Figure 2. Internetwork cascading mechanisms.

Comparative illustration of the (a) “Coupled Topological” model¹⁷ in which failures propagate immediately from the power network to the communications network and the (b) “Intermediate” Smart Grid model where failures can propagate within the power network and have a chance of causing communications failures. In the Coupled Topological model, an initiating disturbance ① causes ② edge failures in the power grid as well as ③ node and edge failures in the communications (comm) network. As a result, the size of the giant component is reduced to 0.8N. In our smart grid models, the initiating failure① potentially causes overloads③, which causes an edge failure and #x02464; a loss of power at the “sink” node. This may (depending on the availability of backup power) cause a communication node failure ⑥ and thus communication link failures ⑦, which fracture the communication network and prevent messages from being passed from and to the control center.