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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This article first appeared in the October, 2001 issue of NASA Tech Briefs Magazine.

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