AbstractExtraordinary traffic phenomena caused by network failures, disasters and social accidents cause remarkable deterioration of the network throughput and service grade. Algorithms of traffic control, e.g., originating traffic control, code blocking control, alterante route control and time‐out control, have been investigated and some of them have been implemented as countermeasures.This paper studies analytically the mechanism of congestion and traffic handling behavior of the telecommunication network for focused extraordinary traffic overload in a two‐stage hierarchical network, using an exchange model which has limited call handling capacity. The congestion at every part of the network can be explained by several factors: network configuration; traffic flow pattern of the extraordinary overload; maximum call handling capacity of exchanges; and the number of channels of the links. The increase of repeated calls arising as the result of congestion at exchanges is one of the dominant factors reducing the throughput of the network.