Wireless Ad Hoc and Sensor Networks

98 Wireless Ad Hoc and Sensor NetworksCell loss ratio1.6 × 10−31.41.210.80.60.4AdaptiveOne layerTwo layer w/o trainingTwo layer with trainingBuffer length = 2500.20200 400 600 800 1000 1200 1400 1600 1800Time in msecFIGURE 3.7Cell loss ratio with congestion.congestion control schemes — were deployed at the network switch withbuffer length of 250 cells. The service capacity at the switch for differentintervals of time is given by Equation 3.32. As expected, the CLR for thethreshold, ARMAX, the one-layer NN method increases as the servicecapacity is decreased, reaches a maximum value when the service capacityis reduced to a small value during the time interval of 721 ≤t≤1080msec.The CLR again decreases as the service capacity is increased toward thePCR of the combined traffic.In contrast, the CLR for the two-layer NN method, with and without apriori training, remains near zero throughout the simulation time, evenwhen the service capacity was reduced to 20,000 cells/sec, which impliesthat the two-layer NN controller performs better than all other methodsduring congestion in controlling the arrival rate of the cells into the destinationbuffer. As all the traffic used was of ON/OFF type, the sourcerates were reduced fairly and quickly using the proposed scheme, resultingin a low CLR. Further, a transmission delay of approximately 25 msec(