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<DIV dir=ltr align=left><SPAN class=737274813-30092005><FONT face=Arial
color=#0000ff size=2>Keith / Chris -</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=737274813-30092005><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=737274813-30092005><FONT face=Arial
color=#0000ff size=2>To give a lunar perspective, the LRO is being designed with
a single command rate (4kbps). We have received an action at our
peer-review to include a second, lower rate (1kbps or 2kbps were suggested), but
nothing on the order of a few bps. As for the human missions, at a
minimum, a spacecraft would have to support a voice loop (10-20kbps or so) as
the crew can always throw switches to "command" and that bandwidth can be used
to command from the ground in the event that the crew could not respond.
Again, not on the order of the few bps you have been describing for deep space
robotics.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=737274813-30092005><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=737274813-30092005><FONT face=Arial
color=#0000ff size=2>The other thing to consider is that the architecture should
support human missions beyond Cis-lunar space, and again, those will likely
require higher "minimum" rates than robotics.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=737274813-30092005><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=737274813-30092005><FONT face=Arial
color=#0000ff size=2>- Jason</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=737274813-30092005><FONT face=Arial
color=#0000ff size=2></FONT></SPAN> </DIV>
<DIV align=left><FONT face=Arial
size=2>____________________________________________</FONT></DIV>
<DIV align=left><FONT face=Arial size=2>"It's kind of fun to do the impossible."
- Walt Disney</FONT></DIV>
<DIV align=left><FONT face=Arial size=2></FONT> </DIV>
<DIV align=left><FONT face=Arial size=2>Jason A. Soloff</FONT></DIV>
<DIV align=left><FONT face=Arial size=2>Chief Systems Engineer</FONT></DIV>
<DIV align=left><FONT face=Arial size=2>Exploration Communication &
Navigation Systems</FONT></DIV>
<DIV align=left><FONT face=Arial size=2>Constellation Systems</FONT></DIV>
<DIV align=left><FONT face=Arial size=2></FONT> </DIV>
<DIV align=left><FONT face=Arial size=2>NASA / Goddard Space Flight
Center</FONT></DIV>
<DIV align=left><FONT face=Arial size=2>Code 567 / B19 / S046</FONT></DIV>
<DIV align=left><FONT face=Arial size=2>Greenbelt, MD 20771</FONT></DIV>
<DIV align=left><FONT face=Arial size=2></FONT> </DIV>
<DIV align=left><FONT face=Arial size=2>Phone: (301)286-1368</FONT></DIV>
<DIV align=left><FONT face=Arial size=2>Blackberry: (301)356-3708</FONT></DIV>
<DIV align=left><FONT face=Arial size=2>Fax: (301)286-1750</FONT></DIV>
<DIV align=left><FONT face=Arial size=2>E-Mail: <A
href="mailto:Jason.A.Soloff@nasa.gov">Jason.A.Soloff@nasa.gov</A></FONT></DIV>
<DIV align=left><FONT face=Arial size=2></FONT> </DIV>
<DIV> </DIV><BR>
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<FONT face=Tahoma size=2><B>From:</B> sis-csi-bounces@mailman.ccsds.org
[mailto:sis-csi-bounces@mailman.ccsds.org] <B>On Behalf Of </B>Krupiarz,
Christopher<BR><B>Sent:</B> Wednesday, September 07, 2005 11:12
AM<BR><B>To:</B> Keith Hogie; sis-csi@mailman.ccsds.org<BR><B>Subject:</B> RE:
[Sis-csi] IP Header Compression<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV><SPAN class=658080714-07092005><FONT face=Arial color=#0000ff
size=2>Keith,</FONT></SPAN></DIV>
<DIV><SPAN class=658080714-07092005><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=658080714-07092005><FONT face=Arial color=#0000ff size=2>I do
not have extensive R/F knowledge and, therefore, can't really give you an
answer regarding what we would see at the Moon. However, part of
the Cislunar charter is to extend, where possible, the architecture to Mars
where missions currently do have that low of a bit rate. The answer may
be whether this falls into the "where possible" category or not and your
concern is very valid. If there is someone with greater R/F experience
than I have on this list who could chime in (in particular,thoughts on rates
on the Moon), that would be very helpful.</FONT></SPAN></DIV>
<DIV><SPAN class=658080714-07092005><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=658080714-07092005><FONT face=Arial color=#0000ff size=2>As
for your second point, I'm not sure I follow. Could you elaborate a bit
on how you would see commanding done in an emergency situation without using
an IP packet? I probably got lost along the way, but I made the
assumption that in this architecture all packets that a spacecraft received
would be an IP packet. The hardware decode command (I think equivalent
to our critical commands here) would just be a bit string, but it would still
be in an IP packet.</FONT></SPAN></DIV>
<DIV><SPAN class=658080714-07092005><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=658080714-07092005><FONT face=Arial color=#0000ff size=2>BTW,
I'll have to double check (well, I guess this would be triple check now ;),
but I may have swapped emergency commanding with emergency telemetry
rates. Emergency commanding is ~7.8 bps versus emergency telemetry at 10
bps.</FONT></SPAN></DIV>
<DIV><SPAN class=658080714-07092005><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=658080714-07092005><FONT face=Arial color=#0000ff
size=2>Chris</FONT></SPAN></DIV>
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<DIV></DIV>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left><FONT
face=Tahoma size=2>-----Original Message-----<BR><B>From:</B>
sis-csi-bounces@mailman.ccsds.org [mailto:sis-csi-bounces@mailman.ccsds.org]
<B>On Behalf Of </B>Keith Hogie<BR><B>Sent:</B> Tuesday, September 06, 2005
4:40 PM<BR><B>To:</B> sis-csi@mailman.ccsds.org<BR><B>Subject:</B> Re:
[Sis-csi] IP Header Compression<BR><BR></FONT></DIV>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>
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<P><FONT face=Arial size=2>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).</FONT></P>
<P><FONT face=Arial size=2>Chris</FONT> </P><PRE wrap=""><HR width="90%" SIZE=4>
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</PRE></BLOCKQUOTE><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
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