On Interplanetary Internet (IPN)

During the ACM Turing award, one of the future trends presented by Cerf and Khan is the extension the terrestrial Internet for interplanetary communication. Here’s a brief discussion of the Intreplanetary Internet.

For 40 years NASA has used point to point radio link to send data from the surface of Mars directly to the Deep space stations located in three locations around the globe. Vint Cerf together with some of his colleagues in the Jet Propulsion Lab (JPL) decided to improve the communication between spacecrafts. They decided to use a richer networking architecture than a point to point radio link. Vint Cerf thought that since TCP/IP seems to work well in the terrestrial Internet why don’t they extend and use the same architecture on Mars.  The plan is also an advantage since Mars’ atmosphere is a low delay environment.

The problems arise from Interplanetary communication. The first problem is that the speed of light is too slow. To be able to communicate between Mars and Earth a total of 7 to 40 minutes round trip time is needed, and TCP/IP doesn’t work well with long time delays. Another problem is the celestial motion. Objects in space are constantly moving. Also, transmission of data can be disrupted by other spacecrafts. So to be able to solve the said issues, they decided to create a network architecture that deals with the long delay and disruption between communicating spacecrafts, which they call Delay/Disruption Tolerant Network (DTN). So they implemented and test the model here on Earth.

In January 2004, several rovers landed on Mars, and they are programmed to send data directly back to Earth (using point to point radio link). With the expected speed of 28 kbps, which is very slow. Then, when they turned the radio on, these rovers overheated. They realized that there exists X-band radio on board and in the orbiters of Mars. These orbiters were previously used  to map the surface of Mars and since that project is already finished, they reprogrammed the orbiters and the overheated rovers. The data from the rovers were collected by the orbiters. The orbiters stored the data and when it gets to the right place, it transmits the data to the deep space on Earth. So they used a store and forward technique which is used in terrestrial mobile networks.

When Phoenix Lander landed on Mars, it is not programmed to directly send the data back to Earth, thus it uses the same store and forward technique which is used by the previously overheated networks. So they planned to standardize the store and forward approach for interplanetary communication.

The solution for this is to use the Delay and Disruption Tolerant Network with Bundle protocol for communicating spacecrafts. The details for the DTN and Bundle Protocol is presented in detailed in [1,2,3]. Another transport protocol which is named Saratoga is proposed in [4] to run on top of User Datagram Protocol (UDP). The Saratoga transport protocol is used by the satellites  to communicate with the ground stations on Earth.


[1]  Vinton Cerf, et. al., Interplanetary Internet (IPN): Architectural Design, Jet Propulsion Laboratory, The MITRE Corporation, 2001

[2] Kevin Fall. A delay-tolerant network architecture for challenging internets. In Proceedings of the 2003 conference on Applications, technologies, architectures, and protocols for computer communications (SIGCOMM ’03). ACM, New York, NY, USA, 27-34. DOI=10.1145/863955.863960 http://doi.acm.org/10.1145/863955.863960, 2003

[3] Kevin Fall, Wei Hong, Samuel Madden, Custody Transfer for Reliable Delivery in Delay Tolerant Networks, RT Journal Article, ID 1966918, 2003

[4] Lloyd Wood , Wesley M. Eddy , Will Ivancic , Jim Mckim , Chris Jackson Saratoga: A Delay-Tolerant Networking convergence layer with efficient link utilization, Third International Workshop on Satellite and Space Communications (IWSSC ’07), 2007

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