Tham khảo tài liệu 'quality of service and resource allocation in wimaxfig part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 66 Quality of Service and Resource Allocation in WiMAX The scheduling mechanism in IEEE includes the scheduling of downlink traffic carried out by BS and the scheduling of uplink traffic performed by two schedulers one at the BS and another at the SSs as shown in Figura 5. To perform the allocation of resources the schedulers use information about the QoS requirements and the status of the queues of the connections. At the BS packets from the upper layer are put into different queues. However the optimization of queue can be done and the number of required queues can be reduced. Then based on the QoS parameters and some extra information such as the channel state condition the DL-BS scheduler decides which queue to service and how many service data units SDUs should be transmitted to the SSs. Since the BS controls the access to the medium the second scheduler the UL-BS scheduler makes the allocation decision based on the bandwidth requests from the SSs and the associated QoS parameters. Finally the third scheduler is at the SS. Once the UL-BS grants of the bandwidth for the SS are allocated the SS scheduler decides which queues should use that allocation. While the requests are per connections the grants are per subscriber and the subscriber is free to choose the appropriate queue to service. The SS scheduler needs a mechanism to allocate the bandwidth in an efficient way what is Call Admission Control and is treated in the next section. Fig. 5. Components of the schedulers at BS and SSs 67 Scheduling Mechanisms with Call Admission Control CAC and an Approach with Guaranteed Maximum Delay for Fixed WiMAX Networks 4. Call Admission Control - CAC Typically a Call Admission Control CAC procedure is also implemented at the BS that ensures the load supplied by the SSs can be handled by the network. While the scheduling mechanism ensures that the required amount of resources is allocated to the connections so that the QoS requirements are met the admission control
