the proposed evolutionary game theory based defense scheme can achieve high average delivery ratio, low network overhead and low average transmission delay in various routing attack scenarios. By introducing the game theory, the networks can avoid being attacked and provide normal transmission service. The networks can reach evolutionary strategy stable (ESS) under special conditions after evolution. The initial parameters will affect the convergence speed and the final ESS, but the initial ratio of the nodes choosing different strategies can only affect the game process. [ABSTRACT FROM AUTHOR]

In conventional networks, routing problem can be modeled as the design of an efficient source-to-destination route based on persistent end-to-end paths. However, in a delay tolerant network (DTN), nodes are intermittently connected and thus, the end-to-end paths will not always exist, in which routing is a challenging issue. Previous DTN routing protocols tend to make routing decision based on the nodes’ contact information. In this paper, we observe that considering both the nodes’ contact information and message property such as the time-to-live (TTL) would help to improve the performance. Embedded this idea, we first propose an expected encounter based routing protocol (EER) which distributes multiple replicas of a message proportionally between two encounters according to their expected encounter values. In case of a single replica of a message, EER makes the routing decision by comparing two encountering nodes’ minimum expected meeting delays to destination. We further propose a community aware routing protocol (CAR) which takes advantages of the high contact frequency property of the nodes within the same community. We also propose the buffer management strategies corresponding for the two protocols. We conduct simulations to evaluate our proposed protocols and some existing ones on three metrics: delivery ratio, latency and goodput. The simulation results illustrate that our proposed EER and CAR protocols outperform other existing ones. [ABSTRACT FROM AUTHOR]

Nowadays, distributed storage is adopted to alleviate Delay-tolerant networking (DTN) congestion, but reliability transmission during the congestion period remains an issue. In this paper, we propose a multi-custodians distributed storage (MCDS) framework that includes a set of algorithms to determine when should appropriate bundles be migrated (or retrieved) to (or from) the suitable custodians, so that we can solve DTN congestion and improve reliability transmission simultaneously. MCDS adopts multiple custodians to temporarily store the duplications of migrated bundle for releasing DTN congestion. Thus, MCDS has more opportunities to retrieve the migrated bundles when network congestion is mitigated. Two performance metrics are used to evaluate the simulation results: the goodput ratio (GR) that represents QoS of data transmission, and the retrieved loss ratio (RLR) that reflects the performance of reliability transmission. We also use another distributed storage mechanism based on single-custodian distributed storage (SCDS) to evaluate MCDS. Simulation results show that MCDS has better GR and RLR in almost all simulation cases. For various scenarios, the GR and RLR of MCDS are in the range of 10.6%-18.4% and 23.2%-36.8%, respectively, which are higher than those of SCDS. [ABSTRACT FROM AUTHOR]

In this paper, we propose EPCM (Efficient Prediction-based Context-awareness Matrix) algorithm analyzing connectivity by predicting a cluster's context data such as velocity and direction. In the existing DTN, unrestricted relay node selection cause increasing delay and packet loss as well as overhead from limited storage and capability. The proposed EPCM algorithm analyzes the predicted context data using context matrix and adaptive revision weight, and selects relay node by considering connectivity between the cluster and the base station. To predict the context data, the proposed EPCM algorithm stores the context data in the context matrix at regular time and analyzes stored context data according to the variation of context data. The mobility of relay node can determine to combine the current context data value with the variation of context data. In order to eliminate the error from the irregular movement of the node, we use the adaptive revision weight to evaluate the reliability of the context data stored in the context matrix. Though the predicted context data, we know that any node can move toward the base station and can select relay node among the neighbor node to transfer the message more efficiently. We simulate the packet delivery ratio both of the proposed EPCM algorithm and PROPHET algorithm selecting relay node according to node-to-node contact. Our results of simulation demonstrate the efficiency of the EPCM algorithm that provide the higher packet delivery ratio by applying the context data such as velocity and direction in the relay node selection process. [ABSTRACT FROM AUTHOR]

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In this paper, we use graph analysis to evaluate the network architecture of a large scale delay tolerant network (DTN) of transoceanic aircraft. At LCN (Local Computer Networks) 2014 we analyzed information propagation inside a pure opportunistic version of this network, a scenario constructed from more than 2,500 traces of transatlantic flights in which communications relied only on the sporadic contacts between airplanes. As only a small percentage of the nodes were capable of performing efficient air-to-ground communications we concluded the need to devise a more suitable network architecture by combining opportunistic and satellite communication systems. We propose a generic methodology based on graph analysis (both static and dynamic temporal) to evaluate the different ways to create this new architecture. We show the architectural combination that most improves the network delivery performance while minimizing its deployment costs. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The evolution of VDTN routing came to solve the problem of routing in sparse Vehicular Ad-hoc Networks (VANETs). Recently, the implication of Unmanned Aerial Vehicles (UAVs) in VANET communication has gathered quicker information dissemination than Roadside Units (RSUs) in urban VANETs, where ground vehicles' mobility is restricted by the topology of city roads. Gradually, UAVs are emerging for VDTNs: UAV-aided VDTN (UVDTN) routing field has been introduced for sparse areas in order to reduce the network gaps between Vehicle-to-Vehicle (V2V) connections. Meanwhile, the conventional UVDTN routing protocols expose the short contact opportunity time in the case of Vehicle-to-UAV (V2U) and UAV-to-Vehicle (U2V) connections. This constraint entails more congested bundles' flooding rates and a higher number of lost bundle copies compared to V2V-based forwarding. In this paper, a bio-inspired UVDTN routing protocol is conceived to improve the bundles' forwarding between ground vehicles and UAVs in terms of flooding optimization and Quality-of-Service (QoS) performances for urban VANET environments. For this purpose, a swarm-inspired approach called the Social Spider Optimization (SSO) is proposed. SSO seeks to find a better selection of next Store-Carry-and-Forward (SCF) relay nodes specifically for V2U and U2V connections. In order to control the bundle replication rate and enhance bundles' delivery ratio and delay, the proposed bio-inspired UVDTN protocol adjusts the SCF selection decision. The latter is based on predefined historical knowledge-based forwarding parameters and urban geographic topology information. The proposed bio-inspired routing protocol is simulated using the Opportunistic Network Environment (ONE) simulator and compared to a few VDTN and UVDTN routing protocols. [ABSTRACT FROM AUTHOR]

Delay Tolerant Network (DTN) is a kind of network in which the source may not be able to establish the stable and uninterrupted path to destination due to network partitioning, dynamic topology change and frequent disconnections. In order to dealt disruption and disconnections a store, carry and forward paradigm is used in which node stores the incoming messages in its buffer, carries it while moving and forward when comes within the transmission range of other nodes. Message forwarding contributes and important role in increasing its delivery. For instance, probabilistic routing protocol forwards message to a node having high probability value to meet message destination. These protocols cannot handle a situation in which the node continually transmits messages even the probability difference is very small. In this paper, we have proposed a routing protocol known as Threshold Based best custodian Routing Protocol (TBbcRP) for delay tolerant network. We have proposed a threshold-based method to compute the quality value which is the ability of node to carry message. A self-learning mechanism has been used to remove the delivered messages from the network. Moreover, a buffer aware mechanism has been used that make sure availability of buffer space at receiver before message transmission. We have compared the performance of TBbcRP with Epidemic, PRoPHET and Delegated Forwarding. The proposed TBbcRP outperforms in terms of maximizing the delivery probability, reducing number of transmissions and message drop. [ABSTRACT FROM AUTHOR]

Delay-tolerant networks (DTNs) are network environments that are subject to delays and disruptions. Traditional end-to-end routing protocols fail in such challenging network conditions because of intermittent connections and/or long delays. Research results have shown that per-hop forwarding of multiple copies of the same message to the destination can produce satisfactory routing performance in DTNs. Current methods rely on the fixed setting of a quota value to limit the number of message copies. This paper proposes a dynamic quota-control mechanism, allowing routing to operate effectively with different traffic loads. To remove useless message copies from the network, a low-cost probability-based method is also presented. The proposed routing framework is then extended to interest-based information dissemination, which is used to efficiently disseminate an event message to all interested users. A performance evaluation was conducted using a real social contact trace, and performance comparisons with other DTN routing protocols are provided. [ABSTRACT FROM AUTHOR]

The current Internet design is not capable of supporting communications in environments characterized by very long delays and frequent network partitions. To allow devices to communicate in such environments, delay-tolerant networking solutions have been proposed by exploiting opportunistic message forwarding, with limited expectations of end-to-end connectivity and node resources. Such solutions envision non-traditional communication scenarios, such as disaster areas and development regions. Several forwarding algorithms have been investigated, aiming to offer the best trade-off between cost (number of message replicas) and rate of successful delivered message. Among such proposals, there has been an effort to employ social similarity, inferred from users’ mobility patterns, to improve opportunistic forwarding solutions. However, such proposals present two major drawbacks: first, they focus on distribution of intercontact times over the complete network structure, ignoring the impact that human behavior has on the dynamics of the network; and second, most of the proposed solutions look at challenging networking environments where networks have low density, ignoring the potential use of delay-tolerant networking to support low cost communications in networks with higher density, such as urban scenarios. This paper presents a study of the impact that human behavior has on opportunistic forwarding. Our goal is twofold: (i) to show that performance in low and high density networks can be improved by taking the dynamics of the network into account; and (ii) to show that delay-tolerant networking can be used to reduce communication costs in networks with high density by considering the users’ behavior. [ABSTRACT FROM AUTHOR]

Delay and disruption tolerant networks (DTNs) may experience frequent and long-lived connectivity disruptions. Unlike traditional networks, such as the TCP/IP-based Internet, DTNs are often subject to high latency caused by very long propagation delays (e.g., interplanetary communication) and/or intermittent connectivity. Another feature that sets DTNs apart from conventional networks is that there is no guarantee of end-to-end connectivity between source and destination. Such distinct features pose a number of technical challenges in designing core network functions such as routing and congestion control. In this paper, we survey the state-of-the-art in DTN congestion control. We propose a taxonomy to map the DTN congestion control design space and use it to classify existing DTN congestion control mechanisms. [ABSTRACT FROM AUTHOR]

The increasing pervasiveness of mobile devices with networking capabilities has led to the emergence of Mobile Delay Tolerant Networks (MDTNs). The characteristics of MDTNs, which include frequent and long-term partitions, make message routing a major challenge in these networks. Most of the existing routing protocols either allocate an unlimited number of message copies or use a fixed number of message copies to route a message towards its destination. While the first approach unnecessarily floods the network, the rigidity of the second approach makes it inefficient from the viewpoint of message replication. Hence, the question that we address in this paper is: “how to dynamically allocate message copies in order to strike a balance between the delay and cost of message delivery?”. We present a novel adaptive multi-step routing protocol for MDTNs. In each routing step, our protocol reasons on the remaining time-to-live of the message in order to allocate the minimum number of copies necessary to achieve a given delivery probability. Experiment results demonstrate that our protocol has a higher delivery ratio and a lower delivery cost compared to the state-of-the-art Spray-and-Wait and Bubble protocols. [ABSTRACT FROM AUTHOR]

Internet access can improve people's life quality by helping them to reduce and overcome the poverty and educational gaps. However, most rural communities in the world, specially in underdeveloped countries, do not have access to the Internet. Delay/Disruption Tolerant Networking (DTN) is a recent low-cost technology now being used to provide connectivity to rural towns were some transportation means periodically arrive. DTNs can be implemented to connect communities to Internet, since this technology takes advantage of the existing people's transportation infrastructure using it to move packets and messages to and from Internet. This paper proposes a DTN mathematical optimization model that maximizes the availability probabilities of the paths from sources to destinations. We also present an opportunistic forwarding algorithm that takes into account the availability probability of a node's neighbors to decide if a node should forward a message or store the message until a node with a higher availability probability contacts it. This algorithm was tested in five different scenarios and in all of them it found a path to the destination. [ABSTRACT FROM AUTHOR]

In wireless networks, topology control can improve energy effectiveness and increase the communication capacity. In predictable delay tolerant networks (PDTNs), intermittent connectivity, network partitioning, and long delays make most of the researchers focus on routing protocol, and the research on topology control is in the very early stage. Most existing topology control approaches for PDTN assume the underlying connections are deterministic, which excludes a large amount of probabilistic connections existing in the challenged environments. In this paper, probabilistic connections are taking into consideration. The predictable delay tolerant networks are modeled as a three dimensional space–time weighted directed graph which includes spatial, temporal and connection probability information. The topology control problem is formulated as finding a sub graph to balance the energy cost and data transferring reliability. This problem is proved to be NP-complete, and two heuristic algorithms are proposed to solve the problem. The first one is to find a sub graph that assures the maximum connection probability between each pair of nodes. The other one is to find the sub graph in which the connection probabilities between each pair of nodes satisfy the given threshold with the minimum energy cost. Extensive simulation experiments demonstrate that the proposed topology control algorithms can achieve our goal. [ABSTRACT FROM AUTHOR]

Social Delay Tolerant Networks (SDTNs) are a special kind of Delay Tolerant Network (DTN) that consists of a number of mobile devices with social characteristics. The current research achievements on routing algorithms tend to separately evaluate the available profit for each prospective relay node and cannot achieve the global optimal performance in an overall perspective. In this paper, we propose a Movement Pattern-Aware optimal Routing (MPAR) for SDTNs, by choosing the optimal relay node(s) set for each message, which eventually based on running a search algorithm on a hyper-cube solution space. Concretely, the movement pattern of a group of node(s) can be extracted from the movement records of nodes. Then the set of commonly visited locations for the relay node(s) set and the destination node is obtained, by which we can further evaluate the co-delivery probability of the relay node(s) set. Both local search scheme and tabu-search scheme are utilized in finding the optimal set, and the tabu-search based routing Tabu-MPAR is proved able to guide the relay node(s) set in evolving to the optimal one. We demonstrate how the MPAR algorithm significantly outperforms the previous ones through extensive simulations, based on the synthetic SDTN mobility model. [ABSTRACT FROM AUTHOR]

Nowadays the growing popularity of wireless networks, combined with a wide availability of personal wireless devices, make the role of human mobility modeling more prominent in wireless networks, particularly in infrastructure-less networks such as Delay Tolerant Networks and Opportunistic Networks. The knowledge about encounters’ patterns among mobile nodes will be helpful for understanding the role and potential of mobile devices as relaying nodes. Data about the usage of Wi-Fi networks can be exploited to analyze the patterns of encounters between pairs of mobile devices and then be extrapolated for other contexts. Since human mobility occurs in different spatial and temporal scales, the role of scale in mobility modeling is crucial. Although spatial properties of mobility have been studied in different scales, by our knowledge there is no fundamental perspective about human mobility properties at different temporal scales. In this paper we evaluate the connectivity properties of node encounters at different temporal durations. We observed that connectivity properties of node encounters follow almost the same trends in different time intervals, although slopes and exponential decaying rates may be different. Our observations illustrate that networks formed from encounters of nodes extracted from Wi-Fi traces do not exhibit a scale free behaviour. [ABSTRACT FROM AUTHOR]

Distributed mobile energy storage (DMES) units, which have been recently available in the form of Plug-in Electric Vehicle (PEV) batteries, provide unique opportunities to enhance the efficiency of the smart grid. On the other hand, without communications, uncoordinated supply may risk the stability of the grid, while mobility and variable availability of the batteries make the planning task challenging for the utilities. In this paper, we propose a four-way handshake protocol and a token-based energy forwarding network model for the electricity distribution system that allows energy to be supplied in a store-and-forward fashion similar to packet delivery in delay-tolerant networks. Based on this model, we develop a novel vehicle-to-grid power flow coordination approach, where the power acquired by the delay-tolerant loads is aggregated into tokens which are then matched with the available capacity of the PEV batteries. Energy transactions between delay-tolerant loads and PEVs rely on their communications with the energy management system at the distribution level. Our four-way handshake protocol assures tokens coming from loads and grants coming from storage are matched properly at the distribution level. Our approach provides a convenient supply for loads via PEV batteries while addressing the mobility of vehicles and preserving fairness. We provide a mathematical analysis of the proposed approach and conduct simulations showing that the proposed protocol is able to provide fair access opportunity to PEV owners. Furthermore, by introducing the queuing theory perspective, we enhance the planning capabilities of utilities. [ABSTRACT FROM AUTHOR]