 to the current value of Maximum Sustained Traffic Rate for the connection. The MS may request changing the size of the UL allocation either by using an Extended Piggyback Request field of the GMSH or the Bandwidth Request field of the MAC signaling headers by sending a codeword over the uplink feedback channel. The BS will not change the size of UL allocations until it receives another bandwidth change request from the MS. The mandatory QoS parameters are the Maximum Sustained Traffic Rate, the Minimum Reserved Traffic Rate, the Maximum Latency, the Request/Transmission Policy, and Unsolicited Grant Interval. The ertPS is designed to support real-time service flows that generate variable-size data packets on periodic basis, such as VoIP with silence suppression. Non-Real-Time Polling Service (nrtPS) offers unicast polls on a regular basis, which ensures that the UL service flow receives request opportunities even during network congestion. The serving BS typically polls nrtPS connections every second and provides timely unicast request opportunities. The Request/Transmission Policy attribute is set such that the MS is allowed to use contention-based or unicast request opportunities for data transmission. The mandatory QoS parameters for this scheduling service are Minimum Reserved Traffic Rate, Maximum Sustained Traffic Rate, Traffic Priority, Uplink Grant Scheduling Type, and Request/Transmission Policy. Best Effort (BE) service is designed to support applications for which no minimum service guarantees (e.g., no rate or delay requirements) are required. The MS is allowed to use contention-based and unicast request opportunities for data transmission. 6.6 IEEE 802.16M QoS CLASSES In addition to the legacy service class attributes, the IEEE 802. 16m defines a new service class attribute called Maximum Sustained Traffic Rate per Flow [2]. The new attribute defines the peak information rate of the service flow. The maximum rate is denoted in bits per second and pertains to the service data units at the input of th