[Css-rasg] Response to action 010 -- concept paper outline

[Roger Thompson]

Erik,

 

On the subject of suggested RA architecture outline, I am still a little
unclear of what the objective is for the concept paper itself.  I would
have thought that the WG tasked to develop the Reference Architecture
would want to have the flexibility to identify and define the set of
views required to support it.  In my experience, it is only when
building a model that it becomes evident which views are required to
capture the key aspects of the modelled system, whilst keeping the model
as simple as possible.

 

I've had a quick look at the UML models we built for the ESA GDSS study
(back in 2005) that was an influence on the early SM&C work.  I am not
suggesting the RA should necessarily follow the approach used there, but
it did highlight a couple of key issues to me.

 

The GDSS model had 4 main views:

-                      Functional View

-                      System View

-                      Service View

-                      Information View

 

The Functional view decomposed the system into [coarse grained] logical
functions that could potentially be deployed at distributed locations
(e.g. Position Determination and Orbit Determination).  Exposed
interfaces between functions corresponded to identified Services (e.g.
Position Service).

 

The System view decomposed the system into deployment entities on which
Functions could be deployed (e.g. Spacecraft, MCS, Ground Station).  In
the context of your proposed views, this probably corresponds to the
Enterprise view.  Superimposed on this, multiple deployment
architectures [scenarios] could be represented by allocating Function
view components to Deployment entities.  These might be regarded as
separate [multiple] Deployment Views.

 

The Service view grouped Services into packages and identified the
dependencies between these (e.g. SM&C MO Services, TM/TC Packet
Services).

 

The Information view described the information items that are referenced
by Services (e.g. Parameter, Tracking Data).

 

A problem we found was that we needed to represent interfaces that
occurred at different layers of the communications protocol stack.  To
do this required different Functional sub-views at each layer, as the
decomposition of the system may appear different at the different layers
(I think we already noted this when discussing the Use Cases at the last
telecom).  To cover the whole scope of CCSDS could require multiple
layers.  For GDSS, we worked with 3 such layers (Application, Service
and Communications) - as we were really only interested in defining the
end-to-end Services, and even here I think it became complex to
represent the potential for multiple underlying communications protocols
to be used by one service.

 

The Reference Architecture is likely to need to show:

-                      Independent Functional views for each Layer

-                      Multiple Deployment views corresponding to
example Scenarios

-                      Multiple Communication views corresponding to
deployment of different Services across different physical interfaces
(from the System view)

 

This could rapidly become way too complicated - we need to be careful
not to create unrealistic expectations on what the RA WG will be able to
achieve.  The model should be as simple as it can be to identify all
CCSDS services and how they interrelate.  On this basis, I would
recommend that the Concept Paper merely identifies the expected Views
together with a brief outline of their expected content.

 

Hope this is of some help in your musings.

 

Roger

 

Roger Thompson

SciSys

Systems and Ground Segment Technology Manager, Space Division

Methuen Park, Chippenham, SN14 0GB, UK

 

Tel:   +44 1249 466452

Mob: +44 7818 593860

 

________________________________

From: css-rasg-bounces at mailman.ccsds.org
[mailto:css-rasg-bounces at mailman.ccsds.org] On Behalf Of Barkley, Erik J
(317H)
Sent: 02 February 2010 06:28
To: CCSDS RA BOF
Subject: [Css-rasg] Response to action 010 -- concept paper outline

 

CCSDS Colleagues,

 

At the December telecon, I took an action to sketch some ideas for the
BOF concept paper.   Attached is a draft sketch of some ideas I think
would be appropriate to include in the draft concept paper. I look
forward to discussing this and subsequent concept paper development plan
at the telecon next week.  If anyone has any comments, questions, etc.
before the telecon please do not hesitate to post a reply prior to the
telecon.  

 

Best regards,

 

-Erik


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