[Sois-tcoa] RE: reference model (2 levels of SOIS-compliance)

[Massimiliano.Ciccone at esa.int]

Dear all,
Sorry for the late answer but I got the flu and come back to work only today.
First of all I would like to remind you all to use the formal channels of
communication (i.e. ccsds mailing list) in order not to remain 'invisible' to
the secretariat.
Second, I noticed that the choice of the reference diagrram model raised some
very critical questions that have been dragged for long time.
One in particular, above all, is:
What does SOIS-compliance mean ?

In my view, I do not feel like precluding system designers the possibility of
experimenting different transport and network layer protocols for
implementing "the same" SOIS standard services; this is why I think that
TCP/UDP SCPS-TP IP etc. should be left in the diadram even if some minor
graphical changes are required (will explain later why).
The problem arises when we start to link protocol to service interfaces. I
doubt that TCP/IP can fullfill ALL the requierments of SOIS services.
In particular, how can TCP/IP guarantee a scheduled/time-constraint delivery
of data onboard the spacecraft ?
In other words, TCONS wg is working on the reccommendation of a standard
service interface as well as the 'ideal' protocol definition for carring on
ALL such services in the best way possible (hopefully); if a system designer
decides not to use TCONS but other protocols instead, then the resulting
system will lose interoperability with other systems implementing TCONS but
it will still meet the requirements for being SOIS-compliant at the SERVICE
INTERFACE level.
At this point we see that 2 degrees of compatibility are emerging:

1) SERVICE INTERFACE LEVEL ONLY
2) SERVICE INTERFACE LEVEL & PROTOCOL LEVEL

Compliance with the SERVICE INTERFACE LEVEL will assure sw re-usability while
compliance with the SERVICE INTERFACE LEVEL & PROTOCOL LEVEL will ensure sw
re-usability as well as interoperability of SOIS implementations.
You can notice how this 2-Levels SOIS-compliance will satisfy all parties
without any major constraint on missions using SOIS.
Having said that, the change that the diagram would need in order to reflect
this concept is that the exposed TCONS service interface is always the same
regardless of the protocols used for implementing a specific service,
otherwise we can say goodbye to the sw re-usability.
Furthermore, the protocols used within the TCONS box can be whatever
combination of TCONS, TCP/IP, UDP/IP, SCPS/TP or any X-PROTOCOL still to be
invented !!
Attached is a revised version of the diagram:
(See attached file: Ref_Model_Max.doc)

What do you think of this approach ?

Looking forward to your comments in order to solve this issue once for all.

regards

Max

SW Engineer
Computers & Data Systems Section
********************************************************************
VITROCISET - 2200 AG Noordwijk The Netherlands
ESTEC - ESA (TEC- EDD)
e-mail: Massimiliano.Ciccone at ESA.int               \|/
Ph: +31-71-5655310                                         @ @
__________________________________o00-(_)-00o___



                                                                                                                                                         
                      Abhijit Sengupta                                                                                                                   
                      <Abhijit.Sengupta at jp         To:      Stuart.Fowell at scisys.co.uk, Steve Parkes <sparkes at computing.dundee.ac.uk>                    
                      l.nasa.gov>                  cc:      c.plummer at skynet.be, Jane.K.Marquart at nasa.gov, Massimiliano.Ciccone at esa.int,                 
                                                   Patrick.Plancke at esa.int, Rick.Schnurr at nasa.gov                                                        
                      01/03/2005 11.21             Subject: RE: reference model                                                                          
                                                                                                                                                         
                                                                                                                                                         






Hi Folks:

Nice to receive comments from you on the reference model. Here is the
changed version and responses to comments.

Have fun!!

Abhijit


________________________________________________
All personal and professional opinions in this email are my own
and do not represent, in any way, the opinion or policy of JPL
________________________________________________
(See attached file: sois-ref-model-w-response.doc)


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