FIGURE 2.9 This figure shows the traffic calling pattern in the AT&T network 30 minutes after the 1989 California earthquake. The shaded lines indicate increases in call volumes above normal. The network is designed and maintained using a linear programming formulation for normal traffic patterns. Following the earthquake, outbound traffic was given priority through dynamic network management controls, and extra capacity was allocated for outbound traffic by an adaptive routing algorithm. Figure courtesy of AT&T.
ratories over the past decade.
Another significant innovation, real-time state-dependent routing, is currently being implemented. Under this scheme, the state of congestion existing at the time of an individual call is used to determine the call's route. The scheme relies on new technology and new conceptual understanding of network behavior, which in turn is derived from mathematics and simulations (see Figure 2.9).