Global guerrillas can gain leverage from small attacks by assiduous study of the dynamics of the networks they attack. Within scale free networks with dynamic flows (electricity, information, etc.), cascades of failure can be induced by attacking central hi-load nodes (see the brief Cascading System Failure for more). These nodes can be identified as those with a high betweeness centrality, a term used to describe those nodes with the largest number of "shortest paths" that pass through them. When these nodes are shut down through an attack, the flow they handle (most likely with expensive high capacity equipment) is automatically routed to other lower capacity nodes that fail under the load (a cascade of failure). Within global guerrilla warfare, these critical nodes are called systempunkts -- the point at which an attack will cause systemic collapse.
A Proposed Defense
Traditional methods of defense against cascading failure include "islanding," homogeneity, and radical redundancy. Unfortunately, all of these techniques are either too drastic (islanding) or expensive (homogeneity and radical redundancy) to be good solutions. Adilson Motter, from the Max Planck Institute, offers a more elegant solution in his paper, "Cascade Control in Complex Networks." He proposes that cascades can be controlled by (he proposes an algorithmic approach):
- Disconnecting peripheral transmitting nodes. Networks with dynamic flows have two types of nodes. Those that transmit flow and those that convey flow. Hi-load nodes, in scale-free networks of this type, are those that convey flow. To protect against too much flow on the remaining low capacity nodes, transmitting (or production) nodes should be selectively disconnected from network. This will allow the network to remain with capacity limitations and thereby limit the spread of the cascade.
- Pruning central links. When central hi-load nodes fail, the loads they previously conveyed are re-routed via new central links. If those overloaded cental links are pruned (eliminated), it may be possible to prevent a general cascade. Essentially, this action will push the cascade back towards the transmitting nodes that are oversupplying the network.