Modelling Information Systems with Modarch

Chantal Panem
panem@cnes.fr
CNES

Abstract:
A system designer is able to specify and evaluate the needs for the
computer ground segment of his project and figure out its operational
behaviour.  But he usually doesn't have means to specify and to predict
what will happen when several parameters change.  With simulation tools
like MODARCH, it is possible to model, design and evaluate the
performances of the hardware/software architecture.  Advanced and graphic
results analysis tools help the system designer to understand and
demonstrate the performances of his system.

Modelling the CLUSTER Data Ground Segment has allowed to determine the
software limits on the existing hardware system.  Chronograms have pointed
out requirements that weren't totally respected.  As soon as the
improvement has been proposed and realised on the model, a sensibility
analysis has seemed essential because all hardware components are shared
by several projects.  With MODARCH, in this multi-project environment,
the system designer can simulate hardware components loads which reduce
all performances.  Graphic plots have shown the maximum percentage of
hardware resource load permitted for each processor, storage, network....

To optimise resources use, several projects run under the same hardware
system, without taking care or without knowledge of how other projects
are usmg the resources.  The result is often a bad surprise.  Modelling
with a tool like MODARCH is a solution to predict the behaviour of a new
system in a multi-project context.

In order to refine and confirm the results obtained by the current model,
the next step will be to model the data archive and transfer service
which is itself a fundamental component of the CNES space data
management system.  The new model will test and evaluate the limits of
the existing hardware architecture and will become the basis for
alternative proposals in order to choose the best solution for the future
overall architecture.

MODARCH is a registered trademark of SIMULOG.