Interplanetary Internet

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The speed of light, illustrated here by a beam of light traveling from the Earth to the Moon, limits the speed at which Interplanetary Internet messages would be able to travel. Due to the vast distances involved, much longer delays are incurred than in the Earth-bound Internet.

The Interplanetary Internet, as presently conceived, is a set of floating nodes in space which can communicate with each other.^[1][2] Because of the large speed of light delays involved with interplanetary distances, the IPN needs a new set of protocols and technology that are tolerant to large delays^[2]. While the Internet as we know it tends to be a busy "network of networks" with high traffic, negligible delay and errors, and a wired backbone, the InterPlanetary Internet is a store-and-forward "network of Internets" that is often disconnected, with a wireless backbone fraught with error-prone links and delays ranging to tens of minutes, even hours, even when there is a connection.

Looking at space communications from the historical perspective, there has been a steady evolution from expensive one-of-a-kind point-to-point architectures, to the re-use of technology on successive missions, to the development of standard protocols agreed upon by space agencies of many countries. This last phase has gone on since 1982 through the efforts of the Consultative Committee for Space Data Systems (CCSDS),^[3] a body composed of the major space agencies of the world. It has ten member agencies, twenty-two observer agencies, and over 100 industrial associates.

The evolution of space data system standards has gone on in parallel with the evolution of the Internet, with conceptual cross-pollination where fruitful, but to a large degree, as a separate evolution. Since the late 1990s, familiar Internet protocols and CCSDS space link protocols have integrated and converged in several ways, for example, the successful FTP file transfer to Earth-orbiting STRV-1b on January 2 1996, which ran FTP over the CCSDS IPv4-like Space Communications Protocol Specifications (SCPS) protocols.^[4][5] Internet Protocol use without CCSDS has taken place on spacecraft, e.g. demonstrations on the UoSAT-12 satellite, and operationally on the Disaster Monitoring Constellation. Having reached the era where networking and IP on-board spacecraft have been shown to be feasible and reliable, a forward-looking study of the bigger picture was the next phase.

ICANN meeting, Los Angeles, USA, 2007

The Interplanetary Internet study at NASA's Jet Propulsion Laboratory (JPL) was started by a team of scientists at JPL led by Vinton Cerf and Adrian Hooke.^[6] Cerf is one of the pioneers of the Internet on Earth, and currently holds the position of distinguished visiting scientist at JPL. Hooke is one of the directors of the CCSDS.

While IP-like SCPS protocols are feasible for short hops, such as ground station to orbiter, rover-to-lander, lander-to-orbiter, probe-to-flyby, and so on, delay-tolerant networking is needed to get information from one region of the solar system to another. It becomes apparent that the concept of a "region" is a natural architectural factoring of the InterPlanetary Internet.

A "region" is an area where the characteristics of communication are the same.^[7] Region characteristics include communications, security, the maintenance of resources, perhaps ownership, and other factors.^[7] The Interplanetary Internet is a "network of regional internets."

What is needed then, is a standard way to achieve end-to-end communication through multiple regions in a disconnected, variable-delay environment using a generalized suite of protocols. Examples of regions might include the terrestrial Internet as a region, a region on the surface of the moon or Mars, or a ground-to-orbit region.

The recognition of this requirement led to the concept of a "bundle" as a high-level way to address the generalized Store-and-Forward problem. Bundles are an area of new protocol development in the upper layers of the OSI model, above the Transport Layer with the goal of addressing the issue of bundling store-and-forward information so that it can reliably traverse radically dissimilar environments constituting a "network of regional internets."

Bundle Service Layering, implemented as the Bundling protocol suite for delay-tolerant networking, will provide general purpose delay-tolerant protocol services in support of a range of applications: custody transfer, segmentation and reassembly, end-to-end reliability, end-to-end security, and end-to-end routing among them. The Bundle Protocol was first tested in space on the UK-DMC Disaster Monitoring Constellation satellite in 2008.^[8][9]

The Deep Impact mission

An example of one of these end-to-end applications flown on a space mission is CFDP, used on the comet mission, Deep Impact. CFDP is the CCSDS File Delivery Protocol^[10] an international standard for automatic, reliable file transfer in both directions. CFDP should not be confused with Coherent File Distribution Protocol, which unfortunately has the same acronym and is an IETF-documented experimental protocol for rapidly deploying files to multiple targets in a highly-networked environment.

In addition to reliably copying a file from one entity (i. e. a spacecraft or ground station) to another entity, the CCSDS CFDP has the capability to reliably transmit arbitrary small messages defined by the user, in the metadata accompanying the file, and to reliably transmit commands relating to file system management that are to be executed automatically on the remote end-point entity (i. e., a spacecraft) upon successful reception of a file.

The dormant InterPlanetary Internet Special Interest Group of the Internet Society has worked on defining protocols and standards that would make the IPN possible.^[11] The Delay-Tolerant Networking Research Group (DTNRG) is the primary group researching Delay-tolerant networking which has several major arenas of application in addition to the Interplanetary Internet, including stressed tactical communications, sensor webs, disaster recovery, hostile environments, and remote outposts.^[12] As an example of a remote outpost, imagine an isolated Arctic village or a faraway island, with electricity, and one or more computers but no communication connectivity. With the addition of a simple wireless hotspot in the village, plus DTN-enabled devices on, say, dog sleds or fishing boats, a resident would be able to check their e-mail or click on a Wikipedia article, and have their requests forwarded to the nearest networked location on the sled's or boat's next visit, and get the replies on its return.

As of 2005^[update], NASA has canceled plans to launch the Mars Telecommunications Orbiter in September 2009; it had the goal of supporting future missions to Mars and would have functioned as a possible first definitive Internet hub around another planetary body.

[edit] See also

• InterPlaNet
• Delay-tolerant networking
• Intergalactic Computer Network

[edit] References

[edit] External links

• The Consultative Committee for Space Data Systems (CCSDS)
• CCSDS History
• Participation in CCSDS
• Proximity-1 links Mars Comms, Disney & Interplanetary Internet
• ISO Feature: Deep Impact
• ISO Feature: Mars and Prox-1
• NASA'S MESSENGER & CFDP
• The InterPlaNetary Internet Project IPN Special Interest Group
• Overview - Delay-Tolerant Networks - IPN Phase II: The Next Steps
• Delay-Tolerant Networking - An Approach to InterPlanetary Internet
• Delay-Tolerant Network Architecture: The Evolving Interplanetary Internet
• The Interplanetary Network: A Strategy for Building Re-Usable International Space Communications Infrastructure
• The Delay-Tolerant Networking Research Group (DTNRG)
• Burleigh, Scott, CCSDS File Delivery Protocol in Delay-Tolerant Networking, GSAW 2003
• Burleigh, Scott, Operating CFDP in the Interplanetary Internet