Delay/disruption-tolerant networking (DTN) is a networking technology conceived to manage opportunistic connections with no consistent end-to-end link connectivity which is common in both terrestrial and space communication environments. DTN is recognized as a baseline technology for implementing deep-space networks. Considered as the primary transport protocol of DTN in space, Licklider transmission protocol (LTP) is expected to provide reliable data delivery service in a challenging networking environment regardless of presence of random link disruptions and/or extremely long propagation delays. The National Aeronautics and Space Administration (NASA) has implemented the use of DTN protocols on the International Space Station (ISS) for data delivery to the earth ground station. However, little work has been done in studying the performance of LTP for reliable data/file delivery in such a communication environment, especially in presence of link disruption. There is a lack of a solid performance evaluation of LTP for its use in the space station communications. In this paper, an analytical framework is presented to evaluate the performance of LTP for reliable file delivery between the space station and the ground stations with a focus on the effect of link disruption, which may occur either over the downlink or over the uplink. The effect of data loss due to channel error is also integrated. Realistic data block transmission experiments using a PC-based experimental infrastructure are conducted to validate the analytical models.

Contact Graph Routing (CGR) is the state-of-the-art deterministic routing approach for scheduled space Delay-tolerant Networks (DTN). Indeed, CGR outlined the Schedule-Aware Bundle Routing (SABR) recommended standard from the Consultative Committee for Space Data Systems (CCSDS). The core approach exploits the predictability of space node mobility patterns and link availability, which is imprinted in time-varying graphs fed to Dijkstra and Yen's algorithms for route computation (pathfinding). This paper addresses the scalability issues CGR faces when computing routes over large-scale contact plans spanning several nodes and long-term planning horizons. After an in-depth analysis of the main CGR computation limitations, we propose multipath-tracking and tree-caching embedded in the Shortest-Path tree routing for Space Networks (SPSN) routing scheme. Simulation results show that SPSN's route computation time does not increase with increasing contact plan horizon while slightly improving on CGR's delivery rate.

Recently, the availability of innovative and affordable COTS (Commercial Off-The-Shelf) technological solutions and the ever-improving results of microelectronics and microsystems technologies have enabled the design of ever smaller yet ever more powerful satellites. The emergence of very capable small satellites heralds an era of new opportunities in the commercial space market. Initially applied only to scientific missions, Earth observation and remote sensing, small satellites are now being deployed to support telecommunications services. This review paper examines the operational features of small satellites that contribute to their success. An overview of recent advances and development trends in the field of small satellites is provided, with a special focus on telecommunication aspects such as the use of higher frequency bands, optical communications, new protocols, and advanced architectures.

Delay/disruption tolerant networking (DTN) was proposed for reliable data transfer despite frequent link disruptions and long propagation delay that are typical of the deep-space communication environment. DTN communications rely heavily on its core bundle protocol (BP) for reliable data delivery. To date, little work has been seen in theoretical analysis of the performance of BP in deep-space communications. In particular, an analytical understanding of the performance of BP for reliable data delivery in a deep-space communication environment in the presence of link disruptions is quickly needed. In this paper, we present a study of the effect of link disruption on transmission performance of BP, in both analytical and experimental manners, in a deep-space communications system characterized by link disruptions accompanied by an extremely long propagation delay and lossy data links. For the first time, an analytical framework is built to estimate the effect of link disruption on the total bundle delivery time of BP depending on its starting time with respect to bundle delivery. The analytical models are validated by running experiments using a test bed.

Ring Road Networks (RRNs) have been introduced as a solution to transfer data between different ground stations by means of a world-wide message-ferry system built upon low Earth orbit (LEO) satellites. The objective of this work is to study the benefits and challenges of including Inter-Satellite Links (ISL) capabilities into RRNs. In this context, an appealing RRN case study is presented and evaluated through simulations based on Delay/Disruption-tolerant Network (DTN) protocols and algorithms. Results show that even though the overall delivery metrics improve with ISLs, network congestion impedes a more efficient utilization of the communication resources.

In this paper, we propose a novel congestion control framework for delay- and disruption tolerant networks (DTNs). The proposed framework, called Smart-DTN-CC, adjusts its operation automatically as a function of the dynamics of the underlying net- work. It employs reinforcement learning, a machine learning technique known to be well suited to problems in which the environment, in this case the network, plays a crucial role; yet, no prior knowledge about the target environment can be assumed, i.e., the only way to acquire information about the environment is to interact with it through continuous online learning. Smart-DTN-CC nodes get input from the environment (e.g., its buffer occupancy, set of neighbors, etc), and, based on that information, choose an action to take from a set of possible actions. Depending on an action's effectiveness in controlling congestion, it will be given a reward. Smart-DTN-CC's goal is to maximize the over- all reward which translates to minimizing congestion. To our knowledge, Smart-DTN-CC is the first DTN congestion control framework that has the ability to automatically and continuously adapt to the dynamics of the target environment. As demonstrated by our experimental evaluation, Smart-DTN- CC is able to consistently outperform existing DTN congestion control mechanisms under a wide range of network conditions and characteristics.

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.

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.

Visualization tools play a key role in the exploration of outer space. Since it is difficult and expensive to send humans to other planets, immersive visualization of such hostile environments is as close as we will get for some time. Visualization is also used in a variety of supporting roles for deep space missions, from simulation and rehearsal of planned operations to analysis of spacecraft state to analysis of science data returned from a variety of instruments. The panelists will discuss their experiences in collecting data in deep space, transmitting it to Earth, processing and visualizing it here, and using the visualization to drive the continued mission. This closes the loop, making missions more responsive to their environment, particularly in-situ operations on planetary surfaces and within planetary atmospheres.

A web-based system for the computer mediation of work through an organization was developed at the Jet Propulsion Laboratory.A distinctive feature of this system, named '%rWWorkflow", is the careful separation of process mediation from product data management.This paper describes the design, functionality, and user interface of the system, discusses the , role WWWorkflow fulfills in organizational intranets, and concludes with lessons learned from deployment the Jet Propulsion Laboratory and at the Johnson Space Center, Houston.