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Chapter 6Optimisation of CRA using adaptive CSAs pthe cc), very large delays are evident. At this point, the Es value that still offersacceptable delays (for IP traffic only) under 500 ms was Es-6. The other two values Es-5 and Es-9, (not included in Figure 6.14), showed the same results as for Es-7 and Es-8,respectively.In terms of system throughput, the difference of using distinct Es values was much lesssignificant. In general, regardless of the Entry spreading factor, the maximum systemthroughput ranged between 54.5 and 55% of the cc.b) Results for VoIP traffic using the splitting tree algorithmResults from simulations for VoIP traffic (see Figure 6.15), revealed that delays ofunder 30 ms can be obtained for all values of the Es factor, given an offered load up to46% of the cc (with 145 active stations). Optimum system performance is obtained withEs-6 and Es-7, achieving a maximum system throughput over 45% of the cc, as shownin Figure 6.16. In general, it was found that by defining small values for the Entryspreading factor (e.g.: Es-4), at high traffic loads (above 45% of the cc), NIUs with newarrivals are forced to transmit in one of the next three available contention-basedminislots, reserved for new incoming packets with probability of 3/4 = 0.75. This leadsto a higher risk of collision when more than two NIUs are competing for requesttransmission.10009008003 Mbps Upstream9.7 Kbps kbps VoIPTree CRAMean Access Delay700600500400300200Es-4Es-6 / Es-7Es-8/ Es-91000140 145 150 155umber of Active StationsFigure 6.15 – Mean access delay vs. No. of active stationsfor different Entry spreading factors and VoIP traffic.6-22