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Lloyd Wood wrote:
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<pre wrap="">At Thursday 08/02/2007 12:30 -0800, Scott Burleigh wrote:
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<pre wrap="">Assi Friedman wrote:
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<pre wrap="">I would like to point out that a lot of discussion needs to go into the physical/link layers of this migration. CCSDS as-is is has its history significantly influenced from the STDN era. This history does not make it very conducive to IP in space.
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<pre wrap="">Hi, Assi. Can you go into a little more detail on why the CCSDS link-layer protocols are not very conducive to IP in space?
Since they were designed for use in -- and are heavily (and very successfully) used in -- space, and are the international standard link protocols for communication with spacecraft, I'm guessing it's not the "in space" part of the problem that you think the protocols are not suitable for. So I'm concluding that you think that they are not a suitable medium for carrying IP packets, right? Is there something about IP packets that makes them okay to carry in Ethernet frames, PPP, SONET, etc. but not okay to carry in, say AOS frames?
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<pre wrap="">Migrating to IP will require us to address the physical/link layers.
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<pre wrap="">"Require" is kind of a strong word to use here. Are you saying that it's impossible to convey IP traffic over the CCSDS link protocols? Or are you saying that it's just operationally more expensive to convey IP traffic to and from spacecraft over CCSDS link protocols than over some other link protocols? In either case, can you point to some published studies that demonstrate the deficiencies of the CCSDS links?
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"Operationally more expensive" would be accurate. See
K. Hogie, E. Criscuolo and R. Parise, Putting more Internet nodes in space, CSC World, Computer Sciences Corporation, pp. 21-23, April/June 2006.
K. Hogie, E. Criscuolo and R. Parise, Using standard Internet Protocols and applications in space, Computer Networks, special issue on Interplanetary Internet, vol. 47 no. 5, pp. 603-650, April 2005.
<a class="moz-txt-link-freetext" href="ftp://ftp-eng.cisco.com/lwood/cleo/hogie-papers/README.html">ftp://ftp-eng.cisco.com/lwood/cleo/hogie-papers/README.html</a>
L.</pre>
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Thanks, Lloyd. I was actually hoping for a study that demonstrated the
specific, quantitative performance inferiority of, say, AOS as compared
to frame relay/HDLC -- in terms of measured throughput, undetected bit
errors, etc. over some interval of operation. Or, alternatively, a
detailed cost breakdown of the expense of engineering, procuring, and
operating the communication systems on two spacecraft that exercise the
same applications and have comparable traffic loads but that use
different link-layer and physical-layer protocols -- again, AOS vs
frame relay/HDLC. I thought that was the sort of thing Assi was
talking about when he spoke of CCSDS link protocols not being very
conducive to IP in space, and I'm not spotting these kinds of numbers
in either of the papers you point to. But I may have misunderstood
Assi's point, and in any case these papers are a good place to start.<br>
<br>
Scott<br>
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