Carlo Caini

Contact graph routing in DTN space networks: overview, enhancements and performance

Delay- and Disruption Tolerant Networks (DTNs) are based on an overlay protocol and on the store-carry-forward paradigm. In practice, each DTN node can store information for a long time before forwarding it. DTNs are particularly suited to cope with the challenges imposed by the space environment. This paper is focused on routing in space DTNs, and in particular on contact graph routing (CGR) and its most representative enhancements, available in the literature, which are briefly surveyed in this work. Moreover, the applicability and the obtained performance of the DTN protocol stack and of the CGR have been evaluated by presenting results from real experimental experiences such as the Deep Impact Network experiment (employing the EPOXI space cruise), the JAXA jointly performed space link demonstrations with NASA (where the JAXAs GEO relay satellite called Data Relay Test Satellite has been used), the Space Data Routers European Project, and the pilot operation of a DTN implementation on the International Space Station (ISS).

Application of Contact Graph Routing to LEO satellite DTN communications

Delay-/Disruption-Tolerant Networking, which originated from research on deep space communications, has enlarged its scope to encompass all challenged networks, including LEO satellite communications. Focusing on single satellite or incomplete constellation cases, the advantages of DTN mainly relate to its ability to cope with disruption and intermittent connectivity, typical of LEOs. This, however, requires the adoption of routing solutions specifically designed for DTNs. Among the many proposals, Contact Graph Routing, designed by NASA for deep space, seems particularly appealing, as it takes advantage of the a priori knowledge of “contacts” between DTN nodes, a characteristic peculiar to both deep space and LEO environments. This paper aims to investigate the suitability of CGR in LEO satellite DTN communications, by focusing on two practical application scenarios: Earth observation and data mule. Results, obtained through a Linux testbed running ION, the DTN Bundle protocol and CGR implementation developed by NASA, highlight the advantages of CGR when applied to LEO satellite communications.

Moon to earth DTN communications through lunar relay satellites

Although Delay-/Disruption- Tolerant Networking, which originated from research on an Interplanetary Internet, has enlarged its scope to encompass all challenged networks, space applications are still one of its most important application fields. This paper deals with DTN communication from Moon to Earth, based on the use of a lunar satellite acting as a “data-mule” to collect data from a Lander located on the far side of the Moon. To make the scenario more interesting and complex from the point of view of possible security threats, we assume that data must be transferred to a non-institutional user connected to the Space Agency Control Centre via Internet. In particular, the paper investigates the state-of-the-art ability of ION, the NASA implementation of the DTN Bundle Protocol (BP), to cope with the many challenges of the space scenario under investigation, such as intermittent links, low bandwidth, relatively high delays, network partitioning, DTN routing, interoperability between LTP and TCP BP Convergence layers and security threats. To this end, the first part of the paper contains three brief overviews of the DTN architecture, the Bundle Security Protocol and the ION implementation. These facilitate comprehension of the following sections, dedicated to a detailed description of the experiment scenario and, most essentially, to the in depth discussion of the numerical results obtained with the latest ION version (3.0).

Mars to Earth communications through orbiters: Delay‐Tolerant/Disruption‐Tolerant Networking performance analysis

SUMMARY n nDelay-Tolerant/Disruption-Tolerant Networking (DTN) architecture will be used in future deep space missions, to enable autonomous networking operations and disruption-tolerant data communications. Therefore, it is worth analyzing the performance of the DTN Bundle Protocol (BP) in a realistic deep space environment, reproducing the characteristics of Mars missions. After a comprehensive introduction on data communications between Mars and Earth, the paper presents the essential features of both the BP DTN architecture and the Licklider Transmission Protocol (LTP), adopted here as BP convergence layer on deep space links, thanks to its ability to cope with the very long delays typical of this environment. The focus of our experiments is on analysis of the bundle flow from a Mars lander to an Earth control center through an intermediate relay node, for which two configurations are considered, inspired to Odyssey and Mars Reconnaissance Orbiter missions, respectively. Results are obtained by means of a test bed consisting of some GNU/Linux personal computers running either Interplanetary Overlay Network (ION) or DTN2 BP implementations. The analysis of results aims to highlight the role played by BP and LTP in tackling the challenges of Mars to Earth communications. Copyright

Analysis of contact graph routing enhancements for DTN space communications

Summary n nIn this paper, we analyze the performance of two contact graph routing (CGR) enhancements, namely, CGR with earliest transmission opportunity (CGR-ETO) and overbooking management. CGR-ETO aims to improve the accuracy of predicted bundle delivery time by exploiting existing information on queueing delay, in routing decisions. Overbooking management aims to proactively handle contact oversubscription, which occurs when high-priority bundles are forwarded to a contact that is already fully subscribed by lower-priority bundles. These two enhancements have been recently included in the official CGR version as part of the Interplanetary Overlay Network delay-tolerant/disruption-tolerant networking implementation maintained by the National Aeronautics and Space Administration. In parallel to the comparative evaluation of the enhancements against the original CGR, we introduce an experimental version of CGR-ETO that exploits information on locally routed data to calculate queueing delays in all hops through the path to destination, rather than in the first hop only. We evaluate the aforementioned enhancements in a set of emulation experiments conducted on a GNU/Linux testbed and compare official and experimental versions of CGR. Results show that the two enhancements are complementary and can significantly improve routing decisions compared with older versions of CGR, particularly in the presence of parallel routes and traffic of different priorities. These advantages are further extended when the experimental version of ETO is considered. Copyright

Toward a unified routing framework for delay-tolerant networking

Routing in Delay-/Disruption-Tolerant Networking (DTN) has long been recognized as a challenging research topic. The difficulty lies in the fact that link intermittency and network partitioning, possibly coupled with long delays, prevent the use of Internet solutions based on an up-to-date comprehensive knowledge of network topology, as communicated by routing protocols. In the literature on DTN routing, there is a dichotomy between solutions designed for deterministic (e.g., space flight) networks, such as Contact Graph Routing (CGR), and the wide variety of protocols designed for opportunistic terrestrial networks. After a discussion of the origin and motivations of this duality, the paper presents an opportunistic extension of CGR (OCGR). The aim is to try to resolve the DTN routing dichotomy by providing a unified approach suitable for all DTN environments.

DTN LEO Satellite Communications through Ground Stations and GEO Relays

LEO satellites are characterized by intermittent connectivity with their ground stations. Contacts are short and separated by long intervals, which with urgent data can become a critical factor. To solve this problem, the use of GEO satellites as relay has recently been suggested. This solution is appealing, but has some limits, especially with polar orbits, as the link between the LEO satellite and the GEO relay is affected by long disruptions over polar regions. Moreover, the bandwidth available may be limited and difficult to fully exploit. In this paper, we show that GEO relays are complementary rather than alternative to ground stations, and that the enabling technology for their combined use is DTN (Delay-/Disruption- Tolerant Networking) architecture and related protocols, including CGR (Contact Graph Routing). To demonstrate this, a series of experiments carried out on a testbed running ION, the NASA implementation of the DTN protocols and CGR, is discussed in the paper.

From the far side of the Moon: Delay/disruption-tolerant networking communications via lunar satellites

Delay/Disruption-Tolerant Networking (DTN) originated from research on Interplanetary Internet and still today space applications are the most important application field and research stimulus. This paper investigates DTN communications between the Earth and the far side of the Moon, by means of a lunar orbiter acting as relay. After an introductory part, the paper presents a comprehensive analysis of the DTN performance that can be achieved on the identified communication scenario. The focus is on the evaluation of the state-of-the-art ability of Interplanetary Overlay Network (ION), the NASA DTN implementation of Bundle Protocol (BP) and Contact Graph Routing (CGR), to meet the many challenges of the space communication scenario investigated (and more generally of a future interplay-netary Internet): intermittent links, network partitioning, scarce bandwidth, long delays, dynamic routing, handling of high priority and emergency traffic, interoperability issues. A study of security threats and Bundle Security Protocol (BSP) countermeasures complete the work. The many results provided, confirm the essential role of DTN in future space communications.

DTNperf_3: A further enhanced tool for Delay-/Disruption- Tolerant Networking Performance evaluation

Delay-/Disruption- Tolerant Networking (DTN) was first conceived to cope with the impairments of Inter-Planetary Internet. Then its scope was enlarged to cover all “challenged networks”, where long delays, disruption, link intermittency and other challenges prevent, or make difficult, the use of ordinary Internet architecture. To assess DTN performance in such heterogeneous scenarios as space communications (including both satellite and deep space) and wireless sensor networks, it is essential to develop suitable evaluation tools, with highly flexible use. In this paper we present the third major release of DTNperf, a client-server evaluation tool designed to assess goodput and to provide logs in DTN Bundle Protocol (BP) architectures. It has been greatly extended in many respects, including full support of both DTN2 and ION (the BP reference implementation and that developed by NASA JPL, respectively). The aim of the paper is to present both new and enhanced features and a variety of application examples, mainly focused on satellite and space communications, in order to promote its use within the DTN community. DTNperf_3 is to be included in DTN2, as were previous versions, and for the first time also in ION.

Latency Analysis of Real-Time Web protocols over a Satellite Link

In the era of social networks, always-on connectivity and remote communication, the tools we use to work and play with rely heavily on the World Wide Web protocols. The Web is no more a collection of static sites and download-only content, but rather it is a place where real-time collaboration happens. In this new Web, called the Real-Time Web, a small latency between the browser and the Web server is a critical element. How does the Real-Time Web perform over a satellite link? What should application developers choose to build interactive applications over a satellite link, given the broad range of available protocols and techniques? To answer these urgent questions this article will compare the latency shown by some of the most significant new Web solutions in the presence and in the ansence of a GEO satellite link.