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<title>IP Header Compression</title>
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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'>In the tumbling S/C scenario, a major concern
was that the commands be short enough to allow a complete one to be seen while
the S/C is “looking” in the direction of the antenna. This is where
the difference in overhead between a CCSDS packet and an IP header might make
or break the recovery effort.<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>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>John Pietras<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>Howard Weiss<br>
<b><span style='font-weight:bold'>Sent:</span></b> Wednesday, September 07,
2005 9:00 AM<br>
<b><span style='font-weight:bold'>To:</span></b> Keith Hogie<br>
<b><span style='font-weight:bold'>Cc:</span></b> sis-csi@mailman.ccsds.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [Sis-csi] IP Header
Compression</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=2 color=black face=Helvetica><span
style='font-size:10.0pt;font-family:Helvetica'>Keith,<br>
<br>
When we first started working on SCPS (way, way, way back in what seems now
like the stone ages) we were faced with this same dilemma - how to allow
emergency mode messages in w/o having to deal with the on-board computer and
the protocol stack. Honestly, this was something we never looked at when
we started researching the ways in which upper layer protocols would be used in
a spacecraft. I guess we were all network weenies who figured that the
CD&H would be just <i><span style='font-style:italic'>like </span></i>an IP
router (or just an IP router if IP were used vs. NP) and all would be
good. So, the idea for hardware command decoders being able to handle
emergency-mode commanding (e.g., reset, safe-mode) came up to bite us back in
the mid-90s because of the kinds of heroic efforts that the UKs STRV team used
to recover a tumbling micro-sat by constantly shooting CCSDS telecommands at it
to cause it to go into safe-mode. We realized at that time that if uppler
layer protcols were to be used aboard spacecraft that the command decoders
would have to be able to parse and handle these types of emergency mode
commands outside of the protocol stack. Security, however becomes
paramount at the space link if such hardware command decoding is employed.<br>
<br>
Howie Weiss<br>
</span></font><br>
Keith Hogie wrote: <o:p></o:p></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'>Chris,<br>
<br>
I agree we need to consider issues with small packets and low rates, but
how low do we need to go. In all of the missions I have seen (non deep
space), the lowest data rates are 125 bps. This is over an order of
magnitude difference from your 10 bps. <br>
<br>
For the Cislunar environment, we need to figure out what some of our
limits are. Do we really want to burden the Cislunar design with issues
that only relate to Deep Space?<br>
<br>
Also, for hardware decode commands like hardware reset, I'm not sure if
packet sizes or IP or CCSDS headers really matter. Isn't a hardware
decode command just a string of bits (hopefully long enough to be unique) that
get grabbed by hardware without any special packet knowledge. That would
mean that this bit string can be carried inside any packet and the only length
that matters is the length of the hardware command bitstring.<br>
<br>
Keith Hogie<br>
<br>
Krupiarz, Christopher wrote:<br>
<br>
<o:p></o:p></span></font></p>
<p><font size=2 color=black face=Arial><span style='font-size:10.0pt;
font-family:Arial'><!-- Converted from text/rtf format -->I was curious about
thoughts as to if and where we would address IP header compression in the Green
Book. On some our missions (and I think this is typical at least in deep
space), if we have a reset of the system, the spacecraft may come up in an
emergency mode of receiving 10 bps. Hence, every bit is quite valuable at
this point. With a CCSDS header, we're looking at 6 bytes (plus a couple
of bytes if a secondary header is used). If we move to IPv6, this becomes
40. At 10 bps, that's an additional uplink time of 25-26 seconds before a
command can be received which is long enough to envision some nightmare
scenarios. Clearly IP header compression would alleviate this concern but
I'm not sure where it fits or if it is needed in this doc (I hope I didn't miss
it somewhere).</span></font><o:p></o:p></p>
<p><font size=2 color=black face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Chris</span></font> <o:p></o:p></p>
<pre style='text-align:center' wrap=""><font size=2 color=black
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<hr size=4 width="90%" align=center>
</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'>_______________________________________________<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'>Sis-CSI mailing list<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'><a
href="mailto:Sis-CSI@mailman.ccsds.org">Sis-CSI@mailman.ccsds.org</a><o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'><a
href="http://mailman.ccsds.org/cgi-bin/mailman/listinfo/sis-csi">http://mailman.ccsds.org/cgi-bin/mailman/listinfo/sis-csi</a> <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
cols=72><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><pre
wrap=""><font size=2 color=black face="Courier New"><span style='font-size:
10.0pt'><o:p> </o:p></span></font></pre><pre style='text-align:center'><font
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<hr size=4 width="90%" align=center>
</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'>_______________________________________________<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'>Sis-CSI mailing list<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'><a
href="mailto:Sis-CSI@mailman.ccsds.org">Sis-CSI@mailman.ccsds.org</a><o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'><a
href="http://mailman.ccsds.org/cgi-bin/mailman/listinfo/sis-csi">http://mailman.ccsds.org/cgi-bin/mailman/listinfo/sis-csi</a><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>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><br>
<br>
<o:p></o:p></span></font></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'>Howard Weiss<o:p></o:p></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'>SPARTA, Inc.<o:p></o:p></span></font></pre><pre><st1:Street
w:st="on"><st1:address w:st="on"><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt'>7075 Samuel Morse Drive</span></font></st1:address></st1:Street><o:p></o:p></pre><pre><st1:place
w:st="on"><st1:City w:st="on"><font size=2 color=black face="Courier New"><span
style='font-size:10.0pt'>Columbia</span></font></st1:City>, <st1:State w:st="on">MD</st1:State> <st1:PostalCode
w:st="on">21046</st1:PostalCode></st1:place><o:p></o:p></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'>410.872.1515 x201 || 410.872.8079 (fax)<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'>Mike Nichols: "Cheer up, life isn't everything!"<o:p></o:p></span></font></pre></div>
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