This chapter has presented evidence to show that overloads occur frequently in telephony networks, and can greatly exceed the capacity of the terminating lines (and of the network) to handle the surge of calls. The typical causes of overloads are media-stimulated events, emergencies and equipment failures. Their impact on the network is to reduce effective switch throughput (ultimately leading to switch failure) and to generate high levels of repeat attempts - most of which will fail to complete successfully, but nevertheless consume network resources, thereby reducing the capacity available to other, non-event, call streams. It is not economic to provide sufficient network or terminating line capacity to handle such events; consequently overload controls are necessary to ensure that switches are protected and ineffective traffic is minimised.
Adaptive Network Overload Controls, Page 1 of 2
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