Introduction to Cyber-Warfare - Proiect SEMPER FIDELIS

204 11. CYBER WARFARE AGAINST INDUSTRY(at coarse-grain resolution) as a network where the nodes are major service providers andedges represent their connections. In the next chapter, we look at how power grids can alsobe represented as a network.The main concern with these types of networks is that when certain key nodes or edges aretaken off-line, the effect of the failure can be compounded as other nodes may depend on it.For instance, the decommissioning of a certain rail line may have an effect on the whole railsystem as other trains would then have to be rerouted. Further, if there was no alternativeroute for that single line, certain stations would become unreachable. Another real-world exampleof this is a 1990 incident, in which a phone switch in New York City conducted a selfresetonce it hit its load limit for calls. When the switch returned back online, it attempted tohandle signals that had collected while it was down. This dearth of signals, in turn, causedother switches to overload—leading to a cascading failure in the phone system. Over a 9-hperiod, approximately 50% of calls failed to go through and AT&T lost an estimated $60 millionin unconnected calls (in addition to losses incurred by businesses dependent on thephone system at that time). 11The ideas of certain nodes becoming disconnected from the rest of the network (theunreachable stations) and that of missing nodes or edges causing signals to be transferredto other nodes are often referred to as network fragmenting and cascading failures, respectively.We will discuss cascading failures in more detail in the next chapter in connection withpower grids. Here, we shall briefly introduce the idea of network fragmentation.When describing a network, we say that there is a path between two nodes if there is asequence of edges that ultimately connects them. For instance, in Figure 11.2A, there is a pathbhbhAa j a jccgdidiefeOriginal networkB Network after removal of node gbhbha j a jCdiefNetwork after removal of nodes g and ciefDNetwork after removal of nodes g, c, and dFIGURE 11.2Example network and the fragmentation effect of removing select nodes.