Delay/Disruption Tolerant Networks Research Articles

Deepwater Monitoring System in Underwater Delay/Disruption Tolerant Network

This paper proposes a deepwater monitoring system built with sensors distributed in Campos Basin offshore area. The underwater communications are undertaken by underwater acoustic modems installed on the sensors and vessels used for logistic support of the oil exploration. However, the vessels may not be within sensor range at all times, requiring the use of DTN (Delay/Disruption Tolerant Network). This work investigates the Monitoring system feasibility, analyzing the network behavior using ONE (Opportunistic Network Environment) simulator, adjusting the simulation scenarios to the characteristics of the Brazilian oil exploration area.

A DTN-Based Sensor Data Gathering for Agricultural Applications

This paper presents our field experience in data collection from remote sensors. By letting tractors, farmers, and sensors have short-range radio communication devices with delay-disruption tolerant networking (DTN), we can collect data from those sensors to our central database. Although, several implementations have been made with cellular phones or mesh networks in the past, DTN-based systems for such applications are still under explored. The main objective of this paper is to present our practical implementation and experiences in DTN-based data collection from remote sensors. The software, which we have developed for this research, has about 50 kbyte footprint, which is much smaller than any other DTN implementation. We carried out an experiment with 39 DTN nodes at the University of Tokyo assuming an agricultural scenario. They achieved 99.8% success rate for data gathering with moderate latency, showing sufficient usefulness in data granularity.

Improving performance in delay/disruption tolerant networks through passive relay points

In this paper, we study the case of a limited number of mobile nodes trying to communicate in a large geographic area, forming a delay/disruption tolerant network (DTN). In such networks the mobile nodes are disconnected for significantly long periods of time. Traditional routing protocols proposed for mobile ad hoc networks or mesh networks, which assume at least one path between each source and destination, are ineffective in DTNs. One approach to improve communication is through gossip based protocols because these protocols do not rely on a fixed path. Another approach is to control the movement of the mobile nodes and/or use special mobile nodes called ferry nodes. Others try to employ a fixed infrastructure including stationary relay points. One scheme in stationary relay point approach is to use base stations as relay points which need their own power supply. In this paper, we study a passive approach where mobile nodes deposit/retrieve messages to/ from known stationary locations in the geographic region. Messages are delivered from a source by being deposited at one or more locations that are later visited by the destination. A proposed implementation of our approach using read/writable passive Radio Frequency Identification (RFID) tags, one per point location, is considered in this work. Passive RFID technology is desirable because it operates wirelessly and without the need for attached power. Our simulation results indicate that our approach can achieve competitive message delay and delivery rates. We also demonstrate several techniques for optimizing the stationary relay node placement, namely relay pruning, probability based relay distribution and a genetic algorithm; the genetic algorithm is shown to provide the best solutions to this problem.

Adaptive Asynchronous Sleep Scheduling Protocols for Delay Tolerant Networks

In this paper, we focus on power management for Delay/Disruption Tolerant Network (DTN), and propose two asynchronous clock-based sleep scheduling protocols that are distributed, adaptive, and energy efficient. Moreover, the sleep schedules can be constructed using simple systematic algorithms. We also discuss how the proposed protocols can be implemented in mobile devices for adapting to dynamic network conditions in DTN. Theoretical analysis is given to demonstrate the energy efficiency and scalability of the proposed protocols. Simulation results show that the proposed protocols reduce the energy consumption in the idle listening mode up to 35 percent in comparison with other existing asynchronous clock-based sleep scheduling protocols, and more than 90 percent compared with the protocol without power management, while maintaining comparable packet delivery delay and delivery ratio.

도시 환경에서 지역적 주기성을 이용한 DTN 라우팅 기법

Delay/Disruption Tolerant Network (DTN)은 엔드-투-엔드 연결이 없더라도 중간 노드들의 이동성과 저장공간을 활용하여 궁극적으로 데이터를 전달시켜 주는 네트워크 패러다임으로써 장시간 전송을 요하는 고용량 데이터전송 또는 높은 이동성의 무선통신, 행성간 통신 같은 불완전한 망 연결에 적합하다. 본 논문에서는 노드의 지역적 주기성을 이용하는 새로운 DTN 라우팅 기법을 제안한다. 각각의 노드가 주기적으로 방문하는 고유의 영역을 가지는 성질을 지역적 주기성이라 정의하고 실제 상하이 4000대의 택시 데이터를 분석하여 이를 실험적으로 입증한다. 또한 각 차량 고유의 지역적 주기성을 대표하는 값으로써 Weighted Center (WC)의 개념을 소개한다. 도시 환경에서 곳곳에 고르게 분포되어 있는 Access Point (AP) 들을 통해 차량들이 자신이 속한 그리드의 정보를 얻고 이를 통해 자신의 WC를 계산할 때, 자신과 주변 차량들의 WC정보만을 이용해 메시지의 경로를 결정 하는 분산화된 Diff WC라우팅 기법을 제안한다. 신뢰도 높은 데이터를 제공하는 1486대의 상하이 택시 환경에서의 시뮬레이션을 통해 ECT, LET 등의 기존 DTN 라우팅 방식과 비교하여 10%~110%의 전달률 개선이 가능함을 검증한다. The Delay/Disruption Tolerant Network (DTN) is a network designed to operate effectively using the mobility and storage of intermediate nodes under no end-to-end guaranteed network. This new network paradigm is well-suited for networks which have unstable path and long latencies (e.g. interplanetary network, vehicular network). In this paper, we first found that each taxi has its own regularly visiting area and define this property as spatial regularity. We analyze 4000 taxi trace data in Shanghai and show the existence of spatial regularity experimentally. Based on a spatial regularity in urban environment, we present a new DTN routing method. We introduce a Weighted Center (WC) which represents spatial regularity of each node. Through the association with evenly distributed access points (APs) in urban environment, most of vehicles get their grid locations and calculate their WCs. Since our routing method only uses neighbors' WCs for building routing paths, it can be regarded as distributed and practical protocols. Our experiments involving realistic network scenarios created by the traces of about 1500 Shanghai taxies show that our routing method achieves the higher performance compared to ECT, LET by 10%~110%.

Reasonable routing in delay/disruption tolerant networks

Delay/disruption tolerant networking (DTN) is an approach to networking where intermittent connectivity exists: it is often afforded by a store and forward technique. Depending on the capability of intermediary nodes to carry and forward messages, messages can be eventually delivered to their destination by mobile nodes with an appropriate routing protocol. To have achieved a successful delivery, most DTN routing protocols use message duplication methods. Although messages are rapidly transferred to the destination, the redundancy in the number of message copies increases rapidly. This paper presents a new routing scheme based on a stochastic process for epidemic routing. Message redundancy is efficiently reduced and the number of message copies is controlled reasonably. During the contact process of nodes in the network, the number of message copies changes, and according to the variability in the number of copies, we construct a special Markov chain, birth and death process, on the number of message copies then calculate and obtain a stationary distribution of the birth and death process. Comparing the theoretical model with the simulation we have performed we see similar results. Our method improves on time-to-live (TTL) and antipacket methods, in both redundancy and delivery success efficiency.

Licklider Transmission Protocol (LTP)-Based DTN for Cislunar Communications

Delay/disruption-tolerant networking (DTN) technology offers a new solution to highly stressed communications in space environments, especially those with long link delay and frequent link disruptions in deep-space missions. To date, little work has been done in evaluating the performance of the available “convergence layer” protocols of DTN, especially the Licklider Transmission Protocol (LTP), when they are applied to an interplanetary Internet (IPN). In this paper, we present an experimental evaluation of the Bundle Protocol (BP) running over various “convergence layer” protocols in a simulated cislunar communications environment characterized by varying degrees of signal propagation delay and data loss. We focus on the LTP convergence layer (LTPCL) adapter running on top of UDP/IP (i.e., BP/LTPCL/UDP/IP). The performance of BP/LTPCL/UDP/IP in realistic file transfers over a PC-based network test bed is compared to that of two other DTN protocol stack options, BP/TCPCL/TCP/IP and BP/UDPCL/UDP/IP. A statistical method of t-test is also used for analysis of the experimental results. The experiment results show that LTPCL has a significant performance advantage over Transmission Control Protocol convergence layer (TCPCL) for link delays longer than 4000 ms regardless of the bit error rate (BER). For a very lossy channel with a BER of around 10-5, LTPCL has a significant goodput advantage over TCPCL at all the link delay levels studied, with an advantage of around 3000 B/s for delays longer than 1500 ms. LTPCL has a consistently significant goodput advantage over UDPCL, around 2500-3000 B/s, at all levels of link delays and BERs.

Introduction of the Parameter "Approach Ratio" for the Improvement of Higher Delivery Rate with Suppressing Network Resource Consumption in Delay Tolerant Network

SUMMARY The delay/disruption tolerant network (DTN) has been researched actively in the last years because of its high applicability to ubiquitous network services such as sensor networks and intelligent transport system (ITS) networks. An efficient data forwarding method for those network services is one of the key components in DTN due to the limitation of wireless network resources. This paper proposes a new DTN scheme for vehicle network systems by introducing the parameter, “approach ratio”, which represents node movement history. The proposal utilizes passive copy strategy, where nodes within one hop area of packet forwarders receive, copy and store packets (namely, passive copies) for future forwarding, in order to obtain higher delivery rate and lower delivery delay whilst suppressing the network resource consumption. Depending on its approach ratio, a node with passive copy decides whether it forwards the passive copy or not by referring to the approach ratio threshold. The approach ratio allows our proposal to adjust the property of both single-copy type scheme, that can lower network resource consumption, and multi-copy type scheme, that can enhance the performance of delivery rate and delay time. In simulation evaluation, the proposal is compared with three typical existing schemes with respect to network consumption, delivery rate and delivery delay. Our proposal shows the superior performance regarding the targeted purpose. It is shown that the approach ratio plays the significant role to obtain the higher delivery rate and lower delay time, while keeping network resource consumption lower.

A novel forwarding scheme for adaptive anycasting in delay/disruption-tolerant networks

Delay/disruption-tolerant networks (DTNs) are characterized by frequent and long duration partitions and end-to-end connectivity may never be present between the source and the destination at the message origination time. Anycast is an important service used for many applications in DTNs such as information exchange in hazards/crisis situation, resource discovery etc. In this paper, we propose classification of DTNs into three subcategories, namely: networks utilizing message ferries (MFN), interplanetary networks (IPN) and intermittently connected mobile Ad hoc networks (ICMAN). Further, we propose a novel anycasting scheme for ICMANs called receivers based forwarding (RBF), which considers the number of anycast receivers available through a link as well as the path length to the nearest receiver through that link in deciding the next hop while forwarding an anycast bundle. Simulation results with respect to link availability, group size and buffer size show that the RBF performs better than the shortest path forwarding (SPF) in term of data delivery ratio, average end-to-end delay and overall data efficiency. Keywords: Delay-tolerant networks, anycast, routing.

Experimental Evaluation of TCP-Based DTN for Cislunar Communications in Presence of Long Link Disruption

Delay/disruption tolerant networking (DTN) technology is considered a new solution to highly stressed communications in space environments. To date, little work has been done in evaluating the effectiveness and performance of the available DTN protocols when they are applied to an interplanetary Internet, especially in presence of a long link disruption. In this paper, we present an experimental investigation of the DTN architecture with a Bundle Protocol (BP) running over TCP-based convergence layer (TCPCL) protocol in a simulated cislunar communication environment characterized by a long link disruption. The intent of this work is to investigate the effectiveness of the TCPCL-based DTN protocol in coping with long link disruptions, through realistic file transfer experiments using a PC-based test-bed. The experiment results show that the DTN protocol is effective in handling a long link disruption experienced in data transmission accompanied by a cislunar link delay and a high BER. The performance of the DTN is most adversely affected by link disruption time in comparison to the effect of link delay and BER. For the transmissions with a very long link disruption of hours, the variations in goodput are nominal with respect to the change in cislunar link delay.

TCP Convergence Layer-Based Operation of DTN for Long-Delay Cislunar Communications

Delay/disruption tolerant networking (DTN) is a class of network techniques developed to accommodate long link delay and frequent link disruptions. Little work has been done in evaluating the effectiveness and performance of the DTN protocols when they are applied for an interplanetary Internet (IPN). In this paper, we present an experimental evaluation of Transmission Control Protocol Convergence Layer (TCPCL)-based operation of DTN-2 (i.e., TCPCL/TCP) for long-delay cislunar communications, partially in comparison with Licklider Transmission Protocol (LTP)-based LTP/User Datagram Protocol (UDP). The experiment is conducted by transmitting a text file using the DTN protocol stack over a PC-based simulation test-bed. According to the experimental results, the TCPCL-based DTN protocol works effectively over less error-prone cislunar links with short delay and has performance advantage over LTP-based DTN. Along with the increase in link delay and channel noise, the performance of TCPCL-based DTN is getting far behind the LTP-based DTN. The TCPCL-based DTN protocol can successfully handle an experimented short link disruption around 30 s-120 s, even with an existence of a very long link delay and a high channel Bit-Error-Rate (BER), but its performance is poor compared to that of the LTP-based DTN.

An efficient genetic algorithm for anycast routing in delay/disruption tolerant networks

Delay/Disruption tolerant networks (DTNs) have the capacity to interconnect devices and areas that are underserved by traditional networks. Anycast routing can be used for many applications in DTNs, and is useful when nodes wish to send messages to at least one, and preferably only one, of the members in a destination group. In this letter, an anycast routing algorithm for DTNs based on genetic algorithms (GAs) is presented. The GA is applied to find the appropriate path combination to comply with the delivery needs of a group of anycast sessions simultaneously. The proposed GA-based solution uses the concept of subpopulation to produce the next generation population, a limited number of solutions to be evaluated, and yields minimum delay to achieve a specified rate of delivery. Via simulations we show that this scheme can produce good results.

HYMAD: Hybrid DTN-MANET routing for dense and highly dynamic wireless networks

Delay/Disruption-Tolerant Network (DTN) protocols typically address sparse intermittently connected networks whereas Mobile Ad-hoc Network (MANET) protocols address the fairly stable and fully connected ones. But many intermediate situations may occur on mobility dynamics or radio link instability. In such cases, where the network frequently splits into evolving connected groups, none of the conventional routing paradigms (DTN or MANET) are fully satisfactory. In this paper we propose HYMAD, a Hybrid DTN-MANET routing protocol which uses DTN between disjoint groups of nodes while using MANET routing within these groups. HYMAD is fully decentralized and only makes use of topological information exchanges between the nodes. The strength of HYMAD lies in its ability to adapt to the changing connectivity patterns of the network. We evaluate the scheme in simulation by replaying synthetic and real life mobility traces which exhibit a broad range of connectivity dynamics. The results show that HYMAD introduces limited overhead and outperforms the multi-copy Spray-and-Wait DTN routing protocol it extends, both in terms of delivery ratio and delay. This hybrid DTN-MANET approach offers a promising venue for the delivery of elastic data in mobile ad-hoc networks as it retains the resilience of a pure DTN protocol while significantly improving performance.

Routing Techniques on Delay/Disruption Tolerant Networks

作为一种新型的体系结构,容延容断网络(delay/disruption tolerant network,简称DTN)近年来得到了广泛的研究与应用.由于其面临的应用环境极为特殊,传统网络的路由协议无法适用于DTN,各种针对DTN的路由技术相继提了出来.在对DTN路由进行形式化分析以后,提出了路由技术的分类方法,然后着重分析并比较了当前一些较为重要的路由技术的核心路由机制和特点.最后总结DTN路由技术的研究现状以及存在的问题,指出未来路由研究的重点.;In the recent years, as a new emerging network architecture, Delay/Disruption Tolerant Networks (DTNs) have received extensive attention and are widely investigated. Since the major application scenarios of DTN are extremely particular routing protocols designed for the traditional networks are not suitable for DTN. Therefore, numerous routing protocols have been proposed for DTN. In this paper, the formulation issues of DTN routing protocols are firstly studied, and the classification concerns are then proposed for those protocols. Thereafter, this paper focuses on analyzing and comparing existing representative DTN routing protocols. Finally, current research status and the existing problems about DTN routing protocols are summarized, the key issues and future trends in DTN routing are pointed out.

DTN Bundle Layer over TCP: Retransmission Algorithms in the Presence of Channel Disruptions

“Challenged n etworks” often violate the TCP design key assumption of continuous path availability from the source to the sink node. These networks are the preferred target of Delay/Disruption Tolerant Networking (DTN), which aims at providing a more robust network architecture. Against disruptions, however, even standard TCP offers a certain level of robustness, through its many retransmission algorithms. This intrinsic TCP resilience against disruptions is retained and enhanced if TCP is inserted in a DTN architecture. Focusing on this, the aim of the paper is to present an in-depth analysis of TCP and DTN bundle protocol retransmission algorithms that are triggered by channel disruptions, thus providing the reader with a comprehensive view of the many mechanisms involved and their complex interactions. The first sections, devoted to the description of TCP and DTN algorithms, are completed by the presentation of some numerical evaluations obtained by means of a Linux testbed. They refer to a GEO satellite environment and clarify the previous algorithm descriptions. Moreover, they also offer the reader some useful insights on both TCP and DTN resilience to disruptions, considering some performance metrics, like the “ maximum tolerable disrupti on length” and the “restart delay”, introduced and explained in the paper.

LOPP: A Location Privacy Protected Anonymous Routing Protocol for Disruption Tolerant Network

In this paper, we propose an anonymous routing protocol, LOPP, to protect the originator's location privacy in Delay/Disruption Tolerant Network (DTN). The goals of our study are to minimize the originator's probability of being localized (Pl) and maximize the destination's probability of receiving the message (Pr). The idea of LOPP is to divide a sensitive message into k segments and send each of them to n different neighbors. Although message fragmentation could reduce the destination's probability to receive a complete message, LOPP can decrease the originator's Pl. We validate LOPP on a real-world human mobility dataset. The simulation results show that LOPP can decrease the originator's Pl by over 54% with only 5.7% decrease in destination's Pr. We address the physical localization issue of DTN, which was not studied in the literature.

A DTN approach to satellite communications

Satellite communications pose serious challenges to transport layer performance, mainly because of long propagation delays (especially in geosynchronous systems) and the possi ble presence of random errors on the satellite link. Solutions that cope with these impairments usually rely upon either the adoption of enhanced versions of transport protocols, or the insertion of intermediate agents, like PEPs (Performance Enhancing Proxies). An alternative approach is to adopt the DTN (Delay/Disruption Tolerant Networking) architecture based on the introduction of the new "bundle" layer in the protocol stack. The aim of the paper is to discuss the advantages and disadvantages of the DTN approach compared to the more conventional solutions mentioned. DTN performance is assessed by considering both fully connected networks and networks where continuous connectivity cannot be guaranteed during data transfer and/or at start-up. Performance is evaluated by using the TATPA testbed (Testbed for Advanced Transport Protocols and Architectures), which is based on a cluster of Linux PCs running the DTNperf application, developed to this end by the authors and now included in the official DTN package. Comparative results show that DTN, coupled with TCP Hybla, outperforms NewReno, offering a performance very close to PEPsal and end- to-end Hybla, which are among the most effective solutions on satellite channels. In addition to these encouraging results, DTN offers an intrinsic greater robustness in intermittent or disruptive environments.

DTN: an architectural retrospective

We review the rationale behind the current design of the Delay/Disruption Tolerant Networking (DTN) Architecture and highlight some remaining open issues. Its evolution, from a focus on deep space to a broader class of heterogeneous networks that may suffer disruptions, affected design decisions spanning naming and addressing, message formats, data encoding methods, routing, congestion management and security. Having now achieved relative stability with the design, additional experience is required in long-running operational environments in order to fine tune our understanding of DTN concepts and the types of capabilities that are worth the investment in implementation complexity. We expect key management, handling of congestion, multicasting capability, and routing to remain active areas of research and development, and that DTN may continue to be an active research endeavor for at least the next few years.

The time-correlated update problem

Recent advances in the fields of sensor networks and mobile robotics have provided the means to place monitoring/sensing equipment in an increasingly wide variety of environments - a significant proportion of which can reasonably be expected to lack traditional network connectivity characteristics [5] [8]. Challenged networks, operating under significant sets of constraints in which disconnected paths and long delays are normal events, have come to be known as Delay/Disruption Tolerant Networks (DTN) [2]. Some examples of environments in which DTN techniques may be required include remote or vast domains such as underground, underwater, outer-space, Arctic, and mountainous environments.

Delay/disruption tolerant mobile ad hoc networks: latest developments

AbstractThere is much research activity in the emerging area of delay/disruption tolerant networks (DTN) in the past few years. DTNs pose many new challenges, and protocols designed for wired Internet or wireless mobile ad hoc networks do not work properly in DTNs. Routing is one of the key components in DTNs and the message ferry (MF) approach has been drawn a lot of attention to support routing in DTNs. Besides the underlying routing protocols, issues in transport layer are also very important and need to be addressed for DTNs. Recently, many new routing protocols, including unicast using the MF approach, inter‐region routing and multicast, have appeared in the literature. There are also a few works addressing issues in the transport layer. This paper provides an overview on recent developments including message ferrying, multicast support, inter‐region routing, and transport layer issues. It also points out some open research issues and intends to motivate new research and development in this area. Copyright © 2007 John Wiley & Sons, Ltd.