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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Having worked on the upper layers of the
AOS, I find <st1:City w:st="on"><st1:place w:st="on">Adrian</st1:place></st1:City>’s
comment completely accurate. We developed the AOS with the idea in mind that
spacecraft, such as the space station, would need balanced protocols. Therefore,
AOS was architected so that the upper layers could be used onboard in a peer
manner and the entire stack used bidirectionally on the space link, where the R/S
applies.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 color=black face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma;color:windowtext;font-weight:bold'>From:</span></font></b><font
size=2 color=black face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma;
color:windowtext'> sis-csi-bounces@mailman.ccsds.org
[mailto:sis-csi-bounces@mailman.ccsds.org] <b><span style='font-weight:bold'>On
Behalf Of </span></b>Keith Hogie<br>
<b><span style='font-weight:bold'>Sent:</span></b> Wednesday, August 24, 2005
12:11 AM<br>
<b><span style='font-weight:bold'>To:</span></b> sis-csi@mailman.ccsds.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [Sis-csi] Cislunar
Section 8</span></font><font color=black><span style='color:windowtext'><o:p></o:p></span></font></p>
</div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'>Adrian J. Hooke wrote: <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Times New Roman"><span
style='font-size:12.0pt;color:blue'>At 12:17 PM 8/23/2005, Keith Hogie wrote:<br>
<br>
</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 color=blue face="Times New Roman"><span
style='font-size:12.0pt;color:blue'>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.</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><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.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><br>
</span></font><font color="#009900"><span style='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>
</span></font> <br>
<br>
<o:p></o:p></p>
<blockquote style='margin-top:5.0pt;margin-bottom:5.0pt' type=cite cite="">
<p class=MsoNormal><font size=3 color=blue face="Times New Roman"><span
style='font-size:12.0pt;color:blue'>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?</span></font><o:p></o:p></p>
</blockquote>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3 color=black
face="Times New Roman"><span style='font-size:12.0pt'><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.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color="#009900" face="Times New Roman"><span
style='font-size:12.0pt;color:#009900'>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. </span></font><br>
<br>
<o:p></o:p></p>
<pre><font size=2 color=black face="Courier New"><span style='font-size:10.0pt'>-- <o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'>----------------------------------------------------------------------<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'> Keith Hogie e-mail: <a
href="mailto:Keith.Hogie@gsfc.nasa.gov">Keith.Hogie@gsfc.nasa.gov</a><o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'> Computer Sciences Corp. office: 301-794-2999 fax: 301-794-9480<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'> <st1:Street
w:st="on"><st1:address w:st="on">7700 Hubble Dr</st1:address></st1:Street>.<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'> <st1:place
w:st="on"><st1:City w:st="on">Lanham-Seabrook</st1:City>, <st1:State w:st="on">MD</st1:State> <st1:PostalCode
w:st="on">20706</st1:PostalCode> <st1:country-region w:st="on">USA</st1:country-region></st1:place> 301-286-3203 @ NASA/Goddard<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'>---------------------------------------------------------------------- <o:p></o:p></span></font></pre></div>
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