An adaptive admission control of Web service based on system model online identification using quantumbehaved
particle swarm optimization(QPSO) is designed and implemented, which dynamically adjusts parameters of PI
controller according to the changes of system model. In order to achieve admission control, a session-based admission timeratio
feedback control mechanism is introduced, which manages the amount of requests that the server can accept during the
control period. The simulation results of Apache Web server compared with several control methods show that the adaptive
control based on online system identification is able to control the system resources of the server more effectually in case of
overload and further improves the service quality.