clude jitter, latency, throughput assurances and are used by BS for prioritizing, policing and scheduling mechanisms. The flow in which a packet is transmitted is based on the content of the IP header field, allowing every 2 A Security Association (SA) is the set of security information shared between BS and one or more of its client units in order to support secure communications across the 802.16 network. Next Generation Mobile Communications Ecosystem application to receive a different service flow. The service flow based QoS mechanisms apply to both DL and UL to provide improved QoS in both directions. WiMAX define five types of service classes, each associated with certain specific QoS specifications: Unsolicited Grant Service (UGS): It is designed to support real-time applications like VoIP that require fixed sized data packets on a periodic basis. UGS packets cannot tolerate long delays in their transmissions and must be transmitted with maximum sustained rate. UGS flows should be disassociated from all the other flows in the scheduler. In addition, piggybacking3 requests are also prohibited for the SS supporting UGS service. Another important parameter that is associated with UGS is Tolerated Grant Jitter. The Tolerated Grant Jitter specifies the maximum amount of time that the transmission may be delayed from the nominal periodic schedule for a particular service flow. Real-Time Polling Service (rtPS): The rtPS is designed to support real time applications that generate variable size data packets on a periodic basis like Streaming Audio and Video. Since transfer of information is periodic in nature a minimum traffic rate reserved is maintained. A fundamental difference between UGS traffic and rtPS traffic is that UGS reserves a permanent portion of the upstream bandwidth that can only be used by it. In the case of rtPS, the excess reserved capacity can be reused by other flows (nrtPS or BE) during inactivity of rtPS. Enhanced Real Time Variable Rate Polling Service (ertPS): It can be used for VoIP servic