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Adrian J. Hooke wrote:
<blockquote
cite="mid6.2.1.2.2.20050823124439.031aa730@mail.jpl.nasa.gov"
type="cite"><font color="#0000ff">At 12:17 PM 8/23/2005, Keith Hogie
wrote:<br>
</font>
<blockquote type="cite" class="cite" cite=""><font color="#0000ff">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.</font></blockquote>
<br>
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
<a href="http://public.ccsds.org/publications/archive/701x0b3.pdf"
eudora="autourl">http://public.ccsds.org/publications/archive/701x0b3.pdf</a>
page
2-3.<br>
</blockquote>
<br>
<font color="#009900">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? <br>
</font> <br>
<blockquote
cite="mid6.2.1.2.2.20050823124439.031aa730@mail.jpl.nasa.gov"
type="cite">
<blockquote type="cite" class="cite" cite=""><font color="#0000ff">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?</font></blockquote>
<br>
The CCSDS space link protocols are cleanly layered:
<a href="http://public.ccsds.org/publications/archive/130x0g1.pdf"
eudora="autourl">http://public.ccsds.org/publications/archive/130x0g1.pdf<br>
<br>
</a>In particular, the current AOS Space Link Protocol as defined
in:<br>
<a href="http://public.ccsds.org/publications/archive/732x0b1.pdf"
eudora="autourl">
http://public.ccsds.org/publications/archive/732x0b1.pdf</a> is
decoupled
from its underlying coding layers.<br>
<br>
The coding layer that underlies AOS or conventional TM space links is
defined in:
<a href="http://public.ccsds.org/publications/archive/131x0b1.pdf"
eudora="autourl">http://public.ccsds.org/publications/archive/131x0b1.pdf</a>
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.<br>
<br>
</blockquote>
<font color="#009900">All of those documents describe how the sync
mark, R-S codeblocks, and </font><font color="#009900">data link
framing </font><font color="#009900"> 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><br>
<pre class="moz-signature" cols="72">--
----------------------------------------------------------------------
Keith Hogie e-mail: <a class="moz-txt-link-abbreviated" href="mailto:Keith.Hogie@gsfc.nasa.gov">Keith.Hogie@gsfc.nasa.gov</a>
Computer Sciences Corp. office: 301-794-2999 fax: 301-794-9480
7700 Hubble Dr.
Lanham-Seabrook, MD 20706 USA 301-286-3203 @ NASA/Goddard
---------------------------------------------------------------------- </pre>
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