Paper A4P2 NASA Earth Science Technology Conference, June 24-26, 2008 1 Delay/Disruption-Tolerant Network Testing Using a LEO Satellite Will Ivancic National Aeronautics and Space Administration (NASA)/Glenn Research Center (GRC), Cleveland, Ohio, United States, wivancic@grc.nasa.gov Wesley M. Eddy Verizon Federal Network Systems / NASA GRC, Cleveland, Ohio, United States, weddy@grc.nasa.gov Lloyd Wood Cisco Systems, Feltham, United Kingdom, lwood@cisco.com Dave Stewart Verizon Federal Network Systems / NASA GRC, Cleveland, Ohio, United States, dstewart@grc.nasa.gov Chris Jackson Surrey Satellite Technology Ltd (SSTL), Guildford, Surrey, United Kingdom, c.jackson@sstl.co.uk James Northam SSTL, Guildford, Surrey, United Kingdom, j.northam@sstl.co.uk Alex da Silva Curiel SSTL, Guildford, Surrey, United Kingdom, a.da-silva-curiel@sstl.co.uk Abstract- Delay/Disruption Tolerant Networking (DTN) “bundles” have been proposed for deep-space communication in the “Interplanetary Internet.” This paper describes the first DTN bundle protocol testing from space, using the United Kingdom Disaster Monitoring Constellation (UK-DMC) satellite in Low Earth Orbit (LEO). The mismatch problems between the different conditions of the private dedicated space-to-ground link and the shared, congested, ground-to-ground links are discussed. DTN, with its ability to transfer files on a hop-by-hop basis across different subnets, is presented as a technology that can be used to alleviate this problem. We describe our operational testing, as well as test configurations, goals and results, and lessons learned. I. INTRODUCTION Delay/Disruption Tolerant Networking (DTN) has been defined as an end-to-end store-and-forward architecture capable of providing communications in highly-stressed network environments. To provide the store-and-forward service, a “bundle” protocol (BP) sits at the application layer of some number of constituent internets, forming a store-and- forward overlay network [1]. Key capabilities of the BP include: • Custody-based retransmission – the ability to take responsibility for a bundle reaching its final destination • Ability to cope with intermittent connectivity. • Ability to cope with long propagation delays. • Ability to take advantage of scheduled, predicted, and opportunistic connectivity (in addition to continuous connectivity). • Late binding of overlay network endpoint identifiers to constituent internet addresses [2]. The DTN protocol suite is intended to consist of a group of well-defined protocols that, when combined, enable a well- understood method of performing store and forward communications. DTN can be thought of as operating across varying conditions across several different axes, depending on the design of the subnet being traversed: • low or high propagation delay • dedicated or shared, congested links • links with intermittent disruption and outages or scheduled planned links. In a low-propagation-delay environment, such as may occur in near-planetary or terrestrial environments, DTN bundle agents can utilize chatty underlying Internet protocols, such as TCP, that negotiate connectivity and handshake connections in real-time. In high-propagation-delay environments such as deep space, DTN bundle agents must use other methods, such as some form of scheduling, to set up connectivity between the two bundle agents, and can use less chatty transfer protocols over IP. Low Earth Orbit (LEO) is a low-propagation-delay environment of less than ten milliseconds delay to ground, with long periods of disconnection between passes over ground stations. For the UK-DMC satellite, contact times consist of 5 to 14 minutes per pass with one or two available ground station contact times per 100 minute orbit – assuming multiple available ground stations. The ground stations are connected across the terrestrial Internet, which has different operating conditions (congestion-sensitive, always on) from the private links between satellite and ground station (intermittent but scheduled, and dedicated to downloading.) II. THE RATE MISMATCH PROBLEM Figure 1 illustrates a LEO satellite ground network with a DTN Bundle Agent sink located at a remote location. The final remote location for the downloaded imagery could be a satellite control station and office or a laptop ‘in the field’ with wireless connectivity – it really doesn’t matter. In this example, an image is to be transferred from the DTN source,