Praise for Fundamentals of WiMAX

7.1 Quality of Service 225buffering packets before forwarding. Overbuilding the network to provide higher bandwidthcapacity and larger buffers is an expensive and inefficient way to provide quality, particularlywhen the quality requirements are very high. Therefore, more clever methods for providing QoSmust be devised and these methods must take into account the particular needs of the applicationor service and optimize the resources used. Different applications require a different mix ofresources. For example, latency-intolerant applications require faster access to bandwidthresources and not memory, whereas latency-tolerant applications can use memory resources toavoid packets being dropped, while waiting for access to bandwidth resources. This fact may beexploited to deliver QoS efficiently. In short, a QoS-enabled network should provide guaranteesappropriate for various application and service types while making efficient use of networkresources.7.1.1 QoS Mechanisms in Packet NetworksProviding end-to-end QoS requires mechanisms in both the control plane and the data plane.Control plane mechanisms are needed to allow the users and the network to negotiate and agreeon the required QoS specifications, identify which users and applications are entitled to whattype of QoS, and let the network appropriately allocate resources to each service. Data planemechanisms are required to enforce the agreed-on QoS requirements by controlling the amountof network resources that each application/user can consume.7.1.1.1 Control Plane MechanismsSuch mechanisms include QoS policy management, signaling, and admission control. QoS policymanagement is about defining and provisioning the various levels and types of QoS services,as well as managing which user and application gets what QoS. Figure 7.1 shows a generalizedpolicy-management system as described by IETF that may be used for managing QoS policies. 2The components of the system include (1) a policy repository, which typically is a directory containingthe policy data, such as username, applications, and the network resources to which theseare entitled; (2) policy decision points (PDP), which translate the higher-level policy data intospecific configuration information for individual network nodes; (3) policy enforcement points(PEP), which are the data path nodes that act on the decisions made by the PDP; and (4) protocolsfor communication among the data store, PDP, and PEP. Examples of these protocolsinclude LDAP (lightweight directory access protocol) [30] for communication between datasource and PDP, and COPS (common open protocol services) [21] for communication betweenPDP to PEP.Signaling is about how a user communicates QoS requirements to a network. Signalingmechanisms may be either static or dynamic. In the static case, the PDP takes the high-level1. Note, though, that unlike wireless, other links are generally considered reliable. Therefore, packetslosses there stem mostly from buffer overflow caused by congestion, not from channel-induced biterrors.2. A similar model is often used for security policies as well.