[Sis-csi] IP Header Compression

[Krupiarz, Christopher]

All,

Sorry if this ends up being a repeat, but this didn't seem to make it to
the mailing list the first time.

Chris

-----Original Message-----
From: Krupiarz, Christopher 
Sent: Wednesday, September 07, 2005 11:12 AM
To: 'Keith Hogie'; sis-csi at mailman.ccsds.org
Subject: RE: [Sis-csi] IP Header Compression


Keith,

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.

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.

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.

Chris

-----Original Message-----
From: sis-csi-bounces at mailman.ccsds.org
[mailto:sis-csi-bounces at mailman.ccsds.org] On Behalf Of Keith Hogie
Sent: Tuesday, September 06, 2005 4:40 PM
To: sis-csi at mailman.ccsds.org
Subject: Re: [Sis-csi] IP Header Compression


Chris,

  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.  

  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?

  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.

Keith Hogie