Wireless Ad Hoc and Sensor Networks

Congestion Control in ATM Networks and the Internet 99Buffer utilization1009896949290Feedback delay = 0ThresholdAdaptiveOne layerTwo layer w/o trainingTwo layer with training8886150 200 250 300 350Buffer length (cells)FIGURE 3.8Buffer utilization.of much higher than 50 msec (>2% of the total time of transmission) wereobserved, partly due to the unsatisfactory controller performance inappropriately reducing/increasing the rate when required. As a result,higher CLR was observed for thresholding, adaptive ARMAX, and onelayerNN whereas the two-layer NN controller was able to store cells inthe buffer (as presented next in the buffer utilization) and able to transmitit during OFF periods, reducing cell delay and cell losses.Figure 3.8 and Figure 3.9 illustrate the buffer utilization for differentcongestion control schemes. Higher buffer utilization resulted in slightlylong cell-transfer delays because of queuing at the buffer. In addition, thebuffer utilization for the case of multilayer NN with training is higherthan the buffer utilization of the NN without training. In spite of largerqueuing delays for the two-layer NN, the overall delay is much smallerthan for the other schemes. Moreover, by suitably adjusting the gainparameter, one can alter the transmission delay and CLR and one canobserve a trade-off.Example 3.3.2: Multiple MPEG SourcesFigure 3.10 shows the multiplexed VBR input traffic created using severalMPEG data sources. Figure 3.11 and Figure 3.12 (same as in Figure 3.7,but with threshold scheme removed) show the CLR with buffer size whenthe service capacity is kept constant at 2400 cells/sec, which is slightly