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Chapter 6Optimisation of CRA using adaptive CSAs pgood performance. In general, simulation showed us that when there are more than 70active stations, a good performance is achieved if we set the initial backoff value in therange [4-5] and the truncated backoff value in the range [6-8].From the previous analysis (for mixed traffic), the maximum system throughputsupported by the network has been reduced from 45% down to 32% of the channelcapacity (see Figure 6.13). This is due to the extended number of stations supported,which produce a larger number of collisions when competing for contention-based slots,and also because the mean packet size has been decreased from 368 bytes, (which is theormalised System Throughput0.353Mbps Upstream0.33 9.6 9.7 Kbps kbps VoIP V Backof f CRAB w[ 4 - 8 ]0.31B w[ 5 - 7 ]B w[ 3 - 6 ]0.29B w[ 4 - 6 ]0.270.25B w[ 2 - 5 ]B w[ 3 - 5 ]0.230.210.19B w[ 2 - 4 ]0.17B w[ 3 - 4 ]0.1591 94 97 100 103 106 109umbe r of Active StationsFigure 6.13 – System throughput vs. No. of active stationsfor different backoff windows and VoIP traffic.average packet size used for Internet traffic, as indicated in Section 5.3.1), to 146 byes(used for VoIP traffic), leading to a higher protocol overhead and a reduction in systemthroughput.6.3.2 Splitting tree algorithm optimisationIn CATV networks, INAs and NIUs that support a splitting tree algorithm, achieve abetter system performance by reducing the collision risk when transmitting reservationrequest messages at the cost of a higher processing times and complexity. This increasein performance is obtained by i) dividing one upstream contention-based slot into threeindependent minislots that carry shortened request messages and ii) providing two6-20