[Sis-csi] RE: networking details

[Scott Burleigh]

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.
>   
An excellent point, Lloyd.  As I was saying earlier, none of us are 
eager to invest resources in work unless we think it will produce 
significant value.  If a careful analysis of documented communication 
system costs leading to verifiable conclusions about mission decisions 
is not something that one considers valuable, then clearly one shouldn't 
spend time on it.

I doubt that a comparative advantage in operational expense can be 
convincingly demonstrated any other way, though.  Absent this sort of 
discipline, it seems to me that all we've got is intuition, vigorous 
assertion, and folklore.  Shouldn't one be able to answer a question 
like "How much is operational expense reduced, given mission parameters 
x, y, z?" with some sort of number?  An estimate, certainly, but still a 
number.

But we have wandered kind of far afield here.  Let's continue this 
off-list, if you like.

Scott
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