[Sls-slp] RE: Encapsulation Service

Greg Kazz greg.j.kazz at jpl.nasa.gov
Wed Apr 19 20:36:51 UTC 2006

At 01:08 PM 4/19/2006, Durst, Robert C. wrote:
>While this is probably the pragmatic approach, the implication of this is 
>that two implementors can provide the same CCSDS service in a way that is 
>not, and cannot be configured to be, interoperable.  I find this 
>disturbing.  This possibility at least  needs to be noted, and added to 
>the list of parameters that are managed among implementors.  This seems 
>like a rather serious flaw to me.  I would much rather see a requirement 
>to implement both and an option to use either on a per-mission 
>basis.  Failing that, I'd like to see a Protocol Implementation 
>Conformance Statement developed and made mandatory, so that there is no 
>ambiguity about what an implementor has implemented.


Actually it is already a managed parameter. It's the PVN , i.e., packet 
version number in the Space Link Identifers blue book. It tells the 
receiver how to interpret the packet, i.e., how to find the length field, 
in order to extract it and assemble it. Encapsulation Packets have a unique 
PVN, so do Space Packets and they are distinct.

So CCSDS has provided a mechanism for space agencies to be interoperable. 
But that doesn't proclude some hypothetical rogue space agency who "gets 
there first" who only chooses to support bit streams instead of CCSDS 
recognized packet version numbers.


 >>I think that it would be useful to summarize the "managed parameters"
 >>somewhere, to make it clear specifically what bilateral
 >agreements are
 >>required to ensure interoperability.  This may be part of the "lore"
 >>within the CCSDS community, but if we want other folks to use
 >this, making
 >>it clear what needs to be agreed upon out-of-band seems important.

Didn't see any comment on this (but then, my comment didn't require 
any).  Any thoughts on an annex to summarize these?

I think we are between messages. You are probably reading that second 
message now. Actually Yamada has already captured the managed parameters in 
Table 5-1 of the Encapsulation Packet service, but he didn' t reference the 
controlling document for each parameter and more cleanly deliniate what 
applies when one use Space packets vs Encapsulation packets.


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