Transport layer protocols and architectures for satellite networks

Designing efficient transmission mechanisms for advanced satellite networks is a demanding task, requiring the definition and the implementation of protocols and architectures well suited to this challenging environment. In particular, transport protocols performance over satellite networks is impaired by the characteristics of the satellite radio link, specifically by the long propagation delay and the possible presence of segment losses due to physical channel errors. The level of impact on performance depends upon the link design (type of constellation, link margin, coding and modulation) and operational conditions (link obstructions, terminal mobility, weather conditions, etc.). To address these critical aspects a number of possible solutions have been presented in the literature, ranging from limited modifications of standard protocols (e.g. TCP, transmission control protocol) to completely alternative protocol and network architectures. However, despite the great number of different proposals (or perhaps also because of it), the general framework appears quite fragmented and there is a compelling need of an integration of the research competences and efforts. This is actually the intent of the transport protocols research line within the European SatNEx (Satellite Network of Excellence) project. Stemming from the authors' work on this project, this paper aims to provide the reader with an updated overview of all the possible approaches that can be pursued to overcome the limitations of current transport protocols and architectures, when applied to satellite communications. In the paper the possible solutions are classified in the following categories: optimization of TCP interactions with lower layers, TCP enhancements, performance enhancement proxies (PEP) and delay tolerant networks (DTN). Advantages and disadvantages of the different approaches, as well as their interactions, are investigated and discussed, taking into account performance improvement, complexity, and compliance to the standard semantics. From this analysis, it emerges that DTN architectures could integrate some of the most efficient solutions from the other categories, by inserting them in a new rigorous framework. These innovative architectures therefore may represent a promising solution for solving some of the important problems posed at the transport layer by satellite networks, at least in a medium-to-long-term perspective. Copyright (c) 2006 John Wiley & Sons, Ltd

Routing in the Space Internet: A contact graph routing tutorial

A Space Internet is possible, as long as the delay and disruption challenges imposed by the space environment are properly tackled. Because these conditions are not well addressed by terrestrial Internet, more capable Delay-Tolerant Networking (DTN) protocols and algorithms are being developed. In particular, the principles and techniques for routing among ground elements and spacecraft in near-Earth orbit and deep-space are enacted in the Contact Graph Routing (CGR) framework. CGR blends a set of non-trivial algorithm adaptations, space operations concepts, time-dynamic scheduling, and specific graph models. The complexity of that framework suggests a need for a focused discussion to facilitate its direct and correct apprehension. To this end, we present an in-depth tutorial that collects and organizes first-hand experience on researching, developing, implementing, and standardizing CGR. Content is laid out in a structure that considers the planning, route search and management, and forwarding phases bridging ground and space domains. We rely on intuitive graphical examples, supporting code material, and references to flight-grade CGR implementations details where pertinent. We hope this tutorial will serve as a valuable resource for engineers and that researchers can also apply the insights presented here to topics in DTN research.Fil: Fraire, Juan Andres. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. Universitat Saarland; AlemaniaFil: De Jonckère, Olivier. Technische Universität Dresden; AlemaniaFil: Burleigh, Scott C.. California Institute of Technology; Estados Unido

Proactive TCP mechanism to improve Handover performance in Mobile Satellite and Terrestrial Networks

Emerging standardization of Geo Mobile Radio (GMR-1) for satellite system is having strong resemblance to terrestrial GSM (Global System for Mobile communications) at the upper protocol layers and TCP (Transmission Control Protocol) is one of them. This space segment technology as well as terrestrial technology, is characterized by periodic variations in communication properties and coverage causing the termination of ongoing call as connections of Mobile Nodes (MN) alter stochastically. Although provisions are made to provide efficient communication infrastructure this hybrid space and terrestrial networks must ensure the end-to-end network performance so that MN can move seamlessly among these networks. However from connectivity point of view current TCP performance has not been engineered for mobility events in multi-radio MN. Traditionally, TCP has applied a set of congestion control algorithms (slow-start, congestion avoidance, fast retransmit, fast recovery) to probe the currently available bandwidth on the connection path. These algorithms need several round-trip times to find the correct transmission rate (i.e. congestion window), and adapt to sudden changes connectivity due to handover. While there are protocols to maintain the connection continuity on mobility events, such as Mobile IP (MIP) and Host Identity Protocol (HIP), TCP performance engineering has had less attention. TCP is implemented as a separate component in an operating system, and is therefore often unaware of the mobility events or the nature of multi-radios' communication. This paper aims to improve TCP communication performance in Mobile satellite and terrestrial networks.Comment: 5 pages, 2 figure

Scalable Schedule-Aware Bundle Routing

This thesis introduces approaches providing scalable delay-/disruption-tolerant routing capabilities in scheduled space topologies. The solution is developed for the requirements derived from use cases built according to predictions for future space topology, like the future Mars communications architecture report from the interagency operations advisory group. A novel routing algorithm is depicted to provide optimized networking performance that discards the scalability issues inherent to state-of-the-art approaches. This thesis also proposes a new recommendation to render volume management concerns generic and easily exchangeable, including a new simple management technique increasing volume awareness accuracy while being adaptable to more particular use cases. Additionally, this thesis introduces a more robust and scalable approach for internetworking between subnetworks to increase the throughput, reduce delays, and ease configuration thanks to its high flexibility.:1 Introduction 1.1 Motivation 1.2 Problem statement 1.3 Objectives 1.4 Outline 2 Requirements 2.1 Use cases 2.2 Requirements 2.2.1 Requirement analysis 2.2.2 Requirements relative to the routing algorithm 2.2.3 Requirements relative to the volume management 2.2.4 Requirements relative to interregional routing 3 Fundamentals 3.1 Delay-/disruption-tolerant networking 3.1.1 Architecture 3.1.2 Opportunistic and deterministic DTNs 3.1.3 DTN routing 3.1.4 Contact plans 3.1.5 Volume management 3.1.6 Regions 3.2 Contact graph routing 3.2.1 A non-replication routing scheme 3.2.2 Route construction 3.2.3 Route selection 3.2.4 Enhancements and main features 3.3 Graph theory and DTN routing 3.3.1 Mapping with DTN objects 3.3.2 Shortest path algorithm 3.3.3 Edge and vertex contraction 3.4 Algorithmic determinism and predictability 4 Preliminary analysis 4.1 Node and contact graphs 4.2 Scenario 4.3 Route construction in ION-CGR 4.4 Alternative route search 4.4.1 Yen’s algorithm scalability 4.4.2 Blocking issues with Yen 4.4.3 Limiting contact approaches 4.5 CGR-multicast and shortest-path tree search 4.6 Volume management 4.6.1 Volume obstruction 4.6.2 Contact sink 4.6.3 Ghost queue 4.6.4 Data rate variations 4.7 Hierarchical interregional routing 4.8 Other potential issues 5 State-of-the-art and related work 5.1 Taxonomy 5.2 Opportunistic and probabilistic approaches 5.2.1 Flooding approaches 5.2.2 PROPHET 5.2.3 MaxProp 5.2.4 Issues 5.3 Deterministic approaches 5.3.1 Movement-aware routing over interplanetary networks 5.3.2 Delay-tolerant link state routing 5.3.3 DTN routing for quasi-deterministic networks 5.3.4 Issues 5.4 CGR variants and enhancements 5.4.1 CGR alternative routing table computation 5.4.2 CGR-multicast 5.4.3 CGR extensions 5.4.4 RUCoP and CGR-hop 5.4.5 Issues 5.5 Interregional routing 5.5.1 Border gateway protocol 5.5.2 Hierarchical interregional routing 5.5.3 Issues 5.6 Further approaches 5.6.1 Machine learning approaches 5.6.2 Tropical geometry 6 Scalable schedule-aware bundle routing 6.1 Overview 6.2 Shortest-path tree routing for space networks 6.2.1 Structure 6.2.2 Tree construction 6.2.3 Tree management 6.2.4 Tree caching 6.3 Contact segmentation 6.3.1 Volume management interface 6.3.2 Simple volume manager 6.3.3 Enhanced volume manager 6.4 Contact passageways 6.4.1 Regional border definition 6.4.2 Virtual nodes 6.4.3 Pathfinding and administration 7 Evaluation 7.1 Methodology 7.1.1 Simulation tools 7.1.2 Simulator extensions 7.1.3 Algorithms and scenarios 7.2 Offline analysis 7.3 Eliminatory processing pressures 7.4 Networking performance 7.4.1 Intraregional unicast routing tests 7.4.2 Intraregional multicast tests 7.4.3 Interregional routing tests 7.4.4 Behavior with congestion 7.5 Requirement fulfillment 8 Summary and Outlook 8.1 Conclusion 8.2 Future works 8.2.1 Next development steps 8.2.2 Contact graph routin

SECURE AND EFFICIENT INFORMATION MANAGEMENT IN DELAY(DISRUPTION) TOLERANT NETWORK

In environments like international military coalitions on the battlefield or multi-party relief work in a disaster zone, multiple teams are deployed to serve different mission goals by the command-and-control center (CC). They may need to survey damages and send information to the CC for situational awareness and also transfer messages to each other for mission purposes. However, due to the damaged network infrastructure in the emergency, nodes need to relay messages using the store and forward paradigm, also called Delay-tolerant Networks (DTNs). In DTN, the limited bandwidth, energy, and contacts among the nodes, and their interdependency impose several challenges such as sensitive data leakage to malicious nodes, redundant data generation, limited and delayed important message delivery, non-interested messages in storage, etc. We aim to focus on solving these challenges. We propose message fragmentation for secure message transfer because existing public-private-key cryptographic approaches may not work due to the unavailability of Public Key Infrastructure (PKI). Besides, to ensure more message delivery, redundant fragments are generated. However, too much redundancy may consume the energy and bandwidth of the nodes while transferring similar messages. Hence, we propose to send diverse content and limit the redundancy. Again, the dynamic environment we consider is prone to many adverse and sudden events. We aim to respond to these events by sending the event-related message to the CC fast with the help of intermediate nodes. The nodes are interested in certain types of content defined by their mission and interest. Therefore, we target to learn nodes\u27 interests using Reinforcement Learning so that the nodes can populate themselves with the messages according to their mission requirements and increase the collaboration among them. Our future work will include machine learning techniques for predicting important places where node encounters the most and to cache data for each other according to their interest, encounter frequency, and encounter locations --Abstract, p. i

Schedule‐Aware Bundle Routing: Analysis and enhancements

The Delay-/Disruption-Tolerant Networking (DTN) architecture was designed to cope with challenges such as long delays and intermittent connectivity. To exploit the a priori knowledge of contacts, typical of space networks, NASA-JPL designed and included in ION (its DTN protocol suite) the Contact Graph Routing (CGR) algorithm. This paper studies the latest version, recently standardized as Schedule-Aware Bundle Routing (SABR) within the Consultative Committee for Space Data Systems (CCSDS). The first part of the paper is devoted to the algorithm analysis, which distinguishes three logical phases to examine sequentially. Following this comprehensive study, three enhancements are proposed, which aim to improve SABR accuracy and resistance against possible loops. They are studied on a simple but challenging DTN topology, implemented on a virtual GNU/Linux testbed. Tests are performed by running the latest version of ION and an independent implementation of SABR developed by the authors, Unibo-CGR. The numerical results are then examined in detail to highlight both SABR mechanisms and the advantages offered by the proposed enhancements

A Novel Approach to Transport-Layer Security for Spacecraft Constellations

Spacecraft constellations seek to provide transformational services from increased environmental awareness to reduced-latency international finance. This connected future requires trusted communications. Transport-layer security models presume link characteristics and encapsulation techniques that may not be sustainable in a networked constellation. Emerging transport layer protocols for space communications enable new transport security protocols that may provide a pragmatic alternative to deploying Internet security mechanisms in space. The Bundle Protocol (BP) and Bundle Protocol Security (BPSec) protocol have been designed to provide such an alternative. BP is a store-and-forward alternative to IP that carries session information as secondary headers. BPSec uses BP’s featureful secondary header mechanism to hold security information and security results. In doing so, BPSec provides an in-packet augmentation alternative to security by encapsulation. BPSec enables features such as security-at-rest, separate encryption/signing of individual protocol headers, and the ability to add secondary headers and secure them at waypoints in the network. These features provided by BPSec change the system trades associated with networked constellations. They enable security at rest, secure content caching, and deeper inspection at gateways otherwise obscured by tunneling

Prediction-enhanced Routing in Disruption-tolerant Satellite Networks

This thesis introduces a framework for enhancing DTN (Delay-/Disruption-Tolerant Networking) routing in dynamic LEO satellite constellations based on the prediction of contacts. The solution is developed with a clear focus on the requirements imposed by the 'Ring Road' use case, mandating a concept for dynamic contact prediction and its integration into a state-of-the-art routing approach. The resulting system does not restrict possible applications to the 'Ring Road,' but allows for flexible adaptation to further use cases. A thorough evaluation shows that employing proactive routing in concert with a prediction mechanism offers significantly improved performance when compared to alternative opportunistic routing techniques

Small satellites and CubeSats: survey of structures, architectures, and protocols

The space environment is still challenging but is becoming more and more attractive for an increasing number of entities. In the second half of the 20th century, a huge amount of funds was required to build satellites and gain access to space. Nowadays, it is no longer so. The advancement of technologies allows producing very small hardware components able to survive the strict conditions of the outer space. Consequently, small satellites can be designed for a wide set of missions keeping low design times, production costs, and deployment costs. One widely used type of small satellite is the CubeSat, whose different aspects are surveyed in the following: mission goals, hardware subsystems and components, possible network topologies, channel models, and suitable communication protocols. We also show some future challenges related to the employment of CubeSat networks

Towards efficacy and efficiency in sparse delay tolerant networks

The ubiquitous adoption of portable smart devices has enabled a new way of communication via Delay Tolerant Networks (DTNs), whereby messages are routed by the personal devices carried by ever-moving people. Although a DTN is a type of Mobile Ad Hoc Network (MANET), traditional MANET solutions are ill-equipped to accommodate message delivery in DTNs due to the dynamic and unpredictable nature of people\u27s movements and their spatio-temporal sparsity. More so, such DTNs are susceptible to catastrophic congestion and are inherently chaotic and arduous. This manuscript proposes approaches to handle message delivery in notably sparse DTNs. First, the ChitChat system [69] employs the social interests of individuals participating in a DTN to accurately model multi-hop relationships and to make opportunistic routing decisions for interest-annotated messages. Second, the ChitChat system is hybridized [70] to consider both social context and geographic information for learning the social semantics of locations so as to identify worthwhile routing opportunities to destinations and areas of interest. Network density analyses of five real-world datasets is conducted to identify sparse datasets on which to conduct simulations, finding that commonly-used datasets in past DTN research are notably dense and well connected, and suggests two rarely used datasets are appropriate for research into sparse DTNs. Finally, the Catora system is proposed to address congestive-driven degradation of service in DTNs by accomplishing two simultaneous tasks: (i) expedite the delivery of higher quality messages by uniquely ordering messages for transfer and delivery, and (ii) avoid congestion through strategic buffer management and message removal. Through dataset-driven simulations, these systems are found to outperform the state-of-the-art, with ChitChat facilitating delivery in sparse DTNs and Catora unencumbered by congestive conditions --Abstract, page iv