[Sis-csi] RE: networking details

[Leigh Torgerson]

ah, the wonders of layering... For making life easier below IP, AOS 
versus frame relay/HDLC issues need to be discussed as Scott and 
others have said. There is an installed base, there are international 
issues to think about, and there are hybrid solutions as Lloyd points 
out like IP/HDLC/AOS - there is more to the story than just counting 
up bit overhead and the impact of fixed-length packets (or the need 
to do bit-stuffing) - We need to see about making the C3I Protocol 
Overhead Study done last November available to the CCSDS working 
group as a start.

But Assi brings up a good point about coding and RF layers that we 
need to worry about - except, as Keith points out, the 
link/coding/and RF layers are not really in our bailiwick (umm, we 
took on some link work by taking on the IP over CCSDS Link WG, but 
Greg Kazz is also the chair of the link WGs in Jean-Luc's Area..) 
Should CCSDS establish some sort of CSI analog in Jean-Luc's Space 
Link Services Area? It would be a good way to get some more 
involvement from ESA and others.

Leigh



At 1:01 AM +0000 2/9/07, Lloyd Wood wrote:
>At Thursday 08/02/2007 16:21 -0800, Scott Burleigh wrote:
>>>"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.
>>>
>>><ftp://ftp-eng.cisco.com/lwood/cleo/hogie-papers/README.html>ftp://ftp-eng.cisco.com/lwood/cleo/hogie-papers/README.html
>>>
>>>L.
>>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.
>
>But you can carry HDLC over AOS and other CCSDS protocols using the 
>bitstream services - the point being that doing that gives you the 
>layering separation of modem-to-other devices, meaning you don't 
>have to change all your installed base or reengineer as much if the 
>modem has to change at a later pooint to support a different 
>physical coding, while still using CCSDS links. You have less 
>integration, and less expensive reengineering of infrastructure, 
>without worrying about how IP packets map to CCSDS frames map to 
>specific codings or reengineering it as the coding choices change. 
>(Then CCSDS is used in the same way as any modem and channel coding 
>- to do the coding alone.)
>
>As for detailed cost breakdowns: "But we are all busy people, Assi. 
>Considering an issue honestly and thoroughly takes time and money, 
>neither of which are ample for our purposes.". Money spent on such a 
>study to "prove" what a large number of missions have demonstrated 
>in practice is likely better spent elsewhere; I'd be very surprised 
>if you find such a specific study done.
>
>cheers,
>
>L.
>
>>   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.
>>
>>Scott
>>
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J. Leigh Torgerson                          ltorgerson at jpl.nasa.gov
Jet Propulsion Laboratory - Communications Systems Research Sec.332
DARPA DTN / DSMS Advanced Protocol Implementation Work Area Manager
(818) 393-0695                                   (818) 393-4643 fax
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