Performance parameters of a switch may be ascertained by observing its behavior during a brief interval of high call volume. This may be achieved by accumulating call messages on a queue before allowing them to be processed together as a group. Without increasing the rate of incident calls, an accumulation of messages is accomplished by altering the amount of time that elapses between transferring the accumulation to a processing queue. In one implementation, test calls are accumulated in call input queue. Ordinarily, these calls are transferred to a second queue for processing every few milliseconds (the transfer period). By increasing the transfer period, an increased number of calls are stored in the call input queue before being transferred to the second queue. This allows a larger number of calls to be processed by the telephone switch in a given cycle and, hence, allows the switch's operation under increased call volumes to be observed.