Praise for Fundamentals of WiMAX

226 Chapter 7 • Networking and Services Aspects of Broadband WirelessPolicyDecisionPoint (PDP)PolicyDataSenderPEPPEPReceiverPEPPolicy Enforcement Point (PEP)Data PathControl PathFigure 7.1 A QoS policy-management systempolicy information in the policy data and creates configuration information that is pushed down toeach PEP that enforces the policies. Policy data is usually created based on service-level agreements(SLA) between the user and the network provider. In the dynamic case, QoS requirementsare signaled by the user or application as needed just prior to the data flow. RSVP (resource reservationprotocol) is a protocol used for such signaling and is covered in Section 7.1.2. When arequest for a certain QoS arrives at the PEP, it checks with the PDP for approval, and, if accepted,allocates the necessary resources for delivering the requested QoS.Admission control, the other important control plane function, is the ability of a network tocontrol admission to new traffic, based on resource availability. Admission control is necessaryto ensure that new traffic is admitted into the network only if such admission will not compromisethe performance of existing traffic. Admission control may be done either at each node ona per-hop basis, just at the ingress-edge node, or by a centralized system that has knowledge ofthe end-to-end network conditions.7.1.1.2 Data Plane MechanismsThese methods enforce the agreed-on QoS by classifying the incoming packets into severalqueues and allocating appropriate resources to each queue. Classification is done by inspectingthe headers of incoming packets; resource allocation is done by using appropriate schedulingalgorithms and buffer-management techniques for storing and forwarding packets in each queue.There are fundamentally two different approaches to how these queues are defined. The firstapproach called per-flow handling, is to have a separate queue for each individual session orflow. In this case, packets belonging to a given session or flow need to be uniquely identified.For IP traffic, this is typically the five fields in the IP header: source and destination IPaddresses, source and destination port addresses, and transport-layer protocol fields. The IntServmethods defined by the IETF use per-flow handling of IP packets. From an end user perspective,