  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.
