12.07.2015 Views

Wireless Ad Hoc and Sensor Networks

Wireless Ad Hoc and Sensor Networks

Wireless Ad Hoc and Sensor Networks

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160 <strong>Wireless</strong> <strong>Ad</strong> <strong>Hoc</strong> <strong>and</strong> <strong>Sensor</strong> <strong>Networks</strong>Source setup requestsPBR/PCRNonlinearB<strong>and</strong>widthEstimator<strong>Ad</strong>aptive controllerNetwork resourcecontroller/schedulerPerformanceevaluationAccept/RejectSource transmissionratePacketloss<strong>Ad</strong>aptiveadmission controllerTraffic<strong>Ad</strong>aptivecongestion controllerDelayPerformanceevaluationQueue lengthRate of changeof queue lengthNetwork informationFIGURE 4.4<strong>Ad</strong>aptive admission controller.equivalent-capacity-based algorithm transforms the traffic characteristics(usually described by three parameters: PBR/PCR, MBR/MCR, <strong>and</strong> peakpacket/cell duration) of a new source into a unified metric, referred to asthe equivalent b<strong>and</strong>width, to reduce the dependence of the proposed controlmechanism on the traffic type. However, the transformation is based oneither a static relationship or simulation curves.The congestion indicator provides an insight into the congestion in thetransmission links based on the burstiness of the existing traffic, so thatfuture congestion can be avoided when a new source is admitted. CLR isthe feedback provided by the system about its performance, which canbe used to provide a closed-loop control system capable of adjusting itselfto provide a stable <strong>and</strong> robust operation. Also, the available buffer spaceis used as an input to the controller <strong>and</strong> is calculated as:ni=∑ i1Available_network_resources = ϕmax− x ( k)(4.27)The network resource estimator keeps track of the available bufferspace at each node/switch fabric. When a new source with a b<strong>and</strong>width

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