Critical load and congestion instabilities in scale-free networks
  We study the tolerance to congestion failures in communication networks with scale-free topology. The traffic load carried by each damaged element in the network must be partly or totally redistributed among the remaining elements. Overloaded elements might fail on their turn, triggering the occurrence of failure cascades able to isolate large parts of the network. We find a critical traffic load above which the probability of massive traffic congestions destroying the network communication capabilities is finite. 
Y. Moreno, R. Pastor-Satorras, A. Vazquez, A. Vespignani