established or modified using service flow management procedures. Adaptive Grant and Polling Service (aGPS) is a new service class defined in IEEE 802.16m where the BS may grant or poll an MS periodically and may negotiate only primary QoS parameters or both primary and secondary QoS parameter sets with the MS. Initially, the BS uses QoS parameters defined in the primary QoS parameter set including primary Grant and Polling Interval (GPI) and primary Grant Size. During the service, the traffic characteristics and QoS requirement may change, for example silence-suppression-enabled VoIP alternates between talk spurt and silence period, which triggers adaptation of QoS parameters. Adaptation includes switching between primary and secondary QoS parameter sets or changing of GPI/Grant Size to values other than those defined in the primary or secondary QoS parameter sets when the traffic can be characterized by more than two QoS states. Depending on the adaptation method specified during the service flow negotiation, the Grant Size or GPI can be changed by the BS on detecting certain traffic conditions, or can be triggered by explicit signaling by the MS. There are three adaptation methods [2]: 1. Implicit: on detecting certain traffic conditions different to those in the pre-negotiated QoS parameter set, the BS automatically changes GPI and/or Grant Size, or switches between GPI_Primary/Grant_Size_Primary and GPI_SecondarylGrant_Size_Secondary, if the secondary QoS parameter set is defined. 2. Explicit, Sustained: the GPI and Grant Size change is triggered by explicit signaling by the MS, such as piggyback bandwidth request, bandwidth request signaling, quick access message in bandwidth request channel, or fast-feedback channel. Such change is sustained until the next change request. If GPI_Secondary or Grant_Size_Secondary is defined, the GPI and Grant Size switches between GPI_Primary/Grant_Size_Primary and GPI_Secondary/Grant_ Size_Secondary, as requested by the explicit signaling; otherwise, GPI and Grant Size cha