Throughput analysis of FETEX-150

A model is developed to calculate the fraction of successfully completed calls during heavy overloads for the Fujitsu FETEX-150 central office switching system. Important user actions such as dialing before dial tone and massive user reattempts are included in the model. These reattempts cause a large increase in the apparent load; a system actually offered 12% more calls than it can handle will see 100% more call attempts than it can handle because of reattempts. Models of dial-tone delay, user behavior, call mixes, and processor work times are combined. The model predicts different levels of overload for different system components. The methods developed should be applicable to other systems