  This paper studies the robustness of large-scale interconnected systems with
respect to external disturbances, focussing on their scalability properties.
Specifically, a notion of scalability is introduced that asks for these
robustness properties to remain unchanged under a structural change of the
system, such as the addition/removal of a subsystem or a change in the
interconnection structure. Both necessary and sufficient conditions, in terms
of the interconnection structure and edge weights, are given under which
elementary structural changes are scalable. The results are illustrated through
a simple example.
