The design and implementation of a session layer for delay-tolerant networks

The DTN architecture is based around sender-initiated unicast communication that is insufficient or inconvenient to meet the needs of many applications. To address these limitations, we define a DTN session layer and associated extensions to the DTN bundle protocol that more naturally support receiver-driven applications and multicast communication. Within a session, we provide mechanisms allowing applications to convey ordering relationships between successive transmissions that can be used by the network to help ensure a distributed application’s delivery ordering expectations are met. We also extend the bundle protocol’s expiration procedures to support more efficient network utilization by allowing in-network deletion of obsolete messages. We present the design rationale and describe our implementation of these mechanisms and discuss their advantages in meeting the needs of several popular types of applications.     

Exploiting the potential of DTN for energy-efficient internetworking

Since its original conception as a space-oriented communications architecture, Delay Tolerant Networking (DTN) has been generalized to address issues in terrestrial networks as well. In this work we employ DTN to form an internetworking overlay that exploits the surplus capacity of last hop wireless channels in order to prolong battery life for mobile networking devices. We propose a novel rendezvous mechanism and show experimentally that the DTN overlay can shape traffic, allowing the wireless interface of the mobile device to switch to the sleep state during idle intervals without degrading performance. The simulation experiments are based on a comprehensive DTN agent that incorporates the rendezvous mechanism and facilitates quantifying energy conservation. The DTN agent, implemented in ns-2, enables the study of additional Bundle Protocol design issues, such as route selection, bundle sizing, retransmission strategies, and highlights the need for cross-layer interaction between DTN and the underlying transport protocol.     

容延容断网络研究及进展

容延容断网络(Delay/Disruption Tolerant Networks, DTN)是基于星际网络而提出的一种异于传统网络的抽象网络模型。从网络协议、路由算法、组播和安全机制4个方面综述DTN的研究概况及进展,分析各种协议、算法、机制的性能及特点并进行比较,指出DTN研究面对的挑战和进一步发展方向。     

容迟网络中的路由算法研究及比较

容迟网络是一类新型的网络,根据不同的网络环境,容迟网络呈现不同的形式。在该类网络中,由于其具有较大且不定的时延以及网络拓扑结构频繁分裂的特性,使得传统的路由协议不能得到有效的利用。为此,路由问题即给出适合于容迟网络中有效的路由协议就成为容迟网络中的关键问题。本文主要针对近年来所提出的多种路由算法,进行分类剖析比较,并给出当前路由协议存在的有待研究解决的问题。     

容迟网络广义k选播路由资源分配模型

容忍网络（DTN）协议现用于缓解移动网络频繁中断和网络分割造成的性能不稳,其核心之一是资源分配。然而在公共交通工具移动网络或物流环境中,现有路由算法的先验知识具有时间的概率不确定性,降低了资源分配效率。提出广义k选播,在许可时间段内对k个路由器之间进行路由和资源分配,分散其时间不确定性的偏差程度。而接入路由器信息矩阵可决定广义k选播集,从而实现对多个目的地的托管传送。在此基础上进一步提出路由资源分配的概率不确定模型。仿真验证其传输性能和鲁棒性整体优于DTN多播路由方案。     

Public key distribution scheme for delay tolerant networks based on two-channel cryptography

A delay tolerant network (DTN) is a store carry and forward network characterized by highly mobile nodes, intermittent connectivity with frequent disruptions, limited radio range and physical obstructions. Emerging applications of DTN include rural DTN, vehicular DTN and pocket DTN. The development of DTN raises a number of security-related challenges due to inconsistent network access and unreliable end-to-end network path. One of the challenges is initial secure context establishment as it is unrealistic to assume that public key infrastructure (PKI) is always globally present and available, hence, the public key management becomes an open problem for DTN. In this paper, for the first time, we propose a dynamic virtual digraph (DVD) model for public key distribution study by extending graph theory and then present a public key distribution scheme for pocket DTN based on two-channel cryptography. By distinguishing between owners and carriers, public key exchange and authentication issues in the decentralized pocket DTN environment can be solved by a two-channel cryptography process and our simulation results have proven it.     

Towards efficient and practical network coding in delay tolerant networks

Network coding techniques offer an emerging solution to efficient data transmission in Delay Tolerant Networks (DTN). To date, abundant techniques have been developed on exploiting network coding in DTN, however, most of them bring additional overhead due to the extra coded message redundancy. In this paper, we analyze the coded message redundancy issue, and then propose NTC, an efficient network coding scheme for DTN. In NTC, a novel metric named “redundancy ratio” is introduced within the anti-entropy message exchange process. We also discuss the design and implementation of practical NTC in detail. To evaluate the performance of our proposed NTC scheme, we implement NTC in ONE, the current state-of-the-art simulator for DTN. Simulation results show that, comparing with existing schemes, our proposed NTC scheme has significant advantages in enhancing the message delivery ratio and reducing the transmission overhead.     

容断/容迟网络通信过程分析

当前,以TCP/IP协议为基础的Internet已经被广泛应用。但是Internet并不能很好应用于,例如星际间卫星网络,军事战场网络等具有较大时延,频繁中断,非对称信道和高误码率等特征的网络。容断/容迟容忍网络(Disruption/Delay Tolerant NetworkDTN)提出了一种架构和解决方案来解决以上环境中所遇到的通信问题。该文的主要内容包括:1)DTN架构和Bundle协议的简介。2)典型DTN应用通信过程和束(bundle)结构的分析。     

基于城市公共交通移动模型的协作延迟容忍网络路由策略

如何利用有限的传输机会可靠地传送车载服务感知信息是智能交通发展的“瓶颈”问题,利用公共交通中车辆的运动规律,提出基于节点之间机会接触来进行消息的逐跳转发策略,同时结合公共交通系统自身的特点,设计了一种基于公共交通移动模型的协作延迟容忍网络（DTN）路由算法TF。首先,根据公共交通移动模型自身的特点,将公交、长途客车等节点按其运动路径进行分组,提出一种基于固定运动路径分组的DTN路由算法;然后,将出租车、行人类节点定义为自由节点,并设计了一种基于转发因子控制的DTN路由策略作为分组路由机制的补充。仿真结果表明,与Epidemic、Prophet以及SAW路由算法相比,TF路由算法具有较高的消息投递率和较低的平均延迟。     

延迟／中断容忍网络发展研究

延迟／中断容忍网络（DTN）具有长延时、某一时刻不存在端到端链路或者链路频繁中断等特点,作为一种新型体系结构,近年来受到广泛关注与研究。介绍了DTN网络的研究现状,分析了其体系结构特点,详细描述了目前DTN关键技术包括网络协议、路由与安全机制方面的研究进展及面临的挑战,最后介绍了DTN在深空探测、军事通信等领域的应用,指出了DTN在未来通信网络发展中的作用。