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Chapter 5Upstream channel capacity and characterisation pThis effect can be clearly appreciated in Figure 5.11, which shows the total bandwidthconsumed by only reservation requests. For the exponential backoff algorithm, with anoffered load of 46% of the link capacity (produced by 34 stations) the bandwidthutilised by successful and unsuccessful requests ranged from 22 to 28.5% of the cc(accordingly to the request size), compared to 12.3 to 20.5% of the link capacityconsumed by the splitting tree algorithm. This difference of approximately of 8% wasaccounted for increased collisions of reservation requests produced by the exponentialbackoff algorithm, which reduces the system throughput as the offered load increases.Results presented in Figures 5.9 to 5.11 indicate that as the reservation request sizeincreases, a gain in system performance is obtained. However, increasing the requestsize to its maximum value of 32-ATM cells, (for this analysis), may have itsconsequences as shown in the following analysis.Bandwidth comsumed by reservationrequet messages (%)40363228242016128Rsv Msg - 6 slotsRsv Msg - 11slotsRsv Msg - 22 slotsRsv Msg - 32 slotsRsv Msg - 6 slotsRsv Msg - 11slotsRsv Msg - 22 slotsRsv Msg - 32 slotsBackoff Tree3 Mbps Upstream32 Kbps kbps IP & 9.7 Kbps kbps VoIPBackoff & Tree AlgorithmsExponentialBackoffSplittingTree420 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50umber of Active StationsFigure 5.11 – Reservation request bandwidth consumed vs. No. of active stations.5-21