The IEEE 802.16e standard is designed to support high bandwidth for the mobile wireless metropolitan area network. In order to support Quality of Service (QoS) for multimedia applications, various bandwidth request and scheduling mechanisms are suggested in WiMAX, in which a subscriber station (SS) sends bandwidth request messages to a base station (BS) and the BS grants the bandwidth according to the available radio resources. In this paper a bandwidth request mechanism for ertPS, rtPS and nrtPS is proposed to enhance the QoS performance of WiMAX network. In the proposed bandwidth request mechanism, the SS requests for the additional bandwidth for the service flows by considering the round trip delay incurred during the bandwidth request grant process. The performance of proposed bandwidth request mechanism is evaluated through simulation by considering the metrics like throughput and delay
