  Industrial Control System (ICS) testbeds serve as a platform for evaluating
and validating control system performances, cybersecurity tools and
technologies. In order to build or enhance an ICS testbed, it is vital to have
a deeper understanding of its design specifications and characteristic
attributes. Satisfying this prerequisite involves examination and assessment of
these attributes for existing testbeds. To further increase confidence in a
testbed's functionality, it is important to perform a comparative analysis of
its specifications with other ICS testbeds. However, at present, there is no
standardized methodology available to provide a comparative assessment of
different testbeds. In this paper, we propose a methodology for analyzing ICS
testbeds, inspired by the Cybersecurity Capability Maturity Model (C2M2). In
particular, we then define a ICS Cybersecurity Testbed Maturity Model, its
domains, and the associated maturity indicator levels. To demonstrate the
benefit of the model, we have conducted a case study analysis for several ICS
testbeds, representing different industrial sectors. Our analysis provides
deeper insights into the relative strengths and limitations of these testbeds,
together with scope for future enhancements, with respect to the domains
defined by the model.
