容迟网络中高传输性能随机路由协议

In Delay Tolerant Networks (DTNs), establishing routing path from a source node to a destination node may not be possible, so the opportunistic routings are widely used. The energy and buffer constraints are general in DTNs composed of the mobile phones or Pads. This paper proposes a novel opportunistic routing protocol, denoted by Large Opporturioty (LAOP ), for the energy and buffer constrained DTNs. The objective of LAOP is to reach many receivers of a message with a small number of transmissions. By LAOP, the sender floods a message when the number of its neighbors is not less than a threshold. We compare the delivery performance of LAOP with other four widely used Delay or Disruption Tolerant Network (DTN) routing protocols, Direct Delivery, Epidemic routing, SprayAndWait and PRoPHET and demonstrate that LAOP can improve the delivery performance and decrease the delivery latency simultaneously.     

Adaptive Spraying for Routing in Delay Tolerant Networks

Message delivery in Delay Tolerant Networks (DTNs) is challenging due to the fact that the network is intermittently connected. Mobility can be exploited to improve DTN performance. In this paper, we propose a DTN routing scheme Adaptive Spraying. Adaptive Spraying exploits mobility pattern and encounter history to predict the number of nodes with no copy a node will encounter within the expected delay. The number of nodes encountered can be viewed as the number of copies disseminated. Each node with copies dynamically chooses the number of copies by itself, instead of a fixed number determined at the source node. We present an analysis of the scheme and validate the analytical results with simulations. Simulation results show that Adaptive Spraying performs well over a variety of environmental conditions such as transmission range and traffic load.     

Selective Message Forwarding in Delay Tolerant Networks

It is challenging to deliver messages in a network where no instant end-to-end path exists, so called delay-tolerant network (DTN). Node encounters are used for message forwarding. In this paper, we propose a DTN routing protocol SMART. SMART utilizes the travel companions of the destinations (i.e. nodes that frequently meet the destination) to increase the delivery opportunities while limiting message overhead to a bounded number. Our approach differs from related work in that it does not propagate node encounter history nor the delivery probabilities derived from the encounter history. In SMART, a message source injects a fixed number of message copies into the network to forward the message to a companion of the destination, which only forwards the message to a fixed number of the destination’s companions. Our analysis and simulation results show that SMART has a higher delivery ratio and a smaller delivery latency than the schemes that only use controlled opportunistically-forwarding mechanism and has a significantly smaller routing overhead than a pure flooding scheme.     

面向能量感知的DTN地理位置路由算法在灾害地域的应用

延迟容错网络中的路由特点是不存在一条端到端的通路.这种特征可用于基础设施被摧毁的灾害地区.使用现有的移动平台如手机,建立一个能源感知的通信网络是一个有吸引力的问题.本文基于预测的路由和传输控制机制,提出了一种地理位置的协议.通过使用雅安地区的实际地图作为实验地图,对比现有的经典协议,可以发现该算法增加了消息投递成功率,降低了传输延时,并大大降低了路由开销.此外,算法的消息传输跳数比其他算法更接近于传染病路由算法.     

延迟容忍网络自适应差错控制方法

根据延迟容忍网络的时延较大、误码率较高等特点,在现有的传输控制层和MAC层差错控制的基础上改进,结合IEEE 802.11 DCF机制的特点,提出一种基于MAC层丢包率的自适应差错控制方案.该方案能有效改善延迟容忍网络的传输时延,满足对时延要求比较敏感的业务的要求.     

Network Coding for Overhead Reduction in Delay Tolerant Networks

Employing Network Coding (NC) in routing protocols for Delay Tolerant Networks (DTNs) is a challenging issue during the last years due to its potential beneficial effect on improving relevant critical metrics. This paper proposes an effective NC scheme intended for sparse DTNs comprising nodes of limited storage capacity. The scheme employs a memory management algorithm that makes optimal use of the limited storage capacity and focuses on unicast sessions where source and intermediate nodes combine only packets belonging to the same generation and destined for the same destination node. Upon having received a sufficient number of linearly independent packets resulting in a matrix of full rank, the destination nodes can apply network decoding to retrieve the information intended for them. The proposed scheme is fully distributed since the network nodes make decisions based on information collected solely from their own buffers. Combined either with Epidemic or probabilistic routing protocols, the scheme manages to drastically reduce the overhead created per source packet.     

容迟／容断网络路由技术研究

容迟／容断网络（DTN）由于其长延迟、高误码率及频繁断路等网络特性不满足互联网较短传输延迟、低误码率及存在端到端路径的基本假设,传统Internet体系结构和协议无法直接用于DTN。DTN路由机制可以按照连接的确定性分为确定性路由和随机性路由。确定性路由主要有基于树的路由、时空路由和修正的最短路径路由等方法;随机性路由主要有流行性路由、基于历史消息的路由、基于模型的路由、可控移动路由和基于编码的路由。DTN在游牧计算、军事战场通信、紧急营救及灾后重建方面具有广泛应用前景。     

Two-Level Community-Based Routing in Delay Tolerant Networks

Delay tolerant networks can not maintain end-to-end connectivity. Thus the routing is one of the critical issues. As we known, the two-level community model including the small community and the big community is proposed for the first time. In the same small community, any two member nodes are friends with each other. And in the same big community which is constructed of some small communities, any two communities have some pairs of friend nodes between them. Based on this model, a two-level community-based routing (TLCR) algorithm is presented in delay tolerant networks. In TLCR, according to the location of packet holder including inside the small community of destination node, inside of the big community and outside of the small community of destination node, and outside of the big community of destination node, the different packet forwarding strategies are investigated. The number of relay nodes selected by a packet holder is decreasing with the holder’s location from inside of the small community of destination node to outside of the big community of destination node. The probability of the source node successfully delivers the packet to the destination node and the copies number corresponding with the above three locations are analyzed, respectively. The simulation results show that TLCR not only improves the delivery ratio but also greatly reduces the resource cost.

     

容迟与容断网络的研究进展

本文简要介绍了容迟与容断网络的基本特征、体系结构、应用领域和比较活跃的研究机构及其主要工作。采用分析和比较的方法,总结了容迟与容断网络路由协议和传输协议的主要研究成果,探讨了相关研究问题,分析比较了容迟与容断网络的仿真工具。最后总结并展望了容迟与容断网络进一步的发展方向。     

Stigmergic Communication for Self-Organized Multi Ferry Delay Tolerant Networks

This paper presents an Adaptive On-the-fly Decision maker for Multi Ferry (A-ODMF) delay tolerant networks. A-ODMF chooses the next node to visit for controlled mobility data ferries. In our assumptions, there is no direct communication among ferries. Therefore, we apply a stigmergic communication among ferries for their coordination. Nodes are employed to act as relays for an indirect signaling of control information among ferries to decrease redundant visits to nodes. Moreover, the self-organized decision maker in A-ODMF adapts its decision functions based on the local observations of a ferry from the delay of delivered messages in the network to increase the efficiency of ferry decisions. A-ODMF also considers the priority of messages in the ferry buffer and delivers high priority messages earlier. The simulation results show that A-ODMF outperforms existing on-the-fly approaches in terms of message latency. In scenarios with high number of ferries, the impact of indirect signaling and the adaptive decision maker in A-ODMF is more significant on the performance improvement. A-ODMF decreases unnecessary visits to nodes and therefore improves the travel time of messages in a ferry buffer. Finally, we study and discuss the impact of increasing the number of ferries and increasing the ferry speed on the performance and cost of a message ferry network. We show that a required performance can be achieved with less cost by increasing the speed of ferries than increasing the number of ferries.     

Context-Aware Routing in Delay and Disruption Tolerant Networks

In this paper, we analyze the problem of context adaptation in delay and disruption tolerant networks (DTNs). Initially, we performed experiments with well-known routing protocols to evaluate how much distinct configurations impact their performance. The results show that the performance is highly configuration dependent and improper configuration can lead to a performance up to 506.6 % worse than the best configuration tested. This motivates us to propose CARTOON (context-aware routing protocol for opportunistic networks), a novel routing protocol for DTNs based on the concept of context-adaptation. We evaluate CARTOON through simulations and the results show that our propose outperformed other well-known protocols, exhibiting results that are, on average, at 95 % of the computed optimum delivery rate.     

Secure Multi-copy Routing in Compromised Delay Tolerant Networks

Routing in delay tolerant networks (DTNs) is challenging due to their unique characteristics of intermittent node connectivity. Different protocols (single-, multi-copy, erasure-coding-based etc.) utilizing store-carry-and-forward paradigm have been proposed to achieve routing of messages in such environments by opportunistic message exchanges between nodes that are in the communication range of each other. The sparsity and distributed nature of these networks together with the lack of stable connectivity between source destination pairs make these networks vulnerable to malicious nodes which might attempt to learn the content of the messages being routed between the nodes. In this paper, we study DTNs in which malicious nodes are present, to which we refer to as compromised DTNs. We discuss and analyze the effects of presence of malicious nodes on routing of messages in compromised DTNs. We propose a two period routing approach which aims at achieving the desired delivery ratio by a given delivery deadline in presence of malicious nodes. Our simulation results with both random networks and real DTN traces show that, with proper parameter setting, the proposed method can achieve delivery ratios which surpass those reached by other algorithms by a given delivery deadline.     

On the Performance of Epidemic Based Routing Protocols for Delivering Multicast Bundles in Delay Tolerant Networks

Epidemic and ts variants are one main category of routing protocols in delay tolerant networks. They are known to be simple, have low latency and high delivery ratio. However, to date, virtually no work has investigated their suitability in delivering multicast bundles. To this end, we have conducted extensive and comprehensive simulation studies to answer this question. Specifically, we compare their delivery ratio, and buffer occupancy level in various multicast scenarios where nodes move according to both random way point model and a trace file containing records of student movements on a campus. Moreover, we tested the influence of key factors such as anti-entropy session, multicast group size, the number of groups and subscribers forwarding policies. We found that, achieving a high delivery ratio is dependent on nodes using anti-entropy session, relay/subscriber ratio and subscribers working as relays. Additionally, we also observed that relay nodes that use epidemic variants experience high buffer occupancy level. In particular, protocols such as epidemic with encounter count (EC) result in 100 % buffer utilization. To solve this problem, we propose EC quota, in which bundles can only be transmitted to \(k\) relay nodes. Our experiments prove that EC quota is capable of reducing the buffer occupancy level of relay nodes by 15–100 % whilst maintaining high delivery ratios.     

On Modeling The Impact of Selfish Behaviors on Limited Epidemic Routing in Delay Tolerant Networks

Transmission opportunity in delay tolerant network (DTN) is uncertain. To improve the routing performance, DTN tries to use every contact between nodes, and one classic policy is epidemic routing algorithm (ER). Due to much energy consumption, L-hop limited ER algorithm is proposed. However, such method does not consider the energy constraint for a specific node. To overcome this problem, we propose the L-count limited ER algorithm, in which each node forwards at most $L$ times. Numerical results show that this new algorithm can get better performance. Both of above algorithms need nodes to work in a cooperative way. However, due to selfish nature of nodes (individual selfishness and social selfishness), they may not be willing to help others. This paper proposes an accurate theoretical framework to evaluate the impact of these behaviors based on nonlinear differential equations (ODE). Simulations based on both synthetic and real motion traces show the accuracy of our theoretical model. Numerical results show that selfish nature can decrease the flooding performance in both algorithms. Under the same selfish behaviors, the performance is decreasing with the number of communities. The deviation of the performance between two algorithms is decreasing with the value of $L$ .     

延迟容忍网络中能量有效的接触探测研究

在延迟容忍网络中,为了发现在其通信范围内的邻居节点,网络中的节点必须不断地探测周围的环境。这个接触探测过程极其耗费能量。如果网络中的节点探测太过频繁,会耗费很多能量,且使得网络能量的使用效率降低。另一方面,稀疏的探测可能导致节点失去和其它节点的接触,从而错失交换数据的机会。因此,在延迟容忍网络中能量效率和接触机会之间存在着一种折中的关系。为了研究这种折中关系,该文首先对基于随机路点模型(Random Way-Point model, RWP)的接触探测过程进行建模,得到恒定探测间隔下接触探测概率的表达式,并且证明在所有平均探测间隔相同的策略中,以恒定间隔探测的策略是最优的。其次,基于提出的理论模型,分析不同情况下能量效率和接触探测概率之间的折中。最后,通过仿真实验验证该理论模型的正确性。     

Memory Forwarding Algorithm in Multiple Communities Delay Tolerant Networks

The routing is one of the key problems in delay tolerant networks (DTNs) because the source and destination often could not find a contemporaneous end-to-end path. In this paper, with the objective of reducing the number of copies, we propose two corresponding routings including a memory forwarding algorithm (MFA) and an extended memory forwarding algorithm (EMFA) for the specific type of node placement in DTNs where the nodes are randomly located and moved at different communities. The main idea of our algorithms are that the node copies a packet to an encountering node or not based on the relationship of their and the destination’s community locations calculated from the memory table, and they are designed for small and moderate number of communities respectively. We then state and analyze the expected number of copies of our algorithms. Simulation results reveal that MFA and EMFA can apparently decrease the number of copies and achieve comparable delivery delays compared with the classic multi-copy routings.     

基于社会特征的能量感知的容迟网组播协议

由于容迟网DTN(Delay-Tolerant Network)节点间连接的间歇性,节点只能依据机会性相遇转发数据.为此,提出基于社会特征的能量感知的容迟网络的组播SCEAM(Social Characteristics Energy-Aware based Multicast)协议.将社会网络思想引入DTN的路由协议,进而选择合适的转发节点传输数据,这充分利用了节点的长期和较稳定的社会特征知识进行决策转发数据.SCEAM协议就利用节点最重要的社会特征——中心度,并考虑节点能量两项信息选择转发节点.仿真数据表明,提出的SCEAM协议在满足数据传输率的要求下,能够支持更多的组播业务,与SDM协议相比,组播业务提高了近27％.     

Social group detection based routing in Delay Tolerant Networks

When implementing Mobile Ad Hoc Networks, a key characteristic of the network is the mobility pattern of the nodes. Based on the application, nodes can follow semi-predictable patterns, such as the routes followed by Vehicular Ad Hoc Networks, or the more strict schedules followed by aerial reconnaissance. Optimal routing schemes tend to take advantage of information regarding these patterns. In social environments, such as wildlife tracking or sending messages between humans, the devices and/or users will follow regular contact habits, tending to encounter social groups in which they participate. By identifying these groups, the patterns are used to optimize routing through a social environment. Dynamic Social Grouping (DSG), used to route messages strictly from a node to a basestation, is ideal for gathering sensor data and updating a shared data cache. In contrast, Dynamic Social Grouping-Node to Node (DSG-N²) is used to route messages between nodes, generally conventional communications. Both of these algorithms can be implemented ad null, meaning the devices initially have no information about their environment, and they work to reduce bandwith and delivery time while maintaining a high delivery ratio. In addition to presenting these two routing schemas, this article compares and contrasts two methods for estimating nodes’ delivery probabilities. The Contact Based Probability is based on encounters with other nodes, and the Performance Based Probability is based on the behavior of previous messages. The probability estimates were then validated with the Oracle analysis, which is based on knowledge of future events. This analysis indicated that DSG-N² probability estimates are comparable to the ideal.     

Determination of Relay Node Based on Fuzzy Logic in Delay Tolerant Network

Wireless Personal Communications - Delay tolerant networks are among mobile ad hoc networks. There is not a complete and connected route between the source and destination in these networks due to...     

一种基于QoS的空间延迟/中断容忍网络拥塞控制方法

为缓解网络拥塞对空间延迟/中断容忍网络产生的影响,该文提出一种基于QoS的网络拥塞控制算法。该算法包括接触拥塞判断和基于QoS的数据转发两种机制,分别从接触剩余可用容量和节点剩余存储空间两方面对每一段接触的拥塞程度进行预测,将接触划分为不同的拥塞等级。在计算路由时,以整段路径中所包含接触的最高拥塞等级为该路径的拥塞等级,并根据该拥塞等级发送不同优先级的数据。实验表明,基于QoS的拥塞控制算法可以提高低优先级数据的传递率并在节点存储空间不足时降低最高优先级数据的传递时延。