  During the concept design of complex networked systems, concept developers
have to ensure that the choice of hardware modules and the topology of the
target platform will provide adequate resources to support the needs of the
application. For example, future-generation aerospace systems need to consider
multiple requirements, with many trade-offs, foreseeing rapid technological
change and a long period for realization and service. For that purpose, we
introduce NetGAP, an automated 3-phase approach to synthesize network
topologies and support the exploration and concept design of networked systems
with multiple requirements including dependability, security, and performance.
NetGAP represents the possible interconnections between hardware modules using
a graph grammar and uses a Monte Carlo Tree Search optimization to generate
candidate topologies from the grammar while aiming to satisfy the requirements.
We apply the proposed approach to a synthetic version of a realistic avionics
application use case. It includes 99 processes and 660 messages. The experiment
shows the merits of the solution to support the early-stage exploration of
alternative candidate topologies. The method vividly characterizes the
topology-related trade-offs between requirements stemming from security, fault
tolerance, timeliness, and the "cost" of adding new modules or links. We also
create a scaled-up version of the problem (267 processes, 1887 messages) to
illustrate scalability. Finally, we discuss the flexibility of using the
approach when changes in the application and its requirements occur.
