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Chapter 7Performance optimisation for the support of TCIS pResults for the complete range of packet sizes and isochronous streams are summarisedin Table 7.6. These results are displayed in terms of maximum number of streamssupported for both protocols. For packet sizes from 64 to 512 bytes, access delays under20 ms were considered. Meanwhile for larger packet sizes, (1024 and 1518 bytes)access delays under 100 ms were used, since it is more likely that larger delays areaccepted for the support of isochronous streams when large packet sizes are utilised.In general, for most of the packet sizes and isochronous streams evaluated, DOCSISoutperformed the DVB/DAVIC protocol. There were just few cases where theDVB/DAVIC supported an increased number of streams, as it was the case of low rateisochronous streams of 16 kbps and 32 kbps for the packet size of 128-bytes.For higher data rate isochronous streams and small packet sizes, there were threeinstances where the DVB/DAVIC protocol failed to provide low transmission delays(under 20 ms). This is because according to the CRGC of the DVB/DAVIC protocol(depicted in Figure 3.3) the minimum packet delay is approximately of the order of 9ms, and the inter-arrival time for the three cases indicated in Table 7.6, were either 8 msor 4 ms. This resulted in infinite queue built-up at the transmitter side causing thestreams to fail. In order to fix this problem, enhanced reservation request mechanismsare required, as introduced in Section 7.2 and [87]. Another possible solution is todecrease the transmission cycle of the DVB/DAVIC signalling frame, as analysed inSection 5.4.6.Table 7.6 – Number of streams supported for DVB/DAVIC and DOCSIS.PacketIsochronous StreamsSize Access 16 kbps 32 kbps 64 kbps 128 kbps(bytes) Delay(ms) DVB DOCSIS DVB DOCSIS DVB DOCSIS DVB DOCSIS64 ≤20 62 62 24 32 No supported 20 No supported 6128 ≤20 96 87 48 43 19 23 No supported 12256 ≤20 108 110 54 54 27 27 12 14512 ≤20 112 125 59 62 31 31 15 151024 ≤100 122 143 61 70 31 35 15 181518 ≤100 125 144 63 71 31 36 15 187-35