ABSTRACT
A strategy is being developed whereby the currentset of internationally standardized space datacommunications protocols can be incrementallyevolved so that a first version of an operational“Interplanetary Internet” is feasible by the end ofthe decade. This paper describes its architecturalconcepts, discusses the current set of standard spacedata communications capabilities that exist tosupport Mars exploration and reviews proposednew developments. We also speculate that thesecurrent capabilities can grow to support futurescenarios where human intelligence is widelydistributed across the Solar System and day-to-daycommunications dialog between planets is routine.∗ This work was performed in part at and under thedirection of the Jet Propulsion Laboratory, CaliforniaInstitute of Technology under a contract with theNational Aeronautics and Space Administration.Copyright © 2002 by the American Institute ofAeronautics and Astronautics, Inc. No copyright isasserted in the United States under Title 17, U.S. Code.The U.S. Government has a royalty-free license toexercise all rights under copyright claimed herein forGovernmental purposes. All other rights are reserved bythe copyright owner.
THE FUTURE:AN INTERPLANETARY INTERNET
In 1998 the US Defense Advanced ResearchProjects Agency (DARPA), as part of its “NextGeneration Internet” initiative, began funding asmall group at NASA's Jet PropulsionLaboratory in Pasadena, California to study thetechnical architecture of an “InterplanetaryInternet”. The idea was to blend ongoing workin standardized space communicationscapabilities with state of the art techniquesbeing developed within the terrestrial Internetcommunity, with a goal of achieving end-toendcommunication in a multi-networkinterplanetary environment. The“Interplanetary Internet” name was deliberatelycoined to suggest a far-future integration ofspace and terrestrial communicationsinfrastructure to support the migration ofhuman intelligence throughout the SolarSystem. Joining the JPL team in this work wasone of the original designers of the Internet andco-inventor of the “Transmission ControlProtocol/Internet Protocol” (TCP/IP) protocolsuite. Support for the work has recentlytransitioned from DARPA to NASA.2The future Interplanetary Internet architecturalconcept is deceptively simple:1. Use Internet or Internet-related protocols toform local networks in low delay, relativelylow noise environments such as aroundEarth, within a free flying spacecraft, onand around another planet, etc.2. A specialized deep space backbone networkof long-haul wireless links interconnectingthese local internets. This interplanetarybackbone is expected to evolve to includemultiple space-based data relay satellites.3. The resulting interplanetary internet thusconsists of a "network of internets". Just asthe familiar TCP/IP suite unites the Earth's"network of networks" into the Internet, theInterplanetary Internet will employ a newoverlay protocol concept called bundling totie together a set of heterogeneous internets.A routing function will direct bundles(messages) through a concatenated series ofInternets, just as the Earth’s current Internetprotocol (IP) routes data through a series ofindependent networks on Earth. To guaranteereliability of the end-to-end transfer, thebundles will also contain retransmissionmechanisms functionally similar to thoseprovided by the terrestrial Internet’sTransmission Control Protocol (TCP).However, the similarity of bundling withTCP/IP ends there.Unlike the Earth’s backbone environment ofcontinuous connectivity, negligible delay andclean data channels, the hallmarks of theinterplanetary backbone are thereforeintermittent connectivity, huge propagationdelays and noisy data channels.While the Earth’s backbone network is wired –large numbers of fiber or copper circuitsinterconnecting fixed hubs – the interplanetarybackbone is dependent on fragile wireless links.In addition, the hubs on the interplanetarybackbone (relay spacecraft or gateways intoremote local Internets) are all moving withrespect to each other. Planets travel in fixedorbits and sometimes bodies like the Sun causeline of sight occultations that last for days onend. Landed vehicles on remote planetarysurfaces will move out of sight of Earth as thebody rotates, and may have to communicatethrough local relay satellites that only providedata transmission contacts for a few minutes ata time.The bundling protocol handles thisenvironment in two ways:• It operates in a “store and forward” mode,very similar to e-mail, where bundles areheld at routers along the way until suchtime as a forward path is established.• It avoids the need for a sender to store datauntil an acknowledgement is received fromthe other end by operating in a "custodial"mode. In this mode, intermediate nodes inthe network can assume responsibility forensuring that bundles reach theirdestinations, allowing senders (andprevious custodians) to reassign resourcesto new observations.• In the presence of high error rate links, thehop-by-hop store-and-forward bundlingmodel with per-hop error control increasesthe probability of successful end to endtransmission.One key problem in the design of anInterplanetary Internet is identifying thecommunicating endpoints. If a common, solarsystem-wide IP address convention wereadopted, then every component of the systemwould need to be upgraded on a commontimescale to preserve the commonality of theaddress space. The current concept is thatrather than have a single address space acrossthe entire Solar System end point identifierscomprise a two-part name. One part of thename (the routing part) gets the bundle3delivered to a remote destination “region” ofthe Interplanetary internet. The second part ofthe name (the administrative part) contains theinformation required to deliver to one or morelocal destinations. Thus for Mars operations therouting part of the name will be used to movethe bundle across the Deep Space backbone tothe entry gateway on the appropriate region onMars, where the administrative part of thename comes into play and identifies the localrecipient(s) on the Martian internet.

Download full report
http://ipnsigreports/IAF-Oct-2002.pdf