Towards Software-Defined Delay Tolerant Networks

Information-Centric Networking (ICN) is a prominent topic in current networking research. ICN design significantly considers the increased demand of scalable and efficient content distribution for Future Internet. However, intermittently connected mobile environments or disruptive networks present a significant challenge to ICN deployment. In this context, delay tolerant networking (DTN) architecture is an initiative that effectively deals with network disruptions. Among all ICN proposals, Content Centric Networking (CCN) is gaining more and more interest for its architectural design, but still has the limitation in highly disruptive environment. In this paper, we design a protocol stack referred as CCNDTN which integrates DTN architecture in the native CCN to deal with network disruption. We also present the implementation details of the proposed CCNDTN. We extend CCN routing strategies by integrating Bundle protocol of DTN architecture. The integration of CCN and DTN enriches the connectivity options of CCN architecture in fragmented networks. Furthermore, CCNDTN can be beneficial through the simultaneous use of all available connectivities and opportunistic networking of DTN for the dissemination of larger data items. This paper also highlights the potential use cases of CCNDTN architecture and crucial questions about integrating CCN and DTN.

In recent years, several investigations have been made on "challenged network" [also known as, delay tolerant network (DTN)] architectures highlighting their advantages and disadvantages. In spite of its inherent shortcomings of unreliability and delay, smart-phone based opportunistic network is gaining immense popularity in the research community due to its applicability in different adverse and extreme communication scenarios where traditional communication infrastructure is either unavailable or incapacitated for a long time. Considerable research has been conducted till date to design efficient network architecture for emergency data dissemination in intermittently connected/challenged networks. Different architectures (ranging from flat to multi-tier) are proposed for implementing opportunistic DTN keeping in view of specific application requirements. However, very few of these proposed architectures have been examined from the perspective of a post disaster communication. Moreover, most DTN architectures are designed by aiming towards increasing delivery probability and reducing latency and as a whole, maximizing network throughput; with very little emphasis on its energy efficiency. The impact of different mobility patterns on existing DTN routing algorithms with respect to data dissemination and energy consumption has also not been studied so far. Our objective, in this paper, is to investigate the impact of different mobility patterns on existing DTN routing protocols and existing DTN architectures and subsequently, come up with a suitable energy efficient DTN framework combining suitable architecture and routing protocol that may be used to offer different disaster management services during post-disaster relief operation. We have done an extensive simulation on ONE simulator with different categories of well-known existing DTN architectures, mobility models, DTN routing protocols to study the network performance in terms of delivery probability, energy efficiency and overhead ratio. Based on the simulation results, we have tried to figure out a suitable combination of energy efficient architecture, mobility model and routing protocol that fits well in the post disaster communication scenario.

The High-Rate Delay Tolerant Networking (HDTN) project has taken a distributed service-based approach to the development of a highly efficient delay tolerant networking (DTN) implementation. Through the analysis of many DTN implementations, system and mission requirements as well as the DTN protocol specifications, HDTN has worked to infuse modern computing technologies into the NASA approach to interplanetary networking.The initial use case of the HDTN software runs on a hypervisor representative of the International Space Station (ISS) DTN Gateway. In this scenario, multiple emulated payloads will send science data through HDTN to a mission operations center. HDTN will provide store and forward capability as well as network flow management.This paper discusses the infusion path of cognitive networking technologies in the NASA Space Communications and Navigation (SCaN) networks using the DTN architecture and protocols as the basis for cognitive routing and network management capabilities. HDTN has been developing the Bundle Protocol encoding and decoding mechanisms and messaging framework that can be used as the basis for integrating DTN with various learning and decision-making processes. The concepts of distributed computing, network virtualization, software defined networking and delay tolerant networking are basic building blocks which will further the development of cognitive networking. In addition to discussion of the HDTN software development and testing, this paper examines the role that each of these technologies play in the evolution of the current state of space networking into an intelligent network of networks.

Delay-tolerant network (DTN) architectures have recently been proposed as a means to enable efficient routing of messages in vehicular area networks (VANETs), which are characterized by alternating periods of connectivity and disconnection. Under such architectures, when multihop connectivity is available, messages propagate at the speed of radio over connected vehicles. On the other hand, when vehicles are disconnected, messages are carried by vehicles and propagate at vehicle speed. Our goal in this paper is to analytically determine what gains are achieved by DTN architectures and under which conditions, using the average message propagation speed as the primary metric of interest. We develop an analytical model for a bidirectional linear network of vehicles, as found on highways. We derive both upper and lower bounds on the average message propagation speed by exploiting a connection with the classical pattern-matching problem in probability theory. The bounds reveal an interesting phase transition behavior. Specifically, we find out that, below a certain critical threshold, which is a function of the traffic density in each direction, the average message speed is the same as the average vehicle speed, i.e., DTN architectures provide no gain. On the other hand, we determine another threshold above which the average message speed quickly increases as a function of traffic density and approaches radio speed. Based on the bounds, we also develop an approximation model for the average message propagation speed that we validate through numerical simulations.

While portable and wireless devices are pouring, a new network technology is needed as a breakthrough. The new network technology features large delays, intermittent connectivity, and absence of an end-to-end path from sources to destinations. A network which has one of those characteristics is called DTNs(Delay Tolerant Networks). The main 4 routing methods have been researched so far in extreme environment. In this paper, we look into the reliability of DTMNs(Delay Tolerant Mobile Networks) in several different situations, and propose an algorithm that selects a positive routine by sending the only information of its position when making a connection to a detected node. We simulate the proposed algorithm here in DTN using ONE simulator. As a result, it shows that the algorithm reduces the number of message transmission each node.

The increase of data-rates that are provided by free-space optical (FSO) communications is essential in our data-driven society. When used in satellite and interplanetary networks, these optical links can ensure fast connections, yet they are susceptible to atmospheric disruptions and long orbital delays. The Delay and Disruption Tolerant Networking (DTN) architecture ensures a reliable connection between two end nodes, without the need for a direct connection. This can be an asset when used with FSO links, providing protocols that can handle the intermittent nature of the connection. This paper provides a review on the theoretical and state-of-the-art studies on FSO and DTN. The aim of this review is to provide motivation for the research of an optical wireless satellite network, with focus on the use of the Licklider Transmission Protocol. The assessment presented establishes the viability of these networks, providing many examples to rely on, and summarizing the most recent stage of the development of the technologies addressed.

This article is the second of a three-part series in which we present the results of a study exploring concepts for improving communications and tracking capabilities of deep space SmallSats. In Part I, we discussed SmallSat direct-to-earth links and SmallSat communications equipment, and provided recommendations for future work. In Part II, we focus on SmallSat navigation options, Disruption Tolerant Networking (DTN), proximity links, and the use of the communication link for science observations, and we provide recommendations for future work. We have examined both radio and optical navigation options, and considered autonomous and semiautonomous navigation to reduce operational costs for planetary SmallSats. We note that communication link resilience to delay and disruption enhances spacecraft autonomy; therefore, we have provided a discussion of DTN to indicate that using DTN allows for automated data transmission and recovery, therefore, reducing manual operations. SmallSats in deep space may utilize a relay spacecraft for communications with earth or function as a relay for landed and in-orbit assets. We present a detailed examination of relay proximity links and networks where we address both proximity hardware and networking scenarios. The proximity link features that we examine include the network architecture and its relationship to DTN, proximity radios and antennas, communications link performance, and proximity navigation. The use of the communication link for science has been practiced by primary missions in deep space scenarios. (Two examples of past planetary radio science experiments can be found in the following: https://solarsystem.nasa.gov/missions/cassini/mission/spacecraft/cassini-orbiter/radio-science-subsystem/ and https://www.boulder.swri.edu/pkb/ssr/ssr-rex.pdf) Likewise, SmallSats can offer their radio links for radio science investigations. This article provides a brief introduction to radio science and presents the prerequisite features necessary for radio science observations by SmallSats. We conclude with nine recommendations based on the findings of the study. These recommendations are guidelines on the design, implementation, and operation of deep space SmallSat communication links. The adoption of some or all of the guidelines should result in an enhanced communication and tracking capability for the deep space SmallSat missions.

Delay Tolerant Network (DTN) is a sparse and intermittently connected mobile wireless network where reliable communication and end-to-end connectivity cannot be assured. In DTN, a node delivers messages to the destination using store and forward scheme. Messages are copied and transferred to multiple relay-nodes in order to increase the opportunity for that message to reach the intended destination. Contact is the time duration for which two or more mobile nodes encounter each other within their radio transmission ranges, and are able to transfer messages. Due to arbitrary node movement, contact time will be varied, and is unlikely to be predictable. In this paper, we propose a fuzzy decision mechanism we called “fuzzy-spray”, to improve the routing and packet transfer efficiency in DTN environment. Fuzzy-spray can reduce overall latency in DTN by intelligently selecting appropriate messages to send to the relay-node during its next contact time. It uses fuzzy logic to prioritize messages that are stored in the buffer, based only on local parameters from each message, namely forward transmission count and message size. There is no need to know a priori information about network such as node mobility model, or node-distribution across the deployed area. The simulation results show that fuzzy-spray has the best performance in terms of overall speed of delivery, and lowest average message delay compared with other existing algorithms.

Despite the notable progress that has been achieved on long-haul radio and optical communications, which are expected to improve the data transfer rates of future space exploration missions, both scheduled and random link outages remain possible. To improve reliability, NASA’s delay-tolerant networking (DTN) architecture offers the Bundle Protocol (BP) and the Licklider Transmission Protocol (LTP) that implement bundle custodial transfer and automatic repeat query retransmissions. We analyze the performance of these protocols considering the default flow control method of LTP, which limits the number of concurrent sessions. We derive the combined BP and LTP throughput and provide approximations for model parameters that are difficult to find exactly. Event-driven simulations suggest that our analysis is reasonably accurate under different channel conditions and protocol settings. The proposed model provides insight into the role of the channel conditions, the workload, and the choice of BPLTP protocol parameters on the performance of a reliable space link.

7 - Assessing the Bundle Protocol (BP) and alternative approaches to data bundling in delay-tolerant networks (DTNs)

Near Earth missions and deep space missions will continue to be a major future space mission. A long link disruption is inevitable in space communications because of spacecraft rotation, planetary bodies and limited relay capability. A few works have been done with delay/disruption tolerant networking (DTN) technology for deep space communications and provided feasibility for its adoption in LEO- space and deep space missions. However, not much work has been done to fully evaluate the performance of DTN in such an environment, especially in the presence of custody and long link transfer. In this article, we present an experimental performance evaluation of DTN architecture and protocol stack with DTN custody transfer and long link break underneath bundle protocol (BP), in typical LEO-satellite and deep space communication infrastructures accompanied. The experiment was conducted by performing realistic file transfers over a PC-based test-bed.

13 - The quest for a killer app for delay-tolerant networks (DTNs)

Many real world networks are characterized by long delays, frequent path breaks, mobility, and lack of infrastructure. Class of networks which can cope up with such environments are called Delay Tolerant Networks (DTN). Architectures with a separate bundle layer, have been implemented in specific applications such as interplanetary networks (IPNs). However, the addition of bundle layer to existing network infrastructure still remains as a challenge. In this paper, we propose Dual-mode TCP which can work in both normal and DTN modes. It analyzes the network behavior and switches to DTN mode when the network exhibits DTN characteristics. For the estimation of network characteristics, Dual-mode TCP analyzes the RTT values and models the network based on RTTs normal distribution. If the network is found to be in DTN mode, the protocol uses a DTN congestion window to get adapted with the high delay environment. The advantage of Dual-mode TCP over traditional TCP is its ability to adapt with DTN environments while preserving the compatibility of TCP. We implemented Dual-mode TCP using light-weight IP and our results show that, in DTN environments, an average improvement of 11.64% in total transmission time can be achieved using Dual-mode TCP as compared to traditional TCP. With varying duration of link delays Dual-mode TCP achieves an average reduction of 36.19% in transmission time.

Delay Tolerant Networking (DTN) has been proposed as a new architecture to provide efficient store-carry-and-forward data transport in satellite networks. Since these networks relay on scheduled contact plans, the Contact Graph Routing (CGR) algorithm can be used to optimize routing and data delivery performance. However, in spite of the various improvements that have been made to CGR, there have been no significant proposals to prioritize traffic with different quality of service requirements. In this work we propose adaptations to CGR that allow performance improvements when sending traffic with different latency constraints, and develop a linear programming optimization model that works as a performance upper bound. The simulation results of the proposed schemes are promising and open the debate on other ways to improve performance while meeting the particular needs of heterogeneous traffic.

Generic prediction assisted single-copy routing in underwater delay tolerant sensor networks