[Sis-csi] Cislunar Section 8

[Adrian J. Hooke]

At 10:11 PM 8/23/2005, Keith Hogie wrote:
>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?

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:

http://www.ccsds.org/docu/dscgi/ds.py/Get/File-517/NASDA_Report_to_CCSDS.pdf

>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.

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.

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.

Best regards

Adrian J. Hooke
Chairman, CCSDS Engineering Steering Group (CESG)  
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