DTN中概率选择的散发等待路由

目前的Internet体系结构和许多协议无法很好地适应延迟较高和间歇性链接的网络,这些网络有它们自己的专有协议,即聚束层协议,而不采用TCP/IP协议。为了实现这样的网络之间的互联,国际上提出了一种在端到端链接和节点资源都受限的新型网络体系和应用接口,即容迟网络（DTN）。文中主要讨论DTN网络的路由算法,在DTN路由算法中,蔓延路由和概率路由能提供较高的报文投递率,较小的投递延迟,但是开销很大。散发等待路由虽然具有较小的开销,但是投递率低、延迟较大,提出了投递效用的概念。在融合概率选择路由和散发等待路由的基础上,提出了具有概率选择的散发等待路由。通过仿真,与其它已有算法相比,显著提高了报文投递效用。     

空间延迟/中断容忍网络拥塞控制策略研究

针对空间延迟/中断容忍网络（DTN, delay/disruption tolerant network）的拥塞控制问题,提出一种基于提前卸载的拥塞控制策略（EOCC,early offloading-based congestion control）。由于空间DTN网络大时延和不能保证时刻存在端到端路径的特点,EOCC主要利用网络节点的本地信息在拥塞发生前就采取措施。具体地,EOCC会时刻监测节点缓存变化速率,在即将发生拥塞时,将消息通过早于最优路径的非最优路径传输,从而缓解节点存储压力。仿真结果表明,采用EOCC的接触图路由获得了更好的性能。     

延迟/中断可容忍网络路由中的关键技术

容迟网络是一种受限网络,以频繁的间断性和高而可变的延迟为特点,在某段时间内可能不存在端到端的路径,使得数据传输受到限制。对路由算法的研究是解决这种网络中数据传输问题的关键。虽然已经有大量的路由算法被提出,但不同的算法的侧重点不一样,有必要对路由涉及到的关键问题和技术做分析研究和总结,以便于将来的研究,目的正是如此,分析了与延迟/中断容忍网络（DTN）路由相关的关键技术。     

DTN中基于泛模板运算的运动模式发现机制

DTN(Delay-Tolerant Network) 用于描述Ad hoc等无线网络中频繁发生长时间网络分割情形。DTN不假设端到端路径一定存在,因此其主要关注点是如何提高成功投递率,而不是延时等QoS参数。运动模式,例如聚类性等对DTN很重要;本文关注于一种宏观的节点运动模式,并提出一个发现和使用运动模式的框架TOM2D(Template-Operation based Mobility Model Discovery)。其基本思想是：节点利用路由信息交互机制维护一个包含所有节点(或相关节点)三维链路容量矩阵,利用图像处理中的模板运算机制从中提取出可能的运动模式,最后用一个通用的数据结构存储这些信息并用于路由决策过程中。由于TOM2D并不依赖于特定的路由协议,本文最后给出了一个基于OLSR和DSDV的例子,仿真结果显示TOM2D确实为路由决策给出了有价值的信息,提高了路由成功率。     

基于动态分段网络编码的DTN高效路由算法

针对DTN现有的动态分段网络编码(Dynamic Segmented Network Coding,DSNC)路由算法在编码包头部存在冗余字段、ACK反馈阶段存在冗余开销和节点因无序转发编码包而影响数据包端到端时延等问题,提出基于动态分段网络编码的DTN高效路由算法—ERBNC(Efficient Routing Based on dynamic segmented Network Coding).该算法通过采取压缩编码包头部字段、删除冗余的ACK分组、设置编码包的发送优先级等措施以减少网络开销和数据包平均端到端时延.仿真结果表明,与DSNC算法相比,ERBNC算法在网络开销和端到端时延方面的性能均得到改善.     

容延容断网络路由算法及其存在问题的探析

容延容断网络(delay/disruption tolerant network,简称DTN)是一种新型网络体系结构.在这一类网络中,节点与节点之间不存在端到端的路径,因此节点之间的通信一般使用"存储-携带-转发"的模式来进行,也就是节点需要先将信息存储起来再携带信息,直到遇到能够将消息转发到目的节点的时候才将消息转发出去.因此在容延容断网络中路由算法的关键性问题是如何以较高的发送成功率和较低的延迟将消息转发到目的节点.DTN网络的应用场景通常由手机、蓝牙设备以及具备WiFi功能的手持电子设备等组成的移动自组网络.本文主要研究DTN路由算法及其存在的问题.     

基于路径稳定性的MAODV路由协议的改进

在Ad Hoc网络中,节点随意快速的移动通常会造成网络拓扑结构的剧烈变化,可能导致传输链路断裂和路径的不稳定。针对这种情况,在分析现有MAODV路由改进技术的基础上,提出了一种改进的、基于路径稳定性的路由协议(RS-MAODV)。新协议与MAODV不同的地方在于:考虑构成路径的链路间的相关性,选择最稳定的路由进行数据传输,以此改善网络性能。利用NS2仿真工具对改进前后网络的丢包率及端到端延迟参数做比较,实验数据表明,改进后协议的网络丢包率及端到端延迟均得到改善。     

DTN网络中基于生灭模型的节点运动模式检测

提出了一种DTN网络中基于生灭模型的节点运动模式检测方法(MMD-BDM, mobility model detection method based on birth and death model)。在节点数据传输过程中,根据数据传输量计算得到各个连通链路采样时刻的信道容量,在本节点构建以信道容量构成的三维时变连通矩阵,并在此基础上推导出基于边连通的节点连通性生灭模型,然后分析节点连通边的生灭特征并以此判断节点的运动模式,以优化DTN网络消息投递过程中的路由转发策略。最后,将该运动模式检测方法应用在喷射路由(SWR, spray and wait routing)和随机网络编码路由(RNCR, random network coding routing)算法中进行了仿真实验,实验表明,该方法能提高DTN网络机会路由的投递率和投递延迟等数据投递性能。     

容迟网络中基于复制策略的单播路由算法研究

容迟/容延网络(Delay Tolerant Network/DTN)泛指由于节点移动、能量管理、调度等原因而出现频繁中断、甚至长时间处于中断状态的一类网络。针对DTN具有的时延高、割裂频繁、节点能量受限、以及节点移动性等特点,通过对DTN中基于复制策略的单播路由策略进行分类和比较,提出了如何优化DTN单播路由算法、提高网络传输率的建议。     

一种基于图神经网络的SDN路由性能预测模型

软件定义网络作为未来网络架构的发展方向,通过分离数据平面与控制平面高效设定路由方案.而在路由方案的优化过程中,准确预估给定路由方案下的网络性能是其关键.本文基于图神经网络建模网络中物理链路与路由方案路径的关系,在给定的路由方案与网络流量下对网络中的各项端到端性能指标(如延迟、抖动)进行准确预估,以辅助优化路由方案.本文...     

面向混合DTN网络的新型传输架构 CAF

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.     

Directional routing and scheduling for green vehicular delay tolerant networks

The vehicle delay tolerant networks (DTNs) make opportunistic communications by utilizing the mobility of vehicles, where the node makes delay-tolerant based “carry and forward” mechanism to deliver the packets. The routing schemes for vehicle networks are challenging for varied network environment. Most of the existing DTN routing including routing for vehicular DTNs mainly focus on metrics such as delay, hop count and bandwidth, etc. A new focus in green communications is with the goal of saving energy by optimizing network performance and ultimately protecting the natural climate. The energy–efficient communication schemes designed for vehicular networks are imminent because of the pollution, energy consumption and heat dissipation. In this paper, we present a directional routing and scheduling scheme (DRSS) for green vehicle DTNs by using Nash Q-learning approach that can optimize the energy efficiency with the considerations of congestion, buffer and delay. Our scheme solves the routing and scheduling problem as a learning process by geographic routing and flow control toward the optimal direction. To speed up the learning process, our scheme uses a hybrid method with forwarding and replication according to traffic pattern. The DRSS algorithm explores the possible strategies, and then exploits the knowledge obtained to adapt its strategy and achieve the desired overall objective when considering the stochastic non-cooperative game in on-line multi-commodity routing situations. The simulation results of a vehicular DTN with predetermined mobility model show DRSS achieves good energy efficiency with learning ability, which can guarantee the delivery ratio within the delay bound.     

A venues‐aware message routing scheme for delay‐tolerant networks

With their proliferation and increasing capabilities, mobile devices with local wireless interfaces can be organized into delay‐tolerant networks (DTNs) that exploit communication opportunities arising out of the movement of their users. As the mobile devices are usually carried by people, these DTNs can also be viewed as social networks. Unfortunately, most existing routing algorithms for DTNs rely on relatively simple mobility models that rarely consider these social network characteristics, and therefore, the mobility models in these algorithms cannot accurately describe users’ real mobility traces. In this paper, we propose two predict and spread (PreS) message routing algorithms for DTNs. We employ an adapted Markov chain to model a node's mobility pattern and capture its social characteristics. A comparison with state‐of‐the‐art algorithms demonstrates that PreS can yield better performance in terms of delivery ratio and delivery latency, and it can provide a comparable performance with the epidemic routing algorithm with lower resource consumption. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance Evaluation of a Power Management Scheme for Disruption Tolerant Network

Disruption tolerant network (DTN) is characterized by frequent partitions and intermittent connectivity. Power management issue in such networks is challenging. Existing power management schemes for wireless networks cannot be directly applied to DTNs because they assume the networks are well-connected. Since the network connectivity opportunities are rare, any power management scheme deployed in DTNs should not worsen the existing network connectivity. In this paper, we design a power management scheme called context-aware power management scheme (CAPM) for DTNs. Our CAPM scheme has an adaptive on period feature that allows it to achieve high delivery ratio and low delivery latency when used with Prophet, a recently proposed DTN routing scheme. Via simulations, we evaluate the performance of the CAPM scheme when used with the Prophet routing scheme in different scenarios e.g. different traffic load, node speeds and sleep patterns. Our evaluation results indicate that the CAPM scheme is very promising in providing energy saving (as high as 80%) without degrading much the data delivery performance.     

A link contact duration-based routing protocol in delay-tolerant networks

Delay Tolerant Networks (DTNs) provide message delivery services to users via intermittently connected nodes. In DTNs, routing is one of the most challenging issues since end-to-end connectivity between nodes may not be available most of the time. Although many routing protocols for DTNs have been proposed, they do not achieve satisfactory performance, since they exploit only some of the network characteristics. In this paper, we present a new DTN routing protocol, called the Link Contact Duration-based Routing Protocol (LCD). Like existing protocols, LCD uses the disconnect duration of a link between two nodes to find the routing path with the shortest end-to-end delay. In addition, LCD uses the contact duration of a link and the number of buffered messages to deliver as many messages as possible in a short time. Our simulation results show that LCD has better performance than existing DTN routing protocols.     

Quota-Based Multicast Routing in Delay-Tolerant Networks

Delay-Tolerant Networks (DTNs) are special types of network environments that are subject to delays and disruptions. Most research efforts on the DTN routing problem are focused on unicast routing but not multicast routing. Moreover existing DTN multicasting approaches are not efficient and flexible. In this paper, we propose a new multicast routing approach which can not only achieve a high delivery rate but also adapt to network conditions. Most importantly, our proposed approach need not maintain group membership. In other words, any interested users can freely join and leave any multicast groups, and this feature suitably fits into DTN environments.     

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.     

Design of efficient lightweight strategies to combat DoS attack in delay tolerant network routing

Delay tolerant networks (DTNs) are characterized by delay and intermittent connectivity. Satisfactory network functioning in a DTN relies heavily on co-ordination among participating nodes. However, in practice, such co-ordination cannot be taken for granted due to possible misbehaviour by relay nodes. Routing in a DTN is, therefore, vulnerable to various attacks, which adversely affect network performance. Several strategies have been proposed in the literature to alleviate such vulnerabilities—they vary widely in terms of throughput, detection time, overhead etc. One key challenge is to arrive at a tradeoff between detection time and overhead. We observe that the existing table-based reactive strategies to combat Denial-of-service (DoS) attacks in DTN suffer from two major drawbacks: high overhead and slow detection. In this paper, we propose three secure, light-weight and time-efficient routing algorithms for detecting DoS attacks (Blackhole and Grey-hole attacks) in the Spray & Focus routing protocol. The proposed algorithms are based on use of a small fraction of privileged (trusted) nodes. The first strategy, called TN, outperforms the existing table-based strategy with 20–30 % lesser detection time, 20–25 % higher malicious node detection and negligible overhead. The other two strategies, CTN_MI and CTN_RF explore the novel idea that trusted nodes are able to utilize each others’ information/experience using their long range connectivity as and when available. Simulations performed using an enhanced ONE simulator reveals that investing in enabling connectivity among trusted nodes (as in CTN_RF) can have significant performance benefits.     

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.     

DTN-Balance: A Forwarding-Capacity and Forwarding-Queue Aware Routing for Self-organizing DTNs

In delay-tolerant networks (DTNs), intermittent network connectivity and lack of global system information pose serious challenges to achieve effective data forwarding. Most state-of-the-art DTN routing algorithms are based on hill-climbing heuristics in order to select the best available next hop to achieve satisfactory network throughput and routing efficiency. An adverse consequence of this approach is that a small subset of good users take on most of the forwarding tasks. This can quickly deplete scarce resources (e.g. storage, battery, etc.) in heavily utilized devices which degrades the network reliability. A system with a significant amount of traffic carried by a small number of users is not robust to denial of service attacks and random failures. To overcome these deficiencies, this paper proposes a new routing algorithm, DTN-Balance, that takes the forwarding capacity and forwarding queue of the relay nodes into account to achieve a better load distribution in the network. For this, we defined a new routing metric called message forwarding utility combining nodal available bandwidth and forwarding workload. Applying small world theory, we impose an upper bound on the end-to-end hop count that results in a sharp increase in routing efficiency. Queued messages in a forwarding node are arranged by DTN-Balance based on message dropping utility metric for a more intelligent decision in the case of a message drop. The performance of our method is compared with that of the existing algorithms by simulations on real DTN traces. The results show that our algorithm provides outstanding forward efficiency at the expense of a small drop in the throughput.