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D O C S I SChapter 7Performance optimisation for the support of TCIS pFigure 7.23 shows the performance comparison when isochronous streams at 32 kbpswere used for small, medium and large packet sizes.From the results for a 64-byte packet size, in Figure 7.23a it can be seen that themaximum number of streams that the DVB/DAVIC protocol can support isapproximately 24, with access delays under 20 ms. The DOCSIS protocol supportsabout 8 streams more than the number achieved by DVB/DAVIC. Results for the othertwo packet sizes (256 and 1024 bytes) show that both protocols support the samenumber of streams for delay sensitive isochronous streams (under 20m), whichcorresponds to 54 and 57 streams for 256 and 1024-byte packet sizes, respectively. Forsome isochronous streams that support larger access delays over 20 ms, e.g. video,audio, the number of streams sustainable resulted in a large figure for the DOCSISprotocol.In terms of system throughput, (see Figure 7.23b) the minimum Ethernet packet sizeyields a maximum system throughput of 1.4Mbps (55% of the cc) for the DOCSISprotocol and 1 Mbps (32% of the cc) for the DVB/DAVIC standard, which indicatesthat the DOCSIS protocol is capable of using approximately 23% of the upstreamchannel capacity for the delivery of more user data. For packet sizes of 256 and 1024bytes, this difference resulted in 25% and 28% in favour of the DOCSIS protocol.Mean Access Delay (m s)1 9 51 8 01 6 51 5 01 3 51 2 01 0 59 07 56 04 53 01 50a) Mean Access DelayD V B64byte-PkDOCSIS1 8 2 4 3 0 3 6 4 2 4 8 5 4 6 0 6 6 7 2D V B256bytePkDOCSISD V B um be r o f A c tiv e Statio nsDOCSIS1024bytePkSystem Throughput (Mbps))2 .52 .32 .11 .91 .71 .51 .31 .10 .90 .70 .5b) System ThroughputDOCSIS256 byte PkD V B64bytePkDOCSIS1024bytePkD V BDOCSISD V B1 8 2 7 3 6 4 5 5 4 6 3 7 2 8 1 9 0 9 9 umbe r o f A ctiv e Statio nsFigure 7.23 - Mean access delay and system throughput, for DVB/DAVIC and DOCSISwith 32 kbps isochronous streams and different packet sizes.7-34