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Chapter 7Performance optimisation for the support of TCIS pFor instance, for packet sizes of 1518 bytes, this difference resulted in approximately2% and 13% of the cc for the DOCSIS and DVB/DAVIC protocols, respectively.C) Maximum network capacityIn this analysis, we now address the maximum scalability of the network in terms ofmean access delays and system throughput/utilisation for an increased networkpopulation. The number of stations was increased to 340 to move beyond saturationpoints. The traffic load generated by each station was a single-Ethernet packet of 1518bytes with an exponentially distributed inter-arrival rate of 1 packet per second. This isequivalent to 12 kbps streams.Results presented in Figure 7.22a tell us that both protocols can support the samenumber of stations, (at least in this traffic situation) with approximately 160 streamssupported, after which delays become too large for the chosen application. It is apparentthat for medium network traffic loads, DVB/DAVIC cable modems provide slightlylower delays than the DOCSIS protocol, due to the faster interaction with the headend.DVB/DAVIC always sends an MCI frame every 3 ms and DOCSIS uses a variablescheme, where the number of minislots described per MAP can be from a few minislotsMean Access Delay (ms)240220200180160140120100806040200a) Mean Access Delay b) Channel CapacityDOCSISDVB20 60 100 140 180 220 260umber of Active StationsChannel Capacity (Mbps)3.02.72.42.11.81.51.20.90.6UtilisationThroughputDVBDOCSISDVB20 60 100 140 180 220 260 300 340 380umbe r of Active StationsFigure 7.22 –Mean access delay and maximum channel capacity,for DVB/DAVIC and DOCSIS, 12.4 kbps streams with packet size = 1518 bytes.7-32