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Chapter 5Upstream channel capacity and characterisation pIn terms of system throughput, as depicted in Figure 5.10 (for large request sizes of 22and 32 ATM slots), the increase was approximately of 12% of the cc when the splittingtree algorithm was selected. Conversely, for short request sizes, the system performanceincrease can be increased up to ≈ 17%. Results for the exponential backoff algorithmrevealed that once the maximum system throughput is reached (which is between 40and 46% of the cc), as the offered load becomes higher, the throughput graduallydeclines. This is to be expected because of the increased likelihood of collisions, whichconsume more bandwidth as the cable network becomes congested.System Throughput (Kbps)20001900180017001600150014001300120011001000900800Rsv 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 AlgorithmsSplittingTreeExponentialBackoff20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50umber of Active StationsFigure 5.10 – System throughput vs. No. of active stations for different request sizes.5-20