Highly reliable, high-speed, unidirectional serial data-communication subsystems have been proposed to be installed in an upgrade of the computing systems aboard the space shuttles. The basic design concept of these serial data links is also adaptable to terrestrial use in applications in which there are requirements for highly reliable serial data communications.

A Unidirectional Serial Data Link according to the proposal would be made from a commercial fiberchannel transmitter and receiver augmented externally with character translators and a Reed- Solomon encoder and decoder.

The hardware and software aspects of the architecture of the data links are dictated largely by a requirement, in the original space-shuttle application, for one computer to monitor the memory transactions and memory contents of other computers in real time with high reliability and without reliance on requests for retransmission. To minimize weight while affording a capability to transfer data at a required rate of 2.56 × 108 bits per second, it was decided that the links would be serial ones of the fiber-channel type. ['Fiber channel' denotes a type of serial computer bus that is used to connect a computer (usually a supercomputer) with a highspeed data-storage device. Depending on the specific application, the physical connection between the transmitter and receiver could be made via an optical fiber or a twisted pair of wires.]

Heretofore, fiber-channel links have ordinarily been bidirectional and have operated under protocols that provide for receiving stations to detect errors and request retransmission when necessary. In the present case, the time taken by processing to request retransmission would conflict with the requirement for realtime transfer of data. To ensure reliability without retransmission, a link according to the proposal would utilize a modified version of the normal fiber-channel character set in conjunction with forward error correction by means of a Reed- Solomon code (see figure). The Reed- Solomon encoding and decoding and the translations between the normal and modified character sets would be effected by logic circuitry external to the fiberchannel transmitter and receiver, which would be commercial off-the-shelf units.

The receiving end of the link could detect and correct errors at a rate as high as 4 million times per second, if necessary. The receiver detects uncorrectable double- byte errors. It has been estimated that uncorrectable-error rate would amount to one failure in about 1019 characters.

This work was done by Robert M. Cole and Jamie Bishop of Lockheed Martin Corp. for Johnson Space Center.

Title to this invention has been waived under the provisions of the National Aeronautics and Space Act {42 U.S.C. 2457(f)}, to Lockheed Martin Corp. Inquiries concerning licenses for its commercial development should be addressed to:

Lockheed Martin Systems Integration
1801 State Route 17C
Building 102
Owego, NY 13827-3998

Refer to MSC-23763, volume and number of this NASA Tech Briefs issue, and the page number.

NASA Tech Briefs Magazine

This article first appeared in the December, 2005 issue of NASA Tech Briefs Magazine.

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