[Sis-csi] Cislunar Section 8

[Keith Hogie]

Adrian J. Hooke wrote:

> At 12:17 PM 8/23/2005, Keith Hogie wrote:
>
>> 3 - The protocol stack diagram is nice but I'm not sure about the AOS 
>> boxes.  Normally AOS is used for data coming down from space.
>
>
> Not so - the original architecture that was developed for ISS was 
> completely symmetric - the AOS frame was intended to be used as either 
> a unidirectional or a bi-directional space link protocol. See 
> http://public.ccsds.org/publications/archive/701x0b3.pdf page 2-3.


I checked that document on Tues. and saw that is said that AOS could be 
used either way.  But the comment was that missions have always used it 
on the downlink only.  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? 
 

>> It also has Reed-Solomon coding on it.  The diagram uses AOS in both 
>> directions.  Are we proposing the use of AOS and Reed-Solomon coding 
>> both ways.  This would require R/S encoders at ground stations and 
>> decoders installed on spacecraft?
>
>
> The CCSDS space link protocols are cleanly layered: 
> http://public.ccsds.org/publications/archive/130x0g1.pdf
>
> In particular, the current AOS Space Link Protocol as defined in:
> http://public.ccsds.org/publications/archive/732x0b1.pdf is decoupled 
> from its underlying coding layers.
>
> The coding layer that underlies AOS or conventional TM space links is 
> defined in: http://public.ccsds.org/publications/archive/131x0b1.pdf 
> and note that it is NOT confined to R-S coding. It may be also 
> expected to evolve as new codes (such as LDPC) mature.
>
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. 

-- 
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  Keith Hogie                   e-mail: Keith.Hogie at gsfc.nasa.gov
  Computer Sciences Corp.       office: 301-794-2999  fax: 301-794-9480
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