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Author(s): Joel Rodrigues | Farid Farahmand | Wai Chen

Journal: Journal of Communications
ISSN 1796-2021

Volume: 5;
Issue: 2;
Start page: 89;
Date: 2010;
Original page

Keywords: Special Issue | Delay Tolerant Networks

ABSTRACT
It is our great pleasure to bring you this special issue of Journal of Communications on delay/disruption-tolerant networking (DTN). The goal of this special issue is to bring together the state-of-the-art research contributions that address various aspects of delay/disruption-tolerant communications, networks, architecture, and applications.The basic concept of DTN was originally derived from the work in Interplanetary Internet (IPN). In the early years of 2000’s, researchers implemented the IPN basic design to terrestrial networks and coined the term delay-tolerant networking (DTN). In spite of its infancy, this field has attracted a growing number of researchers. Today, a large body of academic conferences is solely focused on delay/disruption-tolerant networking. The most attractive feature of DTNs is its ability to address an increasing number of networks that exhibit intermittent connectivity. Having sparse connection can be due to various factors, including sever power fluctuations, wireless range, network partitioning, catastrophic disasters, or malicious attacks. Thus, the so called challenged networks often violate end-to-end network connectivity assumption and therefore, may not be well served by the current end-to-end TCP/IP model. Consequently, applications of DTNs are highly diverse and can be expanded to a wide variety of areas. Examples of such areas are interplanetary networks for deep space communications, sensor networks for ecological monitoring, transient networks to benefit developing communities, ad hoc networks to disseminate information in tactical or roadway environments, and disaster recovery networks to restore communications following a natural disaster. Diversity of network environments and inherent uncertainty about network conditions make design of DTNs highly challenging in terms of architecture, protocol designs, interoperability, security, management, and stability. This special issue has as its objective to compile a set of studies covering different aspects of DTNs and thus, stimulating activity in the research community. We are deeply grateful of receiving so many excellent works. The number of papers submitted to this special issue overwhelmed its capacity. The revision process for all papers was rigorous and thorough, including peer-reviewing from at least three qualified reviewers. For this special issue we were limited to select only six quality papers. These works fall into various areas of DTN design, architecture, simulation, routing, security, and application.  The first paper in this special issue is an invited work by Ari Keränen, Teemu Kärkkäinen, and Jörg Ott. In their contribution, entitled Simulating Mobility and DTNs with the ONE, the authors introduce the Opportunistic Networking Environment (ONE) simulator specifically designed for evaluating DTN routing and application protocols. The authors demonstrate tremendous capabilities supported by the simulator critical to implementing various scenarios in DTN including, mobility and event generation, message exchange, a basic notion of energy consumption, visualization and analysis, interfaces for importing and exporting mobility traces, events, and entire messages. Furthermore, in this work the authors report their results from implementing a set of ready-to-use modules to approximate real-world mobility scenarios including, six configurable well-known DTN routing schemes, and a set of base primitives to design application protocols. Delay/disruptive-tolerant networks are considered to violate the TCP design key assumption of continuous path availability from the source to the sink node. In their work, Understanding the DTN Bundle Layer over TCP: Retransmission Algorithms in the Presence of Channel Disruptions, C. Caini, R. Firrincieli and M. Livini demonstrate that standard TCP can offer a certain level of robustness, through its many retransmission algorithms. This work offers an in-depth analysis of TCP and DTN bundle protocol retransmission algorithms when channel disruptions exist. The authors study end-to-end TCP, single hop DTN and end-to-end DTN, and demonstrate various mechanisms involved in the process and their complex interactions. Through numerical evaluations, the authors evaluate and test TCP and DTN retransmission procedures in the context of a GEO satellite connection undergoing variable length channel disruptions. A critical and challenging aspect of delay/disruptive-tolerant networks is routing. In their work, Adding Redundancy to Replication in Window-aware Delay-tolerant Routing, Gabriel Sandulescu and Simin Nadjm-Tehrani address the routing problem in sparse networks and propose a new routing algorithm that exploits the store and-forward mechanism in delay-tolerant networking. The proposed Opportunistic Routing with Window-Aware Replication (ORWAR) routing algorithm is based on calculation of the maximum deliverable bundle size estimated from the mobility context and it combines selected replication and delivery acknowledgment from existing routing algorithms. The performance of the algorithm is compared with existing algorithms such as Direct Delivery, Epidemic, Prophet, MaxProp and SprayAndWait, as well as SprayAndWait and MaxProp.  Focusing on partially connected VANETs, in A Border Node Based Routing Protocol for Partially Connected Vehicular Ad Hoc Networks, Mingliu Zhang and Richard S. Wolff also investigate routing issues. In their work, the authors propose a Border node Based Routing (BBR) protocol. The BBR protocol is based on broadcast and applies the store-and-forward approach used in epidemic routing. In their work, instead of simply flooding the network, the authors explore a flooding control scheme by only using one-hop neighbor information. The authors compare the performance of BBR with DSR and epidemic routing protocols. In Stochastic Time Evolving Routing Protocol in Delay-Tolerant Networks based on Energy and Delay Metrics, Nesrine Ouferhat and Abdelhamid Mellouk consider Wireless sensor networks (WSN) as a particular type of delay tolerant networks that exhibit intermittent connectivity. In their work they present a new way to make adaptive routing with quality of service in order to improve the end-to-end delay and increase the lifetime of a sensor network. This approach is based on finding the best path in terms of energy and delay to route information using a reinforcement learning paradigm. Thus, an explorer agent is proposed to learn from past experiences in order to choose the next path. Through simulation, the authors demonstrate the efficiency of their proposed approach and compare them to traditional approaches. Security and Limiting unauthorized traffic in delay/disruptive-tolerant networks has been proven to be another challenging area. The final paper in this special issue, Preventing Unauthorized Messages and Achieving End-to-End Security in Delay Tolerant Heterogeneous Wireless Networks, is dedicated to address security in DTNs. In this work Hany Samuel and Weihua Zhuang propose two schemes for preventing unauthorized traffic in a mobile ad hoc network MANET. These techniques are based on utilizing a super architecture, which employs symmetric key cryptography to reduce the computation overhead associated with public key cryptography. The proposed symmetric key based scheme is extended to achieve end-to-end security. The authors carry out extensive simulations evaluating the performance of their proposed schemes in terms of delay and extra message exchanges. In closing, once again, we would like to emphasize that this special issue was only possible through the efforts of our authors and the reviewers who helped in the decision process. It is with gratitude that we thank all of them. 

Tango Jona
Tangokurs Rapperswil-Jona

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