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6.9 QoS FRAMEWORK

There are several components that work to provide QoS support to a connection request. These components can be viewed as the elements of a QoS framework to be set up by a network. This QoS framework has been shown in Fig. 6.16. The different elements of this framework are briefly discussed in the following. In the subsequent sections we provide a more elaborate treatment of these elements.

Call Admission Control: Call admission control tests whether the required resources are available. Then the required resources are reserved during call establishment, so that traffic can flow according to QoS specification. When the life time of a call is over, the call is torn down; this should involve releasing the resources reserved for the call.

Rate Control: Rate control ensures that the source does not violate the traffic (rate) contract, to which it has agreed. A source might violate its prespecified traffic (rate) due to malicious users or inexact traffic characterization.

Service Discipline: Service discipline allocates resources to connections during data transfer, adhering to the reservations made during channel establishment. Three types of resources allocated by a service discipline, namely, bandwidth, processing time (for deciding the time of service), and buffer space.

QoS Renegotiation: A renegotiation request can come either from the user who wants to change his own QoS requirement, or from the network due to overload and congestion.


  

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