Wireless Ad Hoc and Sensor Networks

166 Wireless Ad Hoc and Sensor Networks167 msec (0.1% of 167 sec), and it is used as the target cell transfer delay.The PCR of the MPEG data sources are given by 9,154, 6,106, 6,237, and4,384 cells/sec, respectively, and the combined PCR for all the sources is13,248 cells/sec, with MCR being 3,444 cells/sec. For VBR sources, ameasurement interval of 1/24 sec, which is equal to one frame time, isused.4.6.4 Simulation ExamplesNote that our objective is to demonstrate the performance of bandwidthestimation, allocation scheme, and call admission control scheme foraudio (ON/OFF) and highly bursty video (MPEG data) streaming applications,while meeting the QoS and peak bandwidth constraint of theoutgoing transmission link. Physically available bandwidth at the outgoinglink is taken to be the PCR of all sources and PCR of a singlesource for demonstrating the need for an accurate bandwidth estimationscheme.Three methods will be compared to estimate the bandwidth, availablecapacity, and admission control. The first method assigns bandwidthusing the PCR of the source. The second method presents an adaptivetwo-layer NN algorithm for estimating the traffic and then calculates theavailable capacity. However, in the case of NN with overallocation algorithm,the overallocation factor, ρ, is taken as 0.95 and the bandwidth isBWallocated as ( k ) , instead of BW( k)as suggested in the second method.ρIn the examples, the exponential weight moving average (EWMA) filterwas applied on the bandwidth error for convenience and readability. TheEWMA filter can be mathematically described as,EWMA( k + 1) = τEWMA( k) + ( 1−τ)* b( k), (4.34)where EWMA(k) represents the filtered value of b(k) at the instant k, τ isthe filter constant 0< τ < 1 and b(k) is the bandwidth estimation or bandwidthassignment error. Here, τ is selected as 0.99. Note that a positiveerror value implies that not enough bandwidth is assigned (bandwidthis not estimated accurately), whereas a negative error value implies thatthe assigned bandwidth is not fully utilized.Figure 4.5 shows the number of admitted sources at Switch 1 when thephysically available bandwidth is equal to the PCR of all the sources.Here, all sources are admitted with no service and transmission delays orlosses. Figure 4.6 shows the corresponding plot for Switch 2. The bandwidthestimation algorithm and the NN-based AC are used to admittraffic. The bandwidth prediction error at the switches is shown in Figure 4.7and Figure 4.8. When the physically available bandwidth is equal to the