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<font size="-1"><font face="Helvetica, Arial, sans-serif">John,<br>
<br>
Exactly - and also that the short command be consumed by a hunk of
hardware that doesn't rely on the correct operation of the flight
computer, its software, and its protocol stack - all of which might be
slightly brain-damaged and incapable of acting on the emergency command.<br>
<br>
Howie<br>
</font></font><br>
John Pietras wrote:
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<title>IP Header Compression</title>
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<div class="Section1">
<p class="MsoNormal"><font color="navy" face="Arial" size="2"><span
style="font-size: 10pt; 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 color="navy" face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial; color: navy;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font color="navy" face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial; color: navy;">John Pietras<o:p></o:p></span></font></p>
<p class="MsoNormal"><font color="navy" face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial; color: navy;"><o:p> </o:p></span></font></p>
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<p class="MsoNormal"><b><font color="black" face="Tahoma" size="2"><span
style="font-size: 10pt; font-family: Tahoma; color: windowtext; font-weight: bold;">From:</span></font></b><font
color="black" face="Tahoma" size="2"><span
style="font-size: 10pt; font-family: Tahoma; color: windowtext;">
<a class="moz-txt-link-abbreviated" href="mailto:sis-csi-bounces@mailman.ccsds.org">sis-csi-bounces@mailman.ccsds.org</a>
[<a class="moz-txt-link-freetext" href="mailto:sis-csi-bounces@mailman.ccsds.org">mailto:sis-csi-bounces@mailman.ccsds.org</a>] <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>
<a class="moz-txt-link-abbreviated" href="mailto:sis-csi@mailman.ccsds.org">sis-csi@mailman.ccsds.org</a><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 color="black" face="Times New Roman"
size="3"><span style="font-size: 12pt;"><o:p> </o:p></span></font></p>
<p class="MsoNormal"><font color="black" face="Helvetica" size="2"><span
style="font-size: 10pt; 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 color="black" face="Times New Roman"
size="3"><span style="font-size: 12pt;">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 color="black" face="Arial" size="2"><span
style="font-size: 10pt; 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 color="black" face="Arial" size="2"><span
style="font-size: 10pt; font-family: Arial;">Chris</span></font> <o:p></o:p></p>
<pre style="text-align: center;" wrap=""><font color="black"
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</span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"><o:p> </o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;">_______________________________________________<o:p></o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;">Sis-CSI mailing list<o:p></o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"><a href="mailto:Sis-CSI@mailman.ccsds.org">Sis-CSI@mailman.ccsds.org</a><o:p></o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"><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 color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"> <o:p></o:p></span></font></pre>
<pre cols="72"><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;">----------------------------------------------------------------------<o:p></o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"> 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 color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"> Computer Sciences Corp. office: 301-794-2999 fax: 301-794-9480<o:p></o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"> <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 color="black" face="Courier New" size="2"><span
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w:st="on">USA</st1:country-region></st1:place> 301-286-3203 @ NASA/Goddard<o:p></o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;">---------------------------------------------------------------------- <o:p></o:p></span></font></pre>
<pre wrap=""><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"><o:p> </o:p></span></font></pre>
<pre style="text-align: center;"><font color="black"
face="Courier New" size="2"><span style="font-size: 10pt;">
<hr align="center" size="4" width="90%">
</span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"><o:p> </o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;">_______________________________________________<o:p></o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;">Sis-CSI mailing list<o:p></o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"><a href="mailto:Sis-CSI@mailman.ccsds.org">Sis-CSI@mailman.ccsds.org</a><o:p></o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"><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 color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"> <o:p></o:p></span></font></pre>
<p class="MsoNormal"><font color="black" face="Times New Roman"
size="3"><span style="font-size: 12pt;"><br>
<br>
<o:p></o:p></span></font></p>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;">-- <o:p></o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"><o:p> </o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;">Howard Weiss<o:p></o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;">SPARTA, Inc.<o:p></o:p></span></font></pre>
<pre><st1:Street w:st="on"><st1:address w:st="on"><font color="black"
face="Courier New" size="2"><span style="font-size: 10pt;">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 color="black"
face="Courier New" size="2"><span style="font-size: 10pt;">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 color="black" face="Courier New" size="2"><span
style="font-size: 10pt;">410.872.1515 x201 || 410.872.8079 (fax)<o:p></o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;"><o:p> </o:p></span></font></pre>
<pre><font color="black" face="Courier New" size="2"><span
style="font-size: 10pt;">Mike Nichols: "Cheer up, life isn't everything!"<o:p></o:p></span></font></pre>
</div>
</div>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Howard Weiss
SPARTA, Inc.
7075 Samuel Morse Drive
Columbia, MD 21046
410.872.1515 x201 || 410.872.8079 (fax)
Mike Nichols: "Cheer up, life isn't everything!"</pre>
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