A Fault Tolerance Scheme for Reliable Transfer in Delay Tolerant Networks

Delay Tolerant Network （DTN） is a class of networks that experience frequent and long-duration partitions due to sparse distribution of nodes. It has a broad prospect to new network applications for a better sealability, fault-tolerant, and high performance. In DTNs, path failure occurs frequently, so message transfer is not reliable. Sometimes it is required to change routing even in a very short period, resulting in transmission delay and reception delay. However, some well-known assumptions of traditional networks are no longer true in DTNs. In this paper, we study the problem of path failures in DTNs. The path failure process in DTNs is described when the path appears completely normal, completely failed and partially failed. Traditional approaches based on using precisely known network dynamics have not accounted for message losses. A new fault tolerant scheme to generate redundancy is to use erasure coding and full replication. This can greatly decrease the path failure rate. At last, a traffic DTN model is analyzed. Results reveal the superiority of our scheme in comparison to other present schemes.

Adaptive clustering hierarchy routing for delay tolerant network

Adaptive clustering hierarchy routing(ACHR) establishes a clusters-based hierarchical hybrid routing algorithm with two-hop local visibility for delay tolerant network(DTN).The major contribution of ACHR is the combination of single copy scheme and multi-copy scheme and the combination of hop-by-hop and multi-hop mechanism ACHR,which has the advantages in simplicity,availability and well-expansibility.The result shows that it can take advantage of the random communication opportunities and local network connectivity,and achieves 1.6 times delivery ratio and 60% overhead compared with its counterpart.

Cache-Assign-Forward Architecture for Efficient Communication in Hybrid Delay-Tolerant Networks

Delay-Tolerant Networks (DTNs) are wireless networks that often experience temporary, even long-duration partitioning. Current DTN researches mainly focus on pure delay-tolerant networks that are extreme environments within a limited application scope. It motivates the identification of a more reasonable and valuable DTN architecture, which can be applied in a wider range of environments to achieve interoperability between some networks suffering from frequent network partitioning, and other networks provided with stable and high speed Internet access. Such hybrid delay-tolerant networks have a lot of applications in real world. A novel and practical Cache-Assign-Forward (CAF) architecture is proposed as an appropriate approach to tie together such hybrid networks to achieve an efficient and flexible data communication. Based on CAF, we enhance the existing DTN routing protocols and apply them to complex hybrid delay-tolerant networks. Simulations show that CAF can improve DTN routing performance significantly in hybrid DTN environments.

Energy Based Random Repeat Trust Computation in Delay Tolerant Network

As the use of mobile devices continues to rise,trust administration will significantly improve security in routing the guaranteed quality of service(QoS)supply in Mobile Ad Hoc Networks(MANET)due to the mobility of the nodes.There is no continuance of network communication between nodes in a delay-tolerant network(DTN).DTN is designed to complete recurring connections between nodes.This approach proposes a dynamic source routing protocol(DSR)based on a feed-forward neural network(FFNN)and energybased random repetition trust calculation in DTN.If another node is looking for a node that swerved off of its path in this situation,routing will fail since it won’t recognize it.However,in the suggested strategy,nodes do not stray from their pathways for routing.It is only likely that the message will reach the destination node if the nodes encounter their destination or an appropriate transitional node on their default mobility route,based on their pattern of mobility.The EBRRTC-DTN algorithm(Energy based random repeat trust computation)is based on the time that has passed since nodes last encountered the destination node.Compared to other existing techniques,simulation results show that this process makes the best decision and expertly determines the best and most appropriate route to send messages to the destination node,which improves routing performance,increases the number of delivered messages,and decreases delivery delay.Therefore,the suggested method is better at providing better QoS(Quality of Service)and increasing network lifetime,tolerating network system latency.

Graph-based single-copy routing in delay tolerant networks

This paper presents a new graph-based single-copy routmg method m delay tolerant networks （DTN）. With time goes on in the networks, a DTN connectivity graph is constituted with mobility of nodes and communication, and a corresponding greedy tree is obtained using a greedy algorithm in DTN connectivity graph. While there are some bad nodes such as disabled nodes or selfish nodes in delay tolerant networks, the nodes can choose the next p^oper intermediate node to transmit the mes- sage by comparing the location of neighboring nodes in the greedy tree. The single-copy routing method is very appropriate for energy-constrained, storage-constrained and bandwidth-constrained applications such as mobile wireless DTN networks. We show that delivery ratio is increased significantly by using the graph-based single-copy routing when bad nodes exist.

A Location-Based Content Search Approach in Hybrid Delay Tolerant Networks

In Delay Tolerant Networks （DTNs）, the offiine users can, through the encountering nodes, use the specific peer-to-peer message routing approach to deliver messages to the destination. Thus, it solves the problem that users have the demands to deliver messages while they are temporarily not able to connect to the Internet. Therefore, by the characteristics of DTNs, people who are not online can still query some location based information, with the help of users using the same service in the nearby area. In this paper, we proposed a location-based content search approach. Based on the concept of three-tier area and hybrid node types, we presented four strategies to solve the query problem, namely, Data Replication, Query Replication, Data Reply, and Data Synchronization strategies. Especially we proposed a Message Queue Selection algorithm for message transferring. The priority concept is set associated with every message such that the most ＂important＂ one could be sent first. In this way, it can increase the query success ratio and reduce the query delay time. Finally, we evaluated our approach, and compared with other routing schemes. The simulation results showed that our proposed approach had better query efficiency and shorter delay.

Node Sociability Based Intelligent Routing for Post-Disaster Emergency Networks

In a post-disaster environment characterized by frequent interruptions in communication links,traditional wireless communication networks are ineffective.Although the“store-carry-forward”mechanism characteristic of Delay Tolerant Networks(DTNs)can transmit data from Internet of things devices to more reliable base stations or data centres,it also suffers from inefficient data transmission and excessive transmission delays.To address these challenges,we propose an intelligent routing strategy based on node sociability for post-disaster emergency network scenarios.First,we introduce an intelligent routing strategy based on node intimacy,which selects more suitable relay nodes and assigns the corresponding number of message copies based on comprehensive utility values.Second,we present an intelligent routing strategy based on geographical location of nodes to forward message replicas secondarily based on transmission utility values.Finally,experiments demonstrate the effectiveness of our proposed algorithm in terms of message delivery rate,network cost ratio and average transmission delay.

Offloading Mobile Data from Cellular Networks Through Peer-to-Peer WiFi Communication:A Subscribe-and-Send Architecture

Currently cellular networks do not have sufficient capacity to accommodate the exponential growth of mobile data requirements.Data can be delivered between mobile terminals through peer-to-peer WiFi communications(e.g.WiFi direct),but contacts between mobile terminals are frequently disrupted because of the user mobility.In this paper,we propose a Subscribe-and-Send architecture and an opportunistic forwarding protocol for it called HPRO.Under Subscribe-and-Send,a user subscribes contents on the Content Service Provider(CSP) but does not download the subscribed contents.Some users who have these contents deliver them to the subscribers through WiFi opportunistic peer-to-peer communications.Numerical simulations provide a robust evaluation of the forwarding performance and the traffic offloading performance of Subscribe-and-Send and HPRO.

Performance Analysis of DEBT Routing Protocols for Pocket Switch Networks

Pocket Switched Networks(PSN)represent a particular remittent network for direct communication between the handheld mobile devices.Compared to traditional networks,there is no stable topology structure for PSN where the nodes observe the mobility model of human society.It is a kind of Delay Tolerant Networks(DTNs)that gives a description to circulate information among the network nodes by the way of taking the benefit of transferring nodes from one area to another.Considering its inception,there are several schemes for message routing in the infrastructure-less environment in which human mobility is only the best manner to exchange information.For routing messages,PSN uses different techniques such asDistributed Expectation-Based Spatio-Temporal(DEBT)Epidemic(DEBTE),DEBT Cluster(DEBTC),and DEBT Tree(DEBTT).Understanding on how the network environment is affected for these routing strategies are the main motivation of this research.In this paper,we have investigated the impact of network nodes,the message copies per transmission,and the overall carrying out of these routing protocols.ONE simulator was used to analyze those techniques on the basis of delivery,overhead,and latency.The result of this task demonstrates that for a particular simulation setting,DEBTE is the best PSN routing technique among all,against DEBTC and DEBTT.

DAWN: A Density Adaptive Routing for Deadline-Based Data Collection in Vehicular Delay Tolerant Networks

Vehicular Delay Tolerant Networks （DTN） use moving vehicles to sample and relay sensory data for urban areas, making it a promising low-cost solution for the urban sensing and infotainment applications. However, routing in the DTN in real vehicle fleet is a great challenge due to uneven and fluctuant node density caused by vehicle mobility patterns. Moreover, the high vehicle density in urban areas makes the wireless channel capacity an impactful factor to network performance. In this paper, we propose a local capacity constrained density adaptive routing algorithm for large scale vehicular DTN in urban areas which targets to increase the packet delivery ratio within deadline, namely Density Adaptive routing With Node deadline awareness （DAWN）. DAWN enables the mobile nodes awareness of their neighbor density, to which the nodes＇ transmission manners are adapted so as to better utilize the limited capacity and increase the data delivery probability within delay constraint based only on local information. Through simulations on Manhattan Grid Mobility Model and the real GPS traces of 4960 taxi cabs for 30 days in the Beijing city, DAWN is demonstrated to outperform other classical DTN routing schemes in performance of delivery ratio and coverage within delay constraint. These simulations suggest that DAWN is practically useful for the vehicular DTN in urban areas.

RFID Based Non-Preemptive Random Sleep Scheduling in WSN

In Wireless Sensor Network(WSN),because battery and energy supply are constraints,sleep scheduling is always needed to save energy while maintaining connectivity for packet delivery.Traditional schemes have to ensure high duty cycling to ensure enough percentage of active nodes and then derogate the energy efficiency.This paper proposes an RFID based non-preemptive random sleep scheduling scheme with stable low duty cycle.It employs delay tolerant network routing protocol to tackle the frequent disconnections.A low-power RFID based non-preemptive wakeup signal is used to confirm the availability of next-hop before sending packet.It eliminates energy consumption of repeated retransmission of the delayed packets.Moreover,the received wakeup signal is postponed to take effect until the sleep period is finished,and the waken node then responds to the sending node to start the packet delivery.The scheme can keep stable duty cycle and then ensure energy saving effect compared with other sleeping scheduling methods.

Geographic Information and Node Selfish-Based Routing Algorithm for Delay Tolerant Networks

In Delay Tolerant Networks （DTNs）, some routing algorithms ignore that most nodes are selfish, i.e., nodes are willing to use their own resources to forward messages to nodes with whom they have a relationship. In view of this phenomenon, we propose a routing algorithm based on Geographic Information and Node Selfishness （GINS）. To choose a forwarding node, GINS combines nodes＇ willingness to forward and their geographic information to maximize the possibility of contacting the destination. GINS formulates the message forwarding process as a 0-1 Knapsack Problem with Assignment Restrictions to satisfy node demands for selfishness. Extensive simulations were conducted, and results show that GINS can achieve a high delivery ratio and a lower hop count compared with GRONE and LPHU. Furthermore, its overhead ratio is 25% and 30% less than that of GRONE and LPHU, respectively.

CRSG:A congestion control routing algorithm for security defense based on social psychology and game theory in DTN

The inherent selfishness of each node for the enhancement of message successful delivery ratio and the network overall performance improvement are reflected in the contradiction relationship of competition and cooperation in delay/disruption tolerant networks (DTN). In particular, the existence of malicious node aggravates this contradiction. To resolve this contradiction, social relationship theory and group theory of social psychology were adopted to do an in-depth analysis. The concrete balancing approach which leveraged Nash equilibrium theory of game theory was proposed to resolve this contradiction in reality. Thus, a new congestion control routing algorithm for security defense based on social psychology and game theory (CRSG) was put forward. Through the experiment, this algorithm proves that it can enhance the message successful delivery ratio by more than 15% and reduce the congestion ratio over 15% as well. This algorithm balances the contradiction relationship between the two key performance targets and made all nodes exhibit strong cooperation relationship in DTN.

A maximum flow algorithm for buffer-limited delay tolerant networks

Deep space networks,satellite networks,ad hoc networks,and the Internet can be modeled as DTNs(Delay Tolerant Networks).As a fundamental problem,the maximum flow problem is of vital importance for routing and service scheduling in networks.However,there exists no permanent end-to-end path since the topology and the characteristics of links are time-variant,resulting in a crucial maximum flow problem in DTNs.In this paper,we focus on the single-source-single-sink maximum flow problem of buffer-limited DTNs,followed by a valid algorithm to solve it.First,the BTAG(Buffer-limited Time Aggregated Graph)is constructed for modeling the buffer-limited DTN.Then,on the basis of BTAG,the two-way cache transfer series and the relevant transfer rules are designed,and thus a BTAG-based maximum flow algorithm is proposed to solve the maximum flow problem in buffer-limited DTNs.Finally,a numerical example is given to demonstrate the effectiveness of the proposed algorithm.

A Buffer Scheduling Method Based on Message Priority in Delay Tolerant Networks

Routing protocols in delay tolerant networks usually utilize multiple message copies to guarantee the message delivery, in order to overcome unpredictable node mobility and easily-interrupted connections. A store-carry-and-forward paradigm was also proposed to further improve the message delivery. However, excessive message copies lead to the shortage of buffer and bandwidth. The spray and wait routing protocol has been proposed to reduce the network overload caused by the buffer and transmission of unrestricted message copies. However, when a node＇s buffer is quite constrained, there still exist congestion problems. In this paper, we propose a message scheduling and drop strategy on spray and wait routing protocol （SDSRP）. To improve the delivery ratio, first of all, SDSRP calculates the priority of each message by evaluating the impact of both replicating and dropping a message copy on delivery ratio. Subsequently, scheduling and drop decisions are made according to the priority. In order to further increase delivery ratio, we propose an improved message scheduling and drop strategy on spray and wait routing protocol （ISDSRP） through enhancing the accuracy of estimating parameters. Finally, we conduct extensive simulations based on synthetic and real traces in ONE. The results show that compared with other buffer management strategies, ISDSRP and SDSRP achieve higher delivery ratio, similar average hopcounts, and lower overhead ratio.

OceanRoute: Vessel Mobility Data Processing and Analyzing Model Based on MapReduce

The network coverage is a big problem in ocean communication, and there is no low-cost solution in the short term. Based on the knowledge of Mobile Delay Tolerant Network(MDTN), the mobility of vessels can create the chances of end-to-end communication. The mobility pattern of vessel is one of the key metrics on ocean MDTN network. Because of the high cost, few experiments have focused on research of vessel mobility pattern for the moment. In this paper, we study the traces of more than 4000 fishing and freight vessels. Firstly, to solve the data noise and sparsity problem, we design two algorithms to filter the noise and complement the missing data based on the vessel's turning feature. Secondly, after studying the traces of vessels, we observe that the vessel's traces are confined by invisible boundary. Thirdly, through defining the distance between traces, we design MR-Similarity algorithm to find the mobility pattern of vessels. Finally, we realize our algorithm on cluster and evaluate the performance and accuracy. Our results can provide the guidelines on design of data routing protocols on ocean MDTN.

Intermittent Geocast Routing in Urban Vehicular Delay Tolerant Networks

Nowadays, both vehicular active safety service and user infotainment service have become two core applications for urban Vehicular Delay Tolerant Networks（u VDTNs）. Both core applications require a high data transmission capacity over u VDTNs. In addition, the connection between any two vehicles in u VDTNs is intermittent and opportunistic. Intermittent data dissemination over u VDTNs is a stringent and challenging issue. In this paper,we propose Intermittent Geocast Routing（IGR）. For the first step, IGR has to estimate the active connection time interval via the moving directions and velocities between any two vehicles. Second, the throughput function for u VDTNs is fitted by building a wavelet neural network traffic model. Third, the throughput function within the effective connection time interval is integrated to obtain the forwarding capability estimation of the node. Fourth, a high-efficiency geocast routing algorithm using the node forwarding capability for u VDTNs is designed. Finally, IGR is simulated on the opportunistic Network Environment simulator. Experimental results show that IGR can greatly improve the packet delivery ratio, transmission delay, delay jitter, and packet loss rate compared with the state of the art.

New spray and wait protocol with node activity in heterogeneous delay tolerant networks

The spray and wait protocol is a classic copy-limited spraying protocol in delay tolerant networks, in which, the binary spray mode can be improved for heterogeneous delay tolerant networks. In this article, a new conception of node activity was defined to weigh the importance of nodes in aspect of message dissemination in the whole network. A new spray and wait protocol with node activity was proposed to improve the performance in heterogeneous delay tolerant networks. A mathematical model used under varieties of the spraying protocols was also proposed to analyze the expected delay of the protocol. Simulations show that the spray token proportion with node activity is optimal and the new protocol is of better performance than other related protocols. Therefore, this protocol has high efficiency and good scalability.

Cross-Layer Design for EH Systems with Finite Buffer Constraints

Energy harvesting(EH)technology in wireless communication is a promising approach to extend the lifetime of future wireless networks.A cross-layer optimal adaptation policy for a point-to-point energy harvesting(EH)wireless communication system with finite buffer constraints over a Rayleigh fading channel based on a Semi-Markov Decision Process(SMDP)is investigated.Most adaptation strategies in the literature are based on channeldependent adaptation.However,besides considering the channel,the state of the energy capacitor and the data buffer are also involved when proposing a dynamic modulation policy for EH wireless networks.Unlike the channeldependent policy,which is a physical layer-based optimization,the proposed cross-layer dynamic modulation policy is a guarantee to meet the overflow requirements of the upper layer by maximizing the throughput while optimizing the transmission power and minimizing the dropping packets.Based on the states of the channel conditions,data buffer,and energy capacitor,the scheduler selects a particular action corresponding to the selected modulation constellation.Moreover,the packets are modulated into symbols according to the selected modulation type to be ready for transmission over the Rayleigh fading channel.Simulations are used to test the performance of the proposed cross-layer policy scheme,which shows that it significantly outperforms the physical layer channel-dependent policy scheme in terms of throughput only.

NPBMT: A Novel and Proficient Buffer Management Technique for Internet of Vehicle-Based DTNs

Delay Tolerant Networks(DTNs)have the major problem of message delay in the network due to a lack of endto-end connectivity between the nodes,especially when the nodes are mobile.The nodes in DTNs have limited buffer storage for storing delayed messages.This instantaneous sharing of data creates a low buffer/shortage problem.Consequently,buffer congestion would occur and there would be no more space available in the buffer for the upcoming messages.To address this problem a buffer management policy is proposed named“A Novel and Proficient Buffer Management Technique(NPBMT)for the Internet of Vehicle-Based DTNs”.NPBMT combines appropriate-size messages with the lowest Time-to-Live(TTL)and then drops a combination of the appropriate messages to accommodate the newly arrived messages.To evaluate the performance of the proposed technique comparison is done with Drop Oldest(DOL),Size Aware Drop(SAD),and Drop Larges(DLA).The proposed technique is implemented in the Opportunistic Network Environment(ONE)simulator.The shortest path mapbased movement model has been used as the movement path model for the nodes with the epidemic routing protocol.From the simulation results,a significant change has been observed in the delivery probability as the proposed policy delivered 380 messages,DOL delivered 186 messages,SAD delivered 190 messages,and DLA delivered only 95 messages.A significant decrease has been observed in the overhead ratio,as the SAD overhead ratio is 324.37,DLA overhead ratio is 266.74,and DOL and NPBMT overhead ratios are 141.89 and 52.85,respectively,which reveals a significant reduction of overhead ratio in NPBMT as compared to existing policies.The network latency average of DOL is 7785.5,DLA is 5898.42,and SAD is 5789.43 whereas the NPBMT latency average is 3909.4.This reveals that the proposed policy keeps the messages for a short time in the network,which reduces the overhead ratio.