A query timeout detection algorithm has been proposed to support a protocol for reliable communications over links that are characterized by long delays because of (1) propagation of signals over interplanetary distances and/or (2) intermittency. The protocol could be an interplanetary analogue of Transmission Control Protocol/Internet Protocol (TCP/IP) of the terrestrial Internet. The protocol would enable the interconnection of the terrestrial Internet with the internets planned for Mars and other destinations in the Solar system. Potential beneficiaries include operators of space-exploration missions in the short term and commercial internet users in the long term.
"Timeout" as used here refers to a deadline for determining whether it is necessary to retransmit a packet of data because either the packet or an acknowledgement of the packet was not delivered. Timeout intervals can be estimated from signal-propagation times. However, in the presence of extremely long and variable propagation delays and/or intermittency of communication links, the proposed algorithm would estimate timeout intervals more accurately and thus make it possible to utilize available transmission time more efficiently.
In the proposed algorithm, a timeout interval would be represented as a sum of eight subintervals. Values of some of the subintervals would be estimated initially and used to determine a reasonable future time when their final values must be calculated. At that time, the sum of subintervals would be recalculated to determine a final deadline.
This work was done by Scott C. Burleigh of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp under the Information Sciences category.
NPO-20519
This Brief includes a Technical Support Package (TSP).
Timeout Algorithm for Communications With Long Delays
(reference NPO-20519) is currently available for download from the TSP library.
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Overview
The document is a technical support package prepared by NASA's Jet Propulsion Laboratory (JPL) detailing a timeout algorithm designed for reliable communications over long delays, particularly in interplanetary contexts. Authored by Scott C. Burleigh, the work addresses the challenges posed by the significant propagation delays and intermittent communication links that characterize space exploration missions.
The proposed algorithm serves as a protocol analogous to the Transmission Control Protocol/Internet Protocol (TCP/IP) used on Earth, facilitating the potential interconnection of the terrestrial Internet with future internets planned for Mars and other destinations within the Solar System. This advancement is expected to benefit both space mission operators in the short term and commercial internet users in the long term.
In the context of this algorithm, "timeout" refers to a predetermined deadline for determining whether a data packet or its acknowledgment has been successfully delivered. Given the long and variable propagation times in space communications, the algorithm aims to estimate timeout intervals more accurately. This is crucial for optimizing the use of available transmission time, thereby enhancing the efficiency of communications over long or intermittent links.
The algorithm operates by representing a timeout interval as a sum of eight subintervals. Some of these subintervals are initially estimated to establish a reasonable timeframe for when their final values need to be calculated. At the designated time, the sum of the subintervals is recalculated to determine a final deadline for retransmission, if necessary. This method allows for a more dynamic and responsive approach to managing data transmission in environments where delays can be unpredictable.
Overall, the document outlines a significant advancement in communication technology for space exploration, emphasizing the importance of reliable data transmission in the context of long-distance space missions. The work was conducted under NASA's sponsorship, and while it references specific technologies and methodologies, it clarifies that such references do not imply official endorsements by the U.S. Government or JPL. The research represents a step forward in ensuring that future interplanetary missions can maintain effective communication links, which are vital for mission success and data integrity.
