The introduction of intelligent devices with short range wireless communication techniques has motivated the development of Mobile Ad hoc NETworks (MANETs) during the last few years. However, traditional end-to-end based routing algorithms designed for MANETs are not much robust in the challenged networks suffering from frequent disruption, sparse network density and limited device capability. Such challenged networks, also known as Intermittently Connected Networks (ICNs) adopt the Store-Carry-Forward (SCF) behavior arising from the mobility of mobile nodes for message relaying. In this article, we consider the term ICNs as Delay/Disruption Tolerant Networks (DTNs) for the purpose of generalization, since DTNs have been envisioned for different applications with a large number of proposed routing algorithms. Motivated by the great interest from the research community, we firstly review the existing unicasting issue of DTNs because of its extensive research stage. Then, we also address multicasting and anycasting issues in DTNs considering their perspectives. A detail survey based on our taxonomy over the period from 2006 to 2010 is not only provided but also a comparison is given. We further identify the remaining challenges and open issues followed by an evaluation framework proposed for routing in DTNs. Finally, we summarize our contribution with three future research topics highlighted.

Routing in Delay/Disruption Tolerant Networks: A Taxonomy, Survey and Challenges

The ever increasing volume of air transport necessitates new technologies to be adopted by the flight industry to fulfill the requirements of safety, security, affordability, and environmental friendliness while still meeting the growing demand. What we need to achieve this goal is a new type of aircraft cruise control, interconnecting all the onboard active control systems and making more accurate control decisions than is currently possible, thus improving overall flight efficiency. Active Aircraft envisions such a nervous system of distributed wireless sensor and actuator network components, enabling the early detection of potential problems and quick, accurate reactions to these. As part of this vision, WSANs deployed on aircraft wings help reduce aerodynamic drag and significantly reduce fuel consumption. In this article we first describe this conceptual change in aircraft control technology. We then introduce a WSAN application to reduce skin friction drag and a network topology to enable it. In our application WSANs form virtual flap arrays on the wings to measure the skin friction in real time and to react using synthetic jet actuators, which suck and expel air on the wing to reduce the friction. The Active Aircraft vision imposes stringent performance requirements on the underlying WSAN communication algorithms. The medium access control and routing protocols, in particular, must meet the quality of service criteria set by active control applications. Thus, we also present the application characteristics of Active Aircraft and raise the issue of design considerations with regard to the communication protocols.

Wireless sensor and actuator networks: Enabling the nervous system of the active aircraft

Spectral clustering and its use in bioinformatics

Satellite systems have attracted great attention from academic and industrial communities in recent years. There are many satellites that have been launched for weather forecast, environment monitoring, and target surveillance. One important task of the satellites is to download the data they have collected in space to the ground servers via earth stations (ESs). Since satellites move at high speed along their own orbits and have very limited contact time with ESs, satellites may not be able to download all the data they have to the ground on time. In this paper, we propose a collaborative scheme that allows satellites to offload data among themselves using inter-satellite links (ISLs) before they come into contact with the ES, such that satellites will carry the right amount of data according to the length of their contact time with the ES and the throughput of data downloading at the ES is maximized. We develop an iterative optimization algorithm that jointly schedules data offload among the satellites and data downloading from satellites to the ES. Extensive simulations have been conducted to evaluate the effectiveness of our proposed method. The simulation results show that the data downloading throughput by using ISL data offload can be increased significantly. In many cases, the throughput reaches close to 100% of the capacity of the ES.

Collaborative Data Downloading by Using Inter-Satellite Links in LEO Satellite Networks

Delay and disruption tolerant networks (DTNs) may experience frequent and long-lived connectivity disruptions. Unlike traditional networks, such as the TCP/IP-based Internet, DTNs are often subject to high latency caused by very long propagation delays (e.g., interplanetary communication) and/or intermittent connectivity. Another feature that sets DTNs apart from conventional networks is that there is no guarantee of end-to-end connectivity between source and destination. Such distinct features pose a number of technical challenges in designing core network functions such as routing and congestion control. In this paper, we survey the state-of-the-art in DTN congestion control. We propose a taxonomy to map the DTN congestion control design space and use it to classify existing DTN congestion control mechanisms.

A survey on congestion control for delay and disruption tolerant networks

When designing routing protocols for space-based networks, we must take into consideration the unique characteristics of such networks. Since space-based networks are inherently sparse with constrained resources, one needs to design smart routing algorithms that use the resources efficiently to maximize network performance. In Space Exploration Missions, the trajectories and orbits of spacecraft are predetermined, thus communication opportunities are predictable. This a-priori knowledge can be used to the advantage of scheduling and routing. In this paper, we focus on analyzing Contact Graph Routing (CGR) for space-based networks. CGR makes use of the predictable nature of the contacts to make routing decisions. Mars and Lunar mission-like scenarios were used in our simulations to gather statistics on routing protocol performance in terms of delay and buffer usage. We provide improvements to the underlying cost function of CGR to avoid routing loops and suggest applying Dijkstra's shortest path algorithm for path selection. The cost function change was incorporated into the latest Internet Draft posted for CGR. Dijkstra's shortest path algorithm was successfully implemented and tested in NASA's Interplanetary Overlay Network (ION) implementation of the DTN protocols.

Enhancing Contact Graph Routing for Delay Tolerant Space Networking

Congestion control is an important feature that directly affects network performance Network congestion may cause loss of data or long delays Although this problem has been studied extensively in the Internet, the solutions for Internet congestion control do not apply readily to challenged network environments such as Delay Tolerant Networks (DTN) where end-to-end connectivity may not exist continuously and latency can be high In DTN, end-to-end rate control is not feasible This calls for congestion control mechanisms where the decisions can be made autonomously with local information only We use an economic pricing model and propose a rule-based congestion control mechanism where each router can autonomously decide on whether to accept a bundle (data) based on local information such as available storage and the value and risk of accepting the bundle (derived from historical statistics) Preliminary experimental results show that this congestion control mechanism can protect routers from resource depletion without loss of data

Autonomous Congestion Control in Delay-Tolerant Networks

Space-based multi-hop networking

Precision formation flying (PFF) missions involve the tracking and maintenance of spacecraft in a desired geometric configuration. Autonomous control of the distributed spacecraft requires inter-spacecraft communications with guaranteed performance. We present a network architecture that supports PFF control across the various phases of mission operations, ranging from initial random deployment to precision formation. The architecture incorporates the IEEE 802.11 MAC protocol and utilizes both its distributed control function (DCF) and point coordination function (PCF) modes as appropriate to the PFF operational phase. A proactive routing protocol provides timely topology status. A new application layer protocol is incorporated which provides a simple interface between the PFF control application and the underlying communications network

Esther Jennings

Papers

Enhancing Contact Graph Routing for Delay Tolerant Space Networking

Autonomous Congestion Control in Delay-Tolerant Networks

Space-based multi-hop networking

A network architecture for precision formation flying using the IEEE 802.11 MAC protocol

Autonomous Congestion Control for an Interplanetary Internet