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IEEE 802.16 standard (1), which is known as WiMAX in the industry, was designed mainly for wireless metropolitan area networks (WMAN). Basically, two operational modes are defined by the MAC layer: point to multi-point (PMP) and mesh mode. PMP is a centralized architecture where all traffic between clients or subscriber stations (SS) are controlled by a base station (BS). In mesh mode, traffic can be routed directly between SSs or between the SS and the BS. Two transmission modes are defined by the standard: frequency division multiplexing (FDD) and time division multiplexing (TDD). The MAC layer architecture in WiMAX is designed to support multi-service flows, and thus differentiates mainly four types of service classes: Unsolicited Grant Service (UGS), real-time Polling Service (rtPS), non-real time Polling Service (nrtPS) and Best Effort (BE). Each class is configured with different QoS parameters and thus responds to the QoS requirements of a different type of applications that WiMAX supports.