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<font color="#0000FF">At 10:11 PM 8/23/2005, Keith Hogie wrote:<br>
<blockquote type=cite class=cite cite="">If there are any missions using
AOS in a two-way mode it would be good to know about them. Are
there any ground systems or satellite systems that can use AOS on the
uplink? </font></blockquote><br>
AOS uplinks were primarily intended for high rate human-present
applications where voice, video and computer data are integrated into a
single link. The bidirectional AOS architecture was jointly adopted by
the NASA Associate Administrators for Space Station and Tracking and Data
Acquisition, circa 1990, as the agreed NASA interface standard between
the ISS and its ground support infrastructure. It's not clear what the
ISS ended up implementing on the forward link, but apparently at least
the Japanese Experiment Module (JEM) component of the ISS uses
AOS:<br><br>
<a href="http://www.ccsds.org/docu/dscgi/ds.py/Get/File-517/NASDA_Report_to_CCSDS.pdf" eudora="autourl">
http://www.ccsds.org/docu/dscgi/ds.py/Get/File-517/NASDA_Report_to_CCSDS.pdf<br>
<br>
</a><blockquote type=cite class=cite cite=""><font color="#0000FF">All of
those documents describe how the sync mark, R-S codeblocks, and data link
framing are all directly related to each other. They all show that
the same sync information is used for both the FEC coding and data
framing. This is not the FEC and data link decoupling that has been
used in commercial satellite modems where the link coding is separate
from the data link framing. </font></blockquote><br>
It's not clear why this discussion is single-cylinder focused on
Reed-Solomon coding. The CCSDS coding capabilities are diverse and
include BCH, Convolutional, R-S and Turbo. In the case of block-oriented
codes such as R-S, the codeblock boundaries are delimited by a sync code.
To simplify frame synchronization operations, it is common practice to
size fixed-length telemetry frames to simply map 1:1 into the data space
of the codeblock. The two are only coupled as a matter of engineering
pragmatism.<br><br>
But I digress: the Cislunar WG is chartered to be working on space
internetworking issues. If you want to understand CCSDS space link
framing and coding mechanisms, you should address your questions
elsewhere.<br><br>
Best regards<br>
<x-sigsep><p></x-sigsep>
Adrian J. Hooke<br>
Chairman, CCSDS Engineering Steering Group (CESG) </body>
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